Boron doped amorphous diamond (a-D:B) films, which possess a wide optical gap and good p-type semi-conductive electroconductibility, were prepared using filtered cathodic vacuum arc system, whose target source was highly pure graphite incorporated with boron element. The intrinsic layer and the n-type layer of amorphous silicon solar cells in a configuration of p-i-n were deposited using PECVD technology. The optical gap of the boron doped amorphous diamond films was characterized with a Lambda 950 UV-Vis photometer. The parameters of solar cells, such as open-circuit voltage, short-circuit current, fill factor and efficiency, were also measured. It shows that using the a-D:B films as the window layer of p-i-n structural amorphous silicon solar cell can increase the cell conversion efficiency by a roughly 10% relative improvement compared to the conventional amorphous silicon solar cell because of the enhancement of short wavelength response.