Improvement of the open-circuit voltage of Cu2ZnSnS4 solar cells using a two-layer structure

In Cu2ZnSnS4 (CZTS) photovoltaic cells, a low open-circuit voltage (V-OC) principally causes low conversion efficiency. We investigated the deposition of a CZTS layer by a two-layer process to improve the V-OC of the CZTS cells. In this process, the first CZTS layers near a Mo electrode have a high Cu content and the second layer near the surface has a low Cu content. The two-layer process improved the V-OC of the CZTS cells from 0.66 to 0.78V. Finally, the best CZTS cell showed a conversion efficiency of 8.8%. (C) 2015 The Japan Society of Applied Physics