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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 theoretical SCR recombination velocity is found from expression (26). Figure 4 shows the experimental and theoretical dependencies of the recombination rate in the SCR on the excess concentration, obtained using the parameters from Yoshikawa et al. 58 As can be seen from the figure, the theoretical and experimental dependencies agree well with each other. The figure also shows that at an excess concentration of the order of 3 Â 10 15 cm À3 , which corresponds to the excess concentration at the point of maximum power, the two contributions to expression (26), namely, the SCR recombination velocity S SCR and the recombination velocity in the region that has become neutral, S SCRÀn , become comparable. ...
... In the SCs with well-passivated surfaces, surface recombination affects the efficiency much less than the recombination in the SCR. For example, for the SCs reported by Yoshikawa et al., 58 neglecting the SCR recombination leads to an increase in efficiency by 1%, while neglecting surface recombination increases the efficiency by 0.12%. Since the SCR recombination has a stronger effect than the surface recombination, which is always taken into account, the SCR recombination must also be considered in SC modeling. ...
... Figure 7 shows this curve for the SCs from Ref. 55 (symbols), compared to the theoretical curves obtained in the approximations of six and four recombination channels. Within 55 Sachenko et al., 57 Lin et al., 18 Yoshikawa et al., 58 and Richter et al. 32 The two lowest theoretical curves are plotted under the assumption that the lifetime in the SCR is equal to the bulk lifetime in the sample discussed in Richter et al. 32 the four-channel model, SRH, radiative, Auger, and surface recombination processes are taken into account. The non-radiative exciton Auger recombination and the SCR recombination in the six-channel calculation are also included. ...
Since the photoconversion efficiency η of the silicon-based solar cells (SCs) under laboratory conditions is approaching the theoretical fundamental limit, further improvement of their performance requires theoretical modeling and/or numerical simulation to optimize the SCs parameters and design. The existing numerical approaches to modeling and optimizing the key parameters of high-efficiency solar cells based on monocrystalline silicon, the dominant material in photovoltaics, are described. It is shown that, in addition to the four usually considered recombination processes, namely, Shockley–Read-Hall, surface, radiative, and band-to-band Auger recombination mechanisms, the non-radiative exciton Auger recombination and recombination in the space charge region (SCR) have to be included. To develop the analytical SC characterization formalism, we proposed a simple expression to model the wavelength-dependent external quantum efficiency of the photocurrent near the absorption edge. Based on this parameterization, the theory developed allows for calculating and optimizing the base thickness-dependent short-circuit current, the open-circuit voltage, and the SC photoconversion efficiency. The accuracy of the approach to optimizing solar cell parameters, particularly thickness and base doping level, is demonstrated by its application to three Si solar cells reported in the literature: one with an efficiency of 26.63%, another with 26.81%, and a third with a record efficiency of 27.3%. The results show that the developed formalism enables further optimization of solar cell thickness and doping levels, leading to potential increases in efficiency.
... We apply the formalism above to (i) the Sanyo HIT SC 52,53 , (ii) to a commercial SC with a p-n junction manufactured by the SunPower technology (see Ref. 54 for details), (iii) the HIT SC from Ref. 55, and (iv) to the HIT element with the record for efficiency to date from Ref. 18. In Fig. 1 the experimental EQE(λ ) curves, measured (a) by Yoshikawa et al. 55 and (b) Lin et al. 18 , are compared with the calculated ones. The experimental curves were fitted with Eq. (2) in the long-wavelength (λ > 800 nm) part of the spectrum by varying the parameter b, which turned out to have the value of 1.8 and 1.6, respectively. ...
... This analysis is performed for the above-mentioned SCs based on the respective experimental results and the theory developed in this work. Its results are summarized in Table I, which presents the experimental data for the photoconversion efficiency and the effective lifetimes at the maxima of the τ(∆n) curves found in the literature 18,[52][53][54][55] . Also indicated in this table are the theoretical photoconversion efficiency η 0 theor found under the assumption that the SCR recombination is absent, and the maximum lifetimes calculated with the assumption that the SCR lifetime equals the SRH lifetime in the base region. ...
... The theoretical SCR recombination velocity is found from expression (26). Fig. 2 shows the experimental and theoretical dependencies of the recombination rate in the SCR on the excess concentration, obtained using the parameters from Yoshikawa et al. 55 . As can be seen from the figure, the theoretical and experimental dependencies agree well with each other. ...
Since the photoconversion efficiency of the silicon-based solar cells (SCs) under laboratory conditions is approaching the theoretical fundamental limit, further improvement of their performance requires theoretical modeling and/or numerical simulation to optimize the SCs parameters and design. The existing numerical approaches to modeling and optimization of the key parameters of high-efficiency solar cells based on monocrystalline silicon (c-Si), the dominant material in photovoltaics, are described. It is shown that, in addition to the four usually considered recombination processes, namely, Shockley-Read-Hall, surface, radiative, and band-to-band Auger recombination mechanisms, the non-radiative exciton Auger recombination and recombination in the space charge region (SCR) have to be included. To develop the analytical SC characterization formalism, we proposed a simple expression to model the wavelength-dependent external quantum efficiency (EQE) of the photocurrent near the absorption edge. Based on this parameterization, the theory developed allows for calculating and optimizing the base thickness-dependent short-circuit current, the open-circuit voltage, and the SC photoconversion efficiency. We proved that the approach to optimize the solar cell parameters, especially its thickness and the base doping level, is accurate and demonstrated for the two Si solar cells reported in the literature, one with an efficiency of 26.7 % and the other with the record efficiency of 26.81 %. It is shown that the formalism developed allows further optimization of the solar cell thickness and doping level, thus increasing the SC efficiency to an even higher value.
... eV) [14,15]. For the bottom cell, the best material choice was found to be silicon due to its dominance in the market in terms of low cost, high efficiency [16,17], appropriate low band gap (1.1 eV) [18] and high open-circuit voltage (V oc ) (up to 0.75 V) [19]. Notably, perovskite solar cells can be configured as (p-i-n) or (n-i-p) heterojunction structures or (p-n) homojunction structures [20,21]. ...
... Efficiencies of 27.15% and 13.02% are shown for 1000 µs lifetime for bare and filtered bottom cells, respectively. Recently, the PCE of Si cells has become limited [17,70,71]. The conversion efficiency of mono-facial PV devices is difficult to enhance [72,73]. ...
