ZnSnP2 solar cell with (Cd,Zn)S buffer layer: Analysis of recombination rates

A ZnSnP2 bulk crystal was prepared by flux method and cut into a ZnSnP2 wafer with thickness of 200 mu m, which was utilized as the absorber of a ZnSnP2 solar cell with a Al/ZnO:Al/ZnO/(Cd,Zn)S buffer/ZnSnP2 wafer/Cu structure. A 3.44%-efficient ZnSnP2 solar cell was obtained. Moreover, we assessed performance of the ZnSnP2 solar cell concentrating on main loss mechanisms limiting device efficiency. Based on investigations of the majority carrier barrier at ZnSnP2 and the Cu back electrode, the barrier height is estimated to be 59 meV, which could limit the fill factor of the solar cell and should be decreased. In addition, voltage-independent recombination rates at the buffer/absorber interface (R-0(1)), in the space-charge region (R-0(d)), and in the quasi-neutral region (R-0(b)) of the ZnSnP2 solar cell were determined from illumination dependence of the open-circuit voltage. It was found that R-0(d) is 2.65 x 10(13) cm(-2)s(-1), much high than R-0(1) + R-0(b) of 1.2 x 10(9) cm(-2)s(-1). The high R-0(d) was attributed to the mechanical surface polish of the ZnSnP2 wafer. It is thought that R-0(b) should be lower than Rio because of the large ZnSnP2 grain and non-optimized buffer/absorber interface. These findings suggested that R-0(1) and R-0(d) should be further decreased to enhance photovoltaic performance.