Two-stage method to enhance the grain size of Cu(In,Ga)Se2 absorbers based on sputtering quaternary Cu(In,Ga)Se2 target

Preparing CIGS thin films with grain size above 1 μm based on quaternary CIGS target is difficult, which is a barrier for the further enhancement of CIGS cell efficiency. We proposed a two-stage method to overcome this problem. Cu-rich CIGS thin film was prepared from quaternary CIGS and Cu target and then converted into Cu-poor CIGS by depositing the In2Se3 layer on the Cu-rich CIGS with the subsequent annealing. CIGS absorbers with micrometer-sized crystal based on quaternary CIGS target was prepared. The influence of the In2Se3 deposition on the physical properties of the CIGS absorber and CIGS cells has been investigated. The thickness of In2Se3 layer has been optimized which can result in the highest conversion efficiency of 9.5% in Cu-rich CIGS based solar cells.