The fabrication of amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cell and an understanding of the fundamental conduction mechanism in the device are presented. In the first part, the effect of intrinsic amorphous silicon [a-Si:H(i)] layer thickness on the performance of a-Si: H/c-Si solar cells has been studied. The thickness of a-Si:H(i) layer formed on n-type c-Si substrate was controlled accurately with spectroscopy ellipsometry (SE). Based on SE results, we discuss the influence of the a-Si:H(i) thickness on the interface quality and thereby cell performance. Then, in the latter part, we present the temperature-dependent current density-voltage curves, in the dark, in order to elucidate the dominant transport mechanisms in a-Si: H/c-Si heterojunction solar cells with and without incorporation of a-Si:H(i) layers. Finally, using optimum design considerations, we obtained a solar cell efficiency of 17.43%. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3534202] All rights reserved.