Abstract: The wide-band gap p-type hydrogenated amorphous silicon carbon (p-a-SiC: H) film was used as window layer of silicon heterojunction (SHJ) solar cells. Finite difference time domain (FDTD) simulation results showed that p-a-SiC: H not only significantly reduced the short-wave parasitic absorption loss of the window layer, but also reduced the reflection loss of SHJ solar cells, thereby enhancing the spectral response of SHJ solar cells. Meanwhile, the experimental results showed that the optimized p-a-SiC: H window layer could increase the J_sc of SHJ solar cells to 1.4 mA/cm², and achieved a cell efficiency of 21.8%. This improvement is primarily attributed to the low parasitic absorption of the p-a-SiC: H window layer and its ability to reduce reflection losses in SHJ solar cells.