Unraveling the Hole-Selective Nature of Si/MoOX Heterojunction

MoO_X has emerged as an effective hole-selective layer for Si based heterojunction solar cells on account of its high workfunction. The hole selectivity of MoO_X is fundamentally different from other carrier selective films as it does not have an electron blocking energy barrier in form of conduction band offset with Si. Accordingly, much is unknown about the hole-selective nature of Si/MoO_X junction with many unresolved puzzles. Here, through a combination of detailed modeling and experiments, we provide a coherent, calibrated, and comprehensive model to describe unique hole selective features of Si/MoO_X junctions. The model accurately predicts the dark characteristics (ideality factor and reverse saturation current) and the open-circuit voltage of Si/MoO_X based heterojunction solar cells reported in the literature. In addition, the same model anticipates the trends for solar cells with a-Si as interlayer passivation. As such this work establishes the limits of achievable V_OC and its functional dependence on MoO_X material parameters and, hence, could be of broad interest to enable further performance optimization of solar cells with large workfunction carrier selective layers such as V₂O₅ and WO₃.