NiO serves as a window layer for Si photoelectric devices. Due to the wide energy bandgap of NiO, high optical transparency (over 80%) was achieved and applied for Si photoelectric devices. Due to the high the high mobility, the heterojunction device (Al/n-Si/SiO2/p-NiO/ITO) provide ultimately fast photoresponses of rising time of 38.33 μs and falling time of 39.25 μs, respectively. This functional NiO layer would provide benefits for high-performing photoelectric devices, including photodetectors and solar cells.