NOVELTY - The solar cell useful in roofs of buildings and cars and in portable electronic devices, comprises a back metal-contact layer (20), a positive-type semiconductor layer (30) formed on the back metal-contact layer, a positive-negative (P-N) junction layer (40) formed on the positive-type semiconductor layer, a negative-type semiconductor layer (50) formed on the P-N junction layer, and a transparent and electrically conductive layer (60) having a thickness of 30-300 nm formed on the negative-type semiconductor layer for functioning as a front contact layer.    USE - The solar cell is useful in roofs of buildings and cars and in portable electronic devices.    ADVANTAGE - The solar cell has fewer lattice defects such as dislocations and stacking faults, and high photon-electron conversion efficiency.    DETAILED DESCRIPTION - The solar cell useful in roofs of buildings and cars and in portable electronic devices, comprises a back metal-contact layer (20), a positive-type semiconductor layer (30) formed on the back metal-contact layer, a positive-negative (P-N) junction layer (40) formed on the positive-type semiconductor layer, a negative-type semiconductor layer (50) formed on the P-N junction layer, and a transparent and electrically conductive layer (60) having a thickness of 30-300 nm formed on the negative-type semiconductor layer for functioning as a front contact layer. The positive and negative type semiconductor layers are comprised of nano particles of positive and negative type semi-conductive compounds respectively. The conductive layer is transparent electrically conductive oxide film or carbon nanotube film. A size of each particle in the positive and negative type semi-conductive compounds is 10-100 nm.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a solar cell.    Back metal-contact layer (20)    Positive-type semiconductor layer (30)    Positive-negative junction layer (40)    Negative-type semiconductor layer (50)    Conductive layer. (60)