"Heterojunction with intrinsic thin layer" solar cells combine the high efficiency of crystalline silicon (c-Si) cells, with the low cost of amorphous silicon technology. Here we use detailed numerical modeling and experiments to understand the influence, on the solar cell output parameters, of defects on the front and rear surfaces of the P-type c-Si wafer. Modeling indicates that the defects on the front surface of c-Si reduce the open-circuit voltage and fill factor, while those on the rear surface degrade mainly the short-circuit current density and fill factor, but only when their density exceeds 10(12) cm(-2). (c) 2008 Elsevier B.V. All rights reserved.