Perovskite/Silicon tandem solar cells have earned substantial attention in the field of photovoltaics (PVs) due to their potential high-efficiency energy conversion. The provided TCAD simulation in the current work aims at delivering a novel design for a 4-T Perovskite/PERL p-type Si tandem solar cell. The main structure consists of ITO/CuSCN/Perovskite/PC60PM/AZO/AgNW as the top cell and a conventional PERL p-Si as the bottom cell. Simulation results showed that the proposed top cell structure achieves a significant performance after substituting Zn(O0.3,S0.7) for AZO and PC60PM electron transport layers (ETLs), while replacing CuSCN with CuI as a suitable alternative for the hole transport layer (HTL). These modifications achieved an efficiency of 19.81% for the top cell. The bottom cell also attained a noteworthy level of performance by using bifacial dual-side-textured construction with efficiencies reaching 29.11% and 14.08% for bare and filtered cells, respectively. With these combined modifications, the PCE (power conversion efficiency) reached 33.89%, showing significant improvement compared to the base structure.
... To date, the commercial solar cells with maximum power conversion efficiency (PCE) is the heterojunction (HJT) Si solar cell, is fabricated by LONGi Green Energy Technology 4 Co. Ltd. (showing PCE-26.81%) and Kaneka corporation (showing PCE-26.7%) [10]. ...
... The root-mean-square (rms) surface roughness, average surface roughness, and grain size were determined in various regions through the analysis of AFM images using Gwyddion, a freely available software for scanning probe microscopy (SPM) analysis. 10 The transmission electron microscope (TEM) JEOL 2100F operating at 200 kV was used for the local study of cross section of films. The microscope is equipped with an 4k x 4k camera (OneView -GATAN) to acquire images and with accessories for energy dispersive X ray spectroscopy (EDS). ...
... The dominant techniques in commercial and high efficiency laboratory crystalline silicon solar cells are micron sized random pyramids and periodic inverted pyr-amids respectively. These are formed by alkali etching combined with silicon nitride anti-reflection coating by plasma enhanced chemical vapor deposition (PECVD) [1]. The effect of this is to reduce the light reflections from the surface and create multiple internal reflections to obtain total internal reflection. ...
... Additionally, a stream of cleaning liquid can be directed towards the wafer at a shallow incidence angle. 1 However, the present study focuses only on the use of acoustic energy to clean a wafer. ...
Conventional monocrystalline silicon cell’ upright pyramid structure’ reflectance has been constant from the beginning. To improve the solar cell efficiency, we should also work on prima fascia properties of the solar cell; reflectance is one of them. By using both the software simulation and mask texturization, we already discovered the better solar cell reflectance. But low cost metal-assisted inverted pyramid texturizing After varying different parameters (Texturing Time, Temperature, Cu Particles in the mixture).
By controlling the one-step Cu-aided texturization of silicon wafer, we assembled an inverted pyramid structure, meeting the tradeoff between the light reflection minimization and carrier recombination. This research work focuses on the parameters (Cu-assisted Texturization Time, Hot Plate' Setting Temperature, Cu-particles on a fixed HF:H2O2: H2O ratio) which set out best possible reflectance.
These data were compared with the performance of conventional upright pyramid silicon solar cells as manufactured using identical raw wafers. Importantly, our data demonstrate the better performance and manufacturability of inverted pyramid structured silicon solar cell and as such may open new perspectives for high efficiency solar cell applications.
We discovered a technical solution of such outstanding importance that it can trigger new approaches in silicon wet etching processing and, in particular, photovoltaic cell manufacturing. The so called inverted pyramid arrays, outperforming conventional pyramid textures and black silicon because of their superior light-trapping and structure characteristics, can currently only be achieved using more complex techniques involving lithography, laser processing, etc. Importantly, our data demonstrate a feasibility of inverted pyramidal texturization of silicon by maskless Cu-nanoparticles assisted etching in Cu(NO3)2 / HF / H2O2 / H2O solutions and as such may have significant impacts on communities of fellow researchers and industrialists.
We have found several new research findings like: gradual decrease of the pyramid size when we have varied the Temperature; gradual increase of the nano-pits under the pyramid structure if we increase the texturaztion time more than 20 mins.
... Yoshikawa et al., 2017;Chowdhury et al., 2019) Major challenges associated with the commercialization of PSCs(Nishat et al., 2021;Chowdhury et al., 2023a). ...
Global electricity consumption increases rapidly creating strain on the grid. In contrast, the primary sources of electricity are fossil fuels such as gas, coal, and oil which are non-renewable and limited, resulting in energy crises. Therefore, the global energy crisis remains a big challenge that requires renewable and sustainable solutions. Perovskite solar cell is a type of solar cell that uses a perovskite-structured compound, usually a hybrid organic-inorganic lead or tin halide-based material as the light-harvesting active layer. In the development of perovskite solar cells spanning 2009-2024, exceptional power conversion efficiencies ranging from 3.8 % to 26.1 % have been reported. As such, perovskite solar cells hold significant promise as the next generation of affordable and effective photovoltaic solar cell technology. Moreover, perovskite solar cells have recently gained popularity and presented an excellent commercial opportunity because they are made from readily available and inexpensive raw materials. However, the commercial production and utilization of perovskite solar cells remains immature. It has been shown that perovskite solar cells containing titanium dioxide as the electron transport layer exhibit poor stability, degrading quickly under prolonged exposure to sunlight and humid conditions. These instability concerns are the major drawbacks that threaten efforts that are directed at the commercialization of perovskite solar cells. As such, there are significant efforts to improve the development of scalable fabrication of perovskite solar cells and the establishment of industrial production lines. The main objective of this review is to outline the primary obstacles that hinder the commercialization of perovskite solar cells. Firstly, a brief discussion on the principles of perovskite solar cells is done. Secondly, challenges associated with the commercialization of perovskite solar cells and counterstrategies are discussed. The review concludes by looking at perspectives and prospects highlighting the importance of continued research and collaboration in overcoming challenges to commercialization. We hope that this review will provide useful insights for future research on improving the stability of cutting-edge perovskite devices as they approach commercialization.
... 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 FSF 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) 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.
