A novel selenization-free chalcopyrite CIGSSe formation in a heat-treated Cu2Se/S/Ga3Se2/S/In3Se2 multilayer thin film (ML) and ML/n-Si heterojunction characteristics

•A selenization-free route is used to fabricate a phase of pure chalcopyrite copper indium gallium sulphur selenide (CIGSSe) thin film structures by facile thermal annealing in high vacuum conditions.•The preferential (112) plane orientation is evident from the X-ray diffraction (XRD) analysis.•UV–Vis spectroscopy has revealed high transparency in the infrared (IR) region, and disorders drastically reduced from 189 meV to 59 meV.•Hall measurements have revealed significant evidence by displaying a transformation of n-type to p-type charge carriers upon annealing.•Non-linear rectifying behaviour is confirmed in both cases and the lowest ideality factor of 2.86 for annealed thin film structure upon light illumination. Selenization or sulphurization is a standard method for developing copper-selenium-based ternary to quinary compounds. The route proved effective, but there are concerns about the high-risk management and potential explosion if mishandled. This article discusses a selenization/sulphurization-free fabrication of a CIGSSe thin film structure. Instead of selenization, a Cu2Se/S/Ga3Se2/S/In3Se2 multilayer thin film structure is chosen, and a simple post-annealing in high vacuum is used. The x-ray diffraction analysis hinted at a composite structure in as-deposited and a phase pure dominant chalcopyrite structure in the annealed film. The bandgap of 1.71 eV with a high absorption coefficient of 104/cm with smaller Urbach energy of 59 meV supports the dominant microstructure of the annealed thin film. Room temperature hall measurements also ensured the charge carrier transformation of n-type to p-type during annealing with the carrier concentration of 1016/cm3. The Au/p-CIGS/n-Si/Au heterojunction is developed, and current-voltage measurements are investigated. [Display omitted]