A photoelectric conversion device with improved electric characteristics is provided. The photoelectric conversion device has a structure in which a window layer is formed by a stack of a first silicon semiconductor layer and a second silicon semiconductor layer, and the second silicon semiconductor layer has high carrier concentration than the first silicon semiconductor layer and has an opening. Light irradiation is performed on the first silicon semiconductor layer through the opening without passing through the second silicon semiconductor layer; thus, light absorption loss in the window layer can be reduced.