Zn(O,S) buffer layers grown by atomic layer deposition in Cu2ZnSn(S,Se)4 thin film solar cells

A solar cell is an electrical device that converts light energy into electricity. One of the crucial parts of realizing high-performance thin-film-based solar cells is an n-type buffer layer. Instead of the widely used, but toxic CdS buffer layer, we investigated the possibility of using Zn(O,S) as an alternative material grown by atomic layer deposition (ALD). First of all, structural, electrical, chemical, and optical properties of Zn(O,S) thin films were studied. In addition, this new buffer layer was applied for earth-abundant Cu₂ZnSn(S,Se)₄ solar cells and the highest power-conversion efficiency (PCE, η) of ~2.7% was achieved by optimizing oxygen-to-sulfur (O/S) ratio.