Characterizations of chemical bath-deposited zinc oxysulfide films and the effects of their annealing on copper-indium-gallium-selenide solar cell efficiency

Zinc oxysulfide (Zn(S,O)) thin films are fabricated using a chemical bath deposition method onto glass substrates and the surface of copper-indium- gallium-selenide (CIGS) adsorption layers for solar cell fabrication. The light and electric properties of the Zn(S,O) layers are improved after rapid thermal annealing (RTA). The Zn(S,O) properties of samples annealed under various atmospheres are compared. The resulting annealed Zn(S,O) films are 80-100 nm thick. The band gap decreases from 3.8 eV to 3.3 eV and the light transmittance is improved by more than 95% after annealing under oxygen atmosphere. The oxygen-annealed sample has a S/(S + O) ratio of 0.28 and a S/Zn ratio of 0.72. The CIGS solar cell that consists of the annealed Zn(S,O) buffer layer is more efficient (6.15%) than that of the non-annealed Zn(S,O) (4.56%). The solar cell performance is correlated with the deposited Zn(S,O) characteristics. The significantly higher carrier concentration, increases light transmittance, and improves crystalline structure of the oxygen-annealed Zn(S,O) film contributes to the improved cell performance.