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The efficiency of perovskite solar cells has increased to a certified value of 27% over the past decade, benefiting from the superior properties of metal halide perovskite materials. However, their long-term operational stability is still far inferior to that of commercial crystalline silicon solar cells. A key source of this instability is field-driven ion migration in vertical architectures, along with the consequent degradation at the absorber–electrode interfaces. Compared with the widely investigated vertical structures, back-contacted (BC) perovskite solar cells—wherein both electrodes are positioned on the same side of the absorber—offer a unique route to suppress interfacial ion migration and thereby enhance long-term device stability. These advantages are especially pronounced when combined with single-crystal perovskites, which possess low charge trap densities, long carrier diffusion lengths, and high bulk ion migration barriers. Unfortunately, only a handful of research groups have participated in the development of single-crystal BC perovskite solar cells; thus, the advancement of this area lags far behind that of its vertical counterpart. Therefore, a review that discusses the recent developments and challenges of single-crystal BC perovskite solar cells is urgently required to provide guidelines for this emerging field. In this progress report, we first introduce the main growth methods of single-crystal wafers compatible with BC architectures, followed by an outline of the developmental history of BC perovskite solar cells. Finally, the core bottlenecks facing single-crystal BC devices and corresponding optimization strategies are discussed in detail. Full article

Thin-film solar cells (TFSCs) remain a cornerstone of the global transition toward renewable energy, characterized by consistent reductions in manufacturing costs and steady gains in power conversion efficiency. In addition to electricity generation, TFSCs play an important role in advanced solar thermal cooling, heating, and energy storage systems, where their tunable optical absorption, low thermal mass, and flexibility enable integration with photovoltaic–thermal (PV/T) collectors, thermally driven cooling cycles, and hybrid thermal–electrical storage architectures. This paper provides a comprehensive review of prominent TFSC technologies, including copper indium gallium selenide (CIGS), cadmium telluride (CdTe/CdS), amorphous silicon (a-Si), copper zinc tin sulfide (CZTS), organic photovoltaics (OPVs), and metal halide perovskite solar cells (PSCs), with a focus on their material structures, performance specifications, and current efficiency benchmarks. Compared to state-of-the-art reviews, this article distinguishes itself by addressing next-generation innovations, cross-domain solar thermal–photovoltaic applications, and economic analysis. Specifically, the integration of machine learning and simulation-based material dynamics is examined to accelerate material discovery, process optimization, and the characterization of novel TFPV components relevant to coupled thermal–electrical energy systems. Furthermore, the study explores how additive manufacturing is transforming the industry through the development of high-efficiency electrodes, electrohydrodynamic atomization for thin-film deposition, and the fabrication of flexible solar arrays suitable for thermally integrated and building-scale energy systems, including space applications. By integrating advancements in module efficiency, scalable manufacturing approaches, and techno-economic analysis, this paper positions TFSCs as sustainable, resource-abundant technologies essential for next-generation solar thermal cooling, heating, and energy storage infrastructures. Full article

The substrate plays a critical yet often underappreciated role in determining the performance, stability and manufacturability of photovoltaic devices. While conventional glass and polymer films have enabled the rapid development of solar technologies, emerging applications such as building-integrated photovoltaics, wearable systems and large-area conformal devices demand the use of non-conventional substrates, including ceramics, metals, paper, textiles and elastomeric materials. This review provides a comprehensive analysis of the current state of the art of non-conventional substrates for photovoltaic technologies, with particular emphasis on the interplay between material properties, surface chemistry and deposition processes. These substrates introduce distinct mechanical, thermal and interfacial constraints that fundamentally alter thin-film growth, defect formation and device reliability. Key challenges such as porosity, roughness, thermal transport limitations and outgassing are discussed in relation to nucleation, film continuity and interfacial stability. The role of substrate-dependent effects in both chemical and physical deposition techniques is critically examined, highlighting cases where conventional processing approaches are insufficient. Representative device demonstrations are analyzed to illustrate how substrate selection influences performance and integration strategies across different photovoltaic platforms. Finally, common limitations and emerging opportunities are identified, emphasizing the need for the co-design of substrates, materials and processing routes. This work establishes a unified framework to guide the development of next-generation photovoltaic devices on unconventional substrates. Full article

