Role of in-situ substrate heating and selenium-free annealing on the growth of MoSe2 interlayer in sputtered Cu(In,Ga)Se2 solar cells

Chalcopyrite Cu(In,Ga)Se 2 or CIGSe solar cells (SCs) have demonstrated significant potential in thin film (TF) photovoltaic technologies, achieving record solar cell efficiencies of 23.6 % and commercial solar modules with efficiencies of 19.2 %. Despite these high-efficiency levels, the full potential of CIGSe-based PV technology has not yet been realized, as it is limited by losses related to optics, parasitics, and recombination. This work examines the effects of heat treatment on the electrical and microstructural properties of Mo TFs sputtered by DC, which are crucial as the back-contact layer in CIGSe SCs. Substrate heating and in-situ annealing are suggested during the DC sputtering of Mo TFs, and the results demonstrate a significant improvement in TF crystallinity, minimisation of microstrain, and decreased dislocation density, particularly in the (110) crystal orientation, which enhances electrical resistivity. In contrast to predicted behaviour, films annealed at 500 °C showed unexpectedly lengthy, fibrous grain structures with porosity. Findings here emphasize the significance of heat during and after the deposition process to improve the Mo film microstructure, which influences the electrical performance and interfacial properties of the back-contact layer in CIGSe SCs. Optimizing the microstructural growth of Mo films is essential to raising the stability and efficiency of CIGSE-based solar systems. • Demonstrates selenium-free annealing as a sustainable method for MoSe 2 interlayer formation in CIGSe solar cells. • Reveals the influence of in-situ substrate heating on Mo film morphology and crystallinity. • Establishes clear correlation between processing conditions and interfacial/electrical properties. • Reports novel stress-induced formation of porous, fibrous MoSe 2 grains at 500 °C.