Solar Cell Processing Research Articles

Structural and optical properties of phosphorous doped nanocrystalline silicon deposited using a VHF PECVD process for silicon heterojunction solar cells and optimization of a simple p-n junction cell using SCAP-1D tool.

Initially hydrogenated silicon (Si:H) thin films have been deposited using a plasma-enhanced chemical vapor deposition technique (PECVD) using silane (SiH4) as a precursor gas diluted in an inert gas argon (Ar) environment. Subsequently phosphine gas (PH3) was used as the n-type dopant and the deposition was carried out at a fixed substrate temperature of 200 °C. The PH3 flow rate was varied in the range of 0-1 sccm. The effect of PH3 flow rates on optical, electrical, and structural properties of hydrogenated amorphous and micro/nanocrystalline silicon films has been investigated and detailed analysis is presented. These films may find application in heterojunction solar cells as an emitter layer. Further, a crystalline silicon (c-Si) based simple p-n junction solar cell is simulated using an SCAP-1D tool to observe the effect of layer thickness and doping density on solar cell parameters.

The impact of molecular orientations on the energy levels of A-D-A acceptors: implications for the charge separation driving force of organic solar cells.

The energetic landscape of charge carriers, namely the ionization potential (IP) and electron affinity (EA), can play a crucial role in the charge separation and migration processes for organic solar cells (OSCs). However, the impact of molecular orientations on the energy levels remains elusive, especially in acceptor-donor-acceptor (A-D-A) type nonfullerene acceptors (NFAs) with intrinsic anisotropy. Using the self-consistent quantum mechanics/embedded charge (sc-QM/EC) approach, we have investigated the energy level shifts from the edge-on or face-on surfaces to the bulk phase for three typical NFA crystals, IDIC-4F, INIC-4F, and Y6. The results point out that the surface-to-bulk changes in IP are limited within 0.2 eV for both the orientations due to the mutual counteraction between the electrostatic and induction effects. In sharp contrast, the EA values are substantially decreased from the bulk to the surfaces; especially, for the face-on orientation, the reduction reaches 0.5-0.8 eV. This indicates that the face-on orientation can provide a significant driving force for electrons moving from the surface or the interface to the bulk phase and thus improve the charge separation efficiency. Our work indicates that enhancing the face-on orientation is an effective method to increase the charge separation driving force for the OSCs based on A-D-A NFAs.

Elementary processes in ternary solar cells

We analyze photophysical processes in ternary organic solar cells, integrating molecular dynamics and quantum mechanics. Our results highlight the need for accurate modeling to predict how even small changes in the materials affect the performances.

Research on multi-defects classification detection method for solar cells based on deep learning.

Solar cells are playing a significant role in aerospace equipment. In view of the surface defect characteristics in the manufacturing process of solar cells, the common surface defects are divided into three categories, which include difficult-detecting defects (mismatch), general defects (bubble, glass-crack and cell-crack) and easy-detecting defects (glass-upside-down). Corresponding to different types of defects, the deep learning model with different optimization methods and a classification detection method based on multi-models fusion are proposed in the paper. In the proposed model, in order to solve the mismatch problem between the default anchor boxes size of YOLOv5s model and the extreme scale of the battery mismatch defect label boxes, the K-means algorithm was adopted to re-cluster the dedicated anchor boxes for the mismatch defect label boxes. In order to improve the comprehensive detection accuracy of YOLOv5s model for the general defects, the YOLOv5s model was also improved by the methods of image preprocessing, anchor box improving and detection head replacing. In order to ensure the recognition accuracy and improve the detection speed for easy-detecting defects, the lightweight classification network MobileNetV2 was also used to classify the cells with glass-upside-down defects. The experimental results show that the proposed optimization model and classification detection method can significantly improve the defect detection precision. Respectively, the detection precision for mismatch, bubble, glass-crack and cell-crack defects are up to 95.64%, 91.8%, 93.1% and 98.0%. By using lightweight model to train the glass-upside-down defect dataset, the average classification accuracy reaches 100% and the detection speed reaches 13.29 frames per second. The comparison experiments show that the proposed model has a great improvement in detection accuracy compared with the original model, and the defect detection speed of lightweight classification network is improved more obviously, which confirms the effectiveness of the proposed optimization model and the multi-defect classification detection method for solar cells defect detection.

