Waste- and Cd-Free Inkjet-Printed Zn(O,S) Buffer for Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells

Thin film semiconductors grown using chemical bath methods produce large amounts of waste solvent and chemicals that then require costly waste processing. We replace the toxic chemical bath deposited CdS buffer layer from our Cu(In,Ga)(S,Se)2 (CIGS)-based solar cells with a benign inkjet-printed and annealed Zn(O,S) layer using 230 000 times less solvent and 64 000 times less chemicals. The wetting and final thickness of the Zn(O,S) layer on the CIGS is controlled by a UV ozone treatment and the drop spacing, whereas the annealing temperature and atmosphere determine the final chemical composition and band gap. The best solar cell using a Zn(O,S) air-annealed layer had an efficiency of 11%, which is similar to the best conventional CdS buffer layer device fabricated in the same batch. Improving the Zn(O,S) wetting and annealing conditions resulted in the best device efficiency of 13.5%, showing the potential of this method.