The p-type a-Si:H/n-type c-Si (P+ a-Si:H/N+ c-Si) heterojunction was simulated for developing solar cells with high conversion efficiency and low cost. The characteristic of such cells with different work function of transparent conductive oxide (TCO) were calculated. The energy band structure, quantum efficiency and electric field are analyzed in detail to understand the mechanism of the heterojunction cell. Our results show that the a-Si/c-Si heterojunction is hypersensitive to the TCO work function, and the TCO work function should be large enough in order to achieve high conversion efficiency of P+ a-Si:H/N+ c-Si solar cells. With the optimized parameters set, the P+ a-Si:H/N+ c-Si solar cell reaches a high efficiency (eta) up to 21.849% (FF: 0.866, V-OC: 0.861 V, J(SC): 29.32 mA/cm(2)). (C) 2011 Elsevier Ltd. All rights reserved.