... The longest charge-carrier lifetimes were correlated with the lowest defect densities and therefore usually the highest crystallinity of the bulk material and the interfaces. If we look at the top of the solar cell efficiency charts [1], this is still true given that epitaxially grown GaAs and monocrystalline Si solar cells [2,3] have the highest efficiencies of all single junction solar cells as shown in Fig. 1. What has changed is the ranking among the thin-film technologies that were dominated by Cu(In,Ga)Se2 [4][5][6] and CdTe at least from the perspective of record efficiency on the lab scale. ...
One of the most significant features of lead-halide perovskites are their ability to have comparably slow recombination despite the fact that these materials are mostly processed from solution at room temperature. The slow recombination allows achieving high open-circuit voltages when the lead-halide perovskite layers are used in solar cells. This perspective discusses the state of the art of our understanding and of experimental data with regard to recombination and open-circuit voltages in lead-halide perovskites. A special focus is put onto open questions that the community has to tackle to design future photovoltaic and optoelectronic devices based on lead-halide perovskites and other semiconductors with similar properties.
... Moreover, the all-back-contact design alleviates constraints on contact designs for both polarities, thereby reducing the challenge of balancing passivation and contact resistivity 22-24 . In 2017, Kaneka Corporation in Japan realized heterojunction back contact (HBC) solar cell with an efficiency of up to 26.7% (J SC of 42.5 mA·cm −2 ) 25,26 , and recently, LONGi Corporation in China has announced a new record efficiency of 27.30% 16 . Institute for Solar Energy Research Hamelin (ISFH) in Germany reported a small-area polycrystalline silicon on oxide interdigitated back contact (POLO-IBC) solar cell with an efficiency of 26.1% (J SC of 42.6 mA·cm −2 ) deploying a laser patterning process [27][28][29] . ...
Crystalline-silicon heterojunction back contact solar cells represent the forefront of photovoltaic technology, but encounter significant challenges in managing charge carrier recombination and transport to achieve high efficiency. In this study, we produced highly efficient heterojunction back contact solar cells with a certified efficiency of 27.09% using a laser patterning technique. Our findings indicate that recombination losses primarily arise from the hole-selective contact region and polarity boundaries. We propose solutions to these issues and establish a clear relationship between contact resistivity, series resistance, and the design of the rear-side pattern. Furthermore, we demonstrate that the wafer edge becomes the main channel for current density loss caused by carrier recombination once electrical shading around the electron-selective contact region is mitigated. With the advanced nanocrystalline passivating contact, wafer edge passivation technologies and meticulous optimization of front anti-reflection coating and rear reflector, achieving efficiencies as high as 27.7% is feasible.
... For example, in 2015, company KANEKA, with a strong background in TCOs and silicon thin films, achieved a record PCE of 25.1% in both-side-contacted SHJ solar cells, [152] surpassing the top PCE of PERX solar cells and standing on par with the best PCE of both-side-contacted silicon homojunction (TOP-Con, laboratory scale) solar cells at that time. [153] After moving to the SHJ-IBC cell architecture, they consistently achieved world record PCEs of 26.3%, [154] 26.6%, [155] and 26.7% [156] in less than a year, spanning from July 2016 to March 2017. To date, the highest reported PCE for a single-junction silicon solar cell has reached 26.81% in October 2022, achieved by company LONGi, notably, using both-side-contacted SHJ solar cells. ...
The perovskite/silicon tandem solar cell represents one of the most promising avenues for exceeding the Shockley–Queisser limit for single‐junction solar cells at a reasonable cost. Remarkably, its efficiency has rapidly increased from 13.7% in 2015 to 34.6% in 2024. Despite the significant research efforts dedicated to this topic, the “secret” to achieving high‐performance perovskite/silicon tandem solar cells seems to be confined to a few research groups. Additionally, the discrepancies in preparation and characterization between single‐junction and tandem solar cells continue to impede the transition from efficient single‐junction to efficient tandem solar cells. This review first revisits the key milestones in the development of monolithic perovskite/silicon tandem solar cells over the past decade. Then, a comprehensive analysis of the background, advancements, and challenges in perovskite/silicon tandem solar cells is provided, following the sequence of the tandem fabrication process. The progress and limitations of the prevalent stability measurements for tandem devices are also discussed. Finally, a roadmap for designing efficient, scalable, and stable perovskite/silicon tandem solar cells is outlined. This review takes the growth history into consideration while charting the future course of perovskite/silicon tandem research.
... The effective growth of the TOPCon conguration hinges on four crucial steps: (1) the creation of an ultra-thin SiO x layer, (2) the growth of a highly doped amorphous silicon onto SiO x as the above-mentioned layer, (3) thermal annealing at high temperatures to activate dopants and crystallize the doped amorphous silicon layer, resulting in a multi-crystalline structure, and (4) subsequent hydrogenation handling aer annealing to diminish defect states within the doped polycrystalline silicon layer. 27 Therefore, it becomes evident that advancing and optimizing each of these treating steps can enable the production of high-performance TOPCon devices compared to the PERC conguration. ...
The development of a tunnel oxide interfacial layer capped by a highly doped poly-Si layer is considered one of the most promising methods to reduce charge carrier recombination and improve the performance of conventional PERC devices. The thickness and doping concentration of emitters and BSF layers greatly influence the tunnelling current in TOPCon devices. In this research, we evaluated the performance of tunnel oxide passivated contact (TOPCon) solar cells by conducting an in-depth analysis of various key parameters. The parameter include the type of silicon substrate (n or p-type); the thickness and doping density (Na/Nd) of n, n⁺, p, and p⁺ layers; and surface recombination velocity (front/rear), which were analyzed using AFORS-HET simulation software. A comparative analysis of performance demonstrates that the highest efficiency is achieved in the n-TOPCon solar cell with the following values: Voc = 660.2 mV, Jsc = 45.05 mA cm⁻², FF = 82.87%, and PCE = 25.74%. In the optimized p-TOPCon solar cell, the open circuit voltage (Voc) and fill factor (FF) exhibit improvements of 35.9 mV and 0.39%, respectively. However, the values of Jsc and PCE decrease by 6.44 mA cm⁻² and 2.2%, respectively, in p-TOPCon solar cells. Furthermore, photo-electroluminescence analysis reveals that the n-TOPCon solar cells exhibit a higher maximum photon flux (front/rear) than p-TOPCon solar cells.
