Cu(In,Ga)Se2 Research Articles

Computational Modeling of Graphene-Enhanced Back Surface Fields for Higher Efficiency in Copper Indium Gallium Selenide Solar Cell

The efficiency of CIGS (Copper Indium Gallium Selenide) solar cells has been significantly improved by incorporating Graphene Oxide (GO) or Graphene into their structure, specifically designed as Al/Tungsten Sulphoselenide (WSSe)/CIGS/GO or Graphene. GO or Graphene is employed as a back surface field to enhance charge carrier collection, with GO yielding better results than Graphene. This integration has resulted in a substantial increase in power conversion efficiency (PCE). The optimization process involved fine-tuning various parameters, including thickness adjustments and acceptor concentration levels. Moreover, the analysis addressed key factors such as shunt and series resistance, as well as the impact of temperature. The proposed design achieved a remarkable peak efficiency of 33.28%. In addition, extensive studies on temperature effects were conducted, offering deeper insights into the cell's performance under different conditions. Overall, this innovative structure shows great promise for future fabrication, offering enhanced performance and significant potential for advancing solar cell technology.

A novel acid resource: waste hydrochlorofluorocarbons refrigerants selective leaching Cu-In-Ga-Se (CIGS) and catalyzed mineralization under the hydrothermal atmosphere.

With the upgrading and obsoleting of electric refrigeration equipment, significant amounts of waste hydrochlorofluorocarbon (HCFCs) refrigerants are being generated, bringing serious ozone-depleting and global warming effects. HCFCs, containing chlorine and fluorine, have the potential to be converted into acids by mineralization. Hydrothermal technology possesses a tightly sealed environment and high thermal efficiency, providing significant advantages in treating volatile HCFCs. However, the stable C-F bonds and the by-product CClF=CH2 greatly impede the mineralization of HCFCs. Herein, an indium compound from waste CIGS (CuInxGa1-xSe2) was introduced to promote the process, and this strategy successfully increased the mineralization rates of organic chlorine and fluorine to 99.2% and 95.7%, respectively. The acid produced from HCFCs degradation was utilized for the selective leaching of metals in CIGS. Meanwhile, the leaching product InOOH catalyzed further degradation of HCFCs. We revealed that InOOH can adsorb reactants and provide interfaces, resulting in (i) the elongation of C-X (F, Cl) bonds; (ii) a reduction in the energy barrier of the CClF=CH2 degradation reaction. This study provides a promising approach and theoretical basis for the harmless treatment and resourceful utilization of waste refrigerants containing Cl and F.

Highly efficient narrow bandgap Cu(In,Ga)Se2 solar cells with enhanced open circuit voltage for tandem application

Although an ideal bandgap matching with 0.96 eV and 1.62 eV for a double-junction tandem is hard to realize practically, among all mature photovoltaic systems, Cu(In,Ga)Se2 (CIGSe) can provide the closest bandgap of 1.00 eV for the bottom sub-cell by adjusting its composition. However, pure CuInSe2 (CISe) solar cell suffers strong interfacial carrier recombination. We hereby present approaches to introduce appropriate Ga gradients in both the back and front parts of absorber while maintaining the absorption spectrum close to CISe. With an appropriate front Ga gradient, the open circuit voltage can be enhanced by ~30 mV. With a pre-deposited CIGSe layer and a high copper excess deposition during absorber growth, the Ga diffusion can be well suppressed and a wide U-shaped Ga grading with a minimum bandgap of 1.01 eV has been created. Our optimized narrow-bandgap CIGSe solar cell has achieved a certified record PCE of 20.26%, with a record-low open circuit voltage deficit of 368 mV and a record-high contribution of 10% absolute efficiency to a four-terminal tandem. This work demonstrates the potential of controlling gallium diffusion to improve the performance of narrow bandgap CIGSe solar cells for tandem applications.

