Metal Oxide Heterovalence Multijunctions for Third Generation Solar Cells

An approach to third-generation solar cells with a much better figure of merit, i.e., the efficiency/cost ratio, is proposed. It combines the advantages of low-cost wet-chemical fabrication and high-efficiency inorganic crystalline solar cells. The materials which allow wet-chemical fabrication of inorganic crystalline solar cells are semiconducting metal oxides. An analysis is presented on the challenges in utilizing metal oxides for third-generation solar cells, including the larger-than-optimum band gap and the high densities of native point defects in metal oxides. Strategies to overcome these challenges are outlined. Some of the metal oxides of interest include copper oxides and titanium oxides. The band gaps of copper oxides are around the optimum 1.4 eV for single-junction cells. For 50%-efficient multijunction tandem cells, titanium oxides of different valences offer a continuously-adjustable band gap of 0-3.5 eV, covering the entire solar spectrum