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Simple emitter patterning of silicon heterojunction interdigitated back-contact solar cells using damage-free laser ablation
Abstract
In early 2017, the world record efficiency for single-junction crystalline silicon (c-Si) solar cells was achieved by merging amorphous silicon (a-Si:H)/c-Si heterojunction technology and back-contact architecture. However, to fabricate such silicon heterojunction interdigitated back-contact (SHJ-IBC) solar cells, complex a-Si:H patterning steps are required to form the interdigitated a-Si:H strips at the back side of the devices. This fabrication complexity raises concerns about the commercial potential of such devices. In this work, a novel process scheme for a-Si:H patterning using damage-free laser ablation is presented, leading to a fast, simple and photolithography-free emitter patterning approach for SHJ-IBC solar cells. To prevent laser-induced damage to the a-Si:H/c-Si heterocontact, an a-Si:H laser-absorbing layer and a dielectric mask are deposited on top of the a-Si:H/ c-Si. Laser ablation only removes the top a-Si:H layer, reducing laser damage to the bottom a-Si:H/c-Si heterocontact under the dielectric mask. This dielectric mask is a distributed Bragg reflector (DBR), resulting in a high reflectance of 80% at the laser wavelength and thus providing additional protection to the a-Si:H/c-Si heterocontact. Using such simple a-Si:H patterning method, a proof-of concept 4-cm2 SHJ-IBC solar cell with an efficiency of up to 22.5% is achieved.
... Particularly, rear-side patterning is very complex. Different research groups have successfully implemented laser ablation [25], shadow masking [26], and tunnel-IBC [27] concepts for process simplification of SHJ-IBC solar cell at laboratory scale. ...
... Hence, a process simplification strategy is adopted to make the baseline process commercially-viable. Successful replacement of lithography by laser ablation [25], and wet etching by dry etching technique [28] have already been reported. Another recommendation for in situ processing is "in situ selective deposition". ...
High photo-conversion efficiency and low production cost of silicon solar cells are the keys to maintain the ongoing success of solar energy in the global energy mix. Silicon Heterojunction Interdigitated Back Contact (SHJ-IBC) solar cell has attracted much attention due to its potential in achieving remarkably high energy conversion efficiency. A world-record efficiency of 26.7% was achieved by Kaneka with this
cell structure [1]. In a SHJ-IBC solar cell, unlike its conventional counterparts, both electron and hole collecting contacts are realised on the rear side of the device following an interdigitated pattern. Consequently, the entire fabrication process becomes very demanding, time-consuming and often involves expensive techniques that are not viable for industrial application. Hence, process simplification is indispensable for industrialisation of the SHJ-IBC cell technology. The main goal of this work is to contribute to the simplification of the SHJ-IBC process flow towards an all-dry,
litho-free and leaner sequence that is commercially viable. Towards this goal, a novel in situ repassivation concept is developed to simplify the rear side patterning of the SHJ-IBC solar cell exploring two unique routes, namely, “in situ dry clean” and “in situ partial etch”. The concept effectively replaces the ex situ wet cleaning of NF3/Ar dry-etched surfaces that is performed before repassivation, during rear-side processing. Hence, no vacuum break is required in between the dry etch, cleaning and repassivation steps. Thus, total processing
time is shortened significantly and handling of perilous chemical solutions is avoided.
In the first approach i.e. in situ dry clean route, a stack of intrinsic and p-type doped hydrogenated amorphous silicon (a-Si:H (i/p+)), which serves as the hole contact, is completely etched through the open areas of a patterned dielectric hard mask using NF3/Ar based dry etching technique. Afterwards, a novel “nano-envelope” dry cleaning method is performed, whereby an ultra-thin layer of sacrificial intrinsic hydrogenated amorphous silicon (a-Si:H (i)) is deposited in situ to capture the dry etch contaminants arising from the NF3/Ar plasma. The contaminants are subsequently removed, without causing any plasma damage to the c-Si wafer, by etching the a-Si:H (i) layer with hydrogen-plasma. Finally, a stack of intrinsic and n-type doped hydrogenated amorphous silicon (a-Si:H (i/n+)) is deposited on the cleaned c-Si surface. Thus, interdigitated strips of a-Si:H (i/p+) and a-Si:H (i/n+) are formed in a completely in situ manner that collect holes and electrons, respectively.
In the second approach i.e. in situ partial etch route, only the p-type doped hydrogenated amorphous silicon layer of the a-Si:H (i/p+) stack is etched by controlled dry etching. Dry etch contaminants are removed using an optimised H2-plasma treatment, and an n-type doped hydrogenated amorphous silicon layer (a-Si:H (n+)) is deposited in situ. Surface contamination analysis, passivation studies and contact resistance measurements prove that both in situ approaches are as effective as reference ex situ process. Both approaches are optimised and successfully integrated in SHJ-IBC process flow. Remarkably high open circuit voltage (>720 mV), achieved with both
approaches, implies high-quality passivation of c-Si surface. Solar cells with excellent photo-conversion efficiencies of 22.6% and 22.9% are fabricated following the “in situ dry clean” and the “in situ partial etch” approaches, respectively. These cell results are comparable to that of the reference process. This demonstrates the potential of the in situ repassivation concept in fabrication of high efficiency solar
cells using a simplified, high throughput process.
... 14 Another popular "litho-free" alternative to patterning, which is contact-less and also drastically reduces the number wet chemical steps, is laser ablation-assisted patterning. [15][16][17][18][19][20] In this approach, the pattern is often directly structured onto a sacrificial mask layer on top of the a-Si:H stack to be patterned. While there is a risk of laser-induced thermal damage to the crystalline silicon and the heterocontact in the laser-ablated areas, 19,20 significant strides have been made recently in tackling this issue. ...
... While there is a risk of laser-induced thermal damage to the crystalline silicon and the heterocontact in the laser-ablated areas, 19,20 significant strides have been made recently in tackling this issue. 17 In this approach, etching of the underlying a-Si:H stack is needed, and hence, it is a subtractive route, just like in photolithography. Often, wet etching is used, which is not well-controllable and can lead to processing issues. ...
... The a-Si:H layers are either structured by doping-selective etching in alkaline solutions [5,27] or using additional layers as etching barriers [26,28]. Laser structuring in combination with sacrificial layers has also been investigated [29,30,31], the highest reported efficiency is 22.5 % [31]. ...
... The a-Si:H layers are either structured by doping-selective etching in alkaline solutions [5,27] or using additional layers as etching barriers [26,28]. Laser structuring in combination with sacrificial layers has also been investigated [29,30,31], the highest reported efficiency is 22.5 % [31]. ...
