Cu(In,Ga)Se2 Research Articles

BTO-Coupled CIGS Solar Cells with High Performances

In order to improve the power conversion efficiency (PCE) of Cu(In,Ga)Se2 (CIGS) solar cells, a BaTiO3 (BTO) layer was inserted into the Cu(In,Ga)Se2. The performances of the BTO-coupled CIGS solar cells with structures of Mo/CIGS/CdS/i-ZnO/AZO, Mo/BTO/CIGS/CdS/i-ZnO/AZO, Mo/CIGS/BTO/CdS/i-ZnO/AZO, Mo/CIGS/CdS/BTO/i-ZnO/AZO, Mo/CIGS/BTO/i-ZnO/AZO, Mo/CIGS/CdS/BTO/AZO, and Mo/ CIGS/CdS(5 nm)/BTO(5 nm)/i-ZnO/AZO were systematically studied via the SCAPS-1D software. It was found that the power conversion efficiency (PCE) of a BTO-coupled CIGS solar cell with a device configuration of Mo/CIGS/CdS/BTO/AZO was 24.53%, and its open-circuit voltage was 931.70 mV. The working mechanism for the BTO-coupled CIGS solar cells with different device structures was proposed. Our results provide a novel strategy for improving the PCE of solar cells by combining a ferroelectric material into the p-n junction materials.

Performance and stability enhancement of mixed dimensional bilayer inverted perovskite (BA2PbI4/MAPbI3) solar cell using drift-diffusion model

A variety of classic photovoltaic technologies, such as multi-crystal silicon and copper indium gallium selenide, have been exceeded by organometal halide perovskite solar cells, which have made significant advancements in the cost-effective manufacturing method as well as the high power conversion efficiency. Meanwhile, the unfavourable operational stability of perovskite solar cells is impeding the commercialization of the technology. When exposed to critical environmental factors such as rising moisture and intense sunlight, perovskite solar cells suffer lattice degradation and lose their ability to harvest energy. As a result, enhancing the stability of perovskite cells is one of the most important variables in determining the next wave of progress for the technology. While there have been numerous techniques reported to improve the stability of perovskite-based photovoltaic cell, the construction of a more than one dimension (2D/3D) perovskite as the light absorbing layer has recently emerged as one of the most reliable strategies to stabilise the perovskite-based device without compromising photo physical performance. Herein, we have computationally simulated p-i-n device configuration composed of ITO/NiO/2D perovskite/3D perovskite/PCBM/Au. The Ruddlesden-Popper (RP) phases of two-dimensional perovskite act as a cover layer, which inhibits the deterioration of 3D perovskite in an open-air environment. Both optical and electrical simulation is performed using solar cell capacitance simulator (SCAPS). Simulation findings showed that the enhancements in overall performance are due to the decrease in the trap state's density and better coordination of the band between the 2D/3D perovskite and the hole-transporting materials. Effects of the interfacial defects (2D perovskite/HTL and 3D perovskite/ETL) on solar cell parameters are also performed. Simulation results reveal that the defects at 3D perovskite/ETL interfacial are more dominating in overall performance degradation. Parametric differences, such as thickness of various layers, standard solar spectra, further refine the proposed architecture. The multidimensional-based architecture proposed in this work resulted in a power conversion efficiency (PCE) of 19.6%.

K Improves Cu(In,Ga)Se2 Surface Band Alignment through Reconstruction

K, Rb, and Cs improve Cu(In,Ga)Se2 (CIGS) solar cell performance, but the mechanism remains unclear. Here we use air-free transfer of multiple samples to study KF post-deposition treatments (PDTs) by X-ray photoelectron spectroscopy. The KF PDTs do not change the majority carrier concentration or Cd in-diffusion, but they boost efficiency by 6.1% absolute, improve minority carrier lifetime, and shift the surface valence band further from the Fermi energy. Unlike former reports, the valence-band shift is not a result of lower Cu/(Ga+In) or higher K/(K+Cu) composition ratios. We propose that instead, KF PDTs alter the surface valence-band alignment through a reconstructive phase transformation from chalcopyrite CIGS to K2CuIn3Se6 or KInSe2, which have layered structures. These compounds can leave Cu-free cation planes after K is rinsed away, unlike the structure of chalcopyrite CIGS or CuIn3Se5.

Fingerprints Indicating Superior Properties of Internal Interfaces in Cu(In,Ga)Se2 Thin-Film Solar Cells.

