Interdigitated back contact (IBC) solar cells have great potential for high efficiency because of their unique structure. IBC solar cells demand for high quality of front surface passivation. In this work, 2D numerical simulations have been done to investigate the potential of front surface field (FSF) offered by stack of n-type doped and intrinsic amorphous silicon (a-Si) layers on the front surface of IBC solar cells. Simulations results clearly indicate that the electric field of FSF should be strong enough to repel minority carries and cumulate major carriers near the front surface. However over-strong electric field tends to drive electrons into a-Si layer leading to severe recombination loss. The n-type doped amorphous silicon (n-a-Si) layer has been optimized in terms of doping level and thickness. The optimized intrinsic amorphous silicon (i-a-Si) layer should be as thin as possible with an energy band gap (Eg) larger than 1.4 eV. In addition, the simulations concerning interface defects strongly suggest that FSF is an essential part when the front surface is not passivated perfectly. Without FSF, the IBC solar cells become more sensitive to interface defect density. •We propose the application of stack of amorphous silicon layers as front surface field for diffused IBC solar cells.•We optimized the amorphous silicon layers in terms of doping level, thickness, bandgap and interface defects density.•Heterojunction structure is integrated on the front surface of IBC solar cells and energy band diagrams are analyzed.