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Exceeding conversion efficiency of 26% by heterojunction interdigitated back contact solar cell with thin film Si technology
Abstract
We have developed heterojunction interdigitated back contact solar cell with conversion efficiency of 26.6% (designated area: 180 cm²) independently confirmed by Fraunhofer Institute for Solar Energysystem Callab. Compared to our previous record efficiency (26.3%), the 0.3% absolute improvement can be regarded as ~10% reduction of remaining losses to the theoretical limit (~ 29%). We discuss the analyzed cell properties together with our recent progress to predict how far we can go in reducing the remaining losses in silicon photovoltaic.
... The figure also shows that in the region Δn > 10 15 сm -3 the S SCr values decrease slowly and eventually saturate. Linestheoretical dependences S SC (Δn) (1) and S SCr (Δn) (2) built using the parameters of silicon SC with the record-breaking photoconversion efficiency described in [10]. Triangles -experimental curve [11]. ...
... Triangles -experimental curve [11]. Fig. 1b shows the theoretical dependences of S SC and S SCr , constructed using the parameters of silicon SC with the record-breaking photoconversion efficiency described in [10]. The same figure shows the experimental dependence of the effective recombination rate on Δn for this SC, as well as the theoretical dependence agreed with it and obtained earlier in [11]. ...
... But the main thing is that the non-radiative exciton recombination channel in silicon with the time τ nr is more efficient than the radiative recombination one. Fig. 5, the dependences ) ( n nr and ) ( n r are plotted for the parameters of the silicon SC, which correspond to the experimental data given in [10]. As can be seen from Fig. 5, the value ) ( n r exceeds the value ) ( n nr by more than five times in the whole range of n. ...
An expression for finding the dependence of narrowing the bands in silicon ΔEg on the level of illumination from the intrinsic absorption band (or short-circuit current) has been proposed. This expression is used to find experimental values of ΔEg in high-efficient silicon solar cells. The dependence ΔEg (J) or dependence ΔEg (JI), where JI is the short-circuit current density, has been rebuilt into the ΔEg (ΔnOC) dependence, where ΔnOC is the excitation level in open-circuit conditions. With this aim, the generation-recombination balance equation was solved taking into account six recombination mechanisms in silicon, including Shockley–Reed–Hall recombination, radiative recombination, interband Auger recombination, surface recombination, non-radiative exciton recombination, and recombination in the space charge region. The latter two recombination terms are not taken into account in studies of the key parameters of silicon solar cells and in programs for simulating the characteristics of these solar cells. Therefore, in this work their correct definition was performed, their contribution was compared with the contribution of other recombination mechanisms, and it has been shown that the description of the characteristics and key parameters of silicon SC without taking them into account is insufficiently correct. The experimental dependences ΔEg (ΔnOC) obtained in the work were compared with Schenk’s theory. It has been shown that there is a good agreement between them.
... Even though this technology is still being researched, there is a good probability that it will succeed for several reasons, including cost reductions, high power conversion efficiency (PCE), dependence on high temperatures, and reliable preparation techniques. The Shockley-Quisser limit for Si-based solar cell devices was 26.6%, which is less than the theoretically expected value of 29.4%, according to the most current data available [1][2][3]. As a result, the efficiency is very close to the Shockley-Quisser limit that is anticipated theoretically. The primary reasons for cost and efficiency are extremely high diffusion temperatures and passivation methods [4,5]. ...
... If the doping concentration is NA then the excess hole concentration will also be NA (i.e. n h = NA ) and then n e for p-type semiconductor is [3]: similarly, for an n-type semiconductor with donor density ND ND = n e we have [46,47] The valence band offset (VBO ( ΔE V )) for the absorber and emitter interface for the proposed n-CdS and p-Si heterojunction can be given as: ...
... Also, as the voltage across the terminals of the cell is proportional to the current in the circuit, so the V oc increases proportionally with the J sc along with efficiency, and FF increases with the thickness analogously to V oc and J sc because these are the function of the V oc and the J sc as in Eqs. (1)(2)(3)(4). Further, to analyze the optical response (O.R.) of the cell for different thicknesses of the p-Si absorber layer, the quantum efficiency (Q.E.) and spectral response (S.R.) of HSSC solar device are observed and represented in Figs. 3 and 4. It is seen from the figure that the Q.E. moves towards saturation for the thickness of the absorber layer above 150 µm, and for a thinner absorber layer, the Q.E. is very less. ...
The primary concern of the Si-based solar cells heterostructure devices is the dopant-free selectively contacting carriers with p-type Si wafers. The obvious potential of a highly straightforward fabrication technique and the decreased energy consumption is primarily what has attracted such significant attention. In the present investigations, computational simulation via SCAPS-1D has been executed on p-Si/n-CdS/ALD-ZnO heterojunction solar cells and attained the champion conversion efficiency of∼19.97% with the help of some considerably amended device parameters. With the proper optimization of the device, we have obtained better photovoltaic parameters by varying the thickness of the p-Si, n-CdS, and atomic layer deposited ALD-ZnO, noted the effect of series and shunt resistance, effect of temperature and incident radiation on the p-Si/n-CdS/ ALD-ZnO device. The final proposed photovoltaic parameters have the %PCE = 19.97%, %FF = 83.37%, Jsc = 37.71 mA/cm 2 , and Voc = 635.3 mV. Finally, the collected performance metrics are compared to the findings from comparable experimental setups. After reaching these findings in the experimental laboratory and meeting the demand for renewable energy globally, it is assumed that such a device may be a turning point for future photovoltaic applications.
... Dye-sensitized solar cells in organic solar cells are poor in stability, volatile, easy to leak, and difficult to encapsulate, which still needs further improvement [8]. For amorphous silicon solar cells, heterojunction (HJT) solar cells have the advantages of high PCE (26.7%), low loss and better stability [9]. ...
... The PCE of perovskite/silicon-based HJT TSCs increased from 13.4% to 31.25%, which exceeded the PCE records of crystalline silicon (26.7%) and PSCs (25.2%), but still ultra-high cost and implemented on a small area [9]. It is predicted that the highest PCE of perovskite/silicon-based HJT TSCs can reach 46.1%, which is much higher than the 33% S-Q limit efficiency of single-junction cells. ...
... In TSCs, the silicon-based HJT cell as the bottom cell has a narrow band gap of 1.1 eV and a matched top cell band gap of 1.6-1.9 eV [9]. By adjusting the composition of perovskite materials, the band gap in the range of 1.5-2.3 ...
In recent years, in order to cope with climate and energy issues for green transformation, many countries have successively laid out the solar photovoltaic industry, making the photovoltaic industry the fastest growing industry in the energy sector. Among them, perovskite tandem cells (TSCs) are an important development direction. The stacked cells composed of perovskite top cells (PSCs) and silicon-based heterojunction (HJT) cells currently achieve a maximum photovoltaic conversion efficiency (PCE) of 31.25% and have great potential for development. This paper reviews the research and development process of the perovskite/silicon-based HJT tandem battery, and analyzes the methods to improve its PCE and stability through the research on the structure of the top, bottom and transition layers of the perovskite/silicon-based HJT tandem battery, in order to provide useful information in the industrial development and application.
... with decreasing n is observed in the indicated region (see, for example, the work [19]). How are these two cases different? ...
... kT E T n e n n dy n n n S (19) where ...
... During the calculations, it was assumed that the energy of the deep levels responsible for recombination in SCR E t is close to the middle of the band gap. Then the second terms in the first and second brackets of the denominator (19) can be neglected. Fig. 4 shows the theoretical dependences S SC (n) obtained using the formulas (19), (23) using the above parameters and the value of the coefficient k equal to 2. ...
Theoretical modeling of the optical and photovoltaic characteristics of highly efficient textured silicon solar cells (SC), including short-circuit current, open-circuit voltage and photoconversion efficiency, has been performed in this work. In the modeling, such recombination mechanisms as non-radiative exciton recombination relative to the Auger mechanism with the participation of a deep recombination level and recombination in the space charge region (SCR) was additionally taken into account. In a simple approximation, the external quantum efficiency of the photocurrent for the indicated SC in the long-wavelength absorption region has been simulated. A theory has been proposed for calculating the thickness dependences of short-circuit current, open-circuit voltage and photoconversion efficiency in them. The calculated dependences are carefully compared with the experimental results obtained for SC with the p+-i-α-Si:H/n-c-Si/i-n+-α-Si:H architecture and the photoconversion efficiency of about 23%. As a result of this comparison, good agreement between the theoretical and calculated dependences has been obtained. It has been ascertained that without taking into account recombination in SCR, a quantitative agreement between the experimental and theoretical light I V characteristics and the dependence of the output power in the SC load on the voltage on it cannot be obtained. The proposed approach and the obtained results can be used to optimize the characteristics of textured SC based on monocrystalline silicon.
... Currently, the highest c-Si solar cell efficiency is over 26%, obtained with the combination of IBC and HIT structures called heterojunction back contact (HBC) [8]. Figure 1.3 shows the HBC structure, wherein the front-side passivation and the rear-side emitter and BSF are designed by amorphous-Si. ...
... The full-area light absorption by removing the front-side electrode (feature of IBC) and strong passivation by amorphous-Si (feature of HIT) produced the highest performance in the single-junction c-Si field. Consequently, this HBC structure has led to improvements in c-Si solar cells, which resulted in cell efficiency first exceeding 25% [9,10], then over 26% [11], and now reaching 26.63% [8]. ...
... Improving the cell performances requires advances in solar cell structures, which includes proposal of new structures or optimization of the existing structures. One candidate with the highest c-Si solar cell efficiency adopts HBC, which is a combination of IBC and c-Si / a-Si heterojunction [8]. The highest cell efficiency achieved by a single-junction solar cell is 26.7% [3], which leads to further improvements in c-Si solar cells. ...
Crystalline-Si (c-Si) solar cells are the most common solar cells in the photo-voltaics (PV) market, which occupy approximately 90% of the total market. Several advanced structures have been proposed to improve c-Si solar cell performances , such as passivated emitter and rear cell (PERC), interdigitated back contact (IBC), tunnel oxide passivated contact (TOPCon), and heterojunction with intrinsic thin-layer (HIT) solar cells. The c-Si solar cell performance can be evaluated by numerical simulations in semiconductor devices. Numerical simulations help improve cell performance by varying the cell parameters or testing new schemes with reduced durations and costs, which are unavoidable problems in experiments. Furthermore, numerical simulations provide insights into the physical properties of the device, which are difficult to evaluate while performing experiments. These merits render numerical simulations effective for evaluating c-Si solar cell structures. In this study, the evaluations of advanced c-Si solar cell structures are discussed with new schemes for improving cell performance or for optimization of cell designs. The cell structures of PERC, IBC, and TOPCon are focused upon in this study, which are potential candidates for use in the PV market. These cell structures are evaluated, and the cell designs that improve the cell performances are understood using numerical simulations.