We review the recent progress of silicon heterojunction (SHJ) solar cells. Recently, a new efficiency world record for silicon solar cells of 26.7% has been set by Kaneka Corp. using this technology. This was mainly achieved by remarkably increasing the fill-factor (FF) to 84.9% - the highest FF published for a silicon solar cell to date. High FF have for long been a challenge for SHJ technology. We emphasize with the help of simulations the importance of minimised recombination, not only to reach high open-circuit voltages, but also high FF, and discuss the most important loss mechanisms. We review the different cell-to-module loss and gain mechanisms putting focus on those that impact FF. With respect to industrialization of SHJ technology, we discuss the current hindrances and possible solutions, of which many are already present in industry. With the intrinsic bifacial nature of SHJ technology as well as its low temperature coefficient record high energy production per rated power is achievable in many climate regions.
... Photovoltaic (PV) technology has advanced in recent years as a result of the introduction of numerous solar device architectures [1][2][3][4][5][6][7][8][9][10][11][12]. Due to its cost effectiveness and enhanced performance, the perovskite absorber-based solar structure has become one of the most developing PV technologies [13][14][15][16][17][18][19][20][21]. ...
Abstract—The HTL free perovskite based solar
cell has been suggested in this simulation work,
with CH3NH3PbI3 as the active layer and TiO2 as
the electron transport layer (ETL). To construct
the suggested HTL-free CH3NH3PbI3-based PSC
and simulate its performance at 300K under A.M
1.5 G 1 Sun irradiation, the solar cell capacitance
simulator in one dimension software was used. By
altering the physical characteristics of various
layers, the proposed PSC's output parameters,
such as open circuit voltage (Voc), short-circuit
current density (Jsc), fill factor (FF), power
conversion efficiency, and quantum efficiency, are
analysed. The suggested cell's thermal stability has
also been investigated. The ETL and absorber
thicknesses have been tuned to be 0.025 and 0.50
um, respectively. The active and ETL layers'
acceptor and donor concentrations were tuned to
be 1.00E+17 and 5.00E+21 cm-3, respectively. The
suggested HTL-free CH3NH3PbI3-based PSC has
a conversion efficiency of 18.61%, a Voc of 1.07 V,
a Jsc of 20.73 mA/cm2, and an FF of 83.78%.
These simulation results might aid in the
development of highly efficient and low-cost
perovskite solar cells.
... Thin-film solar cells (TFSCs) are one of the most promising candidates for the photovoltaic applications due to their low material cost, mature vacuum deposition methods, compatibility with mass production, and highly efficient power conversion [2][3][4][5][6][7][8]. Semiconducting materials such as a-Si/μc-Si [9][10][11][12][13], CdTe [14][15][16][17], Cu(In,Ga)Se 2 [18,19], and Cu 2 ZnSn (S,Se) 4 (CZTSSe) [20][21][22] have already been demonstrated as mostly useful absorber layers in the commercial TFSCs. In the previous studies [8,[23][24][25][26], the power conversion efficiency exceeding 22% with the TFSCs based on a-Si/μc-Si, CdTe and Cu(In,Ga)Se 2 at both the laboratory scale and module level has been reported. ...
In the present work, antimony selenide (Sb2Se3)-based solar cell with a back surface field (BSF) layer has been designed and studied. The purpose of this research is to improve the performance of the Sb2Se3-based solar cell by introducing low-cost and widely available barium silicide (BaSi2) material as the BSF layer into the basic Sb2Se3-based heterojunction solar structure. A comparative study on the performance of the conventional Sb2Se3 solar cell structure consisting of Al/FTO/CdS/Sb2Se3/Mo and the proposed structure of Al/FTO/CdS/Sb2Se3/BaSi2/Mo is made. The photovoltaic parameters such as open circuit voltage, short-circuit current density, fill-factor, power conversion efficiency, and quantum efficiency of heterojunction structures are analyzed intensively by using the Solar Cell Capacitance Simulator in One Dimension (SCAPS-1D) program. To optimize the device, the thickness of Sb2Se3 absorber layer is varied from 0.1 to 2 μm. In addition, the effects of acceptor ion and bulk defect densities in Sb2Se3 absorber layer, interface defect density of buffer/absorber and absorber/BSF, back surface recombination velocity, operating temperature, and cell resistances on the overall performances are investigated. The thicknesses of BaSi2 BSF and Sb2Se3 absorber layers are optimized to be 0.3 μm and 1 μm, respectively. The efficiency of the proposed solar structure with a thin 1 μm Sb2Se3 absorber layer is obtained to be 29.35%. The simulation results lead to suggest that the BaSi2 material as a BSF layer would be effective to fabricate low cost and high-efficient Sb2Se3-based thin-film solar cells.
... 30,31 In addition, although IBC solar cells have reached a record efficiency of over 26%, the process flow is complicated and uses ion implantation and the photolithography method to realize the pattern at the rear side, which is challenging for commercialization. 23,32 Using both contact structures for achieving high efficiency offers the advantages of low fabrication cost and fewer process steps compared with IBC cells. To increase the possibility of the commercialization of the passivating contact, a hybrid solar cell that combines both POLO and SHJ solar cells is proposed, which allows for the realization of a low-cost, highefficiency structure. ...
This study proposes a hybrid solar cell structure for a highly efficient silicon solar cell obtained by combining two passivating contact structures, namely, a heterojunction and polysilicon passivating contact. Given that the major cause of the loss in efficiency of crystalline silicon solar cells is carrier recombination at the metal‐semiconductor junction, a passivating contact having high‐quality passivation and a low contact resistance was introduced. In this study, two major passivating contact solar cells were combined. By applying an intrinsic thin amorphous silicon layer at the front and a tunneling oxide at the rear, a hybrid silicon solar cell with an efficiency of 21.8% was fabricated. Moreover, to evaluate the potential efficiency limit and to suggest methods for improving the cell performance of the proposed amorphous silicon emitter tunnel oxide back contact structure, the cell efficiency was simulated, and the result indicated that an efficiency of 26% could be achieved by controlling the thickness and resistivity of the wafer. High‐efficiency hybrid silicon solar cell was achieved by combining twopassivating contact structures, a heterojunction and a polysilicon passivating contact. The efficiency of 21.8% was achieved and the simulation showed that the efficiency can be reached to 26%.
... Among them, the thin film solar cells, have proved themselves the most economical and robust types for roof photovoltaic panel integration and panel arrays for the power plant because of several advantages, e.g., low material cost, mature vacuum deposition methods, and compatibility with mass production [25][26][27][28][29]. The commercial thin film solar cells are fabricated based on semiconducting materials including CdTe [30], Cu(In,Ga)Se 2 [31][32][33], a-Si/μc-Si [34][35][36][37][38]. Yet these materials have problems of low elemental abundance, high toxicity of the (precursor) materials. ...
