Conversion of Light Propagation Direction for Highly Efficient Solar Cells

Optical absorption coefficients are generally inherent to materials and are reduced for longer optical wavelengths, especially below their absorption edges. In tandem solar cells this makes thicker bottom cells necessary to improve their optical absorption efficiencies for longer optical wavelengths. This paper proposes a method to convert the propagation direction of an incident light toward the one parallel to optical absorption layers. High-efficiency optical absorption is demonstrated with thin absorption layers with this method. Drastic reduction of layer thicknesses necessary for high photoelectric conversion efficiencies will reduce the cost and improve the yield of various solar cells.