... In order to further proceed the possibility of achieving higher efficiency, we have explored a HIT (heterojunction solar cell with intrinsic thin layer) module where 2D carbon material (diamane) is used as an emitter layer. It is reported that 26.6 % and more than 30 % efficiency can be achieved for different HIT modules [4,5]. ...
... Single layer graphene is chosen as the front contact or the transparent conducting electrode which allows maximum photons flux to pass through it and no internal and external reflection is chosen for this layer to avoid efficiency loss at the front contact of the cell. The front surface is textured by anisotropic etching to reduce reflection [5]. Additionally, no mismatching between the layers of the cell is considered. ...
In this article, the patentability of novel graphene/diamane interface in HIT solar cell has been explored by simulated a structure modelled as: graphene (TCO) / n-diamane / a-Si: H (i) / p-cSi / Ag (back contact) with the help of software AFORS-HET version 2.5. Here, n-type diamane is used as an emitter layer and graphene as TCO. An efficiency of 31.2 % is achieved with this structure by varying various parameters of n-type diamane, p-crystalline silicon and hydrogenated intrinsic amorphous silicon layer which is pressed in between the two oppositely doped wafer (diamane and c-Si). Furthermore, when ITO is used as TCO then a comparatively low efficiency 27.15 % is achieved and when the commercially available values of silicon's parameters is used for the validation of results then an efficiency of 24.15 % is obtained. Some parameters of a-Si: H (i) has been further optimized and the optimum efficiency 31.2 % has been found at minimum thickness of 3 nm at bandgap 1.6 eV. Finally, we have demonstrated that only carbon material has an ability that its two-dimensional allotropes can be used as an emitter layer as well as efficient transparent conducting electrode.
... Holman et al [10] theoretically demonstrated that the relative efficiency of heterojunction solar cells can be improved by more than 5% by reducing parasitic absorption. To reduce the absorption loss of a-Si:H, several research teams have proposed to improve the parasitic absorption by using the interdigitated back contact (IBC) technique in silicon-based heterojunction solar cells [11][12][13][14][15] . Solar cells combining HIT and IBC technologies have achieved a world record conversion efficiency of over 26% [12,13] . ...
... To reduce the absorption loss of a-Si:H, several research teams have proposed to improve the parasitic absorption by using the interdigitated back contact (IBC) technique in silicon-based heterojunction solar cells [11][12][13][14][15] . Solar cells combining HIT and IBC technologies have achieved a world record conversion efficiency of over 26% [12,13] . However, the cell structures using HIT and IBC technologies are very complex and do not facilitate mass production. ...
Hydrogenated amorphous silicon/crystalline silicon heterojunction solar cells are currently a hot research topic in the field of photovoltaics, where parasitic absorption due to hydrogenated amorphous silicon layers has not been effectively addressed. For this reason, amorphous silicon/crystalline silicon heterojunction solar cells with localized p-n junctions (HACL cells) have been designed, which can significantly improve the parasitic absorption losses while maintaining the original advantages such as high open-circuit voltage. In this paper, we mainly use ATLAS 2D simulation software to conduct device simulation and parameter optimization of HACL cells, and simulate the effects of factors such as passivation inlet region width, insulation layer width, emitter width, passivation inlet region doping concentration and substrate doping concentration on the cell performance, respectively.
... On the other hand, the current record PCE of c-Si solar cells is 26.8% on a practical M6-size cell (274 cm 2 ), 1) and its progress is on-going towards achieving a PCE of 27% or higher by reducing residual losses. 12,13) For c-Si solar cell, huge efforts are being devoted in the industrial field to reduce production-costs (for example, wafer thinning, electrode cost reduction, etc.) in addition to the improvement of PCE. 14) Therefore, it should be significant to develop technology to realize a perovskite/SHJ TSC with both of highefficiency and a reasonable production cost by applying the current c-Si solar cell technologies. ...
... 1) Wide-gap PSC: The maximum obtained on c-Si solar cells is ∼42 mA cm −2 . 12,13) Considering the current matching, the maximum J ph,top and J ph,bottom are 21 mA cm −2 . Since this J ph is lower than obtained world-record perovskite single junction cells, 32) the wider gap perovskite layer with >1.6 eV is needed for the current matching between top and bottom cell. ...
29.2%-conversion efficiency two-terminal (2T) perovskite/heterojunction crystalline Si tandem solar cell using 145 μm-thick Czochralski Si wafer is obtained. Surface passivation of perovskite layer and better light management technique improved conversion efficiency. Toward social implementation, crucial issues on the 2T tandem solar cells with crystalline Si bottom cell are discussed. Four-terminal (4T) tandem solar cells are evaluated as an approach to avoid the crucial issues. Examining our base technologies which realize 22.2%-conversion efficiency perovskite single junction solar cell module and 26%-heterojunction back-contact solar cell, we clarified that the based technologies is ready to realize 30%-conversion efficiency 4T perovskite/heterojunction crystalline Si tandem solar cell with approximately quarter size of industrial crystalline Si solar cell (~64 cm ² ).
... Photovoltaics were first investigated six decades ago in order to harness solar energy. During this investigation, numerous materials such as Si, CIGSSe, CdTe, CZTSSe, Perovskites, and other materials appeared as absorbent layers in solar cells, and Si solar cells now dominate the PV industry [ 1 ] . CIGSSe and CdTe-based solar cells have demonstrated higher efficiency in thin film solar cells [ 3 [ ,] 2 ] but indium (In) is rare in CIGSS, and the toxicity of cadmium (Cd) in CdTe has prevented their widespread usage. ...
... The reason for the decrease of Jsc at the density of defects of 1E10cm -2 with the increase in the thickness of the buffer layer is due to the large numbers of photons having wavelengths less than 500 nm being absorbed before they reach the absorption layer, This contributes to a decrease in the generation of electron-hole pairs in the absorption layer and this was evident in Figure a. 8 in the region. (1). As for the defect density of 1E14cm -2 , we showed a decrease in the quantum efficiency with an increase in thickness in regions (1) and (2) of Figure 6.b, this is due to the increase in surface recombination and the decrease in the diffusion length of the charge carriers, and thus the decrease of Jsc. ...
The simulation model used in this study is the heterojunction solar cell with SnS absorption layer using the AFORS-HET simulation program. Where the effect of interface defect density (Nit) and the location of these levels within the interface on the electrical and optical properties was studied. Through the study, we learned the effect of the locations of the energy levels for defects within the junction, and it was found that the largest effect of the defects is within the locations of the deep energy levels, D.deep traps and A.deep traps within the junction. After that, the effect of interface defect density and its relationship to thickness and impurities concentration of both the buffer and absorption layer were studied, as the increase in the thickness of the absorption layer indicated a clear decrease in the effect of the density of the interface cases, otherwise the increase in the thickness of the buffer layer did not reduce the effect of these defects. The effect of the interface defect density increases with increasing the concentration of impurities in the SnS absorption layer, the effect of the density of the interlayer defects decreases with the increase in the concentration of impurities in the buffer layer.
... Em escala laboratorial, uma célula solar com estrutura PERC* e área de 4 cm 2 , apresentou a eficiência de 25,0 % e foi produzida pela UNSW (University of New South Wales) (Green et al., 2019). A célula solar de silício com maior eficiência já produzida foi desenvolvida por Yoshikawa K. et al. (2017), e atingiu a eficiência de conversão de 26,6 %, confirmada pelo Fraunhofer Institute for Solar Energy Systems. Esta célula solar foi desenvolvida mesclando a configuração de heterojunção com contatos posteriores. ...
Células solares de silício base n com emissor posterior de alumínio ou boro têm potencial de alcançar alta eficiência, apresentam baixa degradação à radiação solar e podem ser fabricadas com a tecnologia atual da indústria. Nesta estrutura de célula solar, o campo retrodifusor frontal (FSF – front surface field) é produzido pela difusão de fósforo, que em dispositivos base p, forma o emissor. O objetivo deste artigo é avaliar a influência da concentração de POCl3 nas características do campo retrodifusor frontal de fósforo em células solares base n, por meio da análise da resistência de folha e do perfil de fósforo. A difusão do fósforo foi realizada na temperatura de 845 °C e variou-se a concentração de POCl3 (CPOCl3) na câmara de processamento de 0,026 % a 0,064 %. As lâminas de Si foram colocadas com a face posterior juntas para reduzir a difusão de fósforo na face posterior onde será formado o emissor. Constatou-se que a resistência de folha no campo retrodifusor frontal de fósforo variou de (48 ± 3) Ω/□ a (72 ± 3) Ω/□, com a redução da concentração de POCl3 de 0,064 % e 0,026 %. A concentração em superfície (CS) de fósforo variou de 7,7x1020 a 1,0x1020 átomos/cm3 e observou-se a tendência de aumento de CS com o aumento da concentração de POCl3. Em relação ao perfil de fósforo verificou-se que, em geral, a concentração de fósforo em função da profundidade é maior para os perfis com maior CPOCl3. A concentração de POCl3 afeta principalmente a concentração de fósforo próximo à superfície, e este parâmetro aumenta até a profundidade de aproximadamente 0,025 µm, formando a “camada morta”. Na face posterior, constatou-se que a profundidade da região altamente dopada e a concentração em superfície são menores que os valores obtidos no campo retrodifusor frontal e não se observou a “camada morta”.
... Many of these theoretical investigations have revealed a very high optical absorption enhancement enabled by the photonic light-trapping structures in silicon solar cells at longer illumination wavelengths [26,37,38]. With the emergence of advanced optical device design and fabrication techniques, several experimental demonstrations of high optical absorption efficiency in solar cells [39,40] and ultrafast photodetectors have been realized [41,[42][43][44][45][46][47][48]. It should be noted that the photodetectors usually operate under reverse bias conditions, while solar cells are designed to operate at maximum power points and used under zero bias. ...