Sb 2 Se 3 as a rising star semiconducting material with a bandgap of 1.1 eV has played a role of the absorber in the thin film solar cells. Regular device architectures such as metal grids/buffer/Sb 2 Se 3 /metal electrode, or transparent electrode film/buffer/Sb 2 Se 3 /metal electrode have been fabricated both experimentally and theoretically and exhibit relatively good photovoltaic performances. Yet the theoretical power-conversion efficiency is not competitive with commercial thin film solar cells. Therefore, we propose an inverted architecture with top illumination through ITO substrate, with allocating the hole transport layer (HTL) on top of Sb 2 Se 3 and stacking electron transport layer beneath the Sb 2 Se 3 . Indeed an optimal power conversion efficiency of 24.7% and fill factor of 80.3% have been simulated in the solar devices with the selected NiO as the HTL. The improvement in solar cell performances stems from the satisfying bandgap alignment and improved hole conductivity due to the high acceptor concentration of the chosen material. Further increase of the device performances depend on the high quality Sb 2 Se 3 thin films, i.e., with negligible defects states and the suppression of defects at the Sb 2 Se 3 /HTL interfaces.
... To support the wide distribution of this promising technology, it is hence crucial to develop simplified, damage-free, and cost-effective preparation processes, while maintaining exceptional solar cell properties. Various alternative patterning techniques for the substitution of photolithography have been presented in the past by ourselves and other groups [9][10][11]. Here we demonstrate the successful development of a photolithography-free patterning technique using solely in-situ shadow masks during plasma-enhanced chemical vapour deposition (PECVD), and show in detail its advantages and challenges as compared to our photolithography-based preparation process. ...
We report on the investigation and comparison of two different processing approaches for interdigitated back contacted silicon heterojunction solar cells: our photolithography-based reference procedure and our newly developed shadow mask process. To this end, we analyse fill factor losses in different stages of the fabrication process. We find that although comparably high minority carrier lifetimes of about 4 ms can be observed for both concepts, the shadow masked solar cells suffer yet from poorly passivated emitter regions and significantly higher series resistance. Approaches for addressing the observed issues are outlined and first solar cell results with efficiencies of about 17 % and 23 % for shadow masked and photolithographically structured solar cells, respectively, are presented.
In the present work, lead-free perovskite solar cell has been structured using CH 3 NH 3 SnI 3 as an absorber layer, P3HT acting as a HTL, and TiO 2 as ETL material. Perovskite solar cell is the originating photovoltaic technology that shows great elevation in its performance during recent years. The fundamental n-i-p planar heterojunction structure of photovoltaic cells has been designed and simulated with solar cell capacitance simulation software (SCAPS-1D). In this study, different parameters like thickness, acceptor density, temperature, and defect density have been varied to increase the device performance. Optimum values of different parameters have been used to attain the good results of the photovoltaic device such as PCE, V OC , FF, and J SC of 27.54%, 1.0216 V, 86.56%, and 31.14 mA/cm ² , respectively. The impact of acceptor density has been varied from 1x10 ⁻¹² cm ⁻³ to 1x10 ⁻²⁰ cm ⁻³ for the proposed device structure. Therefore, the PCE of this device structure increases by using different charge transport materials. This simulation study shows that the proposed cell structure can be used to construct the photovoltaic cell with higher efficiency.
In this work, the use of a novel, large area, mask-less and contact-less patterning technique is demonstrated for the first time, showing the localized deposition of hydrogenated amorphous silicon (a-Si:H) in a desired pattern over the full surface of an M0 (156 mm × 156 mm) solar wafer. The patterning functionality is achieved through a custom-designed RF electrode possessing a series of “slits” and placed in close proximity to the substrate in a plasma enhanced chemical vapor deposition (PECVD) chamber. Under a certain set of process conditions, a plasma only ignites within these slits, and the localized plasma results in localized patterned deposition of a-Si:H with feature widths compatible with application in an interdigitated back contact (IBC) solar cell design (760 μm). The homogeneity of the finger width and thickness over the surface of the M0 wafer is evaluated, with a 37% variation in thickness (at very high deposition rate, ∼1 nm/s) but only a 4.7% variation in finger width (MSE). With this application in mind, the impact of the deposition of such “fingers” on an underlying “blanket” passivation layer is assessed. Passivation is maintained or improved up to a given finger/blanket thickness ratio, above which the passivation is degraded. It is shown that the acceptable process window contains suitable thickness values for heterojunction (HJT) IBC solar cells, and the physical processes at the origin of this phenomenological observation are discussed.
Antimony selenide (Sb2Se3) is a sustainable candidate for renewable energy production. Photovoltaic cells based on Sb2Se3 has grown worldwide interest and attention due to its low cost and outstanding conversion efficiency. Cubic silicon carbide (3C–SiC) is an optimistic material as buffer layer which replacing toxic cadmium sulfide (CdS) and has a large bandgap. We investigate numerically the performance of Sb2Se3 based n-SnO2/n-3C–SiC/p-Sb2Se3 heterojunction solar cell by employing (SCAPS-1D) (one dimensional solar cell capacitance simulator) software. The impact of buffer/absorber layer width, donor/acceptor densities, and operating temperature on device performance is analyzed. Accordingly, the defects come across in p- Sb2Se3 and n-3C–SiC layers along with the role of n-3C–SiC/p-Sb2Se3 interface defects density have been analyzed in detail to deliver guidelines for obtaining optimum efficiency. The anticipated structure offers the maximum efficiency of 23.9% under condition of illumination spectrum of 1.5G. Photovoltaic device performance parameters such as Jsc, Voc, QE, FF and efficiency of the devices have been examined graphically. The optimized structure may have significant impact on future development of advanced photovoltaic devices.
Large-area (251.96 cm²) bifacial interdigitated-back-contact (IBC) solar cells are presented in this work. We employ front floating emitter (FFE) to replace the front surface field (FSF) to simplify the process sequences. A simplified process flow is exploited to fabricate the IBC solar cells through industrial equipment and compatible processes. Double side boron diffusion followed by etch-back to form the emitter and lightly doped front surface, reducing high-temperature influence on the bulk lifetime and fabrication complexity. Ion implantation and anneal process is applied for base doping. The cell conversion efficiency reaches 22.92%, independently certificated by Fraunhofer Institute for Solar Energy System CalLab (Fraunhofer ISE). The IBC solar cells feature an open metallization grid, which offers a bifacial response with the bifaciality reaches to 72%. Only one-step mask and opening procedure was used, which greatly simplified the process. These results demonstrate the feasibility of this simplified process for manufacturing low-cost high-efficiency of IBC cells. Key parameters such as surface recombination J0, metal contact recombination J0-metal, contact resistivity of the cells are extracted by specially designed structures. Loss analysis shows that further efficiency improvement can be attained though reducing the contact resistance and metal contact recombination. The results in this work indicates the potential of this novel process for producing low-cost high-efficient IBC solar cells.
