Solar Cell Processing Research Articles

RETRACTED: Interfacial passivation by Mono-ethanolamine in planar perovskite solar-cell

Aluminium doped zinc oxide (AZO) is a potential replacement for the conventionally used TiO2 as an electron transport layer (ETL) in low-temperature solution processes for hybrid perovskite solar cells (PvSCs). However, the defects and energy-band mismatch at the ETL/perovskite interface accelerate the interfacial carrier's recombination, leading to a decrease in the fill factor (FF) and current density (JSC). To address this issue, a thin interfacial modification layer of monoethanolamine (MEA) has been used which not only reduces the energy barrier between AZO/perovskite for accelerating the charge transfer but also passivates the trap states on the perovskite interface. Due to the synergistic effect of charge extraction promotion and trap density passivation , the champion PvSCs exhibit a higher value of PCE of 8.25 % with a current density (JSC) of 22.59 mA/cm2 and FF of 46.55% compared to the without MEA passivate PvSCs and the device maintains 70% of its topmost PCE after 1000 h under ambient atmosphere, without any encapsulation. This interface engineering based on MEA provides a feasible and excellent strategy to fabricate the PvSCs with improved efficiency and stability of planar device architecture.

Preparation of High Geometric Filling Factor Perovskite Module and Feasibility Study on Electrocatalytic Hydrogen Production

In recent years, perovskite solar cells have achieved high efficiency in small areas, but the industrialization of perovskite solar cells is still hampered by the efficiency loss of cells during area scaling. Series modules are currently the most widely used and effective modular process for perovskite solar cells, a process that requires the patterning of the layer stack in individual cells. This interconnection scheme consists of three lines, P1–P3, which are ablated using a pulsed laser beam. In this work, we developed an efficient perovskite module with a high geometric fill factor (GFF) based on a two-step spin-coating method by optimizing the laser ablation step. We constructed the entire device structure by means of a picosecond green pulsed laser, meanwhile, the dead area is greatly reduced by optimizing the parameters and process, and finally achieving an ultra-high GFF of over 99%. In addition, we investigated the effect of poor P2 and P3 ablation on the perovskite solar modules and compared the performance of the module before and after ablation optimization. We finally obtained a maximum photoelectric conversion efficiency of 22.79% with an aperture area of 12.6 cm2. Concurrently, we conducted electrocatalytic hydrogen production experiments on the prepared perovskite solar modules, and the experimental results have also shown excellent performance and good prospects.

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.

VOC‐losses across the band gap: Insights from a high‐throughput inline process for CIGS solar cells

AbstractBig sets of experimental data are key to assess statistical device performance and to distill underlying trends. This insight, in turn, can then be used to improve on the fabrication process. We here describe a standardized and optimized inline fabrication process and present a statistical analysis of tens of thousands of cells with chalcopyrite‐type Cu(In,Ga)Se2 absorber. The large number of samples allows us to point out where Ag alloying into the absorber offers improvements, and how it couples with compositional and optoelectronic properties. Solar cell parameters as a function of chemical composition of the absorber highlight the importance of fill factor on overall cell performance. Finally, we calculate losses in open‐circuit voltage as a function of band gap energy and show that radiative losses can be reduced by increasing the amount of Cu and/or Ag.

Incorporation of carbon nanotubes in hole transport materials for perovskite solar cells

ABSTRACT Many loss processes in perovskite solar cells (PSCs) take place at interfaces. One effective mitigation strategy is introducing carbon derivatives at the interface of the charge transport layers with the halide perovskite absorber and/or with the contacts. In this work, single-walled carbon nanotubes are incorporated into the hole transporting material (HTM), either as composites or as a separate layer on top of the HTM. Both organic and inorganic hole transport materials are studied to validate this approach for different types of HTMs. It is shown that the CNTs facilitate charge transport from perovskite to the back contact, regardless of the HTM used. The use of CNTs results in an increase in a significant increase in short circuit current and power conversion efficiency. This study illustrates how SWCNTs can be utilised to improve the properties of a wide range of HTMs, which will pave the way for more efficient and PSCs.

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.