The photosensitivity of silicon is inherently very low in the visible electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared wavelengths. Herein, we have experimentally demonstrated a technique utilizing photon-trapping surface structures to show a prodigious improvement of photoabsorption in one-micrometer-thin silicon, surpassing the inherent absorption efficiency of gallium arsenide for a broad spectrum. The photon-trapping structures allow the bending of normally incident light by almost ninety degrees to transform into laterally propagating modes along the silicon plane. Consequently, the propagation length of light increases, contributing to more than an order of magnitude improvement in absorption efficiency in photodetectors. This high absorption phenomenon is explained by FDTD analysis, where we show an enhanced photon density of states while substantially reducing the optical group velocity of light compared to silicon without photon-trapping structures, leading to significantly enhanced light-matter interactions. Our simulations also predict an enhanced absorption efficiency of photodetectors designed using 30 and 100-nanometer silicon thin films that are compatible with CMOS electronics. Despite a very thin absorption layer, such photon-trapping structures can enable high-efficiency and high-speed photodetectors needed in ultra-fast computer networks, data communication, and imaging systems with the potential to revolutionize on-chip logic and optoelectronic integration.
... The solar cell industry has shown significant interest in silicon, it is first most abundant material on Earth, among the PV materials [1,8]. Due to its avail-ability, lack of toxicity, reliability, and efficient fabrication method, silicon is the material most frequently utilized to produce solar cells [9][10][11]. But Si material has been some disadvantage due to its lower absorption coefficient that makes it's become more expensive. ...
... Wafer-based crystalline silicon (c-Si) solar cells are the dominant technology in the global PV market. Aiming at a higher PCE, technology iteration is occurring from the passivated emitter and rear cell (PERC) to tunnel oxide passivated contact (TOPCon) and silicon heterojunction (SHJ) solar cells [1][2][3][4][5][6][7] . ...
Silicon heterojunction (SHJ) solar cells have reached high power conversion efficiency owing to their effective passivating contact structures. Improvements in the optoelectronic properties of these contacts can enable higher device efficiency, thus further consolidating the commercial potential of SHJ technology. Here we increase the efficiency of back junction SHJ solar cells with improved back contacts consisting of p-type doped nanocrystalline silicon and a transparent conductive oxide with a low sheet resistance. The electrical properties of the hole-selective contact are analysed and compared with a p-type doped amorphous silicon contact. We demonstrate improvement in the charge carrier transport and a low contact resistivity (<5 mΩ cm²). Eventually, we report a series of certified power conversion efficiencies of up to 26.81% and fill factors up to 86.59% on industry-grade silicon wafers (274 cm², M6 size).
... The importance of photovoltaics is increasing since it is considered the primary power source for a decarbonized society. Among many varieties of solar cells, silicon heterojunction (SHJ) solar cells using hydrogenated amorphous Si (a-Si:H) exhibit an extremely high conversion efficiency exceeding 25%, [1][2][3][4] leading to high power generation by photovoltaics. The stack of a doped a-Si:H layer and an intrinsic a-Si:H (i-a-Si:H) layer is employed in conventional SHJ solar cells due to its high passivation performance against the c-Si surface. ...
We investigated the effect of the B 2 H 6 plasma treatment at p-type hydrogenated amorphous silicon (p-a-Si:H) surface for high-performance silicon heterojunction (SHJ) solar cells. Secondary ion mass spectroscopy measurements revealed that B concentration at the p-a-Si:H surface is increased by employing the B 2 H 6 plasma treatment. Furthermore, specific contact resistance is decreased by about one-third after the B 2 H 6 plasma treatment. No degradation of passivation performance is induced by the B 2 H 6 plasma treatment. The power conversion efficiency of the SHJ solar cells with the B 2 H 6 plasma treatment is improved by the increase in fill factor (FF) due to decreased series resistance and increased shunt resistance. From numerical simulations, the upward band bending is enhanced at the heterointerface between transparent conductive oxide (TCO) and p-a-Si:H by the B 2 H 6 plasma treatment, which is responsible for the improved FF owing to facilitated tunneling holes from c-Si to p-a-Si:H layers and TCO/p-a-Si:H heterointerface.
... Studies have been conducted to improve the fabrication processes by comprehending the principles of solar cells in order to approach the theoretical limit of efficiency of single junction Si solar cells [3]. The highest efficiency of 26.7 % has been achieved by Kaneka Corporation for silicon waferbased solar cells employing an integrated back contact heterojunction with intrinsic thin layer (IBC-HIT) solar cells [4], [5]. Therefore, a novel structure is required to surpass the efficiency constraints of crystalline silicon solar cells [6]- [8]. ...
Silicon-based tandem solar cells with efficient use of the solar spectrum are desirable for a next generation-commercial photovoltaic system. It has been widely investigated elsewhere using perovskites or III-V cells as top cell materials for high efficiency and stability. However, perovskite and III-V top cells are still unsuitable for mass production as well as expansion and integration with silicon solar cell production processes so far. Two-terminal bifacial Si/Si tandem cell by bonding with transparent conductive adhesive (TCA) is reported here. The current matching can maximize the efficiency by controlling the opening area of the top cell, which makes the bottom cell also able to absorb sunlight in the short wavelength region that is absorbed by the top cell as well, without being limited to the thickness or bandgap of the top cell. The Si/Si tandem solar cell achieved 25.195 mA/cm
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of current density after current matching by 36% opening ratio of top cell.
... 1,2 Recent studies have, therefore, focused on heterojunction solar cell structures, with power conversion efficiencies (PCEs) approaching the SQ limit. Yoshikawa et al., 3 for example, experimentally demonstrated a 26.6% efficient interdigitated back contact (IBC) Si heterojunction solar cell with a realistic module size of 180 cm 2 . Despite the success, silicon-based solar cells are handicapped by the low absorption coefficient in longer wavelengths and high processing temperature of Si (∼1400 ○ C). 4 Moreover, defect levels in amorphous-Si (a-Si) limit the further developments of a-Si/c-Si heterojunctions. ...
Ternary chalcostibite copper antimony selenide (CuSbSe 2 ) can be a potential absorber for succeeding thin film solar cells due to its non-toxic nature, earth-abundance, low-cost fabrication technique, optimum bandgap, and high optical absorption coefficient. The power conversion efficiencies (PCEs) in conventional single heterojunction CuSbSe 2 solar cells suffer from higher recombination rate at the interfaces and the presence of a Schottky barrier at the back contact. In this study, we propose a dual-heterojunction n-ZnSe/ p-CuSbSe 2 / p ⁺ -copper gallium selenide (CGS) solar device, having CGS as the back surface field (BSF) layer. The BSF layer absorbs low energy (sub-bandgap) light through a tail-states-assisted upconversion technique, leading to enhanced conversion efficiency. Numerical simulations were run in Solar Cell Capacitance Simulator-1 dimensional software to examine how the performance of the proposed solar cell would respond under different conditions of absorber layer thickness, doping levels, and defect densities. The simulation results exhibit a PCE as high as 43.77% for the dual-heterojunction solar cell as compared to 27.74% for the single heterojunction n-ZnSe/ p-CuSbSe 2 counterpart, demonstrating the capability of approaching the detailed balance efficiency limit calculated by Shockley–Queisser.
... Moreover, the record efficiency of 26.7% of silicon solar cells [9,10] is very close to the Auger limit of 29.4% [11], and hence further improvement in power conversion efficiency is difficult. Therefore, researchers started exploring new materials like perovskite, an emerging material in this field [12][13][14][15][16][17][18][19]. ...
The high absorption coefficient and low cost with plentiful availability make the material iron pyrite (FeS2) promising for solar cell applications. However, their efficiency in the literature is still around 2.8% due to their low VOC. The presence of an acceptor-type surface inversion layer (SIL) with a significant band gap (0.56 eV–0.72 eV) is the main cause of this low performance. A detailed study considering these two parameters is not available in the literature to relate device performance to underlying phenomena. Therefore, a comprehensive analysis of the band gap and doping variation of SIL was performed in this article to explore the efficiency potential of FeS2 solar cells. The results showed that SIL with a low bandgap is highly undesirable, and it is recommended to fabricate SIL with a higher band gap of 0.72 eV and a doping of 1019 cm-3 in the laboratory to achieve a conversion efficiency of 5.36%. It was also confirmed that FeS2-based solar cells without a SIL layer have the potential to deliver 10.3% conversion efficiency. The results reported in this study will pave the way for underestimating the workings of iron pyrite solar cells and developing highly efficient FeS2 solar cells.
... Si solar cells based on c-Si were first reported in the 1950s, and they have been established as the undoubted market leader, comprising 95% of the total production of commercial PV modules [57,58,133]. It has been proven to be easier to reach near the theoretical efficiency limit in Si solar cells than other PV devices, and they also enjoy advantages such as high operational stability, non-toxicity, cost-effectiveness [57,134,135]. The lower bandgap of Si makes Si solar cell an ideal candidate as the bottom cell of a tandem device. ...
Inorganic-organic metal halide perovskite light harvester-based perovskite solar cells (PSCs) with widely tunable bandgap have achieved rapid growth in power conversion efficiency, which exceeds 25% now. It is deliberated that if a semitransparent solar cell made of wider bandgap materials was placed on top of a narrow bandgap materials-based solar cell such as a silicon solar cell, with proper optical and electrical arrangements, the resultant tandem device consisting of two subcells could more effectively utilize the solar spectrum than a single junction solar cell. In a perovskite/silicon tandem solar cell (PSTSC), a semitransparent PSC with a wider bandgap is placed on top of a narrow bandgap silicon solar cell. The PSC efficiently harvests the higher energy photons in the ultraviolet and visible regions of the solar spectrum while the silicon solar cell can convert the photons of the infrared region to power. The PSTSC is proposed as a potential candidate to overcome the Shockley-Queisser limit of single-junction silicon solar cells. Though the theoretical limit of a PSTSC is calculated as ∼42%, its actual efficiency achieved until now is less than 30%. Therefore, a great scope of research exists in improving the efficiency of PSTSCs. Current issues of stability and upscaling of the device in PSCs are also a matter of concern for PSTSCs. A tandem device consists of multiple parts, and different configurations can be applied, thus tuning the architecture of the device. Altering various parts may result in significant changes in the efficiency of the device. In this review, competing architectures of otherwise comparable devices are compared in terms of photovoltaic properties. Thus, future directions to improve the efficiency of the device based on architecture design are proposed herein. In particular, the influence of the polarity of PSCs and the surface morphology of silicon solar cells (both front and rear) on determining the properties of the PSTSC are discussed.
