Rapid thermal annealing of CIGS thin film as an absorber layer without external selenization

Copper indium gallium diselenide (Cu(In, Ga)Se₂, CIGS) is a promising absorber material for thin-film photovoltaic applications owing to its tunable bandgap and high optical absorption coefficient. However, conventional fabrication of CIGS solar cells typically relies on vacuum-based deposition techniques followed by high-temperature selenization processes, which increase manufacturing cost, process complexity, and environmental concerns. In this study, a solution-based fabrication method that eliminates the need for conventional post-selenization is investigated by introducing intermediate spin-coated selenium (Se) ink layers within CIGS precursor films. The influence of inserting different numbers of Se interlayers (0, 3, and 7 spin-coating cycles) between CIGS precursor layers on film morphology, crystallinity, composition, and device performance was systematically examined. SEM and EDX analyses revealed increased grain size, improved film densification, and enhanced selenium incorporation with increasing numbers of Se interlayers. X-ray diffraction results confirmed improved crystallinity and phase purity, while optical measurements showed a gradual bandgap reduction from 1.238 eV to 1.203 eV with increasing selenium incorporation. The best-performing device (7Se/8CIGS) achieved a power conversion efficiency of 5.13%, which is significantly higher than that of the selenium-free device (3.15%). These results demonstrate that controlled selenium incorporation through spin-coated Se interlayers significantly enhances the structural quality and optoelectronic properties of solution-processed CIGS absorber layers. The proposed strategy provides a scalable and environmentally friendly route for fabricating CIGS thin-film solar cells without hazardous gas-phase selenization processes.