In this study, a hole transport layer (HTL)-free perovskite solar cell (PSC) structure with CH3NH3SnI3 as an active layer and TiO2 as an electron transport layer (ETL) has been proposed for the first time. The solar cell capacitance simulator in one dimension program has been carried out to design the proposed HTL-free CH3NH3SnI3-based PSC and simulate its performance. The output parameters of the proposed PSC, such as open circuit voltage (Voc), short-circuit current density (Jsc), fill factor (FF), power conversion efficiency, and quantum efficiency, are evaluated by varying the physical parameters of various layers. The thermal stability of the proposed cell has also been analyzed. The thicknesses of the ETL and the absorber are optimized to be 0.05 and 1.0 µm, respectively. A conversion efficiency of 26.33% along with Voc of 0.98 V, Jsc of 31.93 mA/cm², and an FF of 84.34% is obtained for the proposed HTL-free CH3NH3SnI3-based PSC. These simulation results would be helpful in fabricating highly efficient and inexpensive PSCs.
Achieving low contact resistivity for the p-contact in silicon heterojunction (SHJ) solar cells is challenging when classic n-type transparent conductive oxides (TCOs), such as indium tin oxide (ITO), are used in the contact stack. Here, we report on SHJ solar cells with interdigitated back-contact (IBC) and a direct aluminum (Al) metallization applied to the p-contact. We find that carefully annealing an Al/a-Si:H(p) (p-type amorphous silicon) contact at moderate temperatures leads to a specific contact resistivity that is half as low as its silver (Ag)/ITO counterpart. This is explained by Al diffusing into a-Si:H(p) upon temperature treatment, forming a partially crystallized aluminum silicide layer. For a sufficiently high doping level in a-Si:H(p), this enables an efficient tunnel-recombination of holes from a-Si:H(p) to the Al contact. An estimate for this tunneling-dominated specific contact resistivity is calculated as a function of the interface doping density. Best fabricated IBC SHJ solar cells with Al p-contact yield a fill factor of 77.5% and a power conversion efficiency of 22.3%. The main differences to devices with an Ag/ITO/a-Si:H(p) contact stack are a decrease in open-circuit voltage by 14 mV and a slightly higher series resistance (R_s). While the first aspect can be ascribed to increased interface recombination, the second one is unexpected and requires further investigation. Interestingly, omitting an intermediate TCO does not lead to current losses in devices with Al contacts, which is further investigated by optical simulations. Finally, electrical equivalent circuit simulations are conducted to describe the electrical behavior of the investigated devices.
Interdigitated back contact (IBC) structures formed by integrating two functional materials of opposite polarity on the rear side of device have attracted a significant attention for optoelectronic device design. Currently, this type of IBC design has been widely developed with a variety of applications in the photovoltaic (PV) community and associated fields. In terms of PV devices, the IBC designs can eliminate the need for a front electrode, endowing a potential in high power conversion efficiency. Moreover, by opening the front surface on IBC structures provides a platform for further designs, which enables us to realize a series of derived applications. This review summarizes the recent progress in IBC based PV devices, including c-Si solar cells (SCs), perovskite SCs, and perovskite/c-Si tandem SCs. Furthermore, the focus herein is focused on the latest advances in the specific applications in the studies of photon recycling, and in-situ/in-operando measurements of photoelectric properties. Finally, a perspective into the remaining challenges and future opportunities to accelerate the practical applications of IBC devices is highlighted.
Lithography-free interdigitated back-contact silicon heterojunction (IBC-SHJ) solar cells with dopant-free metal oxides (TiO2 and MoOx) as the carriers selective transport layers were investigated. Spin-coating and hot-wire reactive-sublimation deposition together with low cost mask technology were used to fabricate the solar cells. Insertion of a SiOx layer with the thickness of about 2.4 nm between the intrinsic amorphous Si (a-Si:H(i)) passivation layer and the spin-coated TiO2 layer greatly improves the solar cell performance due to the enhanced field-effect passivation of the a-Si:H(i)/SiOx/TiO2 layer stack. Efficiency up to 20.24% was achieved on the lithography-free and dopant-free IBC-SHJ devices with a-Si:H(i)/SiOx/TiO2 layer stack as the electron selective transport layer, a-Si:H(i)/MoOx as the hole selective transport layer, and WOx as the antireflection layer. The novel IBC-SHJ solar cells show significant advantages in simplification of the technology and process compared with the IBC-SHJ devices whose back surface pattering and carrier selective layers relied on photolithography and plasma enhanced chemical vapor deposition (PECVD).
Recently, solar photovoltaics (PV) is becoming more economically competitive for meeting electricity generation demands due to its steady cost declines. Crystalline silicon (c-Si) PV dominates the current solar-cell market because of its advantages including abundancy of raw material, low toxicity, scalable technologies, long-term product reliability, and a high theoretical cell efficiency limit.
In early 2017, the world record efficiency for single-junction c-Si solar cells was achieved in a silicon heterojunction interdigitated back-contact (SHJ-IBC) solar cell. However, to fabricate such SHJ-IBC solar cells, complex amorphous silicon (a-Si:H) patterning steps are required to form the interdigitated a-Si:H strips at the back side of the devices. Whereas photolithography is commonly used at laboratory scale, it turns out to be a costly and sophisticated technique and thus not applicable for mass production. Hence, this fabrication complexity raises concerns about the commercial potential of such devices.
This thesis work focuses on development of simple a-Si:H patterning approaches for SHJ-IBC solar cells to replace conventional photolithography and wet chemical processing steps used in the past. Different a-Si:H patterning methods are investigated, including lift-off, laser ablation, dry etching of a-Si:H, and in situ a-Si:H deposition. The combination of laser ablation and lift-off results in a photolithography-free a-Si:H patterning process sequence. All these developed methods have been demonstrated by fabrication of SHJ-IBC solar cells with a best efficiency of 23.3% using photolithography and lift-off. Moreover, an innovative a-Si:H patterning method, namely selective deposition of a-Si:H, is studied in an attempt to replace the lift-off process which is still not an industrially compatible method.
We present a novel process sequence to simplify the rear-side patterning of the heterojunction IBC cells. In this approach, interdigitated strips of a-Si:H (i/p +) and a-Si:H (i/n +) are achieved by partially etching a blanket a-Si:H (i/p +) stack through a hard mask to remove only the p + a-Si:H layer and replace it in situ with an n + a-Si:H layer. This eliminates the ex situ wet clean after dry etch and also prevents re-exposure of the c-Si surface during rear-side processing. High-quality passivation and contact resistance comparable to reference translates into cell performance that is also similar to that of cells from the reference process. The best cell has an efficiency of 22.9% and VOC close to 730 mV, demonstrating that the developed partial etch process sequence can be successfully implemented to achieve cell performance comparable to reference, but with a simpler process.
Thin, light-absorbing films attenuate the Raman signal of underlying substrates. In this article, we exploit this phenomenon to develop a contactless thickness profiling method for thin films deposited on rough substrates. We demonstrate this technique by probing profiles of thin amorphous silicon stripes deposited on rough crystalline silicon surfaces, which is a structure exploited in high-efficiency silicon heterojunction solar cells. Our spatially-resolved Raman measurements enable the thickness mapping of amorphous silicon over the whole active area of test solar cells with very high precision; the thickness detection limit is well below 1 nm and the spatial resolution is down to 500 nm, limited only by the optical resolution. We also discuss the wider applicability of this technique for the characterization of thin layers prepared on Raman/photoluminescence-active substrates, as well as its use for single-layer counting in multilayer 2D materials such as graphene, MoS2 and WS2.