Growth of Cu(In,Ga)Se2 (CIGS) absorbers under Cu-poor conditions gives rise to incorporation of numerous defects into the bulk, whereas the same absorber grown under Cu-rich conditions leads to a stoichiometric bulk with minimum defects. This suggests that CIGS absorbers grown under Cu-rich conditions are more suitable for solar cell applications. However, the CIGS solar cell devices with record efficiencies have all been fabricated under Cu-poor conditions, despite the expectations. Therefore, in the present work, both Cu-poor and Cu-rich CIGS cells are investigated, and the superior properties of the internal interfaces of the Cu-poor CIGS cells, such as the p-n junction and grain boundaries, which always makes them the record-efficiency devices, are shown. More precisely, by employing a correlative microscopy approach, the typical fingerprints for superior properties of internal interfaces necessary for maintaining a lower recombination activity in the cell is discovered. These are a Cu-depleted and Cd-enriched CIGS absorber surface, near the p-n junction, as well asa negative Cu factor (∆β) and high Na content (>1.5 at%) at the grain boundaries. Thus, this work provides key factors governing the device performance (efficiency), which can be considered in the design of next-generation solar cells.

Effectiveness of band discontinuities between CIGS absorber and copper-based hole transport layer in limiting recombination at the back contact

In this work, different copper-based thin-film materials as a hole transport layer (HTL) are introduced in Cu(In,Ga)Se2 (CIGS) solar cells to limit the recombination rate at the back contact and improve efficiency. To survey the impact of different HTLs on the efficiency of CIGS solar cells, an experimental cell with a record efficiency of 23.35% has been modeled. Then, cuprous oxide (Cu2O), cuprous thiocyanate (CuSCN), and copper sulfide (CuS) thin films as an HTL were added separately to the CIGS cell. It was demonstrated that the open-circuit voltage (Voc) is enhanced owing to the reduction of the back interface recombination, and short-circuit current density (Jsc) is improved thanks to the enhancement of carrier collection when Cu2O or CuSCN HTLs are added to the conventional CIGS solar cell. External quantum efficiency (EQE) has also shown a significant increase in long wavelengths of approximately 1000–1200 nm through this approach. The simulated impedance spectroscopy confirms that the use of Cu2O HTL in the CIGS solar cells significantly reduces back surface recombination, which could improve Voc and fill factor (FF) values. In addition, the utilization of Cu2O HTL in the CIGS solar cells reduces Urbach energy (EU), which is attributed to suitable band alignment at Cu2O/CIGS interface. High efficiency of 27.3% was achieved by adding the Cu2O HTL in CIGS solar cell, which is mainly attributed to the additional carrier extraction routes through HTL.

Assessment of a Therapeutic X-ray Radiation Dose Measurement System Based on a Flexible Copper Indium Gallium Selenide Solar Cell.

Several detectors have been developed to measure radiation doses during radiotherapy. However, most detectors are not flexible. Consequently, the airgaps between the patient surface and detector could reduce the measurement accuracy. Thus, this study proposes a dose measurement system based on a flexible copper indium gallium selenide (CIGS) solar cell. Our system comprises a customized CIGS solar cell (with a size 10 × 10 cm2 and thickness 0.33 mm), voltage amplifier, data acquisition module, and laptop with in-house software. In the study, the dosimetric characteristics, such as dose linearity, dose rate independence, energy independence, and field size output, of the dose measurement system in therapeutic X-ray radiation were quantified. For dose linearity, the slope of the linear fitted curve and the R-square value were 1.00 and 0.9999, respectively. The differences in the measured signals according to changes in the dose rates and photon energies were <2% and <3%, respectively. The field size output measured using our system exhibited a substantial increase as the field size increased, contrary to that measured using the ion chamber/film. Our findings demonstrate that our system has good dosimetric characteristics as a flexible in vivo dosimeter. Furthermore, the size and shape of the solar cell can be easily customized, which is an advantage over other flexible dosimeters based on an a-Si solar cell.