... For SHJ solar cells, doped amorphous silicon is conventionally utilized as carrier-selective layer, 7,21,22 and an efficiency of 26.7% has been achieved with a back contact cell structure. 23 To further improve the passivating selective contacts, doped nanocrystalline silicon is introduced into SHJ solar cells due to its high transparency and low contact resistivity. 24 This substitution makes the PCE of double-side SHJ solar cells increase from 25.1% to 26.81%. ...
With the improvement of surface passivation, bulk recombination is becoming an indispensable and decisive factor to assess the theoretical limiting efficiency () of crystalline silicon (c‐Si) solar cells. In simultaneous consideration of surface and bulk recombination, a modified model of evaluation is developed. Surface recombination is directly depicted with contact selectivity while bulk recombination is revised on the aspects of ideality factor and wafer thickness. The of the double‐side silicon heterojunction (SHJ) and double‐side tunneling‐oxide passivating contact (TOPCon) solar cells are numerically simulated using the new model as 28.99% and 29.19%, respectively. However, the of single‐side TOPCon solar cells, the more practicable scenario, is only 27.79%. Besides, the of the double‐side SHJ solar cells would exceed the double‐side TOPCon solar cells if the recombination parameter of the non‐contacted area is higher than 0.6 fA/cm ² , instead of perfect passivation. Our results are instructive in accurately assessing efficiency potential and accordingly optimizing design strategies of c‐Si solar cells.
... mass production. The doped poly-Si films with a thin oxide interlayer the commonly known as tunnel oxide passivated contact (TOPCon) cell technology 6,7 [ Fig. 1(c)], have emerged as industrially viable option due to their compatibility with the existing PERC technology. 1 Additionally, doped hydrogenated amorphous (a-Si) silicon heterojunction (SHJ) cell technology 8,9 [ Fig. 1(d)], has also remained in the race for next generation of industrial solar cells. However, SHJ cell technology which currently holds the single junction crystalline silicon record at 26.8% 10 is not covered in this review. ...
Doped polysilicon (poly-Si) passivating contacts have emerged as a key technology for the next generation of silicon solar cells in mass production, owing to their excellent performance and high compatibility with the existing passivated emitter and rear cell technology. However, the current solar cell architecture based on a rear-side electron-selective (n⁺) poly-Si contact is also approaching its practical limit (∼26%) in mass production. The full potential of doped poly-Si passivating contacts can only be realized through incorporation of both electron-selective and hole-selective (p⁺) poly-Si contacts. While studies of both p⁺ and n⁺ poly-Si contacts commenced simultaneously, significant performance differences have arisen. Phosphorus-doped poly-Si contacts consistently outperform boron-doped counterparts, displaying typically lower recombination current density (J0) values ( 1 – 5 fA/cm² vs 7 – 15 fA/cm²). This discrepancy can be attributed to inadequate optimization of p⁺ poly-Si contacts and fundamental limitations related to boron doping. The poorer passivation of p⁺ poly-Si contacts can be at least partly attributed to boron segregation into the interfacial oxide layers, compromising the interfacial oxide integrity and reducing the chemical passivation effectiveness. This review critically examines the progress of p⁺ poly-Si contacts characterized by cell efficiency and J0 values, delves into existing challenges, identifies potential solutions, and explores some potential solar cell architectures to enhance efficiency by incorporating p⁺ poly-Si contacts.
... The present study is performed and executed under a simulation software called SCAPS-1D which is developed at the Department of Electronics and Information Systems (ELIS) of the University of Ghent, Belgium [30]. The composition of the perovskite layer is obtained from the formula (FASnI3) 1 For an efficient collection of generated electron-hole pairs, the heterojunction at HTL/Pero(M1-M5)/ETL should be aligned in such a manner that it allows efficient separation of the charge carriers. Thus, with this motivation in this work, the bandgap and electron affinity (which plays a vital role in the formation of a heterojunction) of HTL has been varied to design an efficient solar cell. ...
This research work aimed to identify the optimal parameters of the hole transport layer (HTL) for enhancing the power conversion efficiency (PCE) of mixed halide (FASnI3)1–x(MAPbI3)x-based perovskite solar cells (PSCs). The study analyzed the impact of the HTL properties, such as bandgap (Eg), affinity (μ), mobility (μp), and acceptor-doping density (NA), on the photovoltaic (PV) parameters of five different PSCs with x = 0, 0.2, 0.4, 0.6, and 1.0. The study revealed that the influence of χ on open-circuit voltage (VOC) decreases for the HTL with Eg ≥ 2.95 eV, and higher Eg results in higher VOC values. The study also found that the impact of μp on short-circuit current density (JSC) becomes negligible if μp is more than 2 × 10–4 cm2 V–1 s–1, while the influence of NA is negligible for NA of more than 1.5 × 1017 cm–3. Moreover, the impact of μp is negligible on VOC of the cells at the entire NA range, while with an increase in NA, VOC of the cells increases significantly. The study found that the most suitable active layer was with x = 0.2, i.e., (FASnI3)0.8(MAPbI3)0.2, which delivered the highest PCE of 23.05%. The oxidation of Sn2+ to Sn4+ can lead to inherent acceptor doping in the absorber layer, which affects device performance. Therefore, this study also investigated the impact of Sn oxidation on the performance of PSCs with Sn-based absorber layers and found that VOC and fill factor (FF) reduce monotonically as the acceptor doping increases. The reduction in efficiency as a result of Sn oxidation is significant, reducing PCE from 23.05 to 20.86% for the champion device with x = 0.2. The findings of this study contribute to advancing the understanding of mixed halide (FASnI3)1–x(MAPbI3)x PSCs and improving their performance by selecting the appropriate HTL for specific active layers.
... SHJ solar cells have been demonstrated excellent efficiencies beyond 26 %. The prominent ingredient to achieve such high efficiency is attributed to the high open-circuit voltage (V OC ) of above 750 mV associated with the excellent passivation of hydrogenated amorphous silicon (a-Si:H) on the surface of c-Si [7][8][9]. In order to prevent epitaxial growth which mainly deteriorates surface passivation [10,11], underdense interface a-Si:H layer has been investigated systematically [12]. ...
