Role of the intermediate phases InSe and Cu9(In1−xGax)4 in fabricating Cu(In1−xGax)Se2 films by selenization of Cu–In–Ga precursors

Abstract

A cosputtered Cu–In–Ga metal precursor was first selenized in H2Se atmosphere, and then subsequently annealed in N2 atmosphere. The microstructural evolution of Cu(In1−xGax)Se2 (CIGS) films during thermal treatment was investigated, and it was found that the morphology and Ga distribution of the CIGS absorber were governed by selenization and annealing. The intermediate phases InSe and Cu9(In1−xGax)4 formed in the selenization step are beneficial to Ga diffusion and grain growth during annealing. Therefore, the open-circuit voltage and fill factor of a CIGS solar cell were enhanced by the combination of a sufficient amount of intermediate phases and 580 °C annealing, attributed mainly to the higher Ga content near the front surface and better crystallinity of the CIGS absorber. The conversion efficiency of CIGS solar cell was increased 1.24-fold with optimized selenization and annealing conditions.