Carrier transport mechanisms of reactively direct current magnetron sputtered tungsten oxide/n-type crystalline silicon heterojunction

Abstract

For optimizing the performance of tungsten oxide (WOx)/c-Si heterojunction solar cells, it is important to understand the carrier transport process within the device. Recently, several studies examined transport mechanisms; but yet reported not apparently. In this study, the fundamental carrier transport mechanisms in WOx/c-Si heterojunction solar cells and their effects on the device characteristics are investigated. Our results indicate that the trap-assisted-tunneling (TAT) process is the dominant carrier transport mechanism in the forward-bias voltage regime, while the generation of current in the space-charge region is dominant in the reverse-bias voltage regime. Interestingly, it was found that the hole-selective contact with lower oxygen-to-tungsten ratios, which is related to that of high trap densities, can assist the TAT process and increase the fill factor of the device regardless of the film conductivity. This finding is inconsistent with those of previous experiments but is consistent with those of previous simulations. Finally, this confirmation can help with optimization of WOx/c-Si heterojunction solar-cell efficiencies.