High Performing Inverted Flexible Perovskite Solar Cells via Solution Phase Deposition of Yttrium-Doped SnO2 Directly on Perovskite

Solution processing of flexible perovskite solar cells (f-PSCs) provides an avenue for scalable, high-throughput printing of lightweight, scalable, and cost-effective flexible solar cells. However, the deposition of fully solution-processed metal oxide charge transport layers on perovskites has been limited by solvent incompatibilities and high processing temperatures for metal oxide nanoparticles. In this study, we present high-performance, inverted f-PSCs from the direct deposition of yttrium-doped SnO2 nanoparticles functionalized with acetate on top of perovskite as an ink in anhydrous ethanol via blade coating. Yttrium doping improved device performance by improving the charge extraction with a decreased series resistance leading to improvements in the open-circuit voltage and fill factor. The champion power conversion efficiency for 0.1 cm2 devices increased from 14.3% for undoped SnO2 to 16.5% with 2% Y:SnO2 doping, which is unprecedented for f-PSCs on ITO-PET substrates employing SnO2 as an ETL.

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.

P‐9.2: ESL products with amorphous silicon solar cells integrated into the backplane

This paper presents a product combining amorphous silicon solar cells and ESL. This product combines the amorphous silicon solar cell process with the TFT backplane of ESL products. At the same time, this product uses solar cells as the device for collecting light energy, and the new energy conversion equipment collects the electric energy generated by solar energy and generates stable output electric energy to provide ESL devices. This scheme is not only environmentally friendly, but also reduces the thickness of products using external solar cells.

Reduced bimolecular charge recombination in efficient organic solar cells comprising non-fullerene acceptors

Bimolecular charge recombination is one of the most important loss processes in organic solar cells. However, the bimolecular recombination rate in solar cells based on novel non-fullerene acceptors is mostly unclear. Moreover, the origin of the reduced-Langevin recombination rate in bulk heterojunction solar cells in general is still poorly understood. Here, we investigate the bimolecular recombination rate and charge transport in a series of high-performance organic solar cells based on non-fullerene acceptors. From steady-state dark injection measurements and drift–diffusion simulations of the current–voltage characteristics under illumination, Langevin reduction factors of up to over two orders of magnitude are observed. The reduced recombination is essential for the high fill factors of these solar cells. The Langevin reduction factors are observed to correlate with the quadrupole moment of the acceptors, which is responsible for band bending at the donor–acceptor interface, forming a barrier for charge recombination. Overall these results therefore show that suppressed bimolecular recombination is essential for the performance of organic solar cells and provide design rules for novel materials.

Single‐Source Vapor‐Deposition of MA1–xFAxPbI3 Perovskite Absorbers for Solar Cells

AbstractVapor deposition of halide perovskites presents high potential for scalability and industrial processing of perovskite solar cells. It prevents the use of toxic solvents, allows thickness control, and yields conformal and uniform coating over large areas. However, the distinct volatility of the perovskite organic and inorganic components currently requires the use of multiple thermal sources or two‐step deposition to achieve the perovskite phase. In this work, single‐source, single‐step MA1–xFAxPbI3 thin film deposition with tunable stoichiometry by pulsed laser deposition is demostrated. By controlling the laser ablation of a solid target containing adjustable MAI:FAI:PbI2 ratios, the room temperature formation of cubic α‐phase MA1–xFAxPbI3 thin films is demonstrated. The target‐to‐film transfer of the ablated species, including the integrity of the organic molecules and the desired MA+:FA+ ratio, is confirmed by x‐ray photoelectron spectroscopy and solid‐state NMR. Photoluminescence analysis further confirms the shift of the bandgap with varying the MA+:FA+ ratio. Finally, proof‐of‐concept n‐i‐p solar cells with 14% efficiency are demonstrated with as‐deposited non‐passivated pulsed laser deposition (PLD)‐MA1–xFAxPbI3. This study opens the path for future developments in industry‐compatible vapor‐deposition methods for perovskite solar cells.

