As a inexhaustible clean energy, development of solar energy is one of the most effective way to solve the energy crisis and environmental problems. Among the materials for photovoltaic applications, silicon has disadvantages of high cost, high energy consumption and high pollution. CdTe and CdS are highly toxic, which may cause severe pollution. CuInSe2 thin film solar cells are highly restricted by the absence of In and Se. Therefore, developing new photovoltaic materials is necessary. Cuprous oxi...