... TCM as a high resistive window [122], low resistive contact [123] and bilayer supports to carrier extraction by induced field effect [124]. In this perspective, Si HIT and IBC technology is a pioneer [125][126][127] along with related technologies as mentioned earlier [23,24,89,106,118]. In addition to aSi passivation, TCM in both front and rear emitter is shown potential in HIT cell [128]. ...
Massive energy demand and source of energy usages is the key root of global emission and climate change. Solar photovoltaic (PV) is low carbon energy technology currently 3.2% share of global electricity supply. The rapid progress of solar PV is vastly related to increase energy efficiency and lessening of active materials usage. This paper solar PV present significance and most prospective PV materials technical challenges are reviewed for its future advancement. Among the challenges solar energy absorption-related dynamic photo-thermal effect on cells or modules is vital. Transparent passivation contact materials with lower temperature coefficient (TC) and thin active layer resulted in lowering both dynamic photo-thermal outcome and optical to electrical energy gap. Thin active layer minor bulk recombination and sub-band parasitic absorption lessening purpose transparent conductive materials (TCM) based proper band barrier heterointerface is impending. It can optimize desired band absorption and photo-coupling with selective carrier induces greater efficiency. Earlier research though explains it on carrier selectivity prejudice, but how it can lessen the near infrared band optical and associated thermal influence is essential to illustrated. Passivation and TC interrelations hence, field related drift is control over diffusion process loss in advanced bifacial and thin active layer PV technology. Loss lessening pathways thin wafer-based Si, thin film CdTe, organic and perovskite photo coupling with advanced TCM, thus, Si/CdTe and Si/perovskite tandem cells along with OSC building integrated transparent photovoltaic technologies advancement pathways are reported.
... This is the first solar panel in the world. During the development of solar cells, the photoelectric conversion efficiency is an important indicator, which has been improved to 26% [1]. ...
The development history, preparation process, structure and working principle of silicon solar cells and perovskite solar cells are introduced. The main parameters and production processes of the two kinds of solar cells are compared. The advantages and disadvantages of perovskite solar energy compared with existing solar cells in market application are analyzed and summarized, including good light absorption, high energy conversion efficiency and simple process flow, The problems of cost, size and stability of perovskite solar cells in market application are pointed out and the solutions are given. Perovskite solar cells have an excellent development prospect. Short circuit voltage, open circuit current and efficiency exceed those of silicon solar cells and are expected to gradually replace silicon solar cells in the market.
... Over the past decade or so, the number of solar cell installations has increased significantly due to technological advances and cost reductions. With a 26.6% energy conversion efficiency, Si-based solar cells have taken the top spot in the PV industry [1]. Since the 29.4% theoretical limit is currently close, though, the room for improvement is very little. ...
Tandem Solar Cells (TSCs) with multi-junction are capable to break the SQ limit and achieve high PCE through absorbing larger range of light wavelength by multiple absorber layers with different band gaps. Perovskite solar cells are ideal light absorbing materials for TSC because of its high PCE, high suitability with other absorbers, low cost and easy fabrication. Perovskite-based TSCs have so far outperformed single-junction devices in PCE, garnering considerable interest from both academia and material industry. In this review, the basic science of perovskite Tandem Solar Cells (PTSCs) is presented, as well as the construction and properties of PSC as a top cell. Then three main types of PTSCs are introduced: Perovskite/Si, Perovskite/CIGS, and Perovskite/Perovskite including their design, challenges and fabrication methods. Finally, the current status and future prospects for commercialization of PTSCs are also discussed. According to recent developments, PTSCs are considered to be one of the most promising solar cells. Research on PTSCs could contribute to the development of desirable clean energy sources in order to solve the energy crisis and environmental problems of human beings.
... Thanks to the efforts of the academic and industrial researchers. The present world record of the silicon solar cell efficiency is 26.7% [173] with a heterojunction structure, when the highest efficiency limit of such a cell is about 30% [140] at AM 1.5G solar spectrum. The difference between the practical value and the Shockley-Queisser limit could be reduced to a great extent by mitigating optical, recombination and resistive losses occurring in the solar cells. ...
Dissertation: Ph.D. in Optics and Photonics
CREOL, the College of Optics and Photonics, University of Central Florida
This study reviews the current methods of numerical simulations for crystalline-Si (c-Si) photovoltaic (PV) cells. The increased demand for PV devices has led to significant improvements in the performance of solar cell devices. The main contribution comes from c-Si solar cells, which constitute 90% of the industry. Numerical analysis is effective for predicting, developing, and optimizing cell performances as the cell structures become more complex and include several parameters. However, conventional methods cannot simulate improved device structures with complex configurations. Additional physics is necessary to evaluate these cell structures. This study introduces methods for evaluating these cell structures using physical modeling and highlights the latest examples of simulations of c-Si solar cells.
A decentralized energy system requires photovoltaic solutions to meet new aesthetic paradigms, such as lightness, flexibility, and new form factors. Notwithstanding, the materials shortage in the Green Transition is a concern gaining momentum due to their foreseen continuous demand. A fruitful strategy to shrink the absorber thickness, meeting aesthetic and shortage materials consumption targets, arises from interface passivation. However, a deep understanding of passivated systems is required to close the efficiency gap between ultra‐thin and thin film devices, and to mono‐Si. Herein, a (Ag,Cu)(In,Ga)Se2 ultra‐thin solar cell, with 92% passivated rear interface area, is compared with a conventional nonpassivated counterpart. A thin MoSe2 layer, for a quasi‐ohmic contact, is present in the two architectures at the contacts, despite the passivated device narrow line scheme. The devices present striking differences in charge carrier dynamics. Electrical and optoelectronic analysis combined with SCAPS modelling suggest a lower recombination rate for the passivated device, through a reduction on the rear surface recombination velocity and overall defects, comparing with the reference solar cell. The new architecture allows for a 2% efficiency improvement on a 640 nm ultra‐thin device, from 11% to 13%, stemming from an open circuit voltage increase of 108 mV.
The current silicon heterojunction (SHJ) cells utilize indium‐based transparent conductive oxide (TCO) layers for supporting the lateral carrier transport. However, In is a typical rare metal and its consumption in solar cell manufacturing must be minimized for sustainable production. In this work, the possibility to realize high‐efficiency TCO‐free SHJ cells, in which no In‐based material is needed, is examined. It is found that monofacial rear‐junction structure is beneficial to collect minority carriers efficiently without the help of TCO layers, regardless of the wafer polarity. In addition, the contact resistivity of locally metallized area must be minimized for efficient carrier transport. Based on these findings, a TCO‐free SHJ cell showing an efficiency of 22.1%, which is comparable to that of the benchmark SHJ cell with TCO layers, is demonstrated. However, direct metallization of amorphous silicon layers causes the degradation in the photovoltaic property after prolonged annealing, probably due to the metal diffusion into Si. This degradation can be avoided by inserting a thin barrier layer such as a SnO 2 layer. It is indicated in these results that it is possible to realize TCO‐free SHJ cells with high initial efficiencies, and the main obstacle is not the efficiency but the long‐term stability.
Back‐contact perovskite solar cells offer a significant potential to reach high efficiency due to reduced parasitic absorption from the top surface. However, the currently reported efficiencies are considerably lower (<10%) than planar perovskite solar cells (>20%). Herein, back‐contact perovskite solar cells are fabricated to study loss mechanisms that cause low device efficiency. This work spatially resolves the short‐circuit current, open‐circuit voltage, photoluminescence quantum yield, carrier lifetime, and external quantum efficiency of the devices. The results indicate that the front surface recombination, increased nonradiative recombination at hole contact layer/perovskite interface, and the extraction barriers are three main mechanisms limiting devices from achieving high efficiencies.
Indium tin oxide (ITO) is the most widely used transparent conducting oxide (TCO) in optoelectronic applications. In this report, deposition parameters were optimized for making good quality ITO films with emphasis on its application as TCO for solar cells. For this study, process pressure (first series) and substrate temperature (second series) were varied and their effect on the optoelectronic properties of ITO films was explored. Low-pressure (3.8 × 10⁻³ mbar) ITO films were polycrystalline in nature, had high optical transmission (~ 91%), high band gap (3.76 eV) and the lowest sheet resistance (11 Ω/□) value. At this optimized pressure, the substrate temperature was varied from 130 to 200 °C in steps. High transparency and low sheet resistance of ITO films were observed at process pressure of 3.8 × 10⁻³ mbar and substrate temperature of 150 °C. Later, ITO films with optimized deposition parameters were used for fabricating MoO3−x/c-Si(n) heterojunction solar cells with the Voc of 517 mV, Jsc of 39.43 mA/cm² and PCE of 10.17%, without using a-Si:H(i) as a passivating layer.
Solar Photovoltaic (SPV) and wind energy are two major sources of renewable energy that are intermittent in nature. A hybrid system consisting of SPV and Wind Energy Conversion System (WECS) can meet the energy needs as either source can continue to produce energy even if the other is unavailable, and this system is reliable and economical. The primary emphasis of this research is to enhance the efficiency and quality of power output of a grid tie inverter integrated with Hybrid SPV-WECS. The thesis aims to develop and simulate a mathematical model of a hybrid SPV and WECS system that can be integrated with a utility grid through high gain DC-DC Converters (DCDCC), hybrid MPPT, and a reduced switch Multilevel Inverter (MLI) and to characterize its performance and quality of power output.
The SPV and WECS are simulated and integrated together to form a Hybrid SPV-WECS (HSPV-WECS) system and, the performance is evaluated under varied weather situations like Temperature (T), Irradiation (G) and speed of wind. The subsystems of the conventional Grid Tie Inverter (GTI) are simulated and integrated with the simulated HSPV-WECS. The performance of the GTI connected to HSPV-WECS is analyzed. To boost SPV's output voltage to the desired level, a high gain multiple lift Boost Converter (BC) and an Interleaved Boost Converter (IBC) are prosed and incorporated in the simulated GTI. A hybrid MPPT is suggested to track the Maximum Power (Pm) from SPV. A hybrid MPPT that integrates the advantages of Perturb and Observe (P&O) and Fuzzy Logic Based (FLB) MPPTs are utilized for better performance and increased efficiency of SPV when compared with conventional MPPT. The performance of the GTI with high gain DC-DC converts and hybrid MPPT is analyzed.
