The charge transport in Schottky-type solar cells fabricated from graphene/methyl-passivated silicon heterojunctions is studied in detail. The electrical device characteristics are affected by ambient temperature and illumination conditions. Moreover, the presence of deep and shallow interface states influences the current across the junction at forward and reverse bias. In the dark, thermionic emission over the potential barrier is clearly affected by the recombination via interface states, while under illumination those states become electrically inactive. (C) 2014 Elsevier Ltd. All rights reserved.