Ordered Vacancy Compound Formation at the Interface of Cu(In,Ga)Se2 Absorber with Sputtered In2S3‐Based Buffers: An Atomic‐Scale Perspective

The design of a Cd‐free and wider‐bandgap buffer layer is stringent for future Cu(In,Ga)Se2 (CIGSe) thin‐film solar cell applications. For that, an In2S3 buffer layer alloyed with a limited amount of O (well below 25 mol%) has been proposed as a pertinent alternative solution to CdS or Zn(O,S) buffers. However, the chemical stability of the In2S3/CIGSe heterointerface when O is added is not completely clear. Therefore, in this work, the buffer/absorber interface for a series of sputter‐deposited In2S3 buffers with and without O is investigated. It is found that the solar cell with the highest open‐circuit voltage is obtained for the O‐free In2S3 buffer sputtered at 220 °C. This improved open‐circuit voltage could be explained by the presence of a 20 nm‐thick ordered vacancy compound (OVC) at the absorber surface. A much thinner OVC layer (5 nm) or even the absence of this layer is found for the cell with In2(O0.25S0.75)3 buffer layer where O is inserted. The volume fraction of the OVC layer is directly linked with the magnitude of Cu diffusion from the CIGSe surface into the In2(OxS1−x)3 buffer layer. The O addition strongly reduces the Cu diffusion inside the buffer layer up to complete suppression for very high O contents in the buffer. Finally, it is discussed that the presence of the OVC layer may lower the valence band maximum, thereby forming a hole barrier, suppressing charge carrier recombination at the In2(OxS1−x)3/CIGSe interface, which could result in an increased open‐circuit voltage.

Synthesis and characterization of water-based CIGS ink for photovoltaic applications

Due to their many benefits, CIGS (Copper Indium Gallium Selenide, CuInxGa(1−x)Se2) based solar cells are preferred over their alternatives for powering different systems in space applications. The current methods for synthesizing the CIGS thin films are expensive and complicated due to the use of vacuum and/or involvement of high temperatures and a multi-step approach involving a separate selenization step. Ink-jet printing is considered as a simple and affordable process to deposite thin films, which require materials in the ink (particulate dispersion) form. Thus, the presented work focuses on synthesizing a printable CIGS ink using a solution processing route at room temperature without a vacuum environment. The synthesis of CIGS ink is done from a chemical bath containing the ions of its constituents, followed by the addition of a strong reducing agent and continuous, vigorous stirring. An analysis of X-ray diffraction verified the existence of the CIGS crystal structure. With the help of UV–visible spectroscopy, the band gap of the ink was calculated using the Tauc plot method, while morphological studies were done using FESEM and AFM. This effort will contribute to developing an easy-to-use, low-cost method for the continued development of CIGS ink.Graphical

Influence of Bulk Defect Density in CIGS on the Efficiency of Copper Indium Gallium Selenide Photocell

In CIGS-based thin films, bulk defects are believed to represent disturbances in a regular, periodic arrangement within the atoms or the crystalline media, which influence sheet resistivity. In this study, resistivity measurements were carried out on CIGS thin films using the Van Der Pauw technique. Then, a comparison between two Van Der Pauw four-point measurement configurations (aligned and square) was made, which showed that the square configuration was the most appropriate configuration that can be recommended to measure the thin film sheet resistance of CIGS films. Finally, a numerical simulation using SCAPS-1D software was used to study the influence of bulk defect density in CIGS films as an absorber layer in a model photocell. Using the simulated data, three operating zones for the model photocell were identified depending on its bulk defect density concentration. The influence of bulk defects on thickness, band gap, and doping were then analyzed. It was revealed that when the bulk defect density was less than 5 × 1013 cm−3 5.1013 cm−3 for an absorber of thickness in the order of over 3 μm, a band gap between 1.3 eV–1.4 eV and acceptor density of NA = 1016 cm-31016 cm−3 were the optimal operating conditions for the model photocell. It was concluded that the CIGS layer used as an absorber can be improved if its bulk defect density is tuned to optimal levels.

