Recent progress and challenges in CIGS and CZTS thin film photovoltaic technologies. Review

This review provides a comprehensive analysis of the current state, progress, and challenges of thin-film solar cells based on Cu(In,Ga)Se₂ (CIGS) and Cu₂ZnSn(S,Se)₄ (CZTS(Se)) absorber materials. The study highlights the global transition toward renewable energy, emphasizing the advantages of thin-film photovoltaic technologies as cost-effective, material-efficient, and flexible alternatives to conventional crystalline silicon solar cells. CIGS-based devices demonstrate high power conversion efficiencies exceeding 23%, wide tunability of the bandgap, and excellent long-term stability, making them among the most mature thin-film technologies. However, their dependence on scarce and costly elements such as indium and gallium motivates research into earth-abundant alternatives. CZTS(Se) materials, composed of non-toxic and widely available elements (Cu, Zn, Sn, S, Se), offer a sustainable substitute with comparable optical properties and tunable bandgaps (1.0–1.5 eV). Despite lower efficiencies (currently up to 15.8%), ongoing progress in controlling phase purity, defect passivation, and band alignment is rapidly improving device performance. Key research directions include the optimization of absorber synthesis, defect engineering, alkali-metal and cation doping, and development of environmentally benign, cadmium-free device architectures. The review outlines both the technological maturity of CIGS and the emerging potential of CZTS(Se), identifying critical challenges and future pathways toward high-efficiency, sustainable thin-film photovoltaics.