Analysis of Effect of Zn(O,S) Buffer Layer Properties on CZTS Solar Cell Performance Using AMPS

The Cu_2ZnSnS_4 (CZTS)-based solar cell is numerically simulated by a one-dimensional solar cell simulation software analysis of microelectronic and photonic structures (AMPS-1D). The device structure used in the simulation is Al/ZnO:Al/nZn(O,S)/pCZTS/Mo. The primary motivation of this simulation work is to optimize the composition in the ZnO_1-xS_x buffer layer, which would yield higher conversion efficiency. By varying S/(S+O) ratio x, the conduction band offset (CBO) at CZTS/Zn(O,S) interface can range from -0.23 eV to 1.06 eV if the full range of the ratio is considered. The optimal CBO of 0.23 eV can be achieved when the ZnO_1-xS_x buffer has an S/(S+O) ratio of 0.6. The solar cell efficiency first increases with increasing sulfur content and then decreases abruptly for x>0.6, which reaches the highest value of 17.55% by our proposed optimal sulfur content x=0.6. Our results provide guidance in dealing with the ZnO_1-xS_x buffer layer deposition for high efficiency CZTS solar cells.