... In this regard, the pace of production of solar modules has been growing rapidly over the past decade. The majority of solar modules are based on single junction silicon based solar cells (SC), which record efficiency values of 26.6 % are close to theoretically possible efficiency of single junction designs (29 %) [1]. To meet the public demand for solar energy, further efforts are required to increase efficiency of silicon SC, for this purpose multi-junction siliconbased SC are being developed. ...
... SHJ technology is also an ideal bottom cell for future ultra-high-efficiency silicon-based tandem devices. To date, the PCE of SHJ solar cells in the front-back contact and interdigitated back contact implementations has reached 26.81% and 26.7%, respectively, setting the world record for single-junction c-Si solar cells 6,7 . Nevertheless, the 26.81% efficiency was obtained on a mono-facial SHJ solar cell (instead of bifacial) with front fingers and transparent conductive electrodes prepared by a laser transfer process and reactive plasma deposition 6 , respectively, both of which are not industrially compatible for mass production. ...
To unlock the full performance potential of silicon heterojunction solar cells requires reductions of parasitic absorption and shadowing losses. Yet the translation of the hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) window layer and copper-plated electrodes to a cost-effective and scalable production-relevant context remains one of the largest roadblocks towards mainstream adoption of silicon heterojunction technology. Here we address the first challenge by developing an industrial-scale high-frequency plasma-enhanced chemical vapour deposition system with a minimized standing wave effect, enabling the deposition of doped nc-SiOx:H with excellent electron selectivity, low parasitic absorption and high uniformity. Next, we demonstrate seed-free copper plating, resulting in grids with a high aspect ratio and low metal fraction. By implementing the doped nc-SiOx:H window layer, certified efficiencies of 25.98% and 26.41% are obtained for M6-size bifacial silicon heterojunction devices with screen-printed silver electrodes and copper-plated electrodes, respectively. These results underline the performance potential of silicon heterojunction technology and lower the threshold towards their mass manufacturing.
... 21−24 SHJ contacts, which consist of a stack of intrinsic and doped hydrogenated amorphous silicon (a-Si:H), offer excellent surface passivation; the world-record efficiency of 26.7% has been achieved by applying SHJ contacts in an interdigitated back-contact design. 6 However, SHJ technology shows a moderate thermal resilience (<250°C), relatively narrow process windows, and a capital-intensive deposition system is required as well. 25,26 With a conventional both-side contact design, the SHJ device suffers from parasitic absorption of a-Si:H, which limits the short-circuit current density, J SC . ...
Polysilicon passivating contacts, consisting of a stack of tunnel-oxide and doped polysilicon layers, can simultaneously provide excellent surface passivation and low contact resistivity for silicon solar cells. Nevertheless, the microscopic interfacial characteristics of such contacts are not yet fully understood. In this work, by investigating the surface passivation evolution of polysilicon passivating contacts under increasing annealing temperatures, we unveil these characteristics. Before annealing, we find that the Si and O atoms within the tunnel-oxide layer are mostly unsaturated, whereas the O atoms introduce acceptor-like defects. These defects cause Fermi-level pinning and high carrier recombination. During annealing, we identify two distinct chemical passivation regimes driven by surface hydrogenation and oxidation. We attribute the excellent chemical passivation activated by high-temperature annealing (∼850°C) mainly to the tunnel oxide reconstruction, which effectively reduces the acceptor-like state density. During the oxide reconstruction, we also find that subnanometer pits (rather than pinholes) are formed in the oxide. A combination of experimental and theoretical investigations demonstrates these subnanometer pits provide excellent surface passivation and efficient tunneling for majority carriers.
... Therefore, it can be deduced that the FFs of recent champion devices from manufacturers such as LONGi 6 and Maxwell/SunDrive could not have been realized by merely suppressing R S . It also explains why the previous record device from Kaneka Corp. 9 had a lower FF of 84.65% due to the relatively lower V OC of 740.3 mV, despite reaching a low R S of ∼0.2 Ω·cm 2 which with perfect passivation would have yielded a FF of ∼86.5%. 10 These observations then lead to the question: what criteria enable SHJ cells with Auger limited FFs while taking practical surface recombination (expressed here by the saturationcurrent density J 0S ) and R S limits into consideration. ...
... 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”.
The cadmium indium oxide thin film (CdIn2O4) was formed onto a micro glass substrate using the nebulized spray pyrolysis process at substrate temperatures ranging from 350 to 550 °C with a 50 °C interval. The X-ray diffraction investigation revealed the polycrystalline nature of the films with a cubic structure and the preferred orientation along the (222) plane. The optical transmission and optical spectra were obtained using optical analysis and the multiple interference effect was significant in all of these films within the wavelength range of 300–1100 nm. These films were highly adhesive, homogeneous, and shining. Bandgap values ranging from 2.71 to 3.37 eV with direct allowed nature were obtained. The Urbach energy values and skin depth were observed for all the films. The surface ratio of the elements was analyzed using the EDAX spectrum. Scanning electron microscope images exhibited flower-shaped grains. Photoluminescence spectra at room temperature explain the four emission bands in all the samples, such as the sharp dominant peak at 490 nm in the UV–visible region. The electrical parameters were analyzed; the minimum resistivity was 0.51 × 102 Ω cm, and the mobility was 158 cm²/Vs for the film deposited at the substrate temperature of 500 °C.
Key materials and device structures of crystalline silicon heterojunction solar cells.
A higher efficiency of photovoltaic cells can be attained by optimizing their design, selecting the appropriate materials, and implementing of effective passivation process. The present study investigates the influence of the thickness and band gap of different layers of the solar cell and resuting opto-electric performance parameters of both single junction heterojunction (HJ) and heterojunction with intrinsic thin layer (HIT) cells. These cells are made up of a crystalline silicon (c-Si) active layer having back surafce field layer. The reported simulated work was conducted using AFORS-HET, an automated program specifically designed for simulating heterostructures. An efficiency of 26.86% has been attained for a HJ solar cell, this efficiency was further improved to 29.38% for the HIT solar cell by optimising all parameters. These cells require an emitter layer with a bandgap of around 1.4 eV. The optimal values of open-circuit voltage ( V OC ), short-circuit current density (J SC ), and fill factor are determined and found to be: 631.2 mV, 51.16 mA cm ⁻² , and 83.16% for HJ solar cell, and 683 mV, 52.74 mA cm ⁻² , and 81.55% for HIT solar cell. Moreover, the J-V curve, spectral response and quantum efficiency analysis have also been studied.