Will ultrathin CIGS solar cells overtake the champion thin-film cells? Updated SCAPS baseline models reveal main differences between ultrathin and standard CIGS

Cu(In,Ga)Se2 (CIGS) solar cells are amongst the best performing thin-film technologies, with the latest performance gains being mainly due to recent years improvements obtained with post-deposition treatments (PDT). Moreover, thinning of the absorber layer down to sub-micrometre values (ultrathin absorbers) is of extreme importance for CIGS to be even more cost-effective and sustainable. However, electrical and optical limitations, such as rear interface recombination and insufficient light absorption, prevent the widespread implementation of ultrathin CIGS devices. The recent electrical CIGS simulation baseline models have failed to keep up with the experimental developments. Here an updated and experimentally based baseline model for electrical simulations in the Solar Cell Capacitor Simulator (SCAPS) software is presented and discussed with the incorporation of the PDT effects and increased optical accuracy with the support from Finite-Difference Time-Domain (FDTD) simulation results. Furthermore, a champion solar cell with an equivalent architecture validates the developed thin-film model. The baseline model is also applied to ultrathin CIGS solar cell devices, validated with the ultrathin champion cell. Ultimately, these ultrathin models pave the way for an ultrathin baseline model. Simulations results reveal that addressing these absorbers' inherent limitations makes it possible to achieve an ultrathin solar cell with at least 21.0% power conversion efficiency, with open-circuit voltage values even higher than the recent thin-film champion cells.

Development of a P1-filling process to increase the cell performance in the copper indium gallium Selenide photovoltaics by implementation of the inkjet technology

In this paper, the suitability of integrating a digital manufacturing tool i.e. inkjet technology is exemplified to increase the electrical performance of thin-film based Copper Indium Gallium Selenide (CIGS) photovoltaic (PV) modules. Typically, the series connection within the PV module is established conventionally by three adjacent scribing lines at different deposition stages (patterning P1, P2 and P3). The total width of these three scribes is typically in the order of several 100's of microns and is electrically inactive, so these regions are lost areas for current generation (up to 5% “dead area”). To reduce the line width of the first scribe (P1) without compromising on the electrical parameters, we have concentrated on accurately filling of the interconnect P1-trenches with insulating material using inkjet technology, as initial step to realize the concept for dead area reduction by developing a P1-filling process (< 80 μm printed filling width) for laser structured/patterned trenches of ~50 μm width. With the right combination of carefully selected material interface, inkjet printhead, deposition settings, pattern digitalization & other parameters, we are able to develop an industry relevant micro-filling process. And, show an increase in the performance of PV cells, as compared to the reference modules. The results lay the foundation for direct up-scaling to industrial-size substrate areas and open up the possibility to realize all kinds of advanced interconnect schemes for the next generation thin-film CIGS PV modules. • Digital manufacturing of P1-filling for the thin-film photovoltaics in conjunction with laser process. • Approach towards reduction of dead-area in photovoltaics. • Inkjet printing of functional material within μm range channels/trench (< 80 μm). • Increase in photovoltaic performance (fill factor & module efficiency). • P1-filling process developed under ambient condition, without any inert atmosphere.

Tailored Band Structure of Cu(In,Ga)Se2 Thin-Film Heterojunction Solar Cells: Depth Profiling of Defects and the Work Function.

An efficient carrier transport is essential for enhancing the performance of thin-film solar cells, in particular Cu(In,Ga)Se2 (CIGS) solar cells, because of their great sensitivities to not only the interface but also the film bulk. Conventional methods to investigate the outcoming carriers and their transport properties measure the current and voltage either under illumination or dark conditions. However, the evaluation of current and voltage changes along the cross-section of the devices presents several limitations. To mitigate this shortcoming, we prepared gently etched devices and analyzed their properties using micro-Raman scattering spectroscopy, Kelvin probe force microscopy, and photoluminescence measurements. The atomic distributions and microstructures of the devices were investigated, and the defect densities in the device bulk were determined via admittance spectroscopy. The effects of Ga grading on the charge transport at the CIGS-CdS interface were categorized into various types of band offsets, which were directly confirmed by our experiments. The results indicated that reducing open-circuit voltage loss is crucial for obtaining a higher power conversion efficiency. Although the large Ga grading in the CIGS absorber induced higher defect levels, it effectuated a smaller open-circuit voltage loss because of carrier transport enhancement at the absorber-buffer interface, resulting from the optimized conduction band offsets.