A Combination of Silver Nanowires and Al2O3 to Replace ITO and MgF2 in a Cu(In,Ga)Se2 Thin‐Film Solar Cell

AbstractSilver nanowire (AgNW) transparent conducting electrodes can be prepared via a low‐cost process and deliver optoelectronic performance comparable to or even better than that of indium tin oxide (ITO). However, their integration into a real device is challenging, mainly because of the weak adhesion between AgNWs and the underlayer. Furthermore, when AgNWs replace ITO, a different material needs to be considered for the antireflection coating (ARC) of a thin‐film solar cell. A combination of AgNWs and Al2O3 is employed to replace both ITO and the MgF2 in a Cu(In,Ga)Se2 (CIGS) thin‐film solar cell. The quality of the contact between the AgNWs and CdS buffer is improved by introducing a chemical‐bath‐deposited welding layer, which improves the fill factor of the cell from 43.4% to 68.7%. Accordingly, the exposed surface of the CIGS thin‐film solar cell changes from ITO to CdS. Therefore, the commonly used MgF2 ARC is replaced with Al2O3, which is a better match in terms of the refractive index for AgNW‐based CIGS thin‐film solar cells. The adoption of the Al2O3 ARC increases the short‐circuit current density of the cell by 7.3%. In conclusion, a device structure of Al2O3/AgNW/CdS/CIGS/Mo is suggested for CIGS thin‐film solar cells.

Optimizing Wide Band Gap Cu(In,Ga)Se2 Solar Cell Performance: Investigating the Impact of "Cliff" and "Spike" Heterostructures.

In recent years, the efficiency of high-efficiency Cu(In,Ga)Se2 (CIGS) solar cells has been significantly improved, particularly for narrow-gap types. One of the key reasons for the enhancement of narrow-gap device performance is the formation of the "Spike" structure at the CdS/CIGS heterojunction interface. Wide-gap CIGS solar cells excel in modular production but lag behind in efficiency compared to narrow-gap cells. Some studies suggest that the "Cliff" structure at the heterojunction of wide-gap CIGS solar cells may be one of the factors contributing to this decreased efficiency. This paper utilizes the SCAPS software, grounded in the theories of semiconductor physics and photovoltaic effects, to conduct an in-depth analysis of the impact of "Cliff" and "Spike" heterojunction structures on the performance of wide band gap CIGS solar cells through numerical simulation methods. The aim is to verify whether the "Spike" structure is also advantageous for enhancing wide-gap CIGS device performance. The simulation results show that the "Spike" structure is beneficial for reducing interfacial recombination, thereby enhancing the VOC of wide-gap cells. However, an electronic transport barrier may form at the heterojunction interface, resulting in a decrease in JSC and FF, which subsequently reduces device efficiency. The optimal heterojunction structure should exhibit a reduced "Cliff" degree, which can facilitate the reduction of interfacial recombination while simultaneously preventing the formation of an electronic barrier, ultimately enhancing both VOC and device performance.

Effects of heavy alkali metals (Rb, Cs) post-deposition treatments on CuInGaSe2 using a spin-coating technique

Abstract This study used a controlled environment to explore the post-deposition treatment (PDT) effects on CuInGaSe2 (CIGSe2) semiconducting thin films using a non-vacuum spin-coating technique for doping the CIGSe layers with Cs and Rb. The structural characterization confirmed the successful deposition of chalcopyrite structures with no phases belonging to any alkali metals after the PDT, with crystallite sizes in the range between 40-67 nm, and with a slight change in the X Ray Diffraction (XRD) peak positions indicating a change from copper-rich to copper-poor phases. The morphological studies confirmed the increase in grain sizes after the PDT. The EDS chemical studies showed that there is a reduction in the copper content after PDT. The topographical studies showed a change in the surface morphology with modifications of the grain parameters. In addition, the electrical characterization showed a significant increase of the effective carrier mobility after the treatments, consistent with the grain size increase observed by both microscopic (SEM and AFM) studies. Raman characterization of the CIGSe2 films showed the A1 optical phonon mode of CIGS chalcopyrite structures and peaks at lower frequencies belonging to ordered vacancy compounds (OVCs). The deconvolution of the Raman spectroscopy broad peaks for the CIGSe2 films after their PDT confirmed the formation of alk-InSe2 OVC phases on top of the absorber layer.