The need to increase transparency in existing passivating contacts for crystalline silicon solar cells has motivated the development of transparent contacts based on transition metal oxides (TMOs). Among hole-selective materials, molybdenum oxide (MoOx) has achieved the greatest success so far. However, despite providing low contact resistivity, MoOx relies on an intrinsic hydrogenated amorphous silicon (a-Si:H(i)) interlayer to achieve high levels of surface passivation and thus high open-circuit voltage at a device level, partially defeating the objective of improved transparency. Herein, we report unprecedented performance for a-Si:H-free MoOx-based contacts by employing an alternative passivating interlayer based on a well-engineered chlorine-containing Al-alloyed titanium oxide/titanium dioxide (AlyTiOx/TiO2 )stack. The resulting AlyTiOx/TiO2/MoOx stack achieved record levels of passivation, reaching J0 values as low as 16 fA cm−2, closer to values reported for a-Si:H-based contacts, while maintaining lower contact resistivity, well below 100 mΩ cm−2. Additionally, the stack presents improved transparency compared to a-Si:H-based contacts, with gains in short-circuit current density of at least 0.8 mA cm−2. The work pushes the performance of hole-selective passivating contacts based on TMOs to new levels, enabling a record efficiency of 22.53% for cells with fully transparent hole-selective passivating contacts. This work serves as an important stepping stone toward low-thermal-budget, simple manufacturing of high-efficiency solar cells.
Thin films of indium oxide (In2O3) compound on micro glass substrate were synthesized using the Nebulized Spray Pyrolysis (NSP) process at various substrate temperatures from 300 to 550 °C in steps of 50 °C. X-ray diffraction studies exposed the film's polycrystalline nature, with a cubic structure and a preferred orientation along the (222) plane. The optical spectra of these films have been measured in the 300–1100 nm wavelength range. Band gap values of more than 3.45 eV with direct allowed nature, Urbach energy values, and skin depth were observed for all the films. The surface composition of the elements was examined with the EDAX spectrum. Scanning electron microscope (SEM) pictures exhibited flower-like grains. By Hall effect measurement, the electrical parameters were examined which established that the films prepared at 500 °C substrate temperature possess a minimum resistivity of 1.05 × 10² Ω-cm with mobility of 155 cm²/Vs. The room-temperature photoluminescence spectra showed that all samples had four emission bands, including a prominent peak in the UV region at 361 nm.
The wide bandgap oxide is considered a promising passivating contact for Si solar cells due to its low parasitic
absorption and low-temperature process. However, the power conversion efficiencies (PCEs) of these devices
remain unsatisfactory, in addition to the high annealing temperatures and complicated annealing processes.
Employing the low-temperature and simple spin-coating SiO2, we in this work achieved the champion PCE of
22.46 % for the full-area dopant-free AlOx/SiO2/LiF based n-type Si passivating contact homojunction solar cell,
demonstrating the significant advantages of the efficiency and process compared with other dopant-free wide
bandgap oxide based solar cells. The key to success lies in the simultaneous achievement of the ultralow contact
resistivity (ρc) and excellent surface passivation of the AlOx/SiO2/LiF passivating contact. Crucially, we find a
novel pinhole-like carriers transport mechanism in the spin-coating 20 nm-thickness SiO2 layer, resulting in the
ultralow ρc (0.244 mΩ⋅cm2) of the AlOx/SiO2/LiF passivating contact. The pinhole-like carriers transport in spincoating
SiO2 significantly broadens the thickness range of the interfacial passivation layer, enabling the superior
performance of crystalline Si passivating contact solar cells and demonstrating promising application in highefficiency
Si and Si/Perovskite tandem solar cells by the low-temperature and simple process.
As a result of an ongoing global dedication, metal-halide perovskite (PVSK) has proven to be a promising substitute among other developed materials for next-generation photovoltaic cells due to its significantly high efficiency, economical reasons, environmentally friendly processing, and bandgap alterations. In just 12 years, PVSK-based single cells have achieved an efficiency of 26.1%, reaching single-crystal silicon solar cells at 27.6% and silicon heterostructure solar cells at 26.8%. PVSK-based tandem cells also have achieved remarkable attention as a viable candidate for future-generation photovoltaic technology. Currently, a considerable number of reports are documented as evidence of the efforts to integrate the wide-bandgap PVSK either with itself (narrow-bandgap PVSK ([NBG-PVSK]) or other traditional (NBG) cells, including silicon (Si), copper–indium–gallium–selenide, organic solar cells, cadmium telluride (CdTe), and dye-sensitized. Thanks to the substantial growth made in the advances of PVSK-based tandem cells both in the laboratories and in the commercialization sector, this review will systematically elucidate the emergence of PVSK-based cells, their current status, and applications in tandem configurations. Furthermore, this survey will cover the analysis of different strategies and efforts to achieve cutting-edge photovoltaic technology. Finally, the commercialization of different PVSK-based tandem technologies and their prospects are analyzed.
We present a very simple process to fabricate silicon heterojunction back contact (HBC) solar cell. This process can easily form a backside structure using in situ masks without particular patterning process. Based on our silicon heterojunction (SHJ) solar cell process conditions, we optimize the process for HBC solar cell. The intrinsic a-Si: H layer and p-type a-Si: H layer process conditions were adjusted to improve to FF and efficiency. Applying these adjust, we obtained 18.1% efficiency of the HBC solar cell with VOC of 684 mV, JSC of 38.3 mA/cm2, FF of 69.1%. The key factors affecting FF and performance of the HBC solar cell are also discussed.
Solar photovoltaics (PV) are poised to be crucial in limiting global warming by replacing traditional fossil fuel generation. Within the PV community, crystalline silicon (c‐Si) solar cells currently dominate, having made significant efficiency breakthroughs in recent years. These advancements are primarily due to innovations in solar cell technology, particularly in developing passivating contact schemes. As such, this review article comprehensively examines the evolution of high‐efficiency c‐Si solar cells, adopting a historical perspective to investigate the advancements in passivation contact techniques and materials to state‐of‐the‐art cell designs. Additionally, this work deeply studies the recent advances and critical design principles underlying each developed passivation scheme. Eventually, this work identifies existing challenges and proposes insights into future directions for c‐Si solar cells through diverse passivating contact strategies.
