The interface formation between plasma-enhanced chemical vapor-deposited (PECVD) silicon thin films and H-terminated, p-type c-Si was investigated. The formation of hydrogenated amorphous silicon (a-Si:H), epitaxial Si, and mixed phase Si was detected through spectroscopic ellipsometry (SE) and high-resolution transmission electron microscopy (HRTEM). The evolution of the hydrogen content and hydrogen bonding configurations in the films were monitored by attenuated total reflection infrared spectroscopy (FTIR-ATR). The dependence of the hydrogen binding configuration on the film morphology was observed. Even with an observed epitaxial layer in the structure of the intrinsic a-Si:H, a silicon heterojunction (SHJ) solar cell with 9.2% efficiency was obtained, which is the largest-active-area (72 cm(2)) SHJ cell on p-type c-Si. The numerical simulation tool AFORS-HET was used to model the layers and interface properties of the cell. The simulation results were consistent with the experimental results, demonstrating the importance of interface defect passivation in SHJ solar cells.