Effect of the TiO2 electron transport layer thickness on charge transfer processes in perovskite solar cells

Dense TiO2 thin films are widely used as electron transport layers in perovskite solar cells. TiO2 is a high band gap semiconductor with n-type conductivity showing excellent compatibility with metal-halide perovskites in terms of energy alignment providing efficient charge separation and less energy loss of electrons during electron transfer. In this work, TiO2 layers were deposited from TiO2 sol-gel solution by spin-coating methods. The optimization of TiO2 ETL thickness is a necessary procedure to reduce ETL resistance and minimize charge recombination. The thickness reduction leads to a decrease in resistance, however, also enhances charge recombination due to the formation of pin-holes and cracks. We found that TiO2 thickness reduction also causes the TiO2 defects density changes. By studying luminescence spectra of TiO2 with various thicknesses we found that the thickness reduction leads to the increase in the interstitial Ti+3 defects density, while the oxygen vacancies density decreases. Ti+3 species form deep levels trapping free electrons and as result increasing TiO2 resistance. TiO2 films with thicknesses in the range of 40–120 nm were deposited and used as ETL for PSCs with ITO/TiO2/CH3NH3I3PbClx/CuPc/MoOx/Ag structure. Our study revealed two competitive charge transport processes taking place in TiO2: electron transport through the TiO2 conduction band and electron trapping by deep trap levels formed by Ti+3 species. Therefore according to the IV and IS studies, the optimal TiO2 layer thickness at which there is a balance between the competitive charge transport processes is about 60 nm for our deposition condition.

Time of transition processes in a CdS-CIGS structural solar cells in the short-wave part of the absorption spectrum at different loading resistances

Time of transition processes in a CdS-CIGS structural solar cells in the short-wave part of the absorption spectrum at different loading resistances

A Simple Method to Produce an Aluminum Oxide-Passivated Tungsten Diselenide/n-Type Si Heterojunction Solar Cell with High Power Conversion Efficiency

Transition metal dichalcogenide (TMDC) materials are attractive candidates for 2D solar cell devices thanks to their straightforward integration with various substrates and traditional semiconductor technologies, wide band gap ranges over the visible light spectrum, and high absorption coefficient values. Although there are several previous reports on the fabrication of 2D material-based solar cells, difficult and complex processes in the fabrication are highly required to be modified for wider use in daily life applications. Photolithography, the most commonly used manufacturing process for TMDC-based solar cells, is complicated. In this study, we demonstrate that the fabrication of 2D tungsten diselenide (WSe2) by adopting a wet transfer process with thermal release tape simplifies the manufacturing steps for TMDC-based solar cell devices. This simplification not only reduces the production cost by excluding several factors such as transmittance, thermal expansion, surface flatness, and durability but also improves the yield. Furthermore, a proof-of-concept demonstration of creating a WSe2/Si junction with an aluminum oxide (Al2O3) antireflective coating provided a power conversion efficiency of 6.39%, which is a significant improvement over that of a WSe2/Si solar cell without the antireflective coating layer (1.08%).

High efficient perovskite solar cells enhancement via photosystem I proteins

AMX3 (A, M, and X are, respectively, organic cation, metal cation, and halogen anion)-type hybrid Perovskite Solar Cells (PeSCs) initiated a promising new generation of Solar Cells (SCs). Photovoltaics utilizing lead Halide Perovskites (HPe) absorbers swiftly have enhanced Power Conversion Efficiencies (PCEs). Furthermore, for materials used in fabricating process of SCs and Solar Energy Conversion (SEC), using bio-photonic systems has shown great promise. Accordingly, plants' photosynthetic organs have attracted tremendous attention. SEC in the photosynthesis organs of plants has indicated a substantial potential towards the advancement of green renewable energy technologies. The maximum absorption spectrum wavelengths of the principal member of photosynthetic components, the photosystem I (PS1) protein complex, are 430 nm and 665 nm. Hence, they act as a complementary mechanism in PeSCs in which the absorption spectrum infirmity is at the 665 nm wavelength area. In the present research, we enhance the PeSCs via using the photosystem1 protein complex and present their positive obtained results. The device's absorption spectrum and external quantum efficiency (EQE) show advantageous ameliorates. Hereupon, the PCE of the PeSCs, is optimized from 17.84% to 18.63%.