The reduced switch MLI with an auxiliary diode bridge is proposed to integrate the SPV and WECS to the utility grid. The switching losses of the switches used in MLI are analyzed theoretically and compared with simulation results. Also, the MLI is compared to conventional five-level MLIs with respect to number of diodes, capacitors, switches, DC sources, and overall number of components utilized. When comparing the proposed five level MLI to the other three standard MLIs, the results reveal that the proposed five level MLI involves a reduced switch count which minimizes the overall switching losses and hence efficient inverter. The THD of the proposed five level Reduced Switch MLI (RSMLI) is 1.66%, which is within the limits of IEEE regulations. Overall, the results from the simulations indicate that the model performs better and is more efficient.
We have performed simulation studies using AFORS-HET software to understand how dopant concentration (i.e. acceptor concentration here) and thickness of p-layer affect the overall performance of HIT (heterojunction with thin intrinsic layer) p-a-Si:H/i-a-Si:H/(n)c-Si solar cells. Doping of p-layer is increased from 1 × 1019 cm−3 to 5 × 1020 cm−3, and thickness is varied from 5 to 15 nm. The best device performance is achieved at acceptor concentration of 1 × 1020 cm−3 and 5 nm thin p-layer. Solar cell parameters of champion device are current density (Jsc) of 38.22 mAcm−2, open circuit voltage (Voc) of 689.60 mV, fill factor (FF) of 0.83 and conversion efficiency (η) of 22.06%.KeywordsAFORS-HETHIT solar cellSolar cell parameters
The extraction of photogenerated charge carriers and the generation of a photovoltage belong to the fundamental functionalities of any solar cell. These processes happen not instantaneously but rather come with finite time constants, e.g., a time constant related to the rise of the externally measured open circuit voltage following a short light pulse. The present paper provides a new method to analyze transient photovoltage measurements at different bias light intensities combining rise and decay times of the photovoltage. The approach uses a linearized version of a system of two coupled differential equations that is solved analytically by determining the eigenvalues of a 2 × 2 matrix. By comparison between the eigenvalues and the measured rise and decay times during a transient photovoltage measurement, w e determine the rates of carrier recombination and extraction as a function of bias voltage and establish a simple link between their ratio and the efficiency losses in the perovskite solar cell. This article is protected by copyright. All rights reserved.
Ultrathin Al-doped Si oxide (SiO x ) layers were formed by a simple wet chemical treatment, and its hole-selective passivating contact and electrical properties were investigated. From the evaluated contact resistivity ( ρ c ) and saturation current density ( J 0 ), carrier selectivity ( S 10 ) was estimated to be 13.3. Moreover, in Si nitride (SiN y )/Al-doped SiO x stacks, negative values of fixed charge density ( Q f ) were obtained, despite a high positive Q f existing in the single SiN y layer. This result implies that Al-doped SiO x has high negative fixed charges and overcompensates the charge polarity in the stacks, which forms an inversion layer and accumulates holes on the Si surface. Furthermore, the negative fixed charges realize excellent carrier separation by the induced upward band bending. In addition, we proposed novel device architecture named Al-induced charged oxide inversion layer (Al-COIL) solar cells and confirmed device operation in a simple device configuration.
Molybdenum oxide (MoO3‐x, x<3) has been successfully used as an efficient hole‐selective contact material for crystalline silicon heterojunction solar cells. The carrier transport capability strongly depends on its work function, i. e., oxygen vacancies, however, there are lack of effective methods to modulate the multiple oxidation states. In this work, we tune the oxidation states of solution‐processed MoO3‐x by doping Nb5+ to improve its hole‐selective contact performance with silicon. With the optimum doping concentration of 5%, both the reduced Mo5+ and oxygen vacancies increase, resulting in a decrease in the contact resistivity between the MoO3‐x film and p‐type silicon from 161.1 to 62.9 mΩ·cm2, and an increase of the effective carrier lifetime from 165.4 to 391.0 μs simultaneously. Similarly, the doping of Ta5+ or V5+ in MoO3‐x improves the passivated contact performance with silicon, while the former increases the concentration of oxygen vacancies and the latter reduces it. The solar cell with the structure of Ag/MoO3‐x:Nb/p‐Si exhibits a conversion efficiency of 18.37%, which is the highest so far reported for the solution‐processed MoO3‐x/silicon heterojunction. Our work demonstrates a feasible strategy of tuning hole selectivity in MoO3‐x by doping for high efficiency solar cells and other optoelectronic device applications. This article is protected by copyright. All rights reserved.
A two-terminal (2T) perovskite/silicon heterojunction tandem solar cell (PVSK/SHJ) is considered one of the most promising candidates for next-generation photovoltaics with the possibility of achieving a power conversion efficiency (PCE) exceeding 30% at low production cost. However, the current mismatch and voltage loss have seriously decreased the performance of 2T PVSK/SHJ tandem solar cells. Here, we report the composition engineering for perovskite top cells to prepare a high performance 2T tandem cell by tuning CsBr co-evaporating rates and increasing concentrations of FAI/FABr solutions. We show that the variation in composition for the perovskite absorber effectively optimized the band gap and diminished the defects of the top cell. Our investigations reveal that the current mismatch of sub-cells was carefully tuned by introducing CsBr at varied co-evaporating rates and the voltage loss was decreased by increasing concentrations of FAI/FABr solutions. Thus, we achieved a PCE of 23.22% in two-terminal monolithic tandems with an area of 1.2 cm2 by tuning the composition of the perovskite absorber.
Extensive efforts have been made to develop wide‐bandgap metal compound‐based carrier‐selective contacts to improve the performance of crystalline silicon (c‐Si) solar cells, by mitigating the deleterious effects of metal‐Si contact directly. Herein, thermally‐evaporated wide‐bandgap strontium oxide (SrOx) is exploited as an electron‐selective contact for c‐Si solar cells. Benefiting from a lower work function (3.1 eV) of SrOx, a strong downward band bending is achieved at the n‐type c‐Si/SrOx interface, enabling the electron‐selective transport characteristic. Thin SrOx films simultaneously provide moderate surface passivation after annealing and enable a low contact resistivity on c‐Si surfaces. By the implementation of a single‐dielectric‐layer SrOx‐based rear contact, a champion power conversion efficiency of 20.0% is realized on the n‐type c‐Si solar cell featuring an intriguing fill factor of 82.8%. Moreover, electron‐selective SrOx contact is demonstrated to show high thermal stability up to 500 °C. The SrOx layer formed by a facile thermal evaporation process presents a unique opportunity to develop highly efficient and low‐cost c‐Si solar cells. This article is protected by copyright. All rights reserved.
NiOx is a p-type semiconductor material with wide band-gap (3.6-4.0 eV) and good thermal and chemical stability. In terms of energy band structure, NiOx/n-Si possesses low valence band offset to allow holes and high conduction band offset to block electrons. NiOx is thus a promising hole-selective layer for n-type c-Si based heterojunction (HJT) solar cells. However, intrinsic NiOx suffers from low carrier concentration and poor conductivity, which severely limits its development in photovoltaics. This study aimed to obtain Ag-doped NiOx film with high carrier concentration and low resistivity by co-sputtering using high-purity Ag and NiOx target for high efficiency solar cells. The results show that appropriate Ag doping can increase the acceptor concentration of the film, promote the tunnelling effect, reduce interface recombination, and thus improve the device efficiency. When Ag content is 2.4%, the fill factor of Al/ITO/NiOx:Ag/SiOx/c-Si/SiOx/Al solar cell is increased from 52.97% to 68.42%, and the power conversion efficiency reaches 9.11%. Combined with the analysis of AFORS-HET simulation, the mechanism how Ag doping works in the hetrojunction is revealed.
Recently, the focus of solar cell research has shifted from Passivated Emitter and Rear Cell and Passivated Emitter and Rear Locally-diffused solar cells to Heterojunction with Intrinsic Thin Layer solar cells. Compared to the already mass-produced Passivated Emitter and Rear Cell and Passivated Emitter and Rear Locally-diffused solar cells, the passivation with the intrinsic thin layer of amorphous on the wafer surface, the continuous improvement of the emitter thickness, and doping concentration have enabled Heterojunction with Intrinsic Thin Layer solar cells to obtain open-circuit voltage above 750 mV while maintaining a short circuit current density of ~ 40 mA/cm2 and an Fill Factor of ~ 84%. This leads to a theoretical conversion efficiency of 27.5% (monolithic) to 29% (tandem), which is much higher than the theoretical final conversion efficiency of ~ 24.5% achieved by Passivated Emitter and Rear Cell and Passivated Emitter and Rear Locally-diffused solar cells at a short-circuit voltage of 706 mV. To further approach the theoretical maximum efficiency, improvements, and optimization of the fabrication process, as well as change in material of the front emitter layer and thus the band gap, conductivity, and defect density can be adopted. Efficiencies of up to 28.27% were achieved using hydrogenated nanocrystalline silicon with a bandgap of 1.9 eV as the emitter layer.
An exact analytical expression for the probability of photon reabsorption and recycling in an idealized solar cell with two Lambertian surfaces is derived. The existing approximations are found to agree with the exact formula to within 5%. The most accurate approximation turned out to be the simplest one that sets the reabsorption probability to the weak-absorption limit of the cell absorptance. The maximal photoconversion efficiency of a silicon solar cell is evaluated to be 29.5% at the base thickness of 98
$\mu$
m.
The design of carbon material-based heterojunction solar cells (HJSCs) provides a promising approach to convert and collect solar energy. With unique photonic, electronic and mechanical properties, versatile carbon materials have attracted considerable attention in the design of heterojunction structures because of the multi-functional applications of carbon materials in the booming field of photovoltaics (PVs). Significant effort has been devoted to enhancing the light absorption capacity and charge/carrier transporting ability to obtain state-of-the-art HJSCs. This review presents the basic application of various carbon materials for PVs and the basic principles of carbon materials in HJSCs. Several optimisation methods for carbon nanotube (CNT) film modification and cell performance, such as optical property and Fermi level tuning, as well as morphological design and interface engineering, are highlighted in a summary of the state-of-art progress of CNT-based HJSCs. Moreover, the representative applications of carbon materials based flexible HJSCs are discussed. Finally, promising pathways and prospects of CNTs in HJSCs and their advanced devices are proposed using film modification, mechanism modulation, and device design to achieve cost-effective, high-performance, and flexible solar cells (SCs).