Design and Fabrication of Multiple-Color-Generating Thin-Film Optical Filters for Photovoltaic Applications

The use of electric vehicles (EVs) can reduce greenhouse gas emissions, air pollution, dependency on fossil fuels, and their adverse health effects on humans. But, we can only utilize the full environmental benefits of EVs when they are charged with renewable energy sources with zero or low carbon emissions. As a solution, Mobarak et al. [1] suggested integrating low-cost, flexible, and thin-film copper indium gallium selenide (CIGS) solar cells directly onto the steel of all the upward-facing body parts of the vehicles. But, this integration of solar cells comes with an aesthetic drawback. Previously, colorful photovoltaics (PVs) have been designed with one-dimensional (1D) photonic crystals or various 1D and 2D metallic nanostructures for aesthetic building-integrated photovoltaics (BIPVs) [2, 3]. However, the functionality of our application differs from that of BIPV as we need maximum absorption of the solar spectrum to obtain maximum conversion efficiency. Thus, we propose replacing the anti-reflective coating (ARC) present in the solar cells with a notch filter (a narrow high-reflection region in the visible range along with high transmission for the rest of the solar spectrum) to obtain colors.High-performance notch filters with a narrow and ultra-steep notch are well known in literature [4, 5]. Generally, high-performance notch filters are designed with a minimum of 45 layers. It is challenging to use filters with many layers on solar cells due to fabrication and thickness complexities. Thus, we created designs with a maximum of 27 layers for possible integration with photovoltaics. We used OptiLayer [6] to simulate our designs and the gradual evolution technique was used to optimize the designs. We performed our simulations with a multilayer structure of alternating high and low refractive indices of 2.09 and 1.45, respectively, on top of a silicon substrate. We optimized this multilayer structure for three reference wavelengths (400 nm, 550 nm, and 700 nm) resembling three colors. Our designs have notch widths of less than 100 nm for all the reference wavelengths with an average of 70% reflection in the high-reflection region and less than 20% reflection in the high-transmission area.To fabricate our designs, we need materials that are transparent to the solar spectrum targeted by the active material of the solar cells. The materials also need to have refractive indices closer to our simulation. Thus, we chose the combination of silicon nitride and silicon dioxide as our high and low refractive index material, respectively [7, 8]. To better understand our designs’ optical characteristics, we fabricated a scaled-down version of our structure with 5-10 layers. We used electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) to deposit the multilayer structure on silicon wafers. To obtain the silicon nitride and silicon dioxide layers, we used a SiH4/N2/O2/Ar precursor mixture. By tuning the gas flow rate in the reactor chamber, we tuned the stoichiometry and obtained the required refractive index for each layer. To characterize the refractive index and thickness for each layer, we used variable angle spectroscopic ellipsometry (VASE). We made a detailed comparison of our simulation and fabrication results.

(Invited) (Photo)Electrochemical Cells for Hydrogen Production and Carbon Dioxide Utilization

Photoelectrochemical (PEC) and electrochemical cells can produce hydrogen from water and/or can produce useful chemicals from carbon dioxide, and, thus, are the key technologies for construction of carbon neutral society.Direct water splitting using photoelectrochemical cell is one of the promising means to produce hydrogen utilizing solar energy. The most important issue for photoelectrode the central of photoelectrochemical cell is narrow bandgap combined with large reaction driving force. Cu(In,Ga)Se2 (CIGS) which is employed as an absorber material in photovoltaic devices is one of the promising photocathode materials because of its long absorption edge of >1000 nm. [1] However, its driving force for water splitting is limited because of relatively shallow valence band maximum (VBM). The solid solution between ZnSe and CIGS (ZnSe-CIGS) is one of the promising candidates of photocathode material for water splitting because of its long absorption edge, ~900 nm, and large driving force, ~1.0 V. [2] In the present study, we investigated introduction of tellurium during ZnSe-CIGS thin films, and found the tellurium introduction increase grain size of ZnSe-CIGS film. The sequential deposition of Ga-rich layer and In-rich layer resulted in formation of composition gradient which facilitate charge separation thorough conduction band minimum (CBM) gradient. The ZnSe-CIGS base photocathode prepared with employing tellurium introduction and composition gradient showed significantly increased incident photon-to-current conversion efficiencies (IPCEs), close to unity. [3]The electrochemical cell with gas diffusion electrode (GDE) for carbon dioxide reduction reaction (CO2RR) can produce useful chemicals efficiently. Copper species are the catalysts with capable of producing C2 products such as C2H5OH and C2H4. In the present study, Cu2O was examined as an electrocatalyst for CO2RR. A GDE composed of carbon paper coated with Cu2O by electroplating method showed C2H4 production with faradaic efficiency (FE) of >50% and C2H5OH production with FE of >20% under the optimized conditions for >10 hours.References H. Kumagai, T. Minegishi, N. Sato, T. Yamada, J. Kubota, K. Domen, J. Mater. Chem. A, 3, 8300 (2015). H. Kaneko, T. Minegishi, M. Nakabayashi, N. Shibata, K. Domen, Angew.Chem. Int. Ed. 55,15329 (2016). T. Minegishi, S. Yamaguchi, M. Sugiyama, Appl. Phys. Lett. 119, 123905 (2021).

