Effect of Conduction Band Tail of MoO_x on Transport Properties in MoO_x/SiO_x/c-Si Heterojunction

Recent optical absorption experiments [Nano Res. 13, 3416 (2020)] have revealed that carrier transport in MoOx-based crystalline silicon (c-Si) heterojunction solar cells relies on the band-tail states of molybdenum oxide (MoOx) rather than the deep gap states. However, theoretical investigations on the impact of these band-tail states on transport properties remain scarce. In this article, a semi-analytical model including the effect of conduction band tail on the dark current-voltage characteristic is proposed for MoOx/silicon oxide (SiOx)/c-Si heterojunction. We show that the simulated dark current density-voltage curve is in agreement with the reported experimental data, especially under low forward bias voltage. Furthermore, the simulated dark current-voltage characteristics exhibit sensitivity to the characteristic energy, work function, and doping density of MoOx, primarily influenced by the accessible energy range and tunneling probability through ultrathin SiOx. These results emphasize the crucial role of the conduction band tail of MoOx in governing carrier transport in MoOx-based c-Si heterojunction solar cells.