Solar Cell Fabrication Process Research Articles

Oxygen precipitation behavior and its influence on phosphorus gettering in Czochralski silicon

This study investigates the effects of single-step and two-step annealing processes on the formation of oxygen precipitates and their impact on metal impurity gettering in gallium-doped monocrystalline silicon. The research focuses on the competitive relationship between internal gettering by oxygen precipitates and external gettering through phosphorus diffusion. Experimental results show that two-step annealing generates larger and more abundant oxygen precipitates, enhancing the internal gettering effect and reducing the recovery of minority carrier lifetime after phosphorus gettering. Despite this, phosphorus diffusion gettering remains effective in improving minority carrier lifetime, although the degree of improvement depends on the size and quantity of oxygen precipitates. These findings offer valuable insights for optimizing the fabrication process of silicon-based solar cells.

Controllable Crystallization of Perovskite Films during the Blade-Coating Fabrication Process for Efficient and Stable Solar Cells

The scalable production of high-quality perovskite thin films is pivotal for the industrialization of perovskite thin film solar cells. Consequently, the solvent system employed for the fabrication of large-area perovskite films via coating processes has attracted significant attention. In this study, a solvent system utilizing a volatile solvent as the primary reagent has been developed to facilitate the rapid nucleation of volatile compounds. While adding the liquid Lewis base dimethylformamide (DMF) can help to improve the microstructure of perovskite films, its slow volatilization renders the crystal growth process uncontrollable. Based on the solvent system containing DMF and ethanol (EtOH), introducing a small amount of NH4Cl increases the proportion of the intermediate phase in the precursor films. This not only results in a controllable growth process for the perovskite crystals but also contributes to the improvement of the film microstructure. Under the simulated illumination (AM1.5, 1000 W/m2), the photoelectric conversion efficiency (PCE) of the inverted solar cells has been improved to 20.12%. Furthermore, after 500 hours of continuous illumination, the photovoltaic device can retain 95.6 % of the initial, indicating that the solvent system is suitable for the scalable fabrication of high-quality FAPbI3 thin films.

Multi-Terminal GaInP/GaInAs/Ge Solar Cells for Subcells Characterization

Improvement of triple-junction (3J) III-V/Ge solar cells efficiency is hindered by the low current produced by the top and middle cells relative to the bottom cell (Ge). This can be explained by the difficulty of characterizing, on an individual basis, the subcells. We investigate the fabrication process of multi-terminal multi-junction solar cells (MTMJSC) and its potential as a promising architecture to independently characterize subcells of multi-junction solar cells. Here, we study monolithic triple-junction solar cells, with an InGaP top cell, an InGaAs middle cell and a Ge bottom cell interconnected by tunnel junctions. We demonstrate a fabrication process for MTMJSC on commercial wafers for characterization applications purposes. I-V measurements, under illumination, of two-terminals and MTMJSC were compared to validate that the MTMJSC fabrication process does not degrade the cells’ performance. The dark current of each subcell was also measured and an ideal-diode model used to determine the subcells electrical parameters. The results suggest a method to measure the relative absorption and the opto-electrical couplings between the subcells unambiguously, through EQE and electroluminescence measurements, based on basic micro-fabrication processes.

Performance investigation of MAPbI3/MASnI3 based all-perovskite tandem solar cell using SCAPS simulation

Due to the complexity of the fabrication process of tandem solar cells, perovskite materials provide a cost-effective and simpler fabrication solution. In this work, MAPbI3/MASnI3 Perovskite-based Tandem solar cell has been explored numerically by using SCAPS-1D. Methylammonium Lead Iodide (CH3NH3PbI3 or MAPbI3) and Methylammonium Tin Iodide (CH3NH3SnI3 or MASnI3) have been considered as wide bandgap (WBG) and narrow bandgap (NBG) absorber material for the top cell and bottom cell, respectively. WBG top cell and NBG bottom cell are both investigated through the change in the depth of perovskite materials at the current matching conditions at the illumination of Standard AM 1.5 spectrum. The all-perovskite MAPbI3/MASnI3 tandem solar cell with copper (I) oxide (Cu2O) hole transport layer has achieved excellent performance with a maximum power conversion efficiency (PCE) of 32.74% with V oc of 1.68 V, J sc of 24.6 mA cm−2, and fill factor (FF) of 79.39%, respectively.

