High-efficiency cadmium-free Cu(In,Ga)Se/sub 2/ thin-film solar cells with chemically deposited ZnS buffer layers

Cadmium-free Cu(In,Ga)Se/sub 2/ (CICS) thin-film solar cells with a MgF/sub 2//ZnO:Al/CBD-ZnS/CIGS/Mo/SLG structure have been fabricated using chemical bath deposition (CBD)-ZnS buffer layers and high-quality CICS absorber layers grown using molecular beam epitaxy (MBE) system. The use of CBD-ZnS, which is a wider band gap material than CBD-CdS, improved the quantum efficiency of fabricated cells at short wavelengths, leading to an increase in the short-circuit current. The best cell at present yielded an active area efficiency of 16.9% which is the highest value reported previously for Cd-free CIGS thin-film solar cells. The as-fabricated solar cells exhibited a reversible light-soaking effect under AM 1.5, 100 mW/cm/sup 2/ illumination. This paper also presents a discussion of the issues relating to the use of the CBD-ZnS buffer material for improving device performance.