The effect of the band gap of the window layer on the properties of silicon heterojunction solar cells was performed by a set of AMPS simulations. The results show that the short-circuit current increases slightly with the band gap of the window layer, E g2 , increasing. At the ideal defect-free interface case or negligible interface states, E g2 almost has no effect on the open-circuit voltage V OC and the fill factor FF at E g2