A thermodynamic evaluation of metal halides for the recrystallization of Cu(In,Ga)Se2

AbstractCdTe films are deposited at low temperatures and recrystallized to photovoltaic device quality using CdCl2 treatments, leading to competitive manufacturing costs. Cu(In,Ga)Se2 (CIGS) typically requires high‐temperature, low‐rate depositions to produce high‐efficiency devices, resulting in higher costs. A similar metal halide treatment of CIGS has been demonstrated by us previously for some metal halide sources. To understand and optimize the process, a thermodynamic evaluation of candidate metal halides for such treatments is presented as a guide for their selection. By comparing bond dissociation energies, mono‐ and di‐halide compounds are proposed to be ideal compounds to act as transport agents. Known recrystallization and temperature reduction benefits by Ag alloying suggest that Ag halides should be used to aid transport of all species. The high vapor pressure and mobility of Ga compounds still pose a problem for metal halide treatment, resulting in Ga etching and removal of intentional Ga gradients. Less severe but similar issues with In compounds may occur. Cu compounds have low vapor pressures that may limit transport; however, Cu is highly mobile in CIGS, and recrystallization still occurs.

High-yield recycling and recovery of copper, indium, and gallium from waste copper indium gallium selenide thin-film solar panels

A separation process for Cu, In, Ga, and Se (CIGS)-based thin-film solar panels is proposed in this study. Initially, the separation process, by peeling off the panels in a layer-by-layer manner, was achieved by utilizing the different thermal strains of materials inside the CIGS solar panels. Subsequently, the recovery process was performed by annealing the CIGS layers for the removal of Se, and then leaching was performed with nitric acid, followed by the individual extraction of valuable metals. The pH values, concentrations of extractant, stripping agents, organic-aqueous ratios, and reaction time were investigated in detail to optimize the separation conditions for Cu, In, and Ga. First, In was extracted using di-(2-ethylhexyl) phosphoric acid into the organic phase, while Cu and Ga remained in the aqueous phase, by controlling the extraction conditions. After the extraction of In, Ga was extracted using the same extraction agent under different conditions, and nearly pure Cu remained in the residual aqueous solution. Ammonium hydroxide was added to three solutions to form metal hydroxide precipitates. Under the optimal conditions, a recovery rate of >90% could be achieved for In, Ga, and Cu. Furthermore, all as-formed hydroxides were recycled and converted into metal oxides with a purity of >99% by calcination. These findings can provide a pathway for the effective recycling and recovery of Cu, In, and Ga from waste CIGS thin-film solar panels. • A facile and practical method to separate and recover valuable metals respectively from the real commercial thin-film solar panel was demonstrated. • A novel and low-cost physical separation process was induced to peer off the solar panel layer by layer via the extremely low-temperature liquid nitrogen treatment. • An extraction and stripping process was designed to separate Cu, In, and Ga from a complicated multi-element system individually. • Highly pure valuable metal oxides were recovered as the final products, establishing a possible curcular economy model for waste solar panel recycling and recovery.

Experimental investigation to thermal performance of different photo voltaic modules for efficient system design

Due to rapid industrialization, and depletion of fossil fuels, alternative renewable resources are mandatory, where solar thermal energy is one of the promising alternate. In this study, an experimental investigation was conducted to analyze the thermal performance of different photovoltaic-modules under varying climate conditions. These include thin plate Copper indium diselenide, mono-crystalline silicon, micro crystalline silicone, amorphous silicon and poly-crystalline silicon. The analysis was concentrated on the evaluation of module efficiency, solar irradiance absorption rate, maximum power output, performance ratio, normalized power output efficiency and temperature effect on each module at real operational outdoor conditions. Mono-crystalline silicon module showed high average efficiency of 20.8% and average performance ratio 1.21 compared to the other PV modules. It was observed that all types of modules have higher average temperature in summer season and showed low performance ratio and low module efficiency as compared to winter season. Average normalized power out of mono-crystalline silicon 56.2% more efficient than the other modules. The increased thermal performance of mono-crystalline silicon was related with its high absorption rate and high conduction rate. Thus, mono-crystalline silicon PV module is the best potential candidate for solar capturing technique to be utilize in diverse solar thermal energy applications.

