By using transient-capacitance techniques we probe the mechanism of hole transport in amorphous/crystalline silicon heterojunction solar cells. The devices are formed by depositing undoped amorphous silicon followed by p-type amorphous silicon on n-type crystalline silicon wafers. The capacitance transients indicate that hole transport from p-type amorphous silicon to n-type crystalline silicon is hindered by hole accumulation in the depletion region of the crystalline silicon. The results are explained with a model based on electrostatic repulsion owing to hole build-up at the crystalline/amorphous interface. We apply these results to other heterojunction solar cells. (C) 2013 Elsevier B.V. All rights reserved.