Dual-meniscus-assisted roller-coating for scalable and patterned perovskite solar cells

Scaling up the fabrication process for perovskite solar cells has emerged as a prominent research focus in the field of perovskite photovoltaics. Current methods for preparing large-scale perovskite solar cells often struggle to meet the simultaneous requirements of continuous production, high compatibility, and low commissioning costs necessary for industrial-scale manufacturing. Here, the roller coating method is demonstrated to realize the preparation of large-scaled and uniform perovskite films with customized patterning through a facile and stable “touch-and-roll” motion. The unique fabric-based roller and “dual-meniscus” structure guarantee accurate control of ink flow and film thickness, thereby realizing the reproducible preparation on different substrates ranging from rigid glass to flexibe polymer film. The method yielded PSCs with peak efficiencies of 14.11% (0.16 cm2) and 10.61% (1 cm2). This roller coating method exhibits a promising new avenue for advancing the scale and commercial development of perovskite photovoltaics.

Printing PEDOT:PSS optimized using Response surface method (RSM) and genetic algorithm (ga) via modified 3D printer for perovskite solar cell applications

Despite significant improvements in solar cell fabrication processes, there are still significant challenges in the fabrication technology owing to poor production efficiency, large equipment and preparatory costs, substrate dependencies, material limitation, etc. This research proposes the use of a modified extrusion-based three-dimensional (3D) printing technology to print thin films of PEDOT:PSS (Poly 3,4-ethylenedioxythiophene:poly styrene sulfonate) for perovskite solar cell (PSC) applications and beyond. The main objective of the research is to induce the benefits of 3D printing technology into thin film printing for PSC applications. The central composite design (CCD) of the response surface method (RSM) in design expert software (Design Expert V13) and a genetic algorithm (GA) in MATLAB software are used to design and optimize the experiment, respectively. Accordingly, a uniformly thin PEDOT:PSS film with a 115 nm thickness is printed with the modified 3D printer at a print speed of 82 mm/s, a bed temperature of 80 °C, and an extrusion start position of 160 mm with a 0.1 mm inner diameter blunt needle and a 0.25 mm x-distance offset. To validate the printed PEDOT:PSS film for PSC application, other PSC layers, except for aluminum electrodes, are spin-coated on top of the 3D-printed PEDOT:PSS film, and the PSC is tested for its performance using a solar simulator. From the test, a competitive open-circuit voltage of 860 mV was produced. In general, printing PSC layers by modifying a cheap and easily available 3D printer has the benefits of excellent material utilization, substrate independence, rapid design, manufacture, and testing of solar cells in the electronic industry.

Fabrication processes for all‐inorganic CsPbBr3 perovskite solar cells

AbstractAll‐inorganic perovskite solar cells have shown great potential owing to their superior stability against thermal stress and moisture compared to organic–inorganic perovskite solar cells. However, there are some remaining issues in the all‐inorganic perovskite solar cell fabrication process, such as the low solubility of the perovskite precursors and the occurrence of the secondary phases. In this review, we focus on all‐inorganic CsPbBr3 perovskite solar cells and categorize them based on their fabrication process. Various processes and strategies that have been developed to solve the aforementioned issues including the general process of multistep spin coating are thoroughly investigated. Finally, a summary of the various processes for the all‐inorganic CsPbBr3 perovskite solar cells and an outlook for the development of highly efficient all‐inorganic perovskite solar cells are proposed.image

A Definition Rule for Defect Classification and Grading of Solar Cells Photoluminescence Feature Images and Estimation of CNN-Based Automatic Defect Detection Method

A nondestructive detection method that combines convolutional neural network (CNN) and photoluminescence (PL) imaging was proposed for the multi-classification and multi-grading of defects during the fabrication process of silicon solar cells. In this paper, the PL was applied to collect the images of the defects of solar cells, and an image pre-processing method was introduced for enhancing the features of the defect images. Simultaneously, the defects were defined by 13 categories and three divided grades of each under the definition rules of defects that were proposed in accordance with distribution and characteristics of each defect category, and expand data were processed by various data augmentation. The model was therefore improved and optimized based on the YOLOv5 as the feature extractor and classifier. The capability of the model on distinguishing categories and grades of solar cell defects was improved via parameter tuning and image pre-processing. Through experimental analysis, the optimal combination of hyperparameters and the actual effect of data sample pre-processing on the training results of the neural network were determined. Conclusively, the reasons for the poor recognition results of the small target defects and complex feature defects by the current model were found and further work was confirmed under the foundation of the differences in recognition results between different categories and grades.