Chalcopyrite-based thin-film solar cells have great potential for various applications, such as top or bottom cells in tandem devices, in addition to their use as standard single-junction modules due to their tuneable bandgap energy. A bandgap energy E_g > 1.5 eV should be targeted to realize a wide-bandgap top cell, e.g., by increasing the [Ga]/([Ga] + [In]) (GGI) ratio in Cu(In,Ga)Se₂ (CIGS) cells to the range of 0.7–1. A second approach is targeting the second theoretical efficiency maximum at a little lower E_g = 1.34 eV with a GGI around 0.6 for high-efficiency single-junction applications with reduced electrical losses. An industry-relevant (Ag,Cu)(In,Ga)Se₂ (ACIGS) co-evaporation process for wide-bandgap cells fabricated with GGI ratios above 0.6, with moderate [Ag]/([Ag] + [Cu]) (AAC) ratios < 0.1 and in-line RbF-PDT, was established on molybdenum-coated soda-lime glass substrates. Both measures, Ag alloying and RbF-PDT, can increase power conversion efficiency (PCE) mainly due to improved open-circuit voltage (V_OC). In addition, Ag addition can increase fill factor (FF)_, leading to an increase in the PCE for cells with GGI > 0.6 compared to Ag-free reference cells. (Zn,Mg)O, either with a [Mg]/([Mg] + [Zn]) ratio of 0.15 or 0.25, is a good option as high-resistive layer replacing the commonly used i-ZnO in combination with a CdS buffer. Our best ACIGS wide-bandgap solar cells with RbF-PDT and Zn_0.85Mg_0.15O (without anti-reflective coating (ARC)) from various experimental campaigns show a PCE of 12.7% (E_g = 1.50 eV), and with a slightly reduced E_g of 1.45 eV a PCE of 15.5%, with V_OC of 933 mV (V_OC deficit of 517 mV), and a good FF of 73.2%. In the case when the bandgap is significantly lowered to 1.34 eV (GGI = 0.61), to the second theoretical efficiency maximum, we achieved a PCE of 18.2% with ARC for an Ag-free CIGS cell with RbF-PDT. For this cell with a CdS/i-ZnO buffer system the V_OC deficit is 480 mV, and the FF is 78.1%. Full article

In this study, the PV performance of Au/BSF/CTS/CdS/i-ZnO/ITO thin-film solar cell (TFC) structure was systematically investigated using SCAPS-1D software. The effects of several critical parameters, including interface defect density, recombination mechanisms, absorber defect density, operating temperature, parasitic resistances, and different back surface field (BSF) layers, were comprehensively analyzed. The SCAPS-1D software results reveal that the photovoltaic performance is highly sensitive to the defect density at the absorber layer interface. When the interface defect density increased from 10¹² cm⁻³ to 10¹⁶ cm⁻³, the open-circuit voltage ($V_{OC}$) decreased from approximately 0.68 V to 0.45 V, while the power conversion efficiency (PCE) declined from nearly 19% to about 7%. Similarly, an increase in absorber defect density enhanced the Shockley–Read–Hall recombination rate, thereby reducing carrier lifetime and significantly deteriorating PV parameters. The influence of radiative and Auger recombination ($B_{Auger}$) processes was also examined, revealing that higher recombination coefficients lead to substantial reductions in current density and efficiency due to increased carrier losses. Furthermore, the impact of parasitic resistances was evaluated, demonstrating that decrease the series resistance from 9.5 Ω·cm² to 0.5 Ω·cm² increased the fill factor ($FF$) from about 48% to nearly 78%, while the device efficiency improved to approximately 32%. In addition to these parameters, particular emphasis was placed on the investigation of different BSF materials to enhance back contact performance. Various BSF layers, including SnS, PbS, V₂O₅, and Sb₂S₃, were examined to improve band alignment and suppress minority carrier recombination at the rear interface. Among these materials, the SnS BSF layer provided the most favorable band alignment with the CTS absorber, leading to a notable improvement in PV parameters and increasing the efficiency to approximately 25%. Overall, the results demonstrate that optimizing defect densities, recombination mechanisms, parasitic resistances, and especially the selection of appropriate BSF materials plays a crucial role in improving the performance of CTS-based TFCs. Full article