Recycling of end of life photovoltaic solar panels and recovery of valuable components: A comprehensive review and experimental validation

With the current rate of installation of photovoltaic (PV) modules, the total installed capacity is expected to reach 4500 GW by 2050. Given the average life of solar modules is 25 years, after their spent time the installed solar panels will eventually turn into waste. The waste from solar panel modules is expected to reach about 8600 tons by 2030 and it will further increase to 78 million tons by 2050. The waste solar panel should be discarded or recycled appropriately since the toxic substances released from them can affect human health and the environment. Therefore, there is a need to develop a recovery and recycling process for waste produced from solar modules. In this comprehensive work, we have summarized (i) the classification of photovoltaic technology, (ii) review the approaches embraced for photovoltaic (PV) waste management on a global level, (iii) the need for photovoltaic (PV) waste management and brief explanation on the recycling process (Mechanical, thermal, chemical and leaser methods) of solar cells. Also, experimental validation has been provided by the recovery of discrete components from End of Life (EoL) solar panels in an appropriate amount. The recovered material components from the modules were subjected to structural and chemical characterization to attest phase purity of the samples.

Efficient laboratory perovskite solar cell recycling with a one-step chemical treatment and recovery of ITO-coated glass substrates

The proliferation of organic–inorganic perovskite solar cells (PSCs) has garnered considerable attention due to their potential for low-cost, large-scale photovoltaic panel production. However, the inclusion of lead in PSCs poses significant sustainability challenges, necessitating effective end-of-life treatment strategies to mitigate environmental pollution and comply with electronic waste disposal regulations. In this study, we present a novel recycling system for decomposing and reclaiming the constituent materials of a typical PSC. Utilizing a one-step solution process extraction approach, we successfully preserved the chemical composition of each layer, enabling their potential reuse. This recycling method not only addresses the separation of the toxic lead component but also emphasizes the recovery of other valuable PSC layers. Notably, the commonly used hole transport layer in perovskite solar cells is Spiro-OMeTAD, which was successfully extracted with chlorobenzene, with its purity subsequently confirmed. Moreover, the removal of individual layers facilitated the retrieval of indium-doped tin oxide (ITO) conductive glass, a critical substrate in PSC fabrication. Comparative analysis of the physical and electrical properties of recycled and reference ITO substrates revealed minimal discrepancies, indicating the feasibility of reusing recycled substrates without compromising device performance. The proposed recycling technique offers a practical approach to mitigate pollution risks, minimize waste generation during the recycling process of perovskite-based solar cells, and reduce end-of-life recycling costs.

Additive enhanced passivation and lead immobilization of waste expandable polystyrene for perovskite photovoltaics

Every year, millions of tons of expandable polystyrene (EPS) are released into the environment, posing significant environmental pressure due to its slow natural decomposition that takes hundreds of years. Current recycling methods for EPS include organic solvent dissolution and recycling, composite material preparation, and building decoration. However, these methods are costly and have low utilization value. In this study, we propose an innovative approach by incorporating waste EPS into the assembly process of printable mesoscopic perovskite solar cells (p-MPSCs). Our findings reveal that EPS can not only utilize its uncoordinated Pb2+ coordination through the large π bond of the benzene ring, but also the functional groups of C=O and C≡N in its additives, benzophenone peroxide and azobisisobutyronitrile, respectively, play an efficient role in passivating lead defects. Furthermore, EPS effectively acts as a moisture barrier, preventing moisture from entering the interior of the device. This significantly improves device stability and immobilizes lead ions, preventing lead leakage. Our approach not only provides an efficient and environmentally friendly method to recycle EPS, but also offers new solutions to address fundamental scientific challenges in perovskite solar cells, such as lead leakage and stability issues.

The concentration factor on the mixture of Ag paste and H3PO4 solution as a dopant paste for contact formation in silicon solar cells

Screen printing dopant is a new technique to create emitter regions on solar cells. On top of the emitter region, there will be screen-printed metallic contacts that are commonly used silver as front contact. Both processes are performed in separate procedure which requires two different diffusion process involving a high-temperature process. Silver makes good ohmic contact on both light and heavily doped. A solution is proposed by applying a single step of screen printing and annealing process of Ag and phosphorus acid. Simultaneous annealing of Al, Ag, Ag/P screen-printed pastes form diodes with and without heavily doped phosphorous layers under Ag contacts on n-type and p-type silicon wafers by annealing at a constant temperature of 900℃ while varying annealing time from 10-40 seconds at a 10-second interval. The cross-section image of 5% and 10% of Ag/P was measured by using FESEM with EDX report has identified the presence of phosphorus in the Ag/P paste. Dark IV shows an ohmic contact for both p- and n-type. The ability to form the Ag/P paste in the screen-printing process makes it amenable to use as a self-dopant paste process in solar cells.

