TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The N-type transparent amorphous oxide semiconductor layer is formed by zinc oxide (ZnO), mixture of tin oxide and zinc oxide (ZnO-SnO2 mixture), or mixture of zinc oxide and indium oxide (a ZnO-In2O3 mixture), and further comprises aluminum, gallium, indium, boron, yttrium, scandium, fluorine, vanadium, silicon, germanium, zirconium, hafnium, nitrogen, and/or beryllium. The P-type semiconductor substrate comprises P-type silicon wafer, P-type silicon film, or other P-type semiconductor materials. The solar cell comprises P-type semiconductor substrate having first and second surfaces; rear electrode disposed on second surface of the P-type semiconductor substrate; and N-type transparent amorphous oxide semiconductor layer disposed on the first surface of the P-type semiconductor substrate, where N-type transparent amorphous oxide semiconductor layer and the P-type semiconductor substrate construct a P-N diode. The solar cell further comprises front electrode layer formed by metal and/or transparent conductive oxide, and disposed on transparent amorphous oxide semiconductor layer. The transparent conductive oxide comprises indium tin oxide, fluorine-doped tin oxide, aluminum-doped zinc oxide, and/or gallium-doped zinc oxide. Preferred Conditions: The N-type transparent amorphous oxide semiconductor layer serves as window layer and front electrode layer. The N-type transparent amorphous oxide semiconductor layer is formed by single conduction type material layer. The N-type transparent amorphous oxide semiconductor layer is formed by a material layer having conductivity gradient, and portion of the material layer, having lower conductivity, close to the P-type semiconductor substrate while another portion, having higher conductivity, and away from P-type semiconductor substrate.    TECHNOLOGY FOCUS - METALLURGY - Preferred Component: The metal comprises aluminum, silver, molybdenum, titanium, iron, copper, silver, manganese, cobalt, nickel, gold, zinc, tin, indium, chromium, platinum, tungsten, or an alloy.