A GaAs Micro Solar Cell with Output Voltage over 20 V

Abstract

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 × 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.

Analysis of leakage current in GaAs micro-solar cell arrays

“…Lee et al [2] have designed and fabricated Si micro-solar cell arrays with an open-circuit voltage (V oc ) of 150 V in a small size (1 cm 2 ). Ohsawa et al [3] have developed the micro-cells using GaAs as the active material, and a output voltage over 20 V has been obtained in an array of 24 cells within a small area (0.8 mm×1.0 mm). Afterwards, they have increased the number of unit cells up to 120 and a 100 V output voltage was achieved [4].…”

“…Compared with conventional large area GaAs solar cells, a single micro-solar cell in an array shows a certain degree of degradation which is manifested by the two forms: lower V oc and lower fill factor (FF) [3,4]. Ohsawa et al [3] have modeled the single cell and pointed out that the degradation was attributed to contact resistance and substrate leakage current.…”

“…Ohsawa et al [3] have modeