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

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 (D-it) on device performance. Simulation data suggest that the best performance is achievable for wide bandgaps (E-g) and corresponding high valence band edge (E-VB) positions in the NiOx films. Overall, in simulations, the performance remains practically unchanged for the nickel vacancy concentrations [V-Ni] = 10(17)-10(21 )cm(-3), assuming high E-VB and low D-it. The experimental data measured using NiOx films prepared by radio-frequency magnetron sputtering reveal that the increase in [V-Ni] lifts the conductivity, concurrently decreasing E-g and E-VB. As a result, we concluded that the performance of the fabricated sputtered NiOx/Si heterojunction solar cell is limited by high D-it as well as narrow E-g and low E-VB.