Cu(In,Ga)Se2 based ultrathin solar cells the pathway from lab rigid to large scale flexible technology

The incorporation of interface passivation structures in ultrathin Cu(In,Ga)Se2 based solar cells is shown. The fabrication used an industry scalable lithography technique—nanoimprint lithography (NIL)—for a 15 × 15 cm2 dielectric layer patterning. Devices with a NIL nanopatterned dielectric layer are benchmarked against electron-beam lithography (EBL) patterning, using rigid substrates. The NIL patterned device shows similar performance to the EBL patterned device.The impact of the lithographic processes in the rigid solar cells’ performance were evaluated via X-ray Photoelectron Spectroscopy and through a Solar Cell Capacitance Simulator. The device on stainless-steel showed a slightly lower performance than the rigid approach, due to additional challenges of processing steel substrates, even though scanning transmission electron microscopy did not show clear evidence of impurity diffusion. Notwithstanding, time-resolved photoluminescence results strongly suggested elemental diffusion from the flexible substrate. Nevertheless, bending tests on the stainless-steel device demonstrated the mechanical stability of the CIGS-based device.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

A Robust Hydrothermal Sulfuration Strategy toward Effective Defect Passivation Enabling 6.92% Efficiency Sb2S3 Solar Cells

Sulfuration is an efficient route for fabricating metal sulfides photovoltaic devices with high‐quality absorber layer, reduced S vacancy, and high device performance. However, traditional sulfuration processes reported thus far generally suffer from low activity, inert atmosphere, high operating temperature, and ineffective defect passivation, all of which increase manufacturing dangerousness, complicacy, and cost. Simultaneously fulfilling the goals of high reactivity, mild fabrication condition, and efficient defect passivation remain a major challenge for sulfuration, which may be addressed, as demonstrated herein, with the development of a (NH4)2S‐induced hydrothermal sulfuration process in Sb2S3 solar cells. By optimizing the hydrothermal sulfuration process through the use of different amounts of (NH4)2S, an encouraging efficiency of 6.92% has been reached. In addition, the crystallinity of the Sb2S3 film can be obviously improved even under the mild heating conditions (i.e., 160 °C, 120 min). Furthermore, only one hole trap can be identified for the Sb2S3 device after hydrothermal sulfuration, and the trap density is significantly reduced. This innovative sulfuration system introduces a robust approach toward the goal of high‐efficiency metal sulfide solar cells compatible with simple hydrothermal process.

In Situ Absorption Characterization Guided Slot-Die-Coated High-Performance Large-Area Flexible Organic Solar Cells and Modules.

Slot-die coating is recognized as the most compatible method for the roll-to-roll (R2R) processing of large-area flexible organic solar cells (OSCs). However, the photovoltaic performance of large-area flexible OSC lags significantly behind that of traditional spin-coating devices. In this work, two acceptors, Qx-1 and Qx-2, show quite different film-formation kinetics in the slot-die coating process. In situ absorption spectroscopy indicates that the excessive crystallinity of Qx-2 provides early phase separation and early aggregation, resulting in oversized crystal domains. Consequently, the PM6:Qx-1-based 1cm2 flexible device exhibits an excellent power conversion efficiency (PCE) of 13.70%, which is the best performance among the slot-die-coated flexible devices; in contrast, the PM6:Qx-2 blend shows a pretty poor efficiency, which is lower than 1%. Moreover, the 30 cm2 modules based on PM6:Qx-1, containing six 5 cm2 sub-cells, exhibit a PCE of 12.20%. After being stored in a glove box for over 6000h, the PCE remains at 103% of its initial values, indicating excellent shelf stability. Therefore, these results show a promising future strategy for the upscaling fabrication of flexible large-area OSCs.

New insights into the alkoxy effects on auxiliary adsorption and inhibiting charge recombination in dye-sensitized solar cells with high open circuit voltage: a theoretical investigation.

Although introducing an alkoxy group is one of the most popular methods to suppress the interfacial charge recombination process of dye-sensitized solar cells, understanding of its effects is still limited and a microscopic picture of the alkoxy effects is lacking. Two ullazine dyes with distinct alkoxy chains at the donor part are used to investigate the effects of the alkoxy group on the adsorption, dye aggregation and charge recombination process in our study. Different from the usual assumption, we find that alkoxy chains can not only play a shielding role, but can also assist dye adsorption and inhibit the charge recombination process more effectively by covering the TiO2 surface. We also find that the existence of alkyl chains can well inhibit the aggregation of dyes and reduce intermolecular electron transfer. Furthermore, an important structural feature at the interface, the Ti-O interaction between the oxygen atom of the alkoxy group and the Ti atom of the surface is also found to contribute substantially to the interface stability. New insights into the effects of the alkoxy group on auxiliary adsorption and inhibiting charge recombination through reducing the recombination sites pave the way for rational design of sensitizers with high performance.