NOVELTY - A solar cell (100) has a back metal-contact layer (20), a P-type semiconductor layer (30) formed on the back metal-contact layer, a P-N junction layer (40) formed on the P-type semiconductor layer, an N-type semiconductor layer (50) formed on the P-N junction layer, and a transparent electrically conductive layer (60) formed on the N-type semiconductor layer for functioning as a front contact layer. The transparent electrically conductive layer has a basic film (62) and photocatalyst nano-particles (64) dispersed in the basic film.    USE - Solar cell is used for portable electronic device.    ADVANTAGE - The solar cell has excellent photon-electron conversion efficiency.    DETAILED DESCRIPTION - A solar cell has a back metal-contact layer, a P-type semiconductor layer formed on the back metal-contact layer, a P-N junction layer formed on the P-type semiconductor layer, an N-type semiconductor layer formed on the P-N junction layer, and a transparent electrically conductive layer formed on the N-type semiconductor layer for functioning as a front contact layer. The transparent electrically conductive layer has a basic film and photocatalyst nano-particles dispersed in the basic film. The back metal-contact layer is formed of silver, copper, molybdenum, aluminum, copper aluminum alloy, silver copper alloy, or copper molybdenum alloy. The P-type semiconductor layer is formed of P-type amorphous silicon doped with hydrogen, or P-type compound. The N-type semiconductor layer is formed of N-type amorphous silicon doped with hydrogen, or N-type compound. The P-N junction layer is formed of copper-indium-gallium diselenide. The basic film of the transparent electrically conductive layer is transparent electrically conductive oxide film. The photocatalyst nano-particles contain titanium dioxide nano-particles.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the solar cell.    Back metal-contact layer (20)    P-type semiconductor layer (30)    P-N junction layer (40)    N-type semiconductor layer (50)    Transparent electrically conductive layer (60)    Basic film (62)    Photocatalyst nano-particles (64)    Solar cell (100)