III-V solar cells under monochromatic illumination
Photovoltaic cells illuminated with a monochromatic light source have revealed the highest ever reported photon-energy conversion efficiency. In this paper we investigate laser illuminated photovoltaic cells. III-V materials including GaInP, GaAs and GaSb were used to fabricate laser power converters. A special emphasis is given to the GaAs material. Here we report on the use of a lateral conduction layer which reduces the emitter sheet resistance. This solves the problem of ohmic losses due to the high current densities generated in the photovoltaic device. The highest measured efficiency under laser illumination (810 nm, 43 W/cm²) was 53.4 %. The application of laser power converters in electronic circuits often demands for high-voltage devices. We tackle this problem twofold: (i.) we developed a monolithic tandem structure which is adapted to one specific laser type and (ii.) we grew the photovoltaic active layer structure on a semi-insulating wafer and etched segments which are interconnected in series on the wafer. This technology leads to output voltages of up to 6 Volts.