Solar Energy in Space Applications: Review and Technology Perspectives

AbstractSolar cells (SCs) are the most ubiquitous and reliable energy generation systems for aerospace applications. Nowadays, III–V multijunction solar cells (MJSCs) represent the standard commercial technology for powering spacecraft, thanks to their high‐power conversion efficiency and certified reliability/stability while operating in orbit. Nevertheless, spacecraft companies are still using cheaper Si‐based SCs to amortize the launching costs of satellites. Moreover, in recent years, new SCs technologies based on Cu(In,Ga)Se2(CIGS) and perovskite solar cells (PSCs) have emerged as promising candidates for aerospace power systems, because of their appealing properties such as lightweightness, flexibility, cost‐effective manufacturing, and exceptional radiation resistance. In this review the current advancements and future challenges of SCs for aerospace applications are critically discussed. In particular, for each type of SC, a description of the device's architecture, a summary of its performance, and a quantitative assessment of the radiation resistance are presented. Finally, considering the high potential that 2D‐materials (such as graphene, transition metal dichalcogenides, and transition metal carbides, nitrides, and carbonitrides) have in improving both performance and stability of SCs, a brief overview of some important results concerning the influence of radiation on both 2D materials‐based devices and monolayer of 2D materials is also included.

Influence of argon pressure on sputter-deposited molybdenum back contacts for flexible Cu(In,Ga)Se2 solar cells on polyimide films

In this study, polyimide films with various thicknesses and coefficients of thermal expansion were used as candidates of lightweight and flexible substrates for Cu(In, Ga)Se2 (CIGS) solar cells. The influence of the Ar background pressure (PAr) during deposition on the properties of the Mo back contact on the polyimide films was investigated. It was found that the stress condition of the Mo contact was the sum of thermal and intrinsic stresses. The thermal stress depended on the coefficient of thermal expansion (CTE) of polyimide films and induced compressive stresses. The intrinsic stress was largely influenced by the PAr. High PAr caused large tensile intrinsic stress and the subsequent formation of cracks in the Mo layer deposited on the polyimide films, whereas no apparent formation of cracks was observed on the reference rigid-glass substrates. The crack formation in Mo deposited on the polyimide films subsequently caused remarkable increase in sheet resistance, which deteriorated the fill factor of the CIGS solar cells. The decreasing PAr reduced the tensile intrinsic stress in the Mo layer, preventing the detrimental crack formation and improving the fill factor of the CIGS solar cells on the flexible polyimide substrates. The stress condition of the Mo was also found to influence thermal diffusion of alkali metal through the contact. The impact of the Mo stress on alkali metal diffusion was adjustable by varying the thickness of alkali silicate thin layers and/or alkali-metal postdeposition treatment conditions, improving conversion efficiency.

Review of technology specific degradation in crystalline silicon, cadmium telluride, copper indium gallium selenide, dye sensitised, organic and perovskite solar cells in photovoltaic modules: Understanding how reliability improvements in mature technologies can enhance emerging technologies

AbstractA comprehensive understanding of failure modes of solar photovoltaic (PV) modules is key to extending their operational lifetime in the field. In this review, first, specific failure modes associated with mature PV technologies, such as crystalline silicon (c‐Si), copper indium gallium selenide (CIGS) and cadmium telluride (CdTe), are framed by sources of specific failure modes, their development from the early‐developmental stages onwards and their impact upon long term performance of PV modules. These failure modes are sorted by both PV technology and location of occurrence in PV modules, such as substrate, encapsulant, front and rear electrode, absorber and interlayers. The second part of the review is focused on emerging PV technologies, such as perovskites solar cells, dye sensitised and organic PVs, where due to their low to medium technology readiness levels, specific long‐term degradation mechanisms have not fully emerged, and most mechanisms are only partially understood. However, an in‐depth summary of the known stability challenges associated with each emerging PV technology is presented. Finally, in this paper, lessons learned from mature PV technologies are reviewed, and considerations are given in to how these might be applied to the further development of emerging technologies. Namely, any emerging PV technology must eventually pass industry‐standard qualification tests, while warranties for the lifetime of modern c‐Si‐based modules might be extended beyond the existing warranted life of 25 years.

