A GaAs micro solar cell with output voltage over 20 V

Twenty-four micro-solar cells connected in series have been fabricated on s emi-insulating (SI) GaAs substrates for application in the fields of micro- electromechanical systems. The array was formed in an area of 0.8 x 1.0 mm( 2), and exhibited an open-circuit voltage of 22.5 V under illumination of 5 mW at the wavelength of 815 nm. Calculation and experiment has demonstrate d that, unlike conventional solar cells, the shunt resistance deteriorates the output characteristics far more seriously than the series resistance in the case of micro-solar cells. Leakage currents in both the unit diode and the substrate were evaluated separately. A quantitative estimate based on the measurements revealed that photocurrents generated in the surface of th e SI substrate could function as a vital shunt resistance. Light-blocking m etal films were successfully employed to obtain high output voltage.