We fabricated hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction solar cells with different intrinsic buffer layers, to elucidate the effect of the energy band gap, as well as passivation quality on the performance of the a-Si:H/c-Si heterojunction solar cells. Deformation (S-shaped) of J-V characteristics are observed in defiance of surface passivation quality for heterojunction solar cells with intrinsic buffer layers of high energy band gap (E-g > 3.0 eV). The deformation of J-V characteristics could be recovered when the energy band gap does not exceed 1.72 eV. In this given energy band gap, it seem to be that the surface passivation quality plays a role in heterojunction solar cell performance. The electrical-optical simulator, AFORS-HET, is used to determine the probable cause of the change in device performance. We find that the band discontinuities at the a-Si:H/c-Si interface are responsible for such an S-shaped behavior in the high energy band gap of intrinsic buffer layers. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.031111jes] All rights reserved.