Optimizing Perovskite Thin‐Film Parameter Spaces with Machine Learning‐Guided Robotic Platform for High‐Performance Perovskite Solar Cells

AbstractSimultaneously optimizing the processing parameters of functional thin films remains a challenge. The design and utilization of a fully automated platform called SPINBOT is presented for the engineering of solution‐processed functional thin films. The SPINBOT is capable of performing experiments with high sampling variability through the unsupervised processing of hundreds of substrates with exceptional experimental control. Through the iterative optimization process enabled by the Bayesian optimization (BO) algorithm, the SPINBOT explores an intricate parameter space, continuously improving the quality and reproducibility of the produced thin films. This machine learning (ML)‐guided reliable SPINBOT platform enables the acceleration of the optimization process of perovskite solar cells via a simple photoluminescence characterization of films. As a result, this study arrives at an optimal film that, when processed into a solar cell in an ambient atmosphere, immediately yields a champion power conversion efficiency (PCE) of 21.6% with satisfactory performance reproducibility. The unsealed devices retain 90% of their initial efficiency after 1100 h of continuous operation at 60–65 °C under metal‐halide lamps. It is anticipated that the integration of robotic platforms with the intelligent algorithm will facilitate the widespread adoption of effective autonomous experimentation to address the evolving needs and constraints within the materials science research community.

Semiconductor quantum dots as a mechanism to enhance charge transfer processes in polymer solar cells

The light trapping capability of thin film polymer solar absorber, composed of poly (3-hexylthiophene) and [6,6]–phenyl C61- butyric acid methyl ester (P3HT:PC60BM) blend, is improved using ZnS semiconductor quantum dots (QD) as third donor-acceptor (D:A) component. The inherent characteristics of the microwave-assisted synthesized ZnS QD, such as quantum size effect, and multiple exciton generation were leveraged in harvesting high energy photons, which resulted in a better exciton generation, dissociation, and effective charge transport in the polymer medium. The synthesized QD exhibited good phase purity, effective kinetic enhancement, and control of the aggregation process. Hence, the impact of ZnS QD on the performance of thin film polymer solar cells (TFPSC) is evident by a remarkable improvement in the measured photovoltaic parameters. Nonetheless, it is observed that the device performances are generally dependent on the concentration of the QD in the absorber layer. Consequently, the power conversion efficiency has increased by 58% at 3% concentration of QDs by weight. This is an interesting development of TFPSC fabricated under an ambient environment.

Optimized Doping of Diffusion Blocking Layers and Their Impact on the Performance of Perovskite Photovoltaics.

The roll-to-roll printing production process for hybrid organic-inorganic perovskite solar cells (PSCs) demands thick and high-performance solution-based diffusion blocking layers. Inverted (p-i-n) PSCs usually incorporate solution-processed PC70BM as the electron-transporting layer (ETL), which offers good electron charge extraction and passivation of the perovskite active layer grain boundaries. Thick fullerene diffusion blocking layers could benefit the long-term lifetime performance of inverted PSCs. However, the low conductivity of PC70BM significantly limits the thickness of the PC70BM buffer layer for optimized PSC performance. In this work, we show that by applying just enough N-DMBI doping principle, we can maintain the power conversion efficiency (PCE) of inverted PSCs with a thick (200 nm) PC70BM diffusion blocking layer. To better understand the origin of an optimal doping level, we combined the experimental results with simulations adapted to the PSCs reported here. Importantly, just enough 0.3% wt N-DMBI-doped 200 nm PC70BM diffusion blocking layer-based inverted PCSs retain a high thermal stability at 60 °C of up to 1000 h without sacrificing their PCE photovoltaic parameters.

