In this work, a simulation study of various HIT solar cell structures was carried out using AFORS-HET simulation software. The effect of defect states and fixed charges at the a-Si:H/p-Si interface on the solar cell performance was investigated. We found that the defect states located at the upper side of the a-Si:H/p-cSi interface affected the HIT performance more greatly than those located at the bottom side of the a-Si: H/p-c-Si interface. However, compared with interface defect states, interface fixed charges located on both sides of the c-Si wafer had an opposite effect. The crucial role of strong band bending in the crystalline part of the a-Si:H/c-p-Si interface was shown through the variation of interface defect states and interface fixed charges. By optimizing the densities of interface defect states and interface fixed charges, an efficiency of 29.19% was achieved. (C) 2016 Elsevier Ltd. All rights reserved.