Thin-film solar cells (TFSCs) represent a promising frontier in renewable energy technologies due to their potential for cost reduction, material efficiency, and adaptability. This literature review examines the key materials and advancements that make up TFSC technologies, with a focus on Cu(In,Ga)Se₂ (CIGS), cadmium telluride (CdTe), and Cu₂ZnSnS₄ (CZTS) and its sulfo-selenide counterpart Cu₂ZnSn(S,Se)₄ (CZTSSe). Each material’s unique properties—including tuneable bandgaps, high absorption coefficients, and low-cost scalability—make them viable candidates for a wide range of applications, from building-integrated photovoltaics (BIPV) to portable energy solutions. This review explores recent progress in the enhancement of power conversion efficiency (PCE), particularly through bandgap engineering, alkali metal doping, and interface optimization. Key innovations such as silver (Ag) alloying in CIGS, selenium (Se) alloying in CdTe, and sulfur (S) to Se ratio optimization in CZTSSe have driven PCE improvements and expanded the range of practical uses. Additionally, the adaptability of TFSCs for roll-to-roll manufacturing on flexible substrates has further cemented their role in advancing renewable energy adoption. Challenges remain, including environmental concerns, but ongoing research addresses these limitations, paving the way for TFSCs to become a crucial technology for transitioning to sustainable energy systems.

The demand for sustainable and cost-effective materials for photovoltaic technology has led to an increasing interest in Cu₃BiS₃ thin films as potential absorber layers. This review provides a comprehensive overview of the main physical properties, synthesis methods, and theoretical studies of Cu₃BiS₃ thin films for photovoltaic applications. The high optical absorption coefficient and band gap energy around the optimal 1.4 eV make Cu₃BiS₃ orthorhombic Wittichenite-phase a promising viable alternative to conventional thin film absorber materials such as CIGS, CZTS, and CdTe. Several synthesis techniques, including sputtering, thermal evaporation, spin coating, chemical bath deposition, and spray deposition, are discussed, highlighting their impact on film quality and photovoltaic performance. Density Functional Theory studies offer insights into the electronic structure and optical properties of Cu₃BiS₃, aiding in the understanding of its potential for photovoltaic applications. Additionally, theoretical modeling of Cu3BiS3-based photovoltaic cells suggests promising efficiencies, although experimental challenges remain to be addressed. Overall, this review underscores the potential of CBS thin films as sustainable and cost-effective materials for future PV technology while also outlining the ongoing research efforts and remaining challenges in this field.

In response to the increasing demand for sustainable energy solutions, Cu₃BiS₃ (CBS) films emerge as a promising alternative for cost-effective and eco-friendly photovoltaic absorbers. This work explores the synthesis and characterization of CBS films via sulfurization of metallic Cu and Bi precursors deposited using electron beam evaporation. We investigated the effects of both duration and temperature during the Rapid Thermal Processing (RTP) sulfurization. Using SEM/EDS, XRD, Raman spectroscopy, and UV-VIS-NIR transmittance measurements, we demonstrate the successful formation of the CBS Wittichenite phase with band gap energies $$\:{E}_{g}\approx\:1.4\:eV$$ , and absorption coefficients $$\:\alpha\:\ge\:{10}^{4}\:{cm}^{-1}$$ , highlighting the CBS potential as a viable alternative as a photovoltaic absorber. We achieved films with the dominant CBS phase, with large highly crystalline grains but still containing some undesired copper sulphide secondary phases. These films were obtained at low RTP temperatures (350 °C) and short durations (5 min), ensuring both time and energy efficient consumption, in contrast to commonly reported lengthy, high-temperature processes. Graphical abstract

Cu₃BiS₃ (CBS) has emerged as a promising earth-abundant absorber for thin-film photovoltaics, offering a sustainable alternative to conventional technologies. However, ab initio studies on its optoelectronic properties remain scarce and often yield contradictory results. This study systematically examines the influence of two density functional theory (DFT) methodologies, linear combination of atomic orbitals (LCAO) and projector augmented wave (PAW), on the structural and electronic properties of CBS, aiming to establish a reliable computational framework for future research. With this in mind, we also assessed the impact of a wide range of exchange-correlation (XC) functionals within both methods, including 6 from the local density approximation (LDA) family (HL, PW, PZ, RPA, Wigner, XA), 10 from the generalized gradient approximation (GGA) family (BLYP, BP86, BPW91, GAM, KT2, PBE, PBEsol, PW91, RPBE, XLYP), 2 meta-GGA functionals (SCAN, R2SCAN), and the hybrid HSE06 functional. Both LCAO and PAW consistently predict an indirect bandgap for CBS across all XC functionals, aligning with most previous DFT studies but contradicting experimental reports of a direct transition. The LDA and meta-GGA functionals systematically underestimated the CBS bandgap (<1 eV), with further reductions upon structural relaxation. GGA functionals performed better, with BLYP and XLYP yielding the most experimentally consistent results. The hybrid HSE06 functional substantially overestimated the bandgap (1.9 eV), with minimal changes after relaxation. The calculated hole and electron effective masses reveal strong anisotropy along the X, Y, and Z crystallographic directions. Additionally, CBS exhibits an intrinsic p-type nature, as the Fermi level consistently lies closer to the valence band maximum across all methods and functionals. However, the PAW method generally predicted more accurate lattice parameters than LCAO; the best agreement with experimental values was achieved using the PW91 (1.2% deviation) and HSE06 (0.9% deviation) functionals within LCAO. Based on these findings, we recommend the PW91 functional with LCAO for structural optimizations in large supercell studies of CBS dopants and/or defects and BLYP/XLYP for electronic properties.