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 .
We report on the fabrication of back-contacted silicon heterojunction solar cells with conversion efficiencies above 21%. Our process technology relies solely on simple and size-scalable patterning methods, with no high-temperature steps. Using in situ shadow masks, doped hydrogenated amorphous silicon layers are patterned into two interdigitated combs. Transparent conductive oxide and metal layers, forming the back electrodes, are patterned by hot melt inkjet printing. With this process, we obtain high short-circuit current densities close to 40 mA/cm$^{2}$ and open-circuit voltages exceeding 720 mV, leading to a conversion efficiency of 21.5%. However, moderate fill factor values limit our current device efficiencies. Unhindered carrier transport through both heterocontact layer stacks, as well as higher passivation quality over the minority carrier-injection range relevant for solar cell operation, are identified as key factors for improved fill factor values and device performance.
Future wafer-based silicon solar cells will be fabricated on thin (<140 μm) wafers. However, technologies to handle thin wafers during cell processing are not yet available for industry. In this paper, a flow to handle thin wafers during rear side cell processing is developed and demonstrated on 4-in 200 μm-thick wafers. The flow involves bonding the wafers to glass after front-side processing followed by a low-temperature p-n heterojunction formation on the rear side. 2.5 × 2.5 cm$^{2}$ amorphous/crystalline silicon heterojunction interdigitated back-contact solar cells are fabricated by use of lithography while bonded to glass, and they show an efficiency of up to 17.7%. Shunts, infrared light absorption, and rear side interface passivation are identified as the main efficiency losses. Dedicated experiments suggest that the passivation losses are related to the degradation of the adhesive during wafer cleaning. Hence, methods to improve the compatibility of the adhesive with the cleaning process are discussed.
This study deals with the development and optimization of Interdigitated Back Contact (IBC) Silicon Heterojunction (Si-HJ) solar cells based on n-type crystalline silicon (c-Si) substrates. Both one-dimensional (1D) and 2D aspects of IBC Si-HJ cells are explored in this work. Rear Emitter (RE) Si-HJ cells are fabricated to study the influence of the emitter stack on 1D resistive losses. It is shown that the rear emitter stack has to be carefully designed to maintain a high surface passivation level without inducing series resistance (RSeries). On IBC Si-HJ structures, the influence of 2D features such as emitter contact fraction are confirmed both experimentally and by modeling. Using the screen printing technology, 25 cm2 IBC Si-HJ structures have been fabricated with an efficiency of 15.7%.
Silicon heterojunction solar cells consist of thin
amorphous silicon layers deposited on crystalline silicon
wafers. This design enables energy conversion efficiencies
above 20% at the industrial production level. The key feature
of this technology is that the metal contacts, which are
highly recombination active in traditional, diffused-junction
cells, are electronically separated from the absorber by insertion
of a wider bandgap layer. This enables the record
open-circuit voltages typically associated with heterojunction
devices without the need for expensive patterning techniques.
This article reviews the salient points of this technology.
First, we briefly elucidate device characteristics.
This is followed by a discussion of each processing step,
device operation, and device stability and industrial upscaling,
including the fabrication of solar cells with energyconversion
efficiencies over 21%. Finally, future trends are
pointed out.
This paper reports on the development of an innovative back-contacted crystalline silicon solar cell with passivating contacts featuring an interband tunnel junction at its electron-collecting contacts. In this novel architecture, named "tunnel-IBC", both the hole collector patterning and its alignment to the electron collector are eliminated, thus drastically simplifying the process flow. However, two prerequisites have to be fulfilled for such devices to work efficiently, namely (i) lossless carrier transport through the tunnel junction and (ii) low lateral conductance within the hole collector in order to avoid shunts with the neighboring electron-collecting regions. We meet these two contrasting requirements by exploiting the anisotropic and substrate-dependent growth mechanism of n- and p-type hydrogenated nano-crystalline silicon layers. We investigate the influence of the deposition temperature and the doping gas concentration on the structural and the selectivity properties of these layers. Eventually, tunnel-IBC devices integrating hydrogenated nano-crystalline silicon layers demonstrate a conversion efficiency up to 23.9%.
A detailed investigation of the laser damage to amorphous silicon (a-Si:H) layers patterned by laser ablation (LA) and wet chemical etching is presented. This approach can be applied to pattern the rear side of silicon heterojunction interdigitated back-contact solar cells. Only the top sacrificial a-Si:H laser-absorbing layer of an a-Si:H/SiOx/a-Si:H/c-Si stack is ablated. Laser damage in the bottom a-Si:H layer and a-Si:H/c-Si interface is analyzed by both scanning electron microscopy and transmission electron microscopy. We show that the a-Si:H/c-Si passivation is degraded by laser damage and that this degradation can be diminished by increasing laser processing speed. This is attributed to a decrease of laser-irradiated area, and particularly smaller overlapping zones of adjacent laser pulses. The re-passivation quality after LA and wet etching is similar to that of as-passivated samples. This indicates that laser damage is not present in the bulk c-Si substrate but only in the a-Si:H passivation layer, which is removed during subsequent wet etching, thus allowing high quality repassivation.
We present a novel process scheme for a-Si:H patterning using damage-free laser ablation, resulting in a simple, fast, and photolithography-free emitter patterning of silicon heterojunction interdigitated back-contact (SHJ-IBC) solar cells. An a-Si:H laser-absorbing layer and a stack of sacrificial dielectric layers are deposited on top of a-Si:H/c-Si heterocontact to prevent laser damage. Laser ablation only removes the top a-Si:H layer, which limits laser damage to the surface of dielectric layers. These dielectric layers form a distributed Bragg reflector with a high reflectance of 80% at the laser wavelength which results in additional protection of the bottom a-Si:H/c-Si heterocontact. The significant reduction of laser damage is confirmed by atomic-force microscopy and photo-luminescence measurements. Such damage-free laser ablation process was successfully incorporated in a SHJ-IBC process flow and a best efficiency of 21.8% was achieved.
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 2017 are reviewed.
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.
In this work, the efficiency of n-type silicon solar cells with a front side boron-doped emitter and a full-area tunnel oxide passivating electron contact was studied experimentally as a function of wafer thickness W and resistivity ρb. Conversion efficiencies in the range of 25.0% have been obtained for all variations studied in this work, which cover 150 µm to 400 µm thick wafers and resistivities from 1 Ω cm to 10 Ω cm. We present a detailed cell analysis based on three-dimensional full-area device simulations using the solar cell simulation tool Quokka. We show that the experimental variation of the wafer thickness and resistivity at device level in combination with a detailed simulation study allows the identification of recombination induced loss mechanisms. This is possible because different recombination mechanisms can have a very specific influence on the I-V parameters as a function of W and ρb. In fact, we identified Shockley-Read-Hall recombination in the c-Si bulk as the source of a significant FF reduction in case of high resistivity Si. This shows that cells made of high resistivity Si are very sensitive to even a weak lifetime limitation in the c-Si bulk. Applying low resistivity 1 Ω cm n-type Si in combination with optimized fabrication processes, we achieved confirmed efficiency values of 25.7%, with a Voc of 725 mV, a FF of 83.3% and a Jsc of 42.5 mA/cm2. This represents the highest efficiency reported for both-sides contacted c-Si solar cells. Thus, the results presented in this work demonstrate not only the potential of the cell structure, but also that a variation of the wafer thickness and resistivity at device level can provide deep insights into the cell performance.