Bar Coating Process of Two-Dimensional Lead Iodide Perovskite Solar Cells: Effects of Vertical Orientation, Anisotropic Photoconductivity, and Conversion Time

Bar Coating Process of Two-Dimensional Lead Iodide Perovskite Solar Cells: Effects of Vertical Orientation, Anisotropic Photoconductivity, and Conversion Time

Research status of all-inorganic perovskite solar cells: A review

Currently, perovskite solar cells have achieved significant progress in photovoltaic conversion efficiency, mainly using organic/inorganic hybrid materials as the perovskite absorption layer. However, this type of material has defects in thermal stability. In contrast, all-inorganic perovskite materials can effectively solve this problem, and the prepared solar cells have higher stability and longer lifespan than hybrid perovskite solar cells. Therefore, the emergence of all-inorganic perovskite solar cells has attracted widespread attention, and achieved an efficiency of 21.15% in a short period of time. However, due to the short development time of all-inorganic perovskite solar cells but with many reported articles, many researchers cannot clearly understand its current development status. Therefore, this article provides a systematic discussion on the photovoltaic conversion efficiency, working principle and structure, characterization methods, preparation process, and simulation software of all-inorganic perovskite solar cells, in order to provide readers with a clearer understanding. Finally, this article summarizes the current achievements of all-inorganic perovskite solar cells, clarifies the challenges faced in this field, and looks forward to its future development prospects.

(Invited) Progress in Materials and Process for Sustainable Perovskite Solar Cells

All solid-state solar cells based on organometal trihalide perovskite absorbers have already achieved distinguished power conversion efficiency (PCE) to over 25% and further improvements are expected up to 27%. Now, the research on perovskite solar cells (PSCs) has been moving toward commercialization. To facilitate commercialization of these great solar cells, some technical issues such as long-term stability, large scale fabrication process, and Pb-related hazardous materials need to be solved. Also, flexible perovskite solar cell using plastic substrate can be used in niche applications such as portable electrical chargers, electronic textiles, and large-scale industrial roofing.This talk is dealing with our recent efforts to facilitate commercialization of perovskite solar cells. For examples, we introduce a recycling technology of perovskite solar cells, which covers the regeneration process of Pb contained perovskite layer as well as recycling process of Au electrodes and transparent conducting oxide glass. Also, simple fabrication technologies for realizing large scale perovskite module are introduced and recent effort for achieving high efficiency module is going to be presented. Finally, recent interesting results regarding ultra flexible perovskite cells will be discussed.

Theoretical Investigations of Dye-Sensitized Solar Cells

This presentation considers theoretical investigations of dye-sensitized solar cells (DSSC). Theoretical methods were applied to investigate the interactions between titanium dioxide nanoparticles and sensitizers. The ONIOM model was used to obtain the geometries of different conformers of dye molecules with TiO2 and their binding energies. TD-DFT calculations were carried out to obtain the absorption spectra and the relative orbital energy levels of sensitizers and TiO2. The electronic couplings between different sensitizers and TiO2 were calculated using the fragment charge difference method. The redox potentials of the sensitizers are calculated to complete the full working cycle of a DSSC. We observed that the -COOH group is not the only possible binding site, and the sensitizers are more likely to be adsorbed horizontally on the TiO2 surface instead of being perpendicular to the surface having the -COOH group as a linker. The TiO2 nanoparticle was found to have minor influence on the absorptions of the sensitizers with the spectra shift smaller than 0.2 eV. TiO2 has more influence on the absorptions of softer and larger molecules because the interactions between sensitizers and TiO2 twist the conjugated chromophore structures. Compared to the neutral form, the deprotonated anion conformers of the sensitizers have larger binding energy and lower LUMO level against conduction band of TiO2. The gap between the LUMO of sensitizers and conduction band edge of TiO2 might indicate the coupling strength between the sensitizers and TiO2. Several binding groups have shown promising properties for interacting with the TiO2 nanoparticle and generally deprotonated anion forms of the dyes were strongly bonded to the TiO2 nanoparticle. The model and associated calculated results provide close agreement with experimental data and give crucial atomistic information of the relevant processes in dye-sensitized solar cells.