Introduction of the distribution of Cs in Cu(In,Ga)Se2 photovoltaic absorbers following post-deposition treatment with CsF

In recent years, the device performance of Cu(In,Ga)Se2 (CIGS) solar cells has been improved by heavy alkali element post-deposition treatment (Alkali-PDT). Therefore, it is of great significance to study the mechanism of enhancing CIGS device performance through Alkali-PDT. One aspect to be studied is the distribution of heavy alkali elements in the absorber. In this work, the distribution of the heavy alkali element Cs in the absorber after post deposition treatment of CsF (CsF-PDT) and its effect on the device performance are investigated. The experimental results indicate that Cs can enter both the grain interior (GI) and grain boundaries (GB) via the Cu vacancy (VCu). By comparing the distribution of Na and Cs in the film, it can be noticed that Na is mainly distributed at the GB, while Cs is not differently distributed between the GB and GI. This is mainly due to the fact that the presence of Na at GB inhibits the accumulation of Cs there. The distribution of Cs is beneficial in improving the device’s performance by passivating defects, such as InCu.

Efficiency Investigation and Modeling of an Ultra Thin-film CIGS Solar Cell using WxAMPS

The highly efficient CIGS thin-film solar cell is numerically investigated in this paper using solar simulator software wxAMPS (Analysis of Microelectronic and Photonic Structures). WxAMPS is a customized simulation software package mainly used for photovoltaic cells, which supports quick data input and enhanced visualization with its improved user interface. Copper–indium–gallium–diselenide Cu(In, Ga)Se2 (CIGS) is a semiconductor material with chalcopyrite crystal structure that has high conversion efficiency and structural stability. CIGS model- ZnO: Al/ZnO/CdS/CIGS/Mo/substrate is mainly experimental research that considers the physical characteristics, dimensions, and thicknesses of the different layers. The bilayer window and absorber layer with different thicknesses are the critical factors that influence solar cell performance. The bilayer window concept can assist in reducing the loss at the window layer. In this paper, through the numerical simulation, the highest conversion efficiency was achieved, 18.7%, with an optimum bandgap of 1.12 eV with 3000 nm thickness of the absorber layer under AM 1.5G.

Post‐Mortem Analysis of Building‐Integrated Flexible Thin Film Modules

ABSTRACTFlexible, lightweight thin film (TF) photovoltaic (PV) modules offer a unique opportunity for integration into non‐planar surfaces unable to support heavy weights. While such applications increase the potential for PV in urban areas, the reliability implications are yet to be investigated. Here, prototypes of corrugated rooftiles with integrated Cu (In,Ga)Se2 (CIGS) modules were investigated after 3 years of outdoor operation. Their performance before and after the outdoor exposure was compared and defects were localized. An unpackaging method was developed, allowing access to the solar cells for more detailed characterization of present defects without causing additional damage or changes to existing defects. To our knowledge, this was the first time such an unpackaging method was successfully applied to flexible TF PV modules. The relative efficiency loss ranged from 17% to 43%, mostly due to short‐circuit current (ISC) loss and series resistance (RS) increase. The predominant cause of the RS increase was the delamination at the interconnects, ascribed to thermomechanical stresses caused by outdoor temperature fluctuations. The ISC loss was mainly caused by localized delamination of CIGS from the molybdenum (Mo) back‐contact. The occurrence of such delaminated areas pointed to presence of high local stresses during outdoor operation, possibly due to thermal fluctuations, applied deformation and/or mechanical impact. Two other types of delamination defects were found with no observable impact on performance. These results show the necessity for further optimization in the material choice and processing of TF flexible modules, to avoid mechanical stress related failures upon integration into curved surfaces.