Characterization of tunnel oxide passivated contact fabricated by sputtering and ion implantation technique

Tunnel oxide passivated contact (TOPCon) structures using highly doped n-type polycrystalline silicon were fabricated using facing target sputtering and ion implantation techniques for a SiH4-free fabrication process of high-efficiency silicon solar cells. We investigated the structural and electrical properties of the highly doped n-type poly-Si layers to optimize the ion implantation process. We also investigated the surface passivation quality of our TOPCon structure. An effective carrier lifetime of 2.01 ms and an implied open circuit voltage of 704 mV were obtained for our sample annealed at 950 °C. The sample also exhibits a low contact resistance of 3.22 × 10−3 Ω cm−2. Our results open the way for SiH4-free fabrication of silicon solar cells with a TOPCon structure.

Recent Progress of Film Fabrication Process for Carbon-Based All-Inorganic Perovskite Solar Cells

Although the certified power conversion efficiency of organic-inorganic perovskite solar cells (PSCs) has reached 25.7%, their thermal and long-term stability is a major challenge due to volatile organic components. This problem has been a major obstacle to their large-scale commercialization. In the last few years, carbon-based all-inorganic perovskite solar cells (C−IPSCs) have exhibited high stability and low-cost advantages by adopting the all-inorganic component with cesium lead halide (CsPbI3−xBrx, x = 0 ~ 3) and eliminating the hole-transporting layer by using cheap carbon paste as the back electrode. So far, many astonishing developments have been achieved in the field of C−IPSCs. In particular, the unencapsulated CsPbBr3 C-IPSCs exhibit excellent stability over thousands of hours in an ambient environment. In addition, the power conversion efficiencies of CsPbI3 and CsPbI2Br C-IPSCs have exceeded 15%, which is close to that of commercial multicrystalline solar cells. Obtaining high-quality cesium lead halide-based perovskite films is the most important aspect in the preparation of high-performance C-IPSCs. In this review, the main challenges in the high-quality film fabrication process for high performance C-IPSCs are summarized and the film fabrication process strategies for CsPbBr3, CsPbIBr2, CsPbI2Br, and CsPbI3 are systematically discussed, respectively. In addition, the prospects for future film fabrication processes for C-IPSCs are proposed.

SYSTEMATIC FIELD APPLICATION OF ENHANCED PLASMONIC ORGANIC SOLAR CELL: AN OVERVIEW

Organic solar cells (OSCs) have attracted considerable research interest due to their satisfactory properties including light-weight, low-cost, low-temperature fabrication process, semi-transparency and mechanical flexibility. Recent advances in OSCs have demonstrated above 10% efficiency in single-junction cells, indicating a strong competitiveness when compared with the commercial silicon photovoltaic system. To obtain maximum efficiency, there is a trade-off between light absorption and charge transport efficiency. Plasmonic light-trapping scheme is a feasible approach to maximize light absorption while maintaining charge transport efficiency. To give an overall look at the plasmonic organic solar cells, we review the recent progress on plasmonic-enhanced OSCs devices by integration with metal plasmonic enhancers, including both experimental and theoretical works. Among the varying proposed plasmonic structures, nano particles are preferable because of their strong scattering properties, particle size tunability, shape, and dielectric environment. In addition, design approaches based on plasmonics can be used to improve absorption in solar cells, permitting a considerable reduction in the physical thickness of solar cell absorber layers, and yielding novel options for solar-cell designs. Also, the simplicity in plasmonics preparation and integration methods is easily compatible with the standard solar cell fabrication process.

Efficiency enhancement of natural cocktail dyes in a TiO2-based dye-sensitized solar cell and performance of electron kinetics on the TiO2 surface

In this study, natural dye extracts were prepared from the dried leaves of Andrographis paniculata and Psidium guajava (APPG). The study’s objective was to increase the light harvesting phenomenon from solar energy utilizing natural dye from APPG, and the problem statement was to harvest the optimum solar radiation and convert it into electrical energy. Acetone and ethanol were used as solvents during the preparation process. Based on this research, the crystallite size of TiO2 nanoparticles was assessed, the impact of acetone and ethanol on APPG dye was compared, and the absorption, FTIR, and UV-Vis spectra of the solar cell fabrication process using solvents were experimentally explored. APPG leaf extract functions as a dye sensitizer. Cells are precisely sandwiched with a photoanode, TiO2 nanoparticles, an electrolyte (I/I3−), and a cathode. The JV properties of dye extracts utilizing acetone and ethanol were measured using a solar simulator equipped with a 100 mW/cm2 Xenon light and a Keithley 2400 Graphical Series SMU. An experimental DSSC with dye extraction and utilizing acetone solvent yielded a maximum photo-conversion efficiency of 0.6914%, while ethanol yielded a photo-conversion efficiency of 0.5630%. Furthermore, an energy-level diagram was used to explain the electron kinetics of DSSC, and the time required for transfer electron injection in the TiO2 surface from a dye-excited state was 150 ps.

