Carrier selective MoOx/Si heterojunctions: Role of thickness

Abstract

In this work, we presentthickness-dependent change in the hole-blocking property of heterojunctions consisting of wide band-gap MoOxthin films onp-Si substrates. Radio frequency sputter-deposited MoOxfilms are amorphous in nature and compositional analysis reveals an increase in oxygen vacancy with film thickness. The optical band-gap measurementrevealsa systematic red shift with increasing film thickness. Using Kelvin probe force microscopy, it is demonstrated that work function of MoOxfilms increases up to a thickness of 10 nm, while it decreases for higher thicknesses (up to 30 nm). Interestingly, all the MoOx/Si heterojunctions prevent the flow of holes but allow that of electrons. Post-growth annealing of MoOxfilms (at 573 K for 1 h in air) leads to amodificationin thehole-blocking property of the MoOx/Si heterojunctionsanda similar thickness-dependent trend is prevailed(as observed for as-prepared MoOx/Si heterojunctions). Based on our experimental results, it is concluded that a 10 nm-thick MoOx film exhibits the best hole-blocking property, albeit annealing leads to a marginal deterioration in its hole-blocking efficiency. The observed results are very important for the construction of hole-blocking hetero-junction solar cells.