The ambient stability of ambient-processed lead-free perovskite absorbers remains a critical challenge toward scalable, eco-friendly photovoltaics. Herein, we systematically investigate the time-dependent structural and morphological evolution of drop-cast ambient-processed Cs₃Sb₂I₉ thin films, being a potential non-toxic and stable solar absorber candidate (energy bandgap ~2 eV) for solar cells, stored under uncontrolled ambient condition (~60% Relative humidity) for 28 days. Sequential X-ray diffraction (XRD) and surface morphology analyses using scanning electron microscope (SEM) reveal that the films preserve their trigonal P$\overline{3}$m1 phase throughout aging, confirming phase stability. Moderate moisture exposure may induce partial recrystallization and subtle structural reorganization, possibly including minor c-axis realignment, leading to reduced lattice strain and improved crystallite coherence. Even after prolonged aging, no secondary phases or micro-cracks are detected, underscoring the slow degradation kinetics and robust Sb–I bonding that stabilize the layered [Sb₂I₉]³⁻ dimers. The late-stage increase in diffraction intensity and partial recovery of crystallographic parameters could indicate transient structural reorganization, potentially associated with moisture-mediated reordering within an overall degradation pathway. These observations suggest some degree of morphological persistence and structural tolerance of Cs₃Sb₂I₉ under ambient conditions, rather than complete stability. This behavior offers useful insights into ambient processing and the long-term reliability of lead-free perovskite photovoltaics. Full article

Organic-type solar cells containing an active layer of block copolymer donor PTB7-Fx (x = 0, 20, and 100), based on benzo [1,2-b:4,5-b’]dithiophene and variably fluorinated thieno [3,4-b]thiophene units, and fullerene acceptor [6,6]phenyl-C₇₁-methylbutyrate, were constructed. The active layer thin film of the solar cells was obtained from a dichlorobenzene solution at an established concentration via spin-coating of the donor–acceptor mixture in the presence of solvent additives such as 3% diiodooctane and 1% triethyl phosphate. Organic photovoltaic elements with normal device architecture were prepared on glass substrates using an indium tin oxide anode, a spin-coated hole transporting layer of poly(ethylene dioxythiophene):polystyrenesulfonate, the aforementioned active layer, followed by an electron transporting layer of zinc oxide nanoparticles, and finally a magnetron sputtered silver (Ag) top-electrode. The optical properties, thin film morphology, and the thickness of the active layers were investigated. Additionally, current density–voltage characteristics and impedance spectra of photovoltaic devices were measured. It was found that PTB7-Fx:PC₇₁BM-based solar cells processed in the presence of two types of solvent additives, diiodooctane and triethyl phosphate, with a sputtered Ag top-electrode display similar absorption and quantum efficiency spectra, as well as comparable current density–voltage characteristics and efficiencies to the same devices fabricated without additives. The diiodooctane solvent additive preferably dissolves the fullerene component and has a positive effect on fill factor enhancement, impedance spectra improvement, and amelioration in charge carrier transport and collection, whereas the triethyl phosphate solvent additive preferentially dissolves the copolymer donor and has a more pronounced impact on the refined morphology of the thin film active layers. Full article

Perovskite solar cells (PSCs) have quickly achieved certified energy conversion efficiency reaching a certified record of 27.3% for single-junction cells, while having a low mass, thin-film form factor and high specific power, which are attractive for space energy systems. However, their long-term reliability in extraterrestrial environments is not adequately ensured by terrestrial qualification routes, and standardized space-related test protocols remain insufficiently developed. This review critically summarizes the current understanding of the degradation of PSCs under the influence of key environmental factors in space—ionizing and non-ionizing radiation, thermal vacuum exposure and thermal cycling, and ultraviolet radiation AM0, as well as atmospheric oxygen in low orbits. The central task of the work is to develop and justify the need to create specialized PSCs test protocols for space applications, since existing ground standards do not reflect the multifactorial nature and extreme orbital loads. It has been shown that thermal vacuum accelerates ion migration, interphase reactions, and degassing, while AM0 UV and atomic oxygen introduce additional photochemical and oxidative mechanisms of destruction; at the same time, stressors often act synergistically and are not detected by single-factor tests. Next, the limitations of the current IEC and ISOS are discussed and an approach to their expansion is formulated through the ISOS-T-Space and ISOS-LC-Space protocols, which integrate high vacuum, AM0 lighting, extended temperature ranges and controlled particle irradiation. It is concluded that the development and interlaboratory validation of such space-oriented protocols is a key condition for the correct qualification of PSCs and targeted optimization of materials and interfaces to meet the requirements of space energy. Full article