For crystalline-silicon solar cells, voltages close to the theoretical limit are nowadays readily achievable when using passivating contacts. Conversely, maximal current generation requires the integration of the electron and hole contacts at the back of the solar cell to liberate its front from any shadowing loss. Recently, the world-record efficiency for crystalline-silicon single-junction solar cells was achieved by merging these two approaches in a single device; however, the complexity of fabricating this class of devices raises concerns about their commercial potential. Here we show a contacting method that substantially simplifies the architecture and fabrication of back-contacted silicon solar cells. We exploit the surface-dependent growth of silicon thin films, deposited by plasma processes, to eliminate the patterning of one of the doped carrier-collecting layers. Then, using only one alignment step for electrode definition, we fabricate a proof-of-concept 9-cm2 tunnel-interdigitated back-contact solar cell with a certified conversion efficiency >22.5%.
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%.
Inkjet-printing-based fabrication process of the interdigitated back-contact silicon heterojunction solar cells has the potential to reduce the manufacturing costs because of its low machine and material costs and its applicability to thinner fragile silicon substrates than 100 µm. In this study, ink and printing parameters were investigated to obtain the desirable fine patterns and the resultant accuracy of the linewidths was less than ±0.05 mm on a flat surface. The completed cells using inkjet-printing showed almost the same performance of that fabricated by photolithography. In addition, flexible and free-standing cell on a 53-µm-thick Si substrate has been successfully fabricated.
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 June 2016 are reviewed. Copyright
Module-level processing of silicon heterojunction interdigitated back-contacted (SHJ-IBC) solar cells while bonded to glass, in the so-called i2-module concept, is discussed. In this approach, a key challenge is the interdigitated patterning of a-Si:H without compromising on the rear-surface passivation. Process adaptations involving more resistant bonding agents and a milder wet etchant enabled bonded cells with the best efficiency of 21.7% and Voc of 734 mV, which are the highest reported for bonded cells processed partially at module level, and which undoubtedly proves the potential of this i2-module concept to reach high Voc and efficiency. Yet another challenge is to make the process flow cost-effective and industrially-relevant, i.e. a litho-free, all-dry process flow, analogous to thin-film PV module fabrication. As a first step, dry etching of a-Si:H was developed to replace wet etching, and was successfully incorporated in a SHJ-IBC process flow to fabricate freestanding cells with the best efficiency of 22.9% and above 20% on thick (190 μm) and thin (56 μm) EVA-bonded silicon.
Module-level processing of silicon heterojunction interdigitated back-contacted (SHJ-IBC) solar cells, in the i2-module concept, is discussed. The i2-module concept is an elegant approach which enables thin silicon foils (< 50 µm) to be processed with high yield into highly-efficient devices, by integrating cell processing at the module level after bonding such fragile foils to module glass at an early stage. A key challenge for the i2-module SHJ-IBC process flow is the interdigitated patterning of a-Si:H without compromising on the rear-surface passivation. Process adaptations such as the use of more resistant bonding agents and a milder wet etchant has enabled thick bonded cells to be fabricated with the best efficiency of 21.7% and an outstanding Voc of 734 mV, which are the highest reported for bonded cells, processed partially at the module level. Yet another challenge is to make the module-level SHJ-IBC process flow cost-effective and industrially-relevant, i.e. a litho-free, all-dry process flow, analogous to thin-film PV module fabrication. As a first step, dry plasma etching of a-Si:H was developed to replace wet etching, and was successfully incorporated in a SHJ-IBC process flow to fabricate thick freestanding cells with the best cell efficiency of 22.6% and an excellent Voc of 730 mV. The developed process flow will eventually be applied to thin silicon foils bonded to glass.
A novel emitter patterning method for back-contacted Si heterojunction solar cells is presented, which combines laser processing and wet etching of a mask layer stack with self-aligned repassivation, thus reducing the process complexity, as compared with the commonly used emitter patterning methods. Lifetime samples demonstrate that with a suitable mask stack, laser scribing can be performed without inducing laser damage to the passivation. Despite nonoptimal wet etch and repassivation processes which currently limit the obtained lifetime, proof-of-concept cells on p-type wafers fabricated using this novel emitter patterning process and lithographically patterned metallization exhibit an open-circuit voltage of 694 mV and pseudo-fill-factors of 83%. With the laser written mask layers for etching and self-aligned passivation process, we have thus developed the proof-of-concept for a simple, lithography free, and contactless emitter patterning method for industrial applications
A novel process flow, which can allow the formation of interdigitated p- and n-type a-Si strips and corresponding transparent conductive oxide (TCO) and metal layers for silicon heterojunction interdigitated back contact (SHJ-IBC) solar cells using only a single alignment step and without using any resist patterning is presented. The flow is based on the deposition of a-Si, TCO and metal layers through a stack of shadow masks. Three variation of the flow are described. Several key process components to include a-Si deposition and H2 plasma etch through the shadow mask are demonstrated and described.
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 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).
In this study a novel high efficiency crystalline silicon (c-Si) solar cell concept is presented. It combines Interdigitated Back Contact (IBC) structures with Silicon Heterojunction (Si-HJ) technology through the use of Laser assisted patterning steps. The SLASH (Structuring by Laser Ablation of Silicon Heterojunction) IBC cell shows a simplified geometry and a fabrication process compatible with mass production. SLASH IBC cells have been fabricated using optimized parameters for a-Si:H layers patterning and screen printed metallization. The c-Si surface morphology (polishing and texturation process) is shown to have a great impact on the cells parameters. Almost the same cell performances are obtained on alkaline and chemical-mechanical polished surfaces. An efficiency of 19.0% has been obtained on 5*5 cm2 devices proving the high efficiency potential of this simplified IBC structure.
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.
We report on the epitaxial growth, fabrication, and characterization of a resonant-cavity-enhanced separate-absorption and multiplication avalanche photodiode capable of detecting light at 1.55 μm. The device is grown by molecular beam epitaxy with In0.53GaxAl0.47-xAs layers lattice matched to InP. This detector has exhibited a peak external quantum efficiency greater than 70%, a gain of 8, and a dark current of only 50 nA at 90% of breakdown for a 100-μm-diam diode.© 1998 American Vacuum Society.
