A GaAs Micro Solar Cell with Output Voltage over 20 V

Twenty-four micro-solar cells connected in series have been fabricated on semi-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 demonstrated 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 the SI substrate could function as a vital shunt resistance. Light-blocking metal films were successfully employed to obtain high output voltage.