External Gettering of Metallic Impurities by Black Silicon Layer

Black silicon (b‐Si) has many attractive properties and is currently being adopted in various fields of semiconductor technology. It is shown here that b‐Si during thermal activation may serve as an external gettering layer to remove metallic impurities and associated defects from bulk Si. The gettering efficiency by b‐Si is estimated according to the results of studying the resistivity, defect density, interstitial iron concentration, and effective minority carrier lifetime on gettered test and ungettered reference Si samples. It is shown that in the thermal oxidation process, the b‐Si layer serves as an effective drain for excess iron atoms and other fast‐diffusing impurities, thereby significantly reducing the density of oxidation‐induced stacking faults in Si. In addition, the resistivity of the substrates decreases, and the bulk carrier lifetime increases significantly. Finally, gettering by b‐Si is introduced into the solar cells fabrication process and its effect on solar cell current–voltage characteristics is investigated. It has been shown that all electronic parameters of the solar cells are improved. The conversion efficiency of ungettered solar cells is 16.8%, and for gettered solar cells, depending on the oxidation temperature, it increases by 1.36–1.96%.

Effects of the diphenyl ether additive in halogen-free processed non-fullerene acceptor organic solar cells.

The development of an environmentally friendly fabrication process for non-fullerene acceptor organic solar cells is an essential condition for their commercialization. However, devices fabricated by processing the active layer with green solvents still struggle to reach, in terms of efficiency, the same performance as those fabricated with halogenated solvents. The reason behind this is the non-optimal nanostructure of the active layer obtained with green solvents. Additives in solution have been used to fine-tune the nanostructure and improve the performance of organic solar cells. Therefore, the identification of non-halogenated additives and the study of their effects on the device performance and stability are of primary importance. In this work, we propose the use of diphenyl ether (DPE) as additive, in combination with the non-halogenated solvent o-xylene, to fabricate organic solar cells with a completely halogen-free process. Thanks to the addition of DPE, a best efficiency of 11.7% have been obtained for the system TPD-3F:IT-4F, an increase over 15% with respect to the efficiency of devices fabricated without additive. Remarkably, the stability under illumination of the solar cells is also improved when DPE is used. The addition of DPE has effects on the molecular organization in the active layer, with an enhancement in the donor polymer ordering, showing a higher domain purity. The resulting structure improves the charge carrier collection, leading to a superior short-circuit current and fill factor. Furthermore, a reduction of the non-radiative recombination losses and an improved exciton diffusion, are the results of the superior molecular ordering. With a comprehensive insight of the effects of DPE when used in combination with a non-halogenated solvent, our study provides an approach to make the fabrication of organic solar cell environmentally friendlier and more suitable for large scale production.

Epitaxially Grown p‐type Silicon Wafers Ready for Cell Efficiencies Exceeding 25%

Combining the advantages of a high‐efficiency solar cell concept and a low carbon footprint base material is a promising approach for highly efficient, sustainable, and cost‐effective solar cells. In this work, we investigate the suitability of epitaxially grown p‐type silicon wafers for solar cells with tunnel oxide passivating contact rear emitter. As a first proof of principle, an efficiency limiting bulk recombination analysis of epitaxially grown p‐type silicon wafers deposited on high quality substrates (EpiRef) unveils promising cell efficiency potentials exceeding 25% for three different base resistivities of 3, 14, and 100 Ω cm. To understand the remaining limitations in detail, concentrations of metastable defects Fei, CrB and BO are assessed by lifetime‐calibrated photoluminescence imaging and their impact on the overall recombination is evaluated. The EpiRef wafers’ efficiency potential is tracked along the solar cell fabrication process to quantify the impact of high temperature treatments on the material quality. We observe large areas with few structural defects on the wafer featuring lifetimes exceeding 10 ms and an efficiency potential of 25.8% even after exposing the wafer to a thermal oxidation at 1050 °C.

Opportunities and Challenges for Perovskite Solar Cells Based on Vacuum Thermal Evaporation

AbstractDeveloping an effective scalable fabrication process for perovskite solar cells is urgent to getting perovskite photovoltaic technology market‐ready. Perhaps due to the relatively cost‐effective setup and tunable fabrication processes, the vast majority of research efforts have been dedicated to the development of solution‐based scalable processes. Comparatively, the vacuum thermal evaporation processes have not been studied in‐depth, regardless of their advantages in reproducibility, scalability, extendable applications, safety, and toxicity. Here possible opportunities and challenges are discussed in utilizing the vacuum thermal evaporation technique for mass production of large‐area perovskite solar modules. While this process has technical and economical potential, more research should be warranted.