Effect of Ga Variation on the Bulk and Grain‐Boundary Properties of Cu(In,Ga)Se2 Absorbers in Thin‐Film Solar Cells and Their Impacts on Open‐Circuit Voltage Losses

ABSTRACTPolycrystalline widegap Cu(In,Ga)Se2 (CIGSe) absorbers for top cells in photovoltaic tandem devices can be synthesized via [Ga]/([Ga] + [In]) (GGI) ratios of > 0.5. However, the power conversion efficiencies of such high‐GGI devices are smaller than those of the record cells with GGI < 0.5. In the present work, the effects of the GGI ratio on various CIGSe material properties were studied and correlated with the radiative and nonradiative open‐circuit voltage (VOC) deficits of the thin‐film solar cells. Average grain sizes, grain boundary (GB) recombination velocities, fluctuations in luminescence energy distribution, barrier heights at GBs, effective electron lifetimes, and Urbach energies were investigated in five solar cells with GGI ratios from 0.13 to 0.83. It was found that the GGI variation affects GB recombination velocities, fluctuations in spatial luminescence distributions, the average grain size, the electron lifetime, and the Urbach energy. In contrast, the detected ranges of barrier heights at GBs are independent of the GGI ratio. Mainly Ga/In gradients give rise to substantial radiative VOC losses in all solar cells. Nonradiative VOC deficits are dominant especially for solar cells with GGI > 0.5, which can be attributed to low bulk lifetimes and enhanced recombination at GBs in CIGSe absorbers in this compositional range.

Bifacial and Angular‐Resolved Performance Characterization of Ultrathin Cu(In,Ga)Se2 Solar Cells Including Nanostructures

Bifacial solar cells experience growing interest not just for crystalline silicon photovoltaic modules. Thin‐film solar cells deposited on a transparent back contact bring inherent semitransparency, making them ideally suited for bifacial applications. Herein, a systematic investigation of bifacial measurement procedures is performed on semitransparent ultrathin Cu(In,Ga)Se2 (CIGSe) solar cells on transparent conductive oxide, including nanostructures. The measurements are further extended by angular‐resolved performance studies. The bifaciality of the samples is determined to be ≈80% in current and ≈65% in power, and enables the calculation of an equivalent irradiance for solar cell testing under >1 sun front illumination only. The results are compared to bifacial operation, i.e., simultaneous front and rear irradiance, and to the summation of individual front and rear performance measurements up to 1 sun. It is revealed that highly similar results can be obtained for these approaches and that the integration of nanostructures supports device stabilization. Particularly, the higher (75 nm) SiO2 nanomeshes can enable performance enhancement. Furthermore, the angular‐dependent behavior follows the expected trend of reduced illumination intensity according to the cosine of the incident angle. In these findings, the suitability of semitransparent ultrathin CIGSe solar cells for bifacial operation and the benefit of integrated nanostructures is confirmed.

