We have demonstrated that the short-circuit current density and the resulting conversion efficiency of hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction (HJ) solar cells can be improved by applying a high-mobility hydrogen-doped In2O3 (IO:H) film as a transparent conducting oxide (TCO) electrode. The IO:H film has been fabricated by sputtering deposition without substrate heating, followed by post-annealing treatment below 200 degrees C. To incorporate hydrogen into the In2O3 matrix, water vapor has been introduced into a sputtering system during the deposition. The resulting film shows larger mobility and improved transparency in the visible and near-infrared wavelengths, as compared to a conventional Sn-doped In2O3 (ITO) film. In the a-Si:H/c-Si HJ solar cell incorporating IO:H, instead of ITO, reflection and absorption losses induced by TCO are confirmed to be suppressed. The results indicate that IO:H is a quite attractive alternative to ITO for a-Si:H/c-Si HJ solar cells. (C) 2008 Elsevier B.V. All rights reserved.