GaN-based electronics have witnessed an increase in both research and industrial activities, first spurred by the successful demonstration of GaN LEDs, and are now expanding into transistors and photovoltaic cells. In addition, GaN/GaAs heterojunction devices are currently receiving much interest. In this study, we conduct rigorous optoelectronic computational analysis of cubic phase GaN (c-GaN)/GaAs heterojunction solar cells for a comprehensive understanding of the cell. We utilize a compositionally graded GaAs
$_{\text{1}-\textit{x}}$
N
$_{\textit{x}}$
buffer layer to reduce defect states at the heterojunction interface caused by a significant lattice mismatch between c-GaN and GaAs. Furthermore, we enhance the performance of the cell by optimizing GaAs absorber layer thickness and c-GaN buffer layer doping concentration. Moreover, we examine the effects of GaAs
$_{{\text{1}} -\textit{x}}$
N
$_{\textit{x}}$
/GaAs interface recombination velocity (IRV) on the cell. Overall, we achieve
$\sim$
23% power conversion efficiency within 1.25-
$\mu$
m thin-film GaAs at low GaAs
$_{{\text{1} -{ }}\textit{x}}$
N
$_{\textit{x}}$
/GaAs IRV. The analyses and results presented in this study demonstrate the vast application potential of c-GaN/GaAs heterojunction in high-efficiency solar cells.
Antimony sulfide (Sb2S3) and antimony selenide (Sb2Se3) solar cells are considered as emerging photovoltaic devices due to their earth abundance, low cost, non-toxic property and high optical absorption. Also, the buffer layer for the solar cells should be non-toxic. Hence, the need to have a Cd-free buffer layer is a growing interest among the researchers. In this study, we modeled Mo/Sb2S3/TiO2/FTO and Mo/Sb2Se3/TiO2/FTO solar cells and theoretically calculated the effect of different device parameters on the properties of solar cells by SCAPS-1D (Solar Cell Capacitance Simulator) software. By optimizing different properties of Sb2S3 and Sb2Se3likethickness, hole mobility, recombination defect density and their interface, a solar cell efficiency beyond 8 % could be achieved. The optimized thicknesses for Sb2Se3 and Sb2S3absorberswere found to be 900 nm and 300 nm, respectively. A maximum efficiency of 8.67 % and 9.4 % were obtained for Sb2S3 and Sb2Se3 based solar cells, respectively after optimizing all the parameters. These results obtained by simulation study gives us useful insights about the designing and fabrication of Sb2S3 and Sb2Se3 based solar cells.
Thanks to the prominent passivating contact structures, silicon heterojunction (SHJ) solar cell has recently achieved revolutionary advancements in the photovoltaic industry. This is, however, bound to further strengthen its contact performance for gaining the competitive edge in the period of technology transformation. Here, we developed SHJ cells with improved rear contact consisting of a p-type doped nanocrystalline silicon and a tailored transparent conductive oxide. Benefiting from the low contact resistance of hole-selective contacts (< 5 mΩ·cm ² ), a high power conversion efficiency of 26.74% together with a record filling factor (FF) of 86.48% were certified on industrial-grade silicon wafers (274 cm ² , M6 size). The electrical properties of the modified SHJ cells were thoroughly analyzed in comparison with the normal p-type transporting layer counterparts ( i.e. , amorphous silicon), and the improved charge carrier transport in behind were also fully demonstrated.
The ongoing success of tunnel oxide passivating contact (TOPCon) solar cells in the photovoltaic community in conjunction with the continuous advancements in the fabrication technologies of perovskite‐based tandem devices make it possible to access highly‐efficient perovskite/TOPCon tandem solar cells (TSCs). However, the development of such tandem solar cells is still in its infancy. One of the main challenges facing these devices is the balance of passivation and contact properties, especially on the textured crystalline silicon substrates. This article focuses on the double‐textured TOPCon structures, and systematically investigates their passivation and contact properties with the purpose of balancing charge‐carrier recombination and transport properties. The experiment results show that passivation and contact properties of the double‐textured TOPCon structures can be well‐regulated by means of rearranging the schedules of annealing processes and radio frequency powers of SiOx deposition. The mechanisms of charge‐carrier transport on the textured structures are closely studied, suggesting that charge carriers prefer to transport via the valleys of pyramids where the SiOx layer is thin or missing. As a result, the proof‐of‐concept perovskite/TOPCon TSCs featuring the double‐textured structures are successfully fabricated with a remarkable efficiency of 28.49%. Passivation and contact performance of double‐textured tunnel oxide passivating contact (TOPCon) structures are promoted by rearranging the schedules of annealing processes and radio frequency powers of depositing SiOx films, and the underlying mechanisms of charge‐carrier transport on the textured structures are closely studied. The proof‐of‐concept perovskite/TOPCon tandem solar cells featuring double‐textured structures are fabricated, yielding an outstanding efficiency of 28.49%.
Back contact heterojunction (IBC-HIT) solar cells is one of the most promising technology for the upcoming generations of high efficiency crystalline-Silicon (c-Si) based photovoltaic modules [1] . However, the industrialization of the IBC-HIT technology is actually constrained by the complexity of the back side cell processing, which usually involves costly and time consuming photolithography steps. CEA-INES is currently developing a method based only on laser ablation for the structuration of IBC-HIT solar cells [2] . Laser ablation is indeed a fast and low cost technique that also allows the patterning of the back side amorphous (a-Si:H) layers on large area IBC-HIT solar cells. However laser irradiation might induce some damage at the c-Si/a-Si:H interface thus limiting the final performance of the devices. In this work, we compare the results obtained with our laser patterning process for different stack configurations and laser ablation conditions (532 nm and 355 nm). We will also discuss about the criteria used for the choice of the different materials and the laser ablation conditions needed in order to successfully pattern both the emitter and BSF (Back Surface Field) regions of the cell. Our best cell efficiency achieved up to now is 20.55% on an area of 18.11 cm 2 .
Screen-printing provides an economically attractive means for making Ag electrical contacts to Si solar cells, but the use of Ag substantiates a significant manufacturing cost, and the glass frit used in the paste to enable contact formation contains Pb. To achieve optimal electrical performance and to develop pastes with alternative, abundant and non-toxic materials, a better understanding the contact formation process during firing is required. Here, we use in situ X-ray diffraction during firing to reveal the reaction sequence. The findings suggest that between 500 and 650 °C PbO in the frit etches the SiNx antireflective-coating on the solar cell, exposing the Si surface. Then, above 650 °C, Ag(+) dissolves into the molten glass frit - key for enabling deposition of metallic Ag on the emitter surface and precipitation of Ag nanocrystals within the glass. Ultimately, this work clarifies contact formation mechanisms and suggests approaches for development of inexpensive, nontoxic solar cell contacting pastes.
With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic-inorganic perovskite materials.
The objective of this study is to optimize module technologies to obtain the lowest price per Watt peak ($/W p) ratio and the maximum power output of a flat-plate module for a given number of high-efficiency solar cells. Using B-doped p-type monocrystalline Cz silicon wafers, 500 pieces of full square[Formula: see text] solar cells with a passivated emitter and rear local contacts (PERC) were fabricated with an average efficiency of 20.6% by in-house measurement. The module includes half-cells for low interconnection losses, as well as a novel light-trapping scheme including light capture ribbon connected to the cells and a structured light reflective film between cells combined with an optimized large cell gap. The module using 60 pieces of the 20.6% efficient PERC solar cells has achieved a new world record, with a peak power output of 335.2 Wp in September 2014, demonstrating a large cell-to-module factor, which is defined as Pmmp of module divided by the sum of cell Pmmp. The CTM factor of the champion module is greater than 1.11.
We analyze the optical losses that occur in interdigitated back-contacted amorphous/crystalline silicon heterojunction solar cells. We show that in our devices, the main loss mechanisms are similar to those of two-side contacted heterojunction solar cells. These include reflection and escape-light losses, as well as parasitic absorption in the front passivation layers and rear contact stacks. We then provide practical guidelines to mitigate such reflection and parasitic absorption losses at the front side of our solar cells, aiming at increasing the short-circuit current density in actual devices. Applying these rules, we processed a back-contacted silicon heterojunction solar cell featuring a short-circuit current density of 40.9 mA/cm2 and a conversion efficiency of 22.0%. Finally, we show that further progress will require addressing the optical losses occurring at the rear electrodes of the back-contacted devices.
We report on the fabrication of back-contacted silicon heterojunction solar cells with conversion efficiencies above 21%. Our process technology relies solely on simple and size-scalable patterning methods, with no high-temperature steps. Using in situ shadow masks, doped hydrogenated amorphous silicon layers are patterned into two interdigitated combs. Transparent conductive oxide and metal layers, forming the back electrodes, are patterned by hot melt inkjet printing. With this process, we obtain high short-circuit current densities close to 40 mA/cm$^{2}$ and open-circuit voltages exceeding 720 mV, leading to a conversion efficiency of 21.5%. However, moderate fill factor values limit our current device efficiencies. Unhindered carrier transport through both heterocontact layer stacks, as well as higher passivation quality over the minority carrier-injection range relevant for solar cell operation, are identified as key factors for improved fill factor values and device performance.
Recently, several parameters relevant for modeling crystalline silicon solar cells were improved or revised, e.g., the international standard solar spectrum or properties of silicon such as the intrinsic recombination rate and the intrinsic carrier concentration. In this study, we analyzed the influence of these improved state-of-the-art parameters on the limiting efficiency for crystalline silicon solar cells under 1-sun illumination at 25 °C, by following the narrow-base approximation to model ideal solar cells. We also considered bandgap narrowing, which was not addressed so far with respect to efficiency limitation. The new calculations that are presented in this study result in a maximum theoretical efficiency of 29.43% for a 110-μm-thick solar cell made of undoped silicon. A systematic calculation of the I--V parameters as a function of the doping concentration and the cell thickness together with an analysis of the loss current at maximum power point provides further insight into the intrinsic limitations of silicon solar cells.