Improving power conversion efficiency (PCE) in photovoltaics has driven innovative approaches in solar cell design and technology. Silicon heterojunction (SHJ) solar cells exhibit advantages in PCE due to their effective passivating contact structures. SHJ–interdigitated back contact (SHJ–IBC) solar cells have the potential to surpass traditional SHJ cells, attributed to their advantage in short‐circuit current ( J SC ). Herein, Silvaco Atlas technology computer‐aided design is used to create digital twins of high‐efficiency SHJ solar cells with amorphous silicon and nanocrystalline silicon hole selective contact (HSC) layers. Using parameters from digital twins of SHJ solar cells, the practical efficiency limit of SHJ–IBC solar cells is assessed. The results show that SHJ–IBC cells can achieve potential efficiencies of 27.01% with amorphous HSC and 27.38% with nanocrystalline HSC. Further efficiency augmentation to 27.51% can be achieved by narrowing the gap from 80 to 20 μm. This study not only advances comprehension of SHJ–IBC solar cells but also provides insights into optimizing geometrical configurations for improved performance. The utilization of digital twins provides a valuable tool for predicting and evaluating the performance of SHJ–IBC solar cells, contributing substantively to the ongoing development of high‐efficiency photovoltaic technology.
Developing a vacuum-free and low-temperature deposition technique for dopant-free carrier-selective materials without sacrificing their performance can reduce the fabrication cost and CO2 footprint of silicon heterojunction (SHJ) solar cells. In this contribution, to activate the full capacity of the solution-processed TiOx as an electron-selective passivation contact, the effects of various pre- and postdeposition treatments on the passivation quality and contact resistivity are investigated simultaneously. It is demonstrated that the electrical properties of a thin TiOx layer spin-coated on an n-type silicon substrate can be remarkably improved through tailor-made pre- and postdeposition treatments. A notable low surface recombination velocity (SRV) of 6.54 cm/s and a high implied open-circuit voltage (iVoc) of 706 mV are achieved. In addition, by inserting a 1 nm LiFx buffer layer between TiOx and Al metal contact, a low contact resistivity (ρc) of 15.4 mΩ·cm² is extracted at the n-Si/SiOx/TiOx heterojunction. Our results bring the solution-processed TiOx electrical properties to a level on par with those of state-of-the-art pure TiOx layers deposited by other techniques. Chemical and electrical characterizations elucidate that the improved electrical properties of the investigated Si/SiOx/TiOx heterojunction are mediated by the concomitant involvement of chemical and field-effect passivation.
Investigations of atomic-layer deposition of GaP layers on Si substrates with different orientations and with different preliminary surface treatment have been carried out. The deposition of GaP was carried out by the method of plasma enhanced atomic-layer deposition using in situ treatment in argon plasma. It was shown that at the initial stage of the growth of GaP layers on precisely oriented (100) Si substrates and with misorientation, two-dimensional growth occurs both after chemical and plasma surface treatment. Upon growth on (111) substrates, after plasma treatment of the surface, a transition to three-dimensional growth is observed, at which the size of islands reaches 30–40 nm. The smallest root-mean-square roughness of the surface of the growing GaP layers (<0.1 nm) was achieved for (100) substrates with a misorientation of 4°. The GaP layers grown on (100) substrates had a roughness of ~0.1 nm, and on substrates with the (111) orientation—0.12 nm. It was found that the surface treatment of Si substrates with the (100) orientation in hydrogen plasma leads to a slight increase in the surface roughness of growing GaP layers (0.12–0.14 nm), which is associated with the effect of inhomogeneous etching of silicon in hydrogen plasma. When treating the (100) silicon surface in argon plasma, the surface roughness does not change significantly in comparison with the chemical surface treatment. On the surface of substrates with preliminary deposition of an epitaxial Si layer with a thickness of 4 nm, the morphology of GaP layers is the same as in the case of using hydrogen plasma.
Silicon solar cells are a mainstay of commercialized photovoltaics, and further improving the power conversion efficiency of large-area and flexible cells remains an important research objective1,2. Here we report a combined approach to improving the power conversion efficiency of silicon heterojunction solar cells, while at the same time rendering them flexible. We use low-damage continuous-plasma chemical vapour deposition to prevent epitaxy, self-restoring nanocrystalline sowing and vertical growth to develop doped contacts, and contact-free laser transfer printing to deposit low-shading grid lines. High-performance cells of various thicknesses (55–130 μm) are fabricated, with certified efficiencies of 26.06% (57 μm), 26.19% (74 μm), 26.50% (84 μm), 26.56% (106 μm) and 26.81% (125 μm). The wafer thinning not only lowers the weight and cost, but also facilitates the charge migration and separation. It is found that the 57-μm flexible and thin solar cell shows the highest power-to-weight ratio (1.9 W g⁻¹) and open-circuit voltage (761 mV) compared to the thick ones. All of the solar cells characterized have an area of 274.4 cm², and the cell components ensure reliability in potential-induced degradation and light-induced degradation ageing tests. This technological progress provides a practical basis for the commercialization of flexible, lightweight, low-cost and highly efficient solar cells, and the ability to bend or roll up crystalline silicon solar cells for travel is anticipated.
We investigate the electrical characteristics of defects at the SiO2/Si interface, within the adjacent Si crystal, and through the depth profile of the bulk defect using three-dimensional deep-level transient spectroscopy (3D-DLTS). These defects are introduced by the reactive plasma deposition technique employed for depositing transparent conductive oxides in the fabrication of carrier-selective contact-type solar cells. To control the surface potential near the Si surface, we apply a varying voltage to obtain DLTS signals as functions of both temperature and Fermi level at the SiO2/Si interface. Using machine learning for 3D-DLTS spectral analysis, we estimate the capture cross sections, energy levels, densities, and depth profiles of these process-induced defects. The experimental results indicate the existence of three types of electron traps within the bulk defects, ranging from the interface to a depth of ∼70 nm. The electrical properties of these bulk defects suggest the presence of oxygen-related defects within Si. On the other hand, regarding the properties of interface defects, the capture cross sections and the defect densities are estimated as a function of their energy levels. They suggest that the defects at the SiO2/Si interface are likely oxygen-related PL centers.