Amorphous Si/SiO2 superlattices, with four periods, have been grown using the two-target alternation magnetron sputtering technique. The thicknesses of Si layers in all the superlattices are 1.0 nm, and those of SiO2 layers in six types of the superlattices are 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 nm. Electroluminescence (EL) from the Au/(Si/SiO2) superlattice/p-Si samples has been observed at a forward bias about 5 V or larger. The influences on the EL spectra from the thicknesses of SiO2 layers in the amorphous Si/SiO2 superlattices and from input electrical power are studied systematically.
To clarify the structure of amorphous silicon (a-Si), with the thickness less than 5nm, affected by the interface between a-Si and a-SiO2 as well as the structural changes after an annealing of 900 degrees C in N-2 gas atmosphere, Raman scattering investigation is carried out in a-Si/SiO2 superlattice (SL) films prepared by the sputtering method. Vibrational motion of strained a-Si at and near a-Si/SiO2 interface is influenced by the vibration of pressed a-SiO2 at the other side of the interface that results a blue shift of transverse optic (TO) -like modes in a-Si. The narrow space of thin (<2.5 nm in this work) a-Si layer impedes the crystallization to a-Si and the relaxation of energy during the crystallization event.
We compare recently reported results of efficient back-contacted amorphous/crystalline silicon heterojunction solar cells with fill factors up to 78.8 #x0025; with calculated #x00A0; j #x2013;V characteristics that are derived from an area-weighted summation of recombination currents taken from lifetime measurements. We compare solar cell structures with and without an intrinsic buffer layer beneath the p-type amorphous silicon emitter. We find that the inclusion of the buffer layer reduces the fill-factor potential by changing the ideality of the recombination current. However, analyzing the series resistance by illumination-dependent #x00A0;j #x2013;V-measurements, we find that the major loss mechanism of the fill factor is the limitation of the charge-carrier transport.
This letter reports interdigitated back contact silicon heterojunction (IBC-SHJ) solar cells which combine the performance benefits of both back contact and heterojunction technologies while reducing their limitations. Low temperature (<200 °C) deposited p- and n-type amorphous silicon used to form interdigitated heteroemitter and contacts in the rear preserves substrate lifetime while minimizes optical losses in the front. The IBC-SHJ structure is ideal for diagnosing surface passivation quality, which is analyzed and measured by internal quantum efficiency and minority carrier lifetime measurements. Initial cells have independently confirmed efficiency of 11.8% under AM1.5 illumination. Simulations indicate efficiencies greater than 20% after optimization.
Lasing action in an In0.1Ga0.9N vertical cavity
surface emitting laser was successfully achieved, for the first time, at
a wavelength of 381 nm. The 3λ vertical cavity comprising an
In0.1Ga0.9N active region was grown on a
GaN/Al0.34Ga0.66N quarter-wave reflector by metal
organic chemical vapor deposition (MOCVD), and covered with a
TiO2/SiO2 reflector by electron-beam evaporation.
The laser was operated at 77 K under optical excitation. We have
observed a significant narrowing of the emission spectrum from 2.5 nm
below the threshold to 0.1 nm (resolution limit) above the threshold,
which is a clear signature of lasing action.
Optical parameters of amorphous films of SiOx and SiNx deposited by plasma-enhanced chemical vapor deposition (PECVD) were extracted from ellipsometry and transmission spectroscopy in order to design Bragg reflectors. Bragg reflectors with a low number of layer pairs (SiOx/Si and SiOx/SiNx) have been grown on planar substrates for wavelengths ranging from 400 to 1600 nm. The Bragg reflectors prepared at 90 °C were patterned by lift-off processing. The growth behavior of Bragg reflectors on different prepatterned substrates was investigated with regard to micromirror application.
The author reviews the progress of surface emitting lasers ranging
from 1.55 to 0.4 μm by considering materials and performance,
including threshold, power output, polarization, RIN, linewidth,
spontaneous emission control, and photon recycling. Some possible
applications are discussed
One of the most often mentioned advantages of back-junction back-contacted silicon solar cells is that this cell structure has no shading losses, because metallization fingers and busbars are both located on the rear side of the solar cell. However, this is only true if only optical shading losses are regarded. In this work electrical shading losses due to recombination in the region of base busbar and fingers are analyzed using two-dimensional numerical device and network simulations. The base doping dependence of these effects is investigated as well as the influence of the rear side passivation. The results of the simulations are compared with EQE maps of back-junction solar cells. The influence of the busbars is quantified and the influence on the overall cell performance is discussed.
Enhanced spontaneous emission has been observed with wavelength‐sized monolithic Fabry–Perot cavities containing GaAs quantum wells. With an on‐resonance cavity structure, the photoluminescence intensity increases in the cavity axis direction, and the spontaneous emission lifetime is experimentally found to decrease.
This paper reports recent progress by SunPower Corporation to commercialize the Generation 3 product. The Generation 3 product has been designed to deliver both increased performance and lower manufacturing cost. Improved performance was achieved through optimization of the diffusion recombination losses. A conversion efficiency of 24.2% was achieved on a champion cell made on production equipment using a production wafer, 155.1cm<sup>2</sup> n-type CZ. This result was verified by the National Renewable Energy testing Laboratory. Modules made with Generation 3 cells were measured by NREL to have > 20.4% total area efficiency (>332W with 1.63m<sup>2</sup> modules). This paper presents the design changes before detailing the resulting performance.