Computational Optimization for CdS/CIGS/GaAs Layered Solar Cell Architecture

Multi-junction solar cells are vital in developing reliable, green, sustainable solar cells. Consequently, the computational optimization of solar cell architecture has the potential to profoundly expedite the process of discovering high-efficiency solar cells. Copper indium gallium selenide (CIGS)-based solar cells exhibit substantial performance compared to those utilizing cadmium sulfide (CdS). Likewise, CIGS-based devices are more efficient according to their device performance, environmentally benign nature, and thus, reduced cost. Therefore, the paper introduces an optimization process of three-layered n-CdS/p-CIGS/p-GaAs (NPP)) solar cell architecture based on thickness and carrier charge density. An in-depth investigation of the numerical analysis for homojunction PPN-junction with the ’GaAs’ layer structure along with n-ZnO front contact was simulated using the Solar Cells Capacitance Simulator (SCAPS-1D) software. Subsequently, various computational optimization techniques for evaluating the effect of the thickness and the carrier density on the performance of the PPN layer on solar cell architecture were examined. The electronic characteristics by adding the GaAs layer on the top of the conventional (PN) junction further led to optimized values of the power conversion efficiency (PCE), open-circuit voltage (VOC), fill factor (FF), and short-circuit current density (JSC) of the solar cell. Lastly, the paper concludes by highlighting the most promising results of our study, showcasing the impact of adding the GaAs layer. Hence, using the optimized values from the analysis, thickness of 5 (μm) and carrier density of 1×1020 (1/cm) resulted in the maximum PCE, VOC, FF, and JSC of 45.7%, 1.16 V, 89.52%, and 43.88 (mA/m2), respectively, for the proposed solar cell architecture. The outcomes of the study aim to pave the path for highly efficient, optimized, and robust multi-junction solar cells.

Role of Ag Addition on the Microscopic Material Properties of (Ag,Cu)(In,Ga)Se2 Absorbers and Their Effects on Losses in the Open‐Circuit Voltage of Corresponding Devices

ABSTRACTAg alloying of Cu(In,Ga)Se2 (CIGSe) absorbers in thin‐film solar cells leads to improved crystallization of these absorber layers at lower substrate temperatures than for Ag‐free CIGSe thin films as well as to enhanced cation interdiffusion, resulting in reduced Ga/In gradients. However, the role of Ag in the microscopic structure–property relationships in the (Ag,Cu)(In,Ga)Se2 thin‐film solar cells as well as a correlation between the various microscopic properties of the polycrystalline ACIGSe absorber and open‐circuit voltage of the corresponding solar cell device has not been reported earlier. In the present work, we study the effect of Ag addition by analyzing the differences in the various bulk, grain‐boundary, optoelectronic, emission, and absorption‐edge properties of ACIGSe absorbers with that of a reference CIGSe absorber. By comparing thin‐film solar cells with similar band‐gap energies ranging from about 1.1 to about 1.2 eV, we were able to correlate the differences in their absorber material properties with the differences in the device performance of the corresponding solar cells. Various microscopic origins of open‐circuit voltage losses were identified, such as strong Ga/In gradients and local compositional variations within individual grains of ACIGSe layers, which are linked to absorption‐edge broadening, lateral fluctuations in luminescence‐energy distribution, and band tailing, thus contributing to radiative VOC losses. A correlation established between the effective electron lifetime, average grain size, and lifetime at the grain boundaries indicates that enhanced nonradiative recombination at grain boundaries is a major contributor to the overall VOC deficit in ACIGSe solar cells. Although the alloying with Ag has been effective in increasing the grain size and the effective electron lifetime, still, the Ga/In gradients and the grain‐boundary recombination in the ACIGSe absorbers must be reduced further to improve the solar‐cell performance.

Crystallization Modulation and Holistic Passivation Enables Efficient Two-Terminal Perovskite/CuIn(Ga)Se2 Tandem Solar Cells

HighlightsIntegrating perovskite solar cells onto irregular rough CuIn(Ga)Se2 (CIGS) surfaces remains a challenge; new strategy was explored to develop monolithic perovskite/CIGS tandem solar cell by manipulating the crystallization of perovskite.Surface reconstruction and field-effect passivation are developed synergistically to issue complex interface relationship between perovskite and C60.The champion power conversion efficiency （PCE） of 24.6% realized, providing significant commercial opportunities for all thin-film-based perovskite/CIGS tandem cells.