Indium Tin Oxide (ITO) is one of the most widely used ohmic materials for fabricating ohmic layers in thin-film solar cells. ITO thin layers have reached almost the maximum theoretical conductivity and the lowest practical resistivity. Along with indium’s toxic environmental impact and the high cost of materials, these are the reasons why new materials for efficient, cheaper thin-film transparent ohmic layers are being examined. One of those materials is copper-doped zinc oxide (ZnO:Cu). In this paper, we present a new approach to copper-doped zinc oxide fabrication methods, based on the modern authorial Physical Vapor Co-Deposition technique, which involves optimizing Cu concentration to fine-tune crystal structure, optical band gap, and electrical properties, creating n-type TCOs essential for efficient charge transport in next-generation thin films perovskite solar cells. Full article

Cu₂ZnSn(S,Se)₄ (CZTSSe) is a candidate thin-film photovoltaic material; however, its performance is restricted by innate defect-induced nonradiative recombination. Low-concentration Ge doping has been identified as an efficient way to mitigate these defects, but the selenization temperature remains an important process parameter that governs the structure and optoelectronic characteristics of CZTSSe absorbers. In the present work, low-concentration Ge-doped Cu₂ZnSn_0.95Ge_0.05S₄ (CZTGS) precursor films were synthesized through a green, n-butylammonium butyrate-based solution approach. The effects of the selenization temperature (530–570 °C) on the microstructure, composition, and photovoltaic performance of Cu₂ZnSn_0.95Ge_0.05(S,Se)₄ (CZTGSSe) films and devices were comprehensively investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometer (EDS), atomic force microscopy (AFM) were performed to comprehensively characterize the synthesized samples, and the results suggested that the selenization temperature dramatically altered the film grain growth, crystallinity, elemental retention and surface roughness. Specifically, the film that underwent selenization at 550 °C presented the best crystallinity, which was accompanied by large-scale even grains, efficient Ge⁴⁺ addition to the kesterite lattice and the lowest surface roughness. These better properties in terms of structure and composition resulted in the lowest carrier transport resistance (R_s = 8.6 Ω∙cm²), improved recombination resistance (R_j = 5.9 kΩ∙cm²), inhibited nonradiative recombination, and prolonged carrier lifetime (τ_EIS = 35.8 μs). Therefore, the resulting CZTGSSe thin-film solar cell had an 8.69% better power conversion efficiency (PCE), while its open-circuit voltage (V_OC) was 0.42 V, the fill factor (FF) was 55.51%, and the short-circuit current density (J_SC) was 37.71 mA·cm⁻². Our results elucidate the mechanism by which the selenization temperature regulates low-concentration Ge-doped kesterite devices and provide more insights into the optimization of processes for cost-effective, high-performance, and green thin-film solar cells. Full article

Over the past two decades, organic semiconductors have attracted significant research interest due to their advantageous features, including low-cost fabrication, lightweight properties, and portability, for photonic device applications. In this study, nickel sulfide doped with cobalt $(\mathrm{N}\mathrm{i}\mathrm{S}/\mathrm{C}\mathrm{o})$ nanocomposites were successfully synthesized via a wet-chemical processing technique and used as a dopant in the active layer of thin-film organic solar cells (TFOSCs). The poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) blend was used as the active layer in this investigation. The devices were fabricated with $\mathrm{N}\mathrm{i}\mathrm{S}/\mathrm{C}\mathrm{o}$ nanocomposites at 1 wt%, 2 wt%, and 3 wt% in the active layer to determine the optimal dopant concentration. However, the experimental evidence clearly showed that the solar cell’s performance depends on the concentration of the $\mathrm{N}\mathrm{i}\mathrm{S}/\mathrm{C}\mathrm{o}$ nanocomposites. As a result, the highest power conversion efficiency (PCE) recorded in this experimental work was 6.11% at a 1% doping concentration, compared with 2.48% for the pristine reference device under AM 1.5G illumination (100 mW/cm²) in ambient conditions. The optical and electrical properties of the active layers are found to be strongly influenced by the inclusion of $\mathrm{N}\mathrm{i}\mathrm{S}/\mathrm{C}\mathrm{o}$ nanocomposites in the medium. However, the device doped with 1 wt% $\mathrm{N}\mathrm{i}\mathrm{S}/\mathrm{C}\mathrm{o}$ nanocomposite exhibits the highest absorption intensity, consistent with the better performance observed in this study, which can be attributed to the localized surface plasmon resonance (LSPR) effect. The optical and morphological characteristics of the synthesized $\mathrm{N}\mathrm{i}\mathrm{S}/\mathrm{C}\mathrm{o}$ nanocomposites were comprehensively analyzed using high-resolution transmission electron microscopy (HRTEM), high-resolution scanning electron microscopy (HRSEM), and additional complementary techniques. Full article

