Improvement of Ohmic Behavior of Back Contact in ZnSnP2 Solar Cells by Inserting Cu3P

One of the main issues for the improvement of solar cells is to develop Ohmic contacts with low contact resistance on absorbers, such as CIGS/MoSe2/Mo. In the case of ZnSnP2 (ZTP)-based solar cells, Cu is used as a back electrode. At the Cu/ZTP interface, Cu3P is formed epitaxially on ZTP due to interdiffusion through annealing process and contributes to the improvement of the carrier transport property across the junction. However, the interdiffusion also causes degradation of electrodes and hence the increase in the series resistance. In this study, we adopt DC sputtering of a Cu3P target on the ZTP wafers before the deposition of Cu electrodes to prepare uniform Cu/Cu3P electrodes. As a result, the degradation of electrodes was suppressed and the low series resistance was obtained in the annealing time range from 5 to 30 min. The Cu/Cu3P stacked electrodes could therefore be a robust Ohmic contact for ZTP.