Life cycle impact of photovoltaic module degradation on energy and environmental metrics

This paper presents the effect of photovoltaic (PV) module degradation on the cumulative energy demand and greenhouse gas emissions of a 4.2 kW dc roof-mounted grid-connected PV system. The estimated lifetime energy generation is coupled with life cycle assessment (LCA) as a way to evaluate the energy consumption and environmental impact. Three cases were evaluated; Case 1 considers the PV module degradation while assuming similar performance ratio (PR) for all conditions; Case 2 represents the most realistic case that considers the degradation and other factors affecting PR; and Case 3 serves as the worst-case scenario where the module degradation is neglected. Furthermore, four different types of PV modules were compared, i.e. mono-crystalline silicon, multi-crystalline silicon, cadmium telluride and copper indium selenide. In this work, system installations in five different countries from several regions were simulated. When applying the Cumulative Energy Demand 1.11 and Intergovernmental Panel on Climate Change 2013 methods, the cumulative energy demand and greenhouse gas emissions vary from 0.341 to 1.457 MJ/kWh and from 20.95 to 90.45 g CO2-eq/kWh respectively across different cases, PV module types and countries. It is found that neglecting the PV module degradation factor in performing LCA of PV system causes a significant underestimation. Also, PV module with a lower degradation rate showed low effect on the metrics. In addition, the metrics also vary with installations in different countries, mainly due to varying irradiation and ambient temperature factors.

Mixed Solvents Assisted Post-Treatment Enables High-Efficiency Single-Junction Perovskite and 4T Perovskite/CIGS Tandem Solar Cells.

The interface between the perovskite layer and the hole transport layer (HTL) plays a vital role in hole extraction and electron blocking in perovskite solar cells (PSCs), and it is particularly susceptible to harmful defects. Surface passivation is an effective strategy for addressing the above concerns. However, because of its strong polarity, isopropyl alcohol (IPA) is used as a solvent in all of the surface treatment materials reported thus far, and it frequently damages the surface of perovskite. In this paper, a method is proposed for dissolving the passivation materials, for example, guanidine bromide (GABr), in mixed solvents (1:1) of IPA and toluene (TL), which can efficiently passivate interface and grain boundary defects by minimizing the IPA solubility of the perovskite surface. As a result, all the performance parameters Voc, Jsc, and FF are improved, and the power conversion efficiency (PCE) increased from 20.1 to 22.7%. Moreover, combining the PSCs with GABr post‐treatment in mixed solvents with copper indium gallium selenide (CIGS) solar cells, a 4‐terminal (4T) perovskite/CIGS tandem device is realized and a PCE of 25.5% is achieved. The mixed solvent passivation strategy demonstrated here, hopefully, will open new avenues for improving PSCs’ efficiency and stability.

Wide‐Gap Chalcopyrite Solar Cells with Indium Oxide–Based Transparent Back Contacts

Herein, the performance of wide‐gap Cu(In,Ga)Se2 (CIGS) and (Ag,Cu)(In,Ga)Se2 (ACIGS) solar cells with In2O3:Sn (ITO) and In2O3:H (IOH) as transparent back contact (TBC) materials is evaluated. Since both TBCs restrict sodium in‐diffusion from the glass substrate, fine‐tuning of a NaF precursor layer is crucial. It is found that the optimum Na supply is lower for ACIGS than for CIGS samples. An excessive sodium amount deteriorates the solar cell performance, presumably by facilitating GaO x growth at the TBC/absorber interface. The efficiency (η) further depends on the absorber stoichiometry, with highest fill factors (and η) reached for close‐stoichiometric compositions. An ACIGS solar cell with η = 12% at a bandgap of 1.44 eV is processed, using IOH as a TBC. The best CIGS device reaches η = 11.2% on ITO. Due to its very high infrared transparency, IOH is judged superior to ITO for implementation in a top cell of a tandem device. However, while ITO layers maintain their conductivity, IOH films show an increased sheet resistance after absorber deposition. Chemical investigations indicate that incorporation of Se during the initial stage of absorber processing may be responsible for the deteriorated conductivity of the IOH back contact in the final device.