Increasing the efficiency of CIGS solar cells due to the reduced graphene oxide field layer of the back surface

Copper indium gallium selenide solar cells (CIGS-SCs) have gained attention due to their cost-effectiveness and environmentally friendly characteristics, making them a promising option for future electricity generation. The efficiency of CIGS-SCs can be enhanced by adding a back surface field layer (BSFL) under the absorber layer to reduce recombination losses. In this study, the electrical parameters, such as the series resistance, shunt resistance, and ideality factor, are calculated for CIGS-SCs with an advanced design, using the SC capacitance simulator (SCAPS) software. The detailed model used in the simulations considers the material properties and fabrication process of BSFL. By utilizing a reduced graphene oxide (rGO) BSFL, a conversion efficiency of 24% and a significant increase in the fill factor are predicted. This increase is primarily attributed to the ability of the rGO layer to mitigate the recombination of charge carriers and establish a quasi-ohmic contact at the metal-semiconductor interface. At higher temperatures, BSFL can become less effective due to an increased recombination and, in turn, a decreased carrier lifetime. Overall, this study provides valuable insights into the underlying physics of CIGS-SCs with BSFL and highlights the potential for improving their efficiency through advanced design and fabrication techniques.

Enhancing Multi-Junction Solar Cell Performance: Advanced Predictive Modeling and Cutting-Edge CIGS Integration Techniques

Historically, multi-junction solar cells have evolved to capture a broader spectrum of sunlight, significantly enhancing efficiency beyond conventional solar technologies. In this study, we utilized Silvaco TCAD tools to optimize a five-junction solar cell composed of AlInP, AlGaInP, AlGaInAs, GaInP, GaAs, InGaAs, and Ge, drawing on advancements documented in the literature. Our research focused on optimizing these cells through sophisticated statistical modeling and material innovation, particularly examining the relationship between layer thickness and electrical yield under one sun illumination. Employing III-V tandem solar cells, renowned for their superior efficiency in converting sunlight to electricity, we applied advanced statistical models to a reference solar cell configured with predefined layer thicknesses. Our analysis revealed significant positive correlations between layer thickness and electrical performance, with correlation coefficients (R2 values) impressively ranging from 0.86 to 0.96 across different regions. This detailed statistical insight led to an improvement in overall cell efficiency to 44.2. A key innovation in our approach was replacing the traditional germanium (Ge) substrate with Copper Indium Gallium Selenide (CIGS), known for its adjustable bandgap and superior absorption of long-wavelength photons. This strategic modification not only broadened the absorption spectrum but also elevated the overall cell efficiency to 47%. Additionally, the optimization process involved simulations using predictive profilers and Silvaco Atlas tools, which systematically assessed various configurations for their spectral absorption and current–voltage characteristics, further enhancing the cell’s performance. These findings underscore the critical role of precise material engineering and sophisticated statistical analyses in advancing solar cell technology, setting new efficiency benchmarks, and driving further developments in the field.

An electro-thermal finite element method (FEM) model for local hotspot kinetics in Cu(In, Ga)Se2 thin-film solar modules

Partial shading can significantly impair the efficiency of thin-film solar cells. When exposed to partial shading, cells within the array tend to become reverse biased, leading to thermal runaway events and the emergence of hotspots. In Cu(In,Ga)Se2 (CIGS) solar cells such hotspots are also associated with so-called worm-like defects. Both theoretical and experimental studies have shown that in CIGS, a positive-feedback loop leads to instability and thermal runaway events. However, we observe an inconsistency between published simulation results and recently published experimental work. In a recent experimental study, it was shown that under certain conditions, a hotspot develops within 1ms, showing signs of melting of the CIGS in an area with a 5μm radius. However, in published simulation results, the time for such high temperatures to develop is in the order of seconds, a discrepancy of three orders of magnitude. In this work, we argue that this discrepancy is explained by the size of the seed defect, demonstrating that the origin of these experimentally observed, fast-developing hotspots is likely microscopic defects. To this end, we developed an electro-thermal finite element model, with very high temporal and spatial resolution. We demonstrate that, assuming a seed defect with a 10nm radius, we can reproduce the experimental results with respect to the size of the defect and the time it took to develop.