We explore substoichiometric molybdenum trioxide (MoO x, x< 3) as a dopant-free, hole-
selective contact for silicon solar cells. Using an intrinsic hydrogenated amorphous silicon
passivation layer between the oxide and the silicon absorber, we demonstrate a high open-
circuit voltage of 711 mV and power conversion efficiency of 18.8%. Due to the wide band
gap of MoO x, we observe a substantial gain in photocurrent of 1.9 mA/cm 2 in the ultraviolet
and visible part of the solar spectrum, when compared to a p-type amorphous silicon emitter …