New Cd-free buffer layer deposited by PVD: In2S3 containing Na compounds

Abstract In this paper it is first shown that In2S3 containing sodium (BINS) thin films can be grown on glass substrates heated at 200 °C. The films have a n-type electrical conductivity and their optical band gap can be managed between 2.15 and 2.90 eV by controlling their sodium content. The wide band gap BINS films (Eg>2.5 eV) have interesting properties to be used as buffer layer in CIGS-based solar cells. In the aim of realizing efficient solar cells, the physico-chemical and electrical properties of Mo/CIGS/BINS structures have first been studied. Then solar cells are studied. For this first study, the thickness of the BINS buffer has been chosen as parameter, whereas the optical band gap of the BINS was constant at 2.8 eV. An efficiency of 8.2% has been reached with a 100 nm thick BINS buffer, while the efficiency of the cell with chemical bath deposited-CdS buffer was 10.2%.