Influence of KCN treatment on CuInS2 thin films

Electrical and compositional properties as well as solar cell performances were studied on polycrystalline CuInS2 films synthesized by sulphurization of copper and indium sandwiches. To study the influence of KCN treatment, each of the samples was divided into two pieces, where one was treated with KCN, and their properties were compared. KCN treatment lowered the initial Cu/In composition ratio which ranged between 1 and 2.1 to slightly less than 1. Also, it increased the resistivity by two orders of magnitude, which is due to the reduction of the carrier concentration by three orders of magnitude. The X-ray diffraction line width is narrowed as well. These results indicate that some CuxS and/or copper are etched during the KCN treatment. Solar cells were fabricated with a chemical bath deposited CdS buffer layer and an atom beam sputtered ZnO window on the CuInS2 thin films. The solar cell conversion efficiency was increased from eta = 2.1% (3.9% after vacuum annealing) to eta = 5.8%.