Enhancement of the conversion efficiency of selective emitter PERC solar cells by post-oxidation

Thermal oxidation has been widely adopted in the fabrication process of silicon solar cells. In this paper, we investigate the effect of thermal oxidation on the performance of passivated emitter and rear cells (PERC) after the diffusion process. It is found that the application of a diffusion furnace for post-oxidation results in the re-doping of phosphorus, which affects the minority carrier lifetime and implied Voc. In comparison, the use of an annealing furnace for post-oxidation brings an improvement of electrical properties of solar cells because of the gettering effect. Furthermore, the increase in thickness of the oxide layer mitigates the laser-induced damage during the laser doping process, which is beneficial for the enhancement of cell efficiency. Batch data shows that post-oxidation using an annealing furnace leads to an absolute efficiency improvement by 0.1%.

In situ modulated photoluminescence study of the hydrogenation processes of tunnel oxide passivating contacts during plasma processes

AbstractCompared to current c‐Si solar cell technologies, fired passivating contacts (FPCs) can reduce the thermal budget of the solar cell fabrication process. In this study, a simplified process flow for the fabrication of these contacts is investigated along with the use of two hole transport materials: p‐type nanocrystalline silicon ((p) nc‐Si:H) and nanocrystalline silicon oxide ((p) nc‐SiOx:H). More specifically, the passivation properties provided by the FPC stack are assessed at different stages of the manufacturing. The hydrogenation process is studied using in situ modulated photoluminescence (MPL) which allows to measure in real time the effective minority carrier lifetime in the sample during a process step. The increase of passivation observed during the deposition of the capping silicon‐nitride (a‐SiNx:H) layer by plasma‐enhanced chemical vapor deposition is shown to be due to both annealing of the sample and the deposition in presence of silane in the plasma, while the exposure to an NH3 and H2 plasma is mostly detrimental for the passivation properties. The in situ MPL measurements additionally allow us to show that the improvement of the passivation properties happens during the first few minutes of a‐SiNx:H deposition.

Etching methods for texturing industrial multi-crystalline silicon wafers: A comprehensive review

Surface texturing for suppressing the reflection losses is the first and foremost step in the solar cell fabrication process. Over the years, multi-crystalline silicon (mc-Si) wafer solar cells dominated the PV market due to their cost-effectiveness. This article reviews various etching methods reported for texturing mc-Si wafers under the light of basic reaction mechanism, general composition of chemicals used, merits, drawbacks, and the progress made towards their commercialization. The article starts with introducing the alkaline etching process used in initial days of mc-Si solar cell production along with its process limitations. Subsequently, evolution of acid texturing process to address the challenges associated with alkaline etching and its journey as an established industrial process are discussed. Thereafter, progressive but expensive texturing methods such as reactive ion etching, laser etching, mechanical grooving and colloidal lithography are also reviewed. Later, the challenges imposed by introduction of diamond wire sawn (DWS) mc-Si wafers on established acid texturing process are presented. Further, remarkable approaches reported towards the effective texturing of DWS mc-Si wafers are discussed. Finally, a summary of reaction chemistry, recent process advances and future roadmap of proposed next-generation texturing scheme known as metal assisted chemical etching is being compiled and presented.

Selection of the ultimate perovskite solar cell materials and fabrication processes towards its industrialization: A review

AbstractHybrid organic–inorganic perovskite materials have become one of the most studied classes of light‐harvesting materials due to their exceptional properties such as high light absorption, long carrier diffusion lengths, bandgap tuning and defect tolerance. Since 2009 that the scientific community has been working on improving the power conversion efficiency (PCE) of perovskite solar cell devices, reaching now an impressive value of 25.5%. Moreover, efficiencies over 18% are often reported by several authors. Since the efficiency goal is almost fulfilled, the scientific community is currently addressing five challenges, with the ultimate objective to make this technology competitive and turn it commercial; these challenges are cost, stability, upscaling, safety and environmental impact. Given the astonishing progresses reached during the past decade and the numerous research groups working to the same goal, it is a matter of time until commercial perovskite solar devices become a reality. In this review work, the most recent achievements regarding this purpose are put together and compared, so as to suggest the most suitable perovskite solar fabrication processes and materials to produce commercial devices.