Accurate modeling of the intrinsic recombination in silicon is important for device simulation as well as for interpreting measured effective carrier lifetime data. In this contribution we study the injection-dependent effective carrier lifetime applying advanced surface passivation techniques based on Al2O3 or SiNx We show that in some cases the measured lifetime data significantly exceeds the previously accepted intrinsic lifetime limit proposed by Kerr and Cuevas [1]. To verify our measurements we independently perform lifetime measurements with different measurement techniques in two different laboratories. Based on effective lifetime measurements we develop an advanced parameterization of the intrinsic lifetime in crystalline silicon at 300 K as a function of the doping density and the injection level, which accounts for Coulomb-enhanced Auger recombination and Coulomb-enhanced radiative recombination.
An accurate quantitative description of the Auger recombination rate in silicon as a function of the dopant density and the carrier injection level is important to understand the physics of this fundamental mechanism and to predict the physical limits to the performance of silicon based devices. Technological progress has permitted a near suppression of competing recombination mechanisms, both in the bulk of the silicon crystal and at the surfaces. This, coupled with advanced characterization techniques, has led to an improved determination of the Auger recombination rate, which is lower than previously thought. In this contribution we present a systematic study of the injection-dependent carrier recombination for a broad range of dopant concentrations of high-purity n-type and p-type silicon wafers passivated with state-of-the-art dielectric layers of aluminum oxide or silicon nitride. Based on these measurements, we develop a general parametrization for intrinsic recombination in crystalline silicon at 300 K consistent with the theory of Coulomb-enhanced Auger and radiative recombination. Based on this improved description we are able to analyze physical aspects of the Auger recombination mechanism such as the Coulomb enhancement.
This work demonstrates the feasibility and usefulness of a new method to analyse the quality of the rear contact of silicon solar cells separated from other ohmic loss channels as e.g. the resistive loss in the front contact grid. The measurement is based on SunsVoc data at high illumination densities between 1 and 1000 suns. Generally the rear contacts can be described as a Schottky diode with a shunt resistor in parallel. At 1 sun operation conditions the back contact is fully dominated by the shunt showing an ohmic behaviour. However, at high illumination densities the Schottky diode can not be shunted completely anymore resulting in an increasing voltage which is opposed to the pn junction voltage. Finally a reversal point in the SunsVoc characteristics can be observed, i.e. the voltage decreases with increasing illumination density. The evaluation of this characteristic behaviour is used to extract physical parameters like the barrier height of the contact. Additionally the contact quality is assessed for different contact types and base doping concentrations. The predicted contact quality is in good correlation with the measured fill factors of the cells.
Our unique, high-efficiency c-Si solar cell, named the HIT cell, has shown considerable potential to improve junction properties and surface passivation since it was first developed. The improved properties in efficiency and temperature dependence compared to conventional p – n diffused c-Si solar cells are featured in HIT power 21TM solar cell modules and other applications which are now on the market. In the area of research, further improvement in the junction properties of the a-Si/c-Si heterojunction has been examined, and the highest efficiency to date of 20.1% has recently been achieved for a cell size of 101 cm². The high open circuit voltage exceeding 700 mV, due to the excellent surface passivation of the HIT structure, is responsible for this efficiency. In this paper, recent progress in HIT cells by Sanyo will be introduced. Copyright © 2000 John Wiley & Sons, Ltd.
In the 1980s, advances in the passivation of both cell surfaces led to the first crystalline silicon solar cells with conversion efficiencies above 20%. With today's industry trend towards thinner wafers and higher cell efficiency, the passivation of the front and rear surfaces is now also becoming vitally important for commercial silicon cells. This paper presents a review of the surface passivation methods used since the 1970s, both on laboratory-type as well as industrial cells. Given the trend towards lower-cost (but also lower-quality) Si materials such as block-cast multicrystalline Si, ribbon Si or thin-film polycrystalline Si, the most promising surface passivation methods identified to date are the fabrication of a p–n junction and the subsequent passivation of the resulting silicon surface with plasma silicon nitride as this material, besides reducing surface recombination and reflection losses, additionally provides a very efficient passivation of bulk defects. Copyright © 2000 John Wiley & Sons, Ltd.
Improving the photoconversion efficiency of silicon solar cells is crucial to further the deployment of renewable electricity. Essential device properties such as lifetime, series resistance and optical properties must be improved simultaneously to reduce recombination, resistive and optical losses. Here, we use industrially compatible processes to fabricate large-area silicon solar cells combining interdigitated back contacts and an amorphous silicon/crystalline silicon heterojunction. The photoconversion efficiency is over 26% with a 180.4 cm 2 designated area, which is an improvement of 2.7% relative to the previous record efficiency of 25.6%. The cell was analysed to characterize lifetime, quantum efficiency, and series resistance, which are essential elements for conversion efficiency. Finally, a loss analysis pinpoints a path to approach the theoretical conversion efficiency limit of Si solar cells, 29.1%.
In this work, we present the results of the replacement of silver screen printing on heterojunction crystalline silicon (c-Si) solar cells with a copper metallization scheme that has the potential to reduce the manufacturing cost while improving their performance. We report for the first time silver-free heterojunction c-Si solar cells on 6-in. wafers. The conversion efficiency reached is a record 22.1% for c-Si technology for this wafer size (Voc = 729 mV, Jsc = 38.3 mA/cm², FF= 79.1%). The total power generated is more than 5 W for 1-sun illumination, which is a world record. Heat-damp reliability tests show comparable performance for mini-modules fabricated with copper metalized as for conventional silver screen printed heterojunction c-Si solar cells.
Suns-V
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measurements exclude parasitic series resistance effects and are, therefore, frequently used to study the intrinsic potential of a given photovoltaic technology. However, when applied to a-Si/c-Si heterojunction (SHJ) solar cells, the Suns-V
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curves often feature a peculiar turnaround at high illumination intensities. Generally, this turn-around is attributed to extrinsic Schottky contacts that should disappear with process improvement. In this paper, we demonstrate that this voltage turnaround may be an intrinsic feature of SHJ solar cells, arising from the heterojunction (HJ), as well as its associated carrier-transport barriers, inherent to SHJ devices. We use numerical simulations to explore the full current-voltage (J-V) characteristics under different illumination and ambient temperature conditions. Using these characteristics, we establish the voltage and illumination-intensity bias, as well as temperature conditions necessary to observe the voltage turnaround in these cells. We validate our turnaround hypothesis using an extensive set of experiments on a high-efficiency SHJ solar cell and a molybdenum oxide (MoO
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) based hole collector HJ solar cell. Our work consolidates Suns-V
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as a powerful characterization tool for extracting the cell parameters that limit efficiency in HJ devices.
In this work, we present the latest result of the Cu electroplated heterojunction by Kaneka Corporation. The top electrode on heterojunction crystalline silicon (c-Si) solar cells usually defined by silver screen printing is replaced with a copper metallization scheme that has the potential to reduce the manufacturing cost while improving the heterojunction performance. We show the progress on the heterojunction c-Si solar cells by Kaneka and report on heterojunction c-Si solar cells on 6 inch wafers with a conversion efficiency of 23.5% independently confirmed by ISE-CALLAB (Voc = 737 mV, Jsc = 39.97 mA/cm2, FF = 79.77%). Heat-damp reliability tests show comparable performance for mini-modules fabricated with copper metalized as for conventional silver screen printed heterojunction c-Si solar cells.
This work explores the application of transparent nitrogen doped copper oxide (CuOx:N) films deposited by reactive sputtering to create hole-selective contacts for p-type crystalline silicon (c-Si) solar cells. It is found that CuOx:N sputtered directly onto crystalline silicon is able to form an Ohmic contact. X-ray photoelectron spectroscopy and Raman spectroscopy measurements are used to characterise the structural and physical properties of the CuOx:N films. Both the oxygen flow rate and the substrate temperature during deposition have a significant impact on the film composition, as well as on the resulting contact resistivity. After optimization, a low contact resistivity of ∼10 mΩ cm2 has been established. This result offers significant advantages over conventional contact structures in terms of carrier transport and device fabrication.
Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since January 2016 are reviewed. Copyright © 2016 John Wiley & Sons, Ltd.
All previous concepts for describing the effective local series resistance of really existing solar cells, as it can be measured e.g. by luminescence imaging, try to describe it by a single local number. In solar cells showing an inhomogeneous saturation current density, this results in different series resistance images for the dark and illuminated case. The reason is the distributed character of the series resistance and the different diode current profiles under these different conditions. In this work the well-known finite element concept is used for describing a solar cell, which contains separate resistors carrying horizontal and vertical currents. A strategy is proposed how to fit these resistors to results of electroluminescence and lock-in thermography images of a real solar cell, leading to separate images of the local horizontal grid resistance, which may also show broken gridlines, and the local vertical'lumped emitter contact resistance'. The latter lumps all resistive inhomogeneities of the cell, caused by a possibly inhomogeneous contact-, emitter-, grid-, bulk-, and back contact resistance. It will be shown that this description of the local series resistance reasonably describes both the dark and illuminated case, even in inhomogeneous multicrystalline silicon solar cells.
Modelling and experimental results on IBC SHJ solar cells are presented in this paper. Different rear emitter designs are studied by 2D simulation and tested on experimental devices. IBC SHJ cells are fabricated with the SLASH process based on laser patterning steps, and the performance of such devices is shown to be limited by the rear emitter geometry (contacting scheme and total emitter fraction). On one hand IBC SHJ cells have to be carefully designed concerning the contacting scheme due to distributed series resistance effects. On the other hand SHJ technology allows a very high surface passivation level, and this reduces the influence of the emitter fraction on the cells performances.
We have achieved a certified 25.1% conversion efficiency in a large area (151.9 cm2) heterojunction (HJ) crystalline Si (c-Si) solar cell with amorphous Si (a-Si)passivation layer. This efficiency is a world record in a both-side-contacted c-Si solar cell. Our high efficiency HJ c-Si solar cells are investigated from the standpoint of the effective minority carrier lifetime (τe), and the impact of τe on fill factor (FF) is discussed. The τe measurements of our high efficiency HJ c-Si solar cells reveal that τe at an injection level corresponding to an operation point of maximum power is dominated by the carrier recombination at the a-Si/c-Si interface. By optimization of the process conditions, the carrier recombination at the a-Si/c-Si interface is reduced, which leads to an improvement of the FF by an absolute value of 2.7%, and a conversion efficiency of 25.1% has been achieved. These results indicate that the reduction of carrier recombination centers at the a-Si/c-Si interface should be one of the most crucial issues for further improvement of FF even in the HJ c-Si solar cells with efficiency over 25%.