Metal–organic chemical vapor deposition (MOCVD) is a crystal growth technique used to achieve high-purity thin films, especially III–V materials, for fabricating semiconductor devices. It allows for thickness tunability, controlled doping, and composition of epilayers. This review focuses on the principle of MOCVD, its historical background, and its applications in III–V semiconductor devices such as solar cells, high electron mobility transistors (HEMTs), light-emitting diodes (LEDs), laser diodes (LDs), and photonic integrated circuits (PICs). This review highlights the recent developments in MOCVD aimed at improving its efficiency, performance, and sustainability. Finally, we emphasize emerging trends and challenges in MOCVD process innovation, reactor design, and material integration that are poised to drive the development of next-generation optoelectronic, photonic, and quantum technologies. Together, these findings underscore MOCVD’s pivotal role in enabling high-performance devices and sustaining leadership in post-Moore semiconductor technologies. Full article

In this work, a study of the chemical composition of the compound Sb₂(S_1−xSe_x)₃ used in thin-film solar cell fabrication, based on correlating data obtained from XRD and XPS analyses, is presented. This approach enables us to propose a mathematical expression for evaluating stoichiometric variations in the material, showing how the variable x evolves as a function of the diffraction angle 2θ. To establish this model, we analyzed the most intense diffraction peak, corresponding to the (221) plane. To validate the proposed method, a series of Sb₂(S_1−xSe_x)₃ thin films with different compositions were synthesized using RF-magnetron sputtering followed by conventional heat treatments in a controlled-atmosphere reaction furnace. The XRD results reveal a systematic 2θ shift in the crystalline diffraction peaks toward the positions of the binary precursor phases—from Sb₂Se₃ to Sb₂S₃—caused by the increased sulfur content during synthesis. XPS measurements confirm the presence of Sb, Se, and S, and high-resolution spectra indicate a decrease in selenium content as the sulfur fraction increases. These results allowed us to elucidate the stoichiometric behavior of antimony sulfoselenide Sb₂(S_1−xSe_x)₃ using trend curves fitted to the characterization data. Full article

The further development of scalable fabrication for perovskite solar cells has been considerably constrained by strong process variability and the lack of a reliable real-time predictive mechanism during the thin-film formation process. Existing machine learning-based methods are incapable of capturing the inherent multi-stage kinetic characteristics and uncertainties of the perovskite crystallization process, as they rely on deterministic point prediction models and flatten time-series signals into static features, which necessitates more advanced modeling strategies. To address these challenges, an in situ process monitoring and predictive modeling framework based on a lightweight probabilistic Transformer is proposed for the scalable preparation of perovskite thin films. The strategically designed inputs, consisting of time-resolved photoluminescence (PL) and diffuse reflectance imaging signals acquired during the vacuum quenching process, enable the model to directly learn the conditional probability distribution of the final device performance metrics. Rather than producing a single predicted value, this method enables the explicit quantification of prediction uncertainty, providing statistical support for uncertainty-aware process assessment. Leveraging its advantages over feed-forward neural networks and traditional tree-based machine learning methods, the proposed Transformer architecture effectively captures the staged and non-stationary kinetic features of thin-film formation. Consequently, it exhibits higher robustness and superior uncertainty calibration capability during the early-stage prediction phase. The results demonstrate that the probabilistic Transformer-based modeling paradigm provides a viable pathway toward uncertainty-aware, data-driven process evaluation in perovskite manufacturing. This framework extends its application beyond perovskite photovoltaic device fabrication, providing a generalizable modeling strategy for real-time predictive assessment in the preparation of other complex materials governed by irreversible stochastic dynamics. Full article

Cd-doped ZnS thin films (0–6 at.%) were deposited by SILAR and assessed as buffer layers for thin-film solar cells. XRD shows a single zinc-blende phase, with a small lattice expansion after Cd incorporation. As the Cd content increases, transmittance decreases and the direct band gap narrows, pushing absorption further into the visible. DFT with mBJ reproduces this redshift and attributes it to Cd-related states near the band edges. Hall measurements indicate stronger n-type transport at higher Cd levels, with lower resistivity, higher mobility, and a larger electron concentration. Overall, about 6% Cd provides a workable balance between transparency, absorption, and conductivity, making ZnS:Cd a suitable buffer-layer candidate. Full article