Interdigitated back contact (IBC) architecture can yield among the highest silicon wafer‐based solar cell conversion efficiencies. Since both polarities are realized on the rear side, there is a definite need for a patterning step. Some of the common patterning techniques involve photolithography, inkjet patterning, and laser ablation. This work introduces a novel patterning technique for structuring the rear side of IBC solar cells using the enhanced oxidation characteristics under the locally laser‐doped n ⁺⁺ back surface field (BSF) regions with high‐phosphorous surface concentrations. Phosphosilicate glass layers deposited via POCl 3 diffusion serve as a precursor layer for the formation of local heavily laser‐doped n ⁺⁺ BSF regions. The laser‐doped n ⁺⁺ BSF regions exhibit a 2.6‐fold increase in oxide thickness compared to the nonlaser‐doped n ⁺ BSF regions after undergoing high‐temperature wet thermal oxidation. The utilization of oxide thickness selectivity under laser‐doped and nonlaser‐doped regions serves two purposes in the context of the IBC solar cell, first patterning rear side and second acting as a masking layer for the subsequent boron diffusion. Proof‐of‐concept solar cells are fabricated using this novel patterning technique with a mean conversion efficiency of 20.41%.
This chapter accounts for an overview of solar cell technologies developed up to now, from the mature silicon-based solar cells to the third-generation photovoltaics. Herein, the most important characteristics, current challenges and strategies for further improvement of each solar cell technology are discussed, aiming to demonstrate possible manufacturing options for the development of the next-generation agrivoltaics. The short life-cycle assessment review on solar cell technologies that is also included at the end of this chapter, provides the reader with a more comprehensive point of view toward the development of greener agrivoltaic energy systems.
This chapter is the forerunner of the cross-sectoral nexus approach of agrivoltaics that the present book introduces, presenting the current challenges on the Water-Energy-Food-Ecosystems (WEFE) nexus, as well as approaches that should be adapted in order to attain sustainable management of the WEFE nexus.
The increasing demand for water, energy and food, due to population growth and urbanization, is aggravated by unprecedented extreme weather and climatic conditions. This situation is most likely to undermine the sustainable and peaceful development of humanity in the next years. Today, more than ever, there is an imperative need to support the identification and development of practical solutions, where the use of nexus strategic plans can lead to improved outcomes in the integrated management of water-energy-food-ecosystems (WEFE) resources. Under the afore-mentioned considerations, the development of agrivoltaic energy systems is nowadays emerging as a very promising cross-sectoral nexus approach that can provide mutual benefits toward the sustainable management of WEFE resources and, therefore, give a quite significant untapped potential for the sustainable development of humanity. Agrivoltaics are hybrids of co-located solar photovoltaic and agriculture infrastructures that can bolster the resilience of renewable energy and food production security, where crops are grown in the partial shade of the solar infrastructure. These energy-and food-generating ecosystems will become a very important—but as yet insufficiently investigated—mechanism for maximizing crop yields, generating renewable energy and efficiently delivering water to plants. The present book contributes to the dissemination of the current knowledge on the modern approach of agrivoltaics, providing a comprehensive state of the art on the field, discussing the current status, the challenges and the future perspectives for their further development, from conceptual designs to practical realizations.
Passivating contacts based on transition metal oxides are of great interest for applications in crystalline silicon (c‐Si) solar cells due to their improved optical transparency and potential cost reduction. In this work, we investigate and optimize contact resistivity and passivation for thermally evaporated Cu 2 O, with and without an Al 2 O 3 interlayer, as a hole‐selective contact to c‐Si. Additionally, we implement an Al y TiO x /TiO 2 stack as a novel passivating tunnel interlayer for hole‐selective contacts, achieving an implied open‐circuit voltage iV oc of 630 mV and a record‐low J 0 of 212 fA/cm ² while maintaining a contact resistivity ρ c of 62 mΩ.cm ² . A record‐low ρ c of 8 mΩ.cm ² for Cu 2 O‐based contacts is also demonstrated at the expense of passivation. The addition of the interlayer resulted in a 2% absolute improvement in the efficiency of proof‐of‐concept c‐Si cells with full‐area rear Cu 2 O contacts, reaching 19.1%.The demonstration of this novel interlayer stack provides new avenues to improve the performance also of other hole‐selective passivating contacts.
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Wide‐bandgap metal compound‐based dopant‐free passivating contacts have been explored to fabricate crystalline silicon (Si) solar cells to mitigate the high carrier recombination rate of metal‐Si contact directly. Here, an over 4‐nm‐thick single‐layer strontium fluoride (SrF x ) and a double‐layer SrF x /lithium fluoride (LiF) films deposited by a facile vacuum thermal evaporation are developed to act as high‐performance electron‐selective contacts. SrF x with ultra‐low work function (2.8 eV) induces a strong downward band bending at the n‐type Si (n‐Si)/SrF x interface, and a dipole active layer exists at the SrF x /aluminum (Al) interface, enabling a low contact resistivity ( ρ c ) of 34.1 mΩ cm ² and thus yielding an impressive fill factor (FF) of 82.8%. Eventually, a power conversion efficiency (PCE) of 20.1% is achieved in the SrF x ‐based solar cell. Moreover, in the n‐Si/SrF x /LiF/Al contact, the diffusion of Li in the SrF x film favors facilitating electron transport as well as relaxing its thickness restriction, inhibiting carrier recombination. And an impressive FF of 83.7% with a low ρ c of 25.9 mΩ cm ² , an improved open‐circuit voltage of 631 mV, and a short‐circuit current density of 39.9 mA/cm ² are attained, resulting in a champion PCE of 21.1%. Double‐layer SrF x /LiF deposited by a simple process provides a grand opportunity to fabricate low‐cost and high‐PCE photovoltaic devices.
The non-radiative recombination caused by perovskite and its relevant interfaces greatly impedes further improving the efficiency and stability of PSCs, hindering their further commercialization. Herein, we introduce a straightforward and...
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 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
oc
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
oc
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
x
) based hole collector HJ solar cell. Our work consolidates Suns-V
oc
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-SiNx: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.