1. Field of the Invention
The present invention relates to a photovoltaic device for converting the energy of solar light or the like into electric energy.
2. Description of the Prior Art
As a photovoltaic device for converting the energy of solar light or the like into electric energy, photovoltaic devices having a variety of structures are known. One example of the photovoltaic devices is a photovoltaic device in which a transparent conductive film 2 composed of SnO.sub.2, ITO or the like is provided on a transparent substrate 1, a photoelectric conversion layer 3 in which a p-type (or n-type) semiconductor layer 3a (or 3c), an intrinsic (i-type) semiconductor layer 3b, and an e-type (or p-type) semiconductor layer 3c (or 3a) are laminated is provided on the transparent conductive film 2, and a back electrode 4 composed of a high-reflective metal such as Ag or Al is provided on the photoelectric conversion layer 3.
In such a photovoltaic device, light is introduced into the above described photoelectric conversion layer 3 through the transparent conductive film 2 from the side of the above described transparent substrate 1 whereby carriers are generated in the above described intrinsic layer 3b to carry out a photoelectric conversion.
Furthermore, there has been developed in recent years a photovoltaic device so constructed that the interface between the transparent conductive film 2 and a photoelectric conversion layer 3 is so textured as to have an irregular shape so that reflection of light from the interface between the transparent conductive film 2 and the photoelectric conversion layer 3 is reduced when the light is introduced into the photoelectric conversion layer 3 through the transparent conductive film 2, thereby increasing the amount of the light introduced into the photoelectric conversion layer 3, and the light introduced into the photoelectric conversion layer 3 is scattered, thereby increasing the optical path length of the light passing through the photoelectric conversion layer 3, whereby many carriers are generated in the intrinsic layer 3b, thereby increasing the conversion efficiency as shown in FIG. 2.
If the interface between the transparent conductive film 2 and the photoelectric conversion layer 3 is formed in an irregular shape, however, the internal electric field in the photoelectric conversion layer 3 comprising a semiconductor junction which constituted by the p-type semiconductor layer 3a, the intrinsic layer 3b, and the n-type semiconductor layer 3c becomes non-uniform in the surface direction of the layer. As shown in FIG. 3, in a portion of the photoelectric converting layer 3 which is in contact with a recess 2a of the transparent conductive film 2 where much light is absorbed, the density of lines of electric force indicated by broken lines is decreased toward the transparent conductive film 2. Consequently, the interval between equipotential lines indicated by dot and dash lines is gradually increased toward the transparent conductive film 2, so that the internal electric field in the photoelectric conversion layer 3 in the portion which is in contact with the recess 2a of the transparent conductive film 2 becomes weak. In the portion of the photoelectric conversion layer 3 where the internal electric field becomes weak, many carriers recombine, whereby fill factor of the photovoltaic device is decreased, thereby preventing an improvement in conversion efficiency.