Improved efficiency of Cu(In,Ga)Se{sub}2 thin film solar cells with chemically deposited ZnS buffer layers by air-annealing -formation of homojunction by solid phase diffusion

摘要

We found that a role of the annealing process in CBD-ZnS/CIGS solar cells is the diffusion of Zn and S into CIGS thin films even at relatively low temperature of 200°C. A new technique to form a homojunction of CIGS thin film solar cells by Zn-diffusion from ZnS layer is proposed. 17.7 % efficiency Cd-free CIGS solar cell has been fabricated by optimizing the annealing process, thickness of buffer layers, and CIGS absorber layers. This result suggests that high efficiency CIGS thin film solar cells can be achieved even if Cd is not utilized.