Hexanary blends: a strategy towards thermally stable organic photovoltaics

Non-fullerene based organic solar cells display a high initial power conversion efficiency but continue to suffer from poor thermal stability, especially in case of devices with thick active layers. Mixing of five structurally similar acceptors with similar electron affinities, and blending with a donor polymer is explored, yielding devices with a power conversion efficiency of up to 17.6%. The hexanary device performance is unaffected by thermal annealing of the bulk-heterojunction active layer for at least 23 days at 130 °C in the dark and an inert atmosphere. Moreover, hexanary blends offer a high degree of thermal stability for an active layer thickness of up to 390 nm, which is advantageous for high-throughput processing of organic solar cells. Here, a generic strategy based on multi-component acceptor mixtures is presented that permits to considerably improve the thermal stability of non-fullerene based devices and thus paves the way for large-area organic solar cells.

Green solvent enabled scalable processing of perovskite solar cells with high efficiency

Green solvent enabled scalable processing of perovskite solar cells with high efficiency

Textured p-type crystalline silicon surfaces obtained by multi-step plasma process for SHJ solar cells

P-type monocrystalline silicon wafers were textured by means of a multi-step plasma etching technique with the aim of greatly reducing their reflectance and effectively exploiting the highest possible amount of solar radiation in heterojunction photovoltaic devices. Suitable surface morphologies, characterized by high light scattering, have to be obtained without damaging the c-Si electrical properties. For this reason, some aspects of the plasma etching process have been studied and improved. Modifications have been made to obtain both “cleaner” processes and energetically lower ion bombardment. By operating at high pressure (0.4 mbar), a process controlled by diffusion of reactive species towards the substrate was favoured. Another innovative aspect consisted in two “reconditioning” plasma processes of the Si surface before the actual silicon removal step with SF6 /O2 gas mixtures. A strong reduction in the average optical reflection down to 5% was obtained coupled with a minority carriers lifetime (τeff) of about 950 μs, value comparable to that of the untreated silicon. An interesting surface morphology, consisting in “U" shaped cavities, was obtained. Texture irregularities were easily removed by acid etching. The moderate depth of the cavities is very promising for an effective passivation with a-Si:H thin films.

Self‐Regulating Process for Large Area Nanowire Solar Cells Based on Thin Polycrystalline Silicon Films Prepared on Glass

Herein, a process for the large‐area passivating and contacting of nanowire‐based solar cells is demonstrated. The nanowire‐based solar cells are prepared on layered laser crystallization (LLC) polycrystalline silicon (pc‐Si) thin films with thickness less than 2 μm. It is demonstrated that the space between the nanowires can be filled with a passivating dielectrics Al2O3 layer, and the nanowire tips can be exposed by a self‐regulating selective etching of the Al2O3 deposited on the tips and that on the sidewalls. The exposed tips of the nanowires can be connected by a transparent conducting aluminum‐doped zinc oxide (Al:ZnO or AZO) layer deposited by atomic layer deposition (ALD). The laser beam‐induced current mapping (LBIC) demonstrates that the current density can increase up to 63% at 633 nm due to light trapping and the superior passivation of the nanowires with an thin pc‐Si film of only 1.73 μm.

Solid Solvation Assisted Electrical Doping Conserves High‐Performance in 500 nm Active Layer Organic Solar Cells

AbstractOrganic solar cells (OSCs) process fascinating solution‐printing capability to achieve low‐cost and large‐scale manufacture. However, the rapid power conversion efficiency (PCE) decay with active layer thickness enlargement inhibits the implement of OSCs’ potential advantages. To overcome the bottlenecks of PCE decay in thick active layer OSCs, the electrical doping with componential selectivity in bulk heterojunction (BHJ) film is achieved by introducing a solid solvation additive. Benefiting from the higher exciton splitting efficiency together with the longer drift (Ldr) and diffusion (Ldiff) lengths, an OSC with 100 nm BHJ film demonstrates a PCE increment from 16.44% to 18.24% with prolonged dark and illuminated storage stabilities. Applying the solid solvation assisted (SSA) doping method in the OSCs with 500 nm active layer, the PCE significantly increases by 31.9%, from the original value of 11.79% to 15.55%. It further improves to 15.84% in a ternary blend thick‐film device, which is the record value to the best of our knowledge. Besides, the SSA doping narrows the PCE gap between the 0.04 and 1 cm2 devices. All improvements demonstrate the great potential of SSA doping for OSC commercial manufacture, since it optimizes the photovoltaic performance under all practical conditions of long‐term, thick‐film, and large‐area.