Sub-Stochiometric Nickel Oxide Hole-Selective Contacts in Solar Cells: Comparison of Simulations and Experiments with Sputtered Films

Abstract

Sub-stochiometric nickel oxide (NiOx) films were investigated as a hole selective contact option in silicon (Si) heterojunction solar cells. Numerical simulations were carried out to evaluate the impacts of the NiOx electronic properties variations and the NiOx/Si interface defect density (Dit) on device performance. Simulation data suggest that the best performance is achievable for wide bandgaps (Eg) and corresponding high valence band edge (EVB) positions in the NiOx films. Overall, in simulations, the performance remains practically unchanged for the nickel vacancy concentrations [VNi] = 1017–1021 cm−3, assuming high EVB and low Dit. The experimental data measured using NiOx films prepared by radio-frequency magnetron sputtering reveal that the increase in [VNi] lifts the conductivity, concurrently decreasing Eg and EVB. As a result, we concluded that the performance of the fabricated sputtered NiOx/Si heterojunction solar cell is limited by high Dit as well as narrow Eg and low EVB.