An energy conversion efficiency of 25.1% was achieved in heterojunction back contact (HBC) structure Si solar cell utilizing back contact technology and an amorphous silicon thinfilm technology. A new patterning process was established, and it was applied to the fabrication process of HBC cells. In addition, the unique technology of the surface mount technology concept contributed to the superior performance of HBC cell. A short circuit current density (Jsc) and an open-circuit voltage (Voc) were 41.7 mA/cm2 and 736 mV, respectively. The high Jsc as well as the high Voc indicates the strength of HBC structure cell. Besides, a high fill factor of 0.82 was obtained, which shows that HBC structure cell does not have any fundamental critical losses caused from series resistance or shunt resistance. Such high values of I-V parameter means that the patterning process was properly performed.
The contact resistance of amorphous Si (a-Si:H)/transparent-conducting oxide (TCO) is evaluated and analyzed in terms of the contribution to the series resistance (R-s) and fill factor (FF) in the Si heterojunction back-contact (HBC) solar cell. It is shown that p-a-Si:H (emitter) and n-a-Si:H (back surface field: BSF)/TCO contact resistance are of similar values (0.37-38 Omega cm(2)) which are much higher than those of doped crystalline Si/metal contacts used in conventional Si solar cells. Of some factors affecting R-s loss in the HBC solar cell, BSF/TCO contact is the most significant one when considering the contact area. By interleaving the n-type microcrystalline Si (n-mu c-Si) between n-a-Si:H and TCO, 6-inch HBC solar cell with 20.5% efficiency is obtained, which was attributed to the reduced R-s and improved FF. It is noteworthy that the variations of R-s and FF are well estimated by measuring BSF-contact resistance, and are close to the empirical data: reduction in R-s to 1.77 Omega cm(2) and the increase in FF by 6.0% compared to the cell without n-mu c-Si interface layer. The results indicate that there is much room for higher efficiency by reducing the emitter- and BSF-contact resistance. Nonetheless, the method developed here can be a powerful tool to analyze the resistance component in HBC cell.
The crystalline silicon heterojunction structure adopted in photovoltaic modules commercialized as Panasonic's HIT has significantly reduced recombination loss, resulting in greater conversion efficiency. The structure of an interdigitated back contact was adopted with our crystalline silicon heterojunction solar cells to reduce optical loss from a front grid electrode, a transparent conducting oxide (TCO) layer, and a-Si:H layers as an approach for exceeding the conversion efficiency of 25%. As a result of the improved short-circuit current (Jsc), we achieved the world's highest efficiency of 25.6% for crystalline silicon-based solar cells under 1-sun illumination (designated area: 143.7 cm2).
The interdigitated back contact (IBC) solar cells developed at the Australian National University have resulted in an independently confirmed (Fraunhofer Institut für Solare Energiesysteme (ISE) CalLab) designated-area efficiency of 24.4 ± 0.7%, featuring short-circuit current density of 41.95 mA/cm2, open-circuit voltage of 703 mV and 82.7% fill factor. The cell, 2 × 2 cm2 in area, was fabricated on a 230 µm thick 1.5 Ω cm n-type Czochralski wafer, utilising plasma-enhanced chemical vapour deposition (CVD) SiNx front-surface passivation without front-surface diffusion, rear-side thermal oxide/low-pressure CVD Si3N4 passivation stack and evaporated aluminium contacts with a finger-to-finger pitch of 500 µm. This paper describes the design and fabrication of lab-scale high-efficiency IBC cells. Characterisation of optical and electronic properties of the best produced cell is made, with subsequent incorporation into 3D device modelling used to accurately quantify all losses. Loss analysis demonstrates that bulk and emitter recombination, bulk resistive and optical losses are dominant and suggests a clear route to efficiency values in excess of 25%. Additionally, laser processing is explored as a means to simplify the manufacture of IBC cells, with a confirmed efficiency value of 23.5% recorded for cells fabricated using damage-free deep UV laser ablation for contact formation. Meanwhile all-laser-doped cells, where every doping and patterning step is performed by lasers, are demonstrated with a preliminary result of 19.1% conversion efficiency recorded. Copyright © 2014 John Wiley & Sons, Ltd.
A new record conversion efficiency of 24.7% was attained at the research level by using a heterojunction with intrinsic thin-layer structure of practical size (101.8 cm2, total area) at a 98-μm thickness. This is a world height record for any crystalline silicon-based solar cell of practical size (100 cm2 and above). Since we announced our former record of 23.7%, we have continued to reduce recombination losses at the hetero interface between a-Si and c-Si along with cutting down resistive losses by improving the silver paste with lower resistivity and optimization of the thicknesses in a-Si layers. Using a new technology that enables the formation of a-Si layer of even higher quality on the c-Si substrate, while limiting damage to the surface of the substrate, the Voc has been improved from 0.745 to 0.750 V. We also succeeded in improving the fill factor from 0.809 to 0.832.
Our unique, high-efficiency c-Si solar cell, named the HIT cell, has shown considerable potential to improve junction properties and surface passivation since it was first developed. The improved properties in efficiency and temperature dependence compared to conventional p – n diffused c-Si solar cells are featured in HIT power 21TM solar cell modules and other applications which are now on the market. In the area of research, further improvement in the junction properties of the a-Si/c-Si heterojunction has been examined, and the highest efficiency to date of 20.1% has recently been achieved for a cell size of 101 cm2. The high open circuit voltage exceeding 700 mV, due to the excellent surface passivation of the HIT structure, is responsible for this efficiency. In this paper, recent progress in HIT cells by Sanyo will be introduced. Copyright © 2000 John Wiley & Sons, Ltd.
The construction of a 22.2% efficient single-crystal silicon solar cell
fabricated at Stanford University is described. The cell dimensions were
3 x 5 mm and 100 microns thick with a base lifetime of 500 microseconds.
The cell featured light trapping between a texturized top surface and a
reflective bottom surface, small point contact diffusions, alternating
between n-type and p-type in a polka-dot pattern on the bottom surface,
and a surface passivation on all surfaces between contact regions.
We present back-contacted amorphous/crystalline silicon heterojunction solar cells (IBC-SHJ) on n-type substrates with fill factors exceeding 78% and high current densities, the latter enabled by a SiNx /SiO2 passivated phosphorus-diffused front surface field. Voc calculations based on carrier lifetime data of reference samples indicate that for the IBC architecture and the given amorphous silicon layer qualities an emitter buffer layer is crucial to reach a high Voc, as known for both-side contacted silicon heterojunction solar cells. A back surface field buffer layer has a minor influence. We observe a boost in solar cell Voc of 40 mV and a simultaneous fill factor reduction introducing the buffer layer. The aperture-area efficiency increases from 19.8 ± 0.4% to 20.2 ± 0.4%. Both, efficiencies and fill factors constitute a significant improvement over previously reported values. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Excitonic effects are known to enhance the rate of intrinsic recombination processes in crystalline silicon. New calculations for the limiting efficiency of silicon solar cells are presented here, based on a recent parameterization for the Coulomb-enhanced Auger recombination rate, which accounts for its dopant type and dopant density dependence at an arbitrary injection level. Radiative recombination has been included along with photon recycling effects modeled by three-dimensional ray tracing. A maximum cell efficiency of 29.05% has been calculated for a 90-μm-thick cell made from high resistivity silicon at 25°C. For 1 Ω cm p-type silicon, the maximum efficiency reduces from 28.6% for a 55-μm-thick cell in the absence of surface recombination, down to 27.0% for a thickness in the range 300–500 μm when surface recombination limits the open-circuit voltage to 720 mV. Copyright © 2002 John Wiley & Sons, Ltd.
Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since July 2011 are reviewed. Copyright © 2011 John Wiley & Sons, Ltd. Consolidated tables showing an extensive listing of the highest independently confirmed efficiencies for solar cells and modules are presented. Guidelines for inclusion of results into these tables are outlined, and new entries since July 2011 are reviewed.
The so-called "limit efficiency" of a silicon solar operating at one-sun is well established at approximately 29%, and laboratory cells have reached 25%. The efficiencies of commercially available silicon solar cells have been increasing over time, however, only recently have the highest performance commercial cells reached 20% efficiency. This presentation discusses the prospects of how the limit efficiency may be approached more closely in practical cells. Surprisingly, presently available silicon has sufficient minority carrier lifetime to achieve the goal. In fact, all aspects are in place for approaching 29% except for the existence of a suitable passivated contact technology.
In this work, we investigated two alternative approaches for the front surface passivation of interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells: (1) with plasma enhanced chemical vapor deposited (PEVCD) a-Si-based stack structure consisting of a-Si:H/a-SiN<sub>x</sub>:H/a-SiC:H, and (2) with physical vapor deposited (PVD) zinc sulfide (ZnS) film. The processing temperatures for both the approaches are under 300°C. Effective surface recombination velocities (SRV) of <; 6.2cm/s and <; 35cm/s are obtained with stack structure and ZnS respectively on n-type float zone (FZ) crystalline silicon (c-Si) wafers. The anti-reflection (AR) properties of these two passivation approaches are studied and the optimization procedure of the stack structure was discussed and shown to improve the photo-generated current. The IBC-SHJ solar cells were fabricated using both the front surface passivation approaches and a 15% cell efficiency was achieved on 150μm thick FZ c-Si wafer without surface texturing and optical optimization.
Back Amorphous-Crystalline Silicon Heterojunction (BACH) photovoltaic device integrates a range of high efficiency features while using low temperature (~200°C) fabrication processes. High efficiency features include back contact metallization, optimum interfacial passivation, and front-side and rear-side reflective coatings and scatterers for maximum light trapping. Two types of BACH cell prototypes were fabricated in this work with the best performing cell having an AM1.5G conversion efficiency of 8.1%, V<sub>OC</sub> = 0.536 V, J<sub>SC</sub> = 20 mA/cm<sup>2</sup> and FF = 75.5%. Theoretically, the BACH solar cell concept has the potential of attaining energy conversion efficiencies in the 20 - 25% range. In this first set of cells, the BACH cell performance is limited by poor surface passivation and un-optimized cell design. Recent experiments with various passivation procedures has led to high minority carrier lifetimes in the ms range while carrying out the processes at low temperature, thus opening the way to higher efficiency BACH cells.