Current-voltage characteristics of photovoltaic solar energy converter cells are obtainable by three methods, which yield different results due to the effects of the cell internal series resistance. The three resultant characteristics are: (1) the photovoltaic output characteristic, (2) the p-n junction characteristic, and (3) the rectifier forward characteristic. Choice of the proper method is necessary for obtaining the correct information for the individual application.Most frequently used, e.g. for the determination of solar converter performance, is the photovoltaic output characteristic. A quick way is described for deriving such a characteristic for any light level from a corresponding characteristic obtained at a different light level. This method involves two translations of the coordinate system and requires only the knowledge of the series resistance and the difference in light intensities or short circuit currents.An inversion of this method permits an easy determination of the series resistance, involving measurements at two arbitrary light levels of unknown magnitude.The effects of series resistance consist at high light levels in a flattening of the photovoltaic output characteristic and a related drop in the maximum power point voltage. The resultant decrease in efficiency has to be overcome by series resistance reduction for solar cell applications with optical concentrators or for space missions in closer sun-proximity. In cell portions progressively further distant from the contact strip increasing cell voltages develop, approaching open circuit condition at very high light intensities. This yields a reduction of current contribution from those portions of the cell and a deviation from the normal proportionality between short circuit current and light intensity.The direct measurability of the p-n junction characteristic at high current densities without series resistance effects by the second method provides a powerful tool to the device development engineer, besides yielding a second method for the determination of the series resistance. Results from the application of this method indicate that, in the current density range as used in solar energy conversion, the silicon solar cell characteristic is much more closely described by the diffusion theory for p-n junctions than was previously believed.ZusammenfassungStrom-Spannungs-Charakteristiken von photoelektrischen Sonnen-energie-Umwandlern kann man nach drei verschiedenen Methoden erhalten. Durch den Einfluss des Innenwiderstandes der Zellen liefert jede ein anderes Ergebnis. Die drei resultierenden Charakteristiken sind: (1) Die photoelektrische Ausgangs-Charakteristik, (2) die p-n-(Übergang-Charakteristik and (3) die Gleichrichter-Durchlass Charakteristik. Um die für die individuelle Anwendung richtige Information zu erhalten, muss in jedem Fall die geeignete Methode ausgewählt werden.In den meisten Fällen wird die photoelektrische Ausgangs-Charakteristic benutzt, z.B. für die Bestimmung der Leistung von Sonnenenergie-Umwandlern. Es wird eine Methode beschrieben, die es gestattet, eine solche Charakteristick für eine beliebige Lichtintensität aus einer entsprechenden anderen mit davon verschiedener Lichtintensität rasch herzuleiten. Die Methode benutzt zwei Koordinaten-Transformationen und erfordert nur die Kenntnis des Innenwiderstandes und die Abhängigkeit der Kurzschluss-Ströme von der Intensität.Eine Umkehrung dieser Methode erlaubt eine einfache Bestimmung des Innenwiderstandes. Dazu genügen Messungen bei zwei beliebigen Intensitäten unbekannter Grösse.Die Wirkung des Innenwiderstandes bei hohen Lichtintensitäten besteht in einer Abflachung der photoelektrischen Ausgangs-Charakteristic und damit einem Abfall der Spannung bei der grössten Leistung. Die daraus resultierende Verkleinerung des Wirkungsgrades muss bei Anwendung von optischen Konzentratoren oder bei Verwendung im Weltraum in grösserer Sonnennahe durch Erniedrigung des Innenwiderstandes ausgeglichen werden. In Zellenbereichen grbsseren Abstands vom Kontaktstreifen whähst die Spannung an und erreicht bei grossen Intensitäten fast die Verhältnisse beim offenen Stromkreis. Das bedingt eine Stromverdrängung von diesen Bereichen der Zelle und eine Abweichung von der normalen Proportionalität von Kurzschluss-Stom und Lichtintensität.Die direkte Messbarkeit der p-n-Übergang-Charakteristik nach der zweiten Methode ohne Innenwider- standseffekte bei hohen Stromdichten erweist sich als hervorragendes Werkzeug für den Entwicklungsingtenieur und liefert daneben noch eine zweite Möglichkeit für die Bestimmung des Innenwiderstandes.Die Ergebnisse der Anwendung dieser Methode zeigen, dass die Charakteristik der Silizium-Photozelle im Stromdichte-Bereich der Sonnenbatterien durch die Diffusionstheorie für p-n-Übergänge weit besser beschrieben wird, als man früher angenommen hatte.RésuméLes caractéristiques Intensité-Tension des cellules de convertisseurs d'énergie solaire photovoltaïques peuvant être obtenues par trois méthodes qui donnent des résultats différents par suite des effets de résistance intérieure en série des cellules. Les trois caractéristiques résultantes sont: (1) la caractéristique de rendement photovoltaïque, (2) la caractéristique de jonction p-n, et (3) la caractéristique de redresseur (vers l'avant). Pour obtenir le renseignement correct relatif à l'application particulière, il est nécessaire de choisir la méthode appropriée.La caractéristique de rendement photovoltaïque est utilisée tr`es fréquemment, par exemple, pour la détermination de la performance du convertisseur solaire. Il est décrit un procédé rapide permettant de tirer cette caractéristique pour tout niveau de lumière d'une caractéristique correspondante obtenue pour un niveau de lumière différent. Cette méthode fait intervenir deux translations du systéme de coordonnées et n'exige que la connaissance de la résistance en série et de la différence des intensités lumineuses des courants de court-circuits.Une inversion de cette méthode permet de déterminer facilement la résistance en série, en faisant intervenir des mesures à deux niveaux de lumières arbitraires de grandeur non connue.A des niveaux lumineux élevés les effets de la résistance en série se traduisent par un aplatissement de la caractéristique de rendement photovoltaïque et en une chute de la tension du point de puissance maximum. La diminution de rendement résultante doit être neutralisée par réduction des résistances en série pour des applications de cellules solaires avec moyens de concentration optiques, ou bien pour des missions spatiales à proximité du soleil. Dans les parties des cellules, progressivement plus éloignées de la bande de contact, il se produit des tensions de cellules croissantes se rapprochant de l'état de circuit ouvert à des intensités lumineuses très élevées, ce qui donne lieu à une réduction de l'apport de courant provenant de ces parties de cellules et à une déviation de la proportionalité normale entre le courant de court-circuit et l'intensité lumineuse. La mesurabilité directe par la deuxième méthode de la caractéristique de jonction p-n à des densités de courant élevées sans effets de résistance en série met à la disposition de l'ingénieur de mise au point un instrument puissant et, en outre, procure une deuxiéme méthode de détermination de la résistance en série. Les résultats de l'application de cette méthode indiquent que dans la gamme des densités de courants utilisées dans la conversion de l'énergie solaire, la caractéristique des cellules solaires au silicium est décrite par la théorie de la diffusion pour des jonctions n-p avec beaucoup plus de precision qu'on ne l'avait pensé auparavant.
To clarify the structure of amorphous silicon (a-Si), with the thickness less than 5 nm, affected by the interface between a-Si and a-SiO2 as well as the structural changes after an annealing of 900°C in N2 gas atmosphere, Raman scattering investigation is carried out in a-Si/SiO2 superlattice (SL) films prepared by the sputtering method. Vibrational motion of strained a-Si at and near a-Si/SiO2 interface is influenced by the vibration of pressed a-SiO2 at the other side of the interface that results a blue shift of transverse optic (TO) -like modes in a-Si. The narrow space of thin (<2.5 nm in this work) a-Si layer impedes the crystallization to c-Si and the relaxation of energy during the crystallization event.
- A Jäger-Waldau
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A. Jäger-Waldau PV Status Report 2017. JRC Science for Policy Report
(Publications office of the European Union, 2017).
ISFH pushes p-type mono cell to record 26.1% conversion efficiency
- M Osborne
M. Osborne ISFH pushes p-type mono cell to record 26.1% conversion efficiency,
PV-Tech (7 February 2018); 〈https://www.pvtech.org/news/isfh-pushes-p-typemono-cell-to-record-26.1-conversion-efficiency〉.
High-efficiency silicon heterojunction solar cells: a review
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S. DeWolf, A. Descoeudres, Z.C. Holman, C. Ballif, High-efficiency silicon heterojunction solar cells: a review, Green 2 (2012) 7-24.
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Harley, W. Mulligan, Generation 3: Improved performance at lower cost, in:
Proceedings of the 35th IEEE Photovoltaic Specialist Conference (PVSC) 275-278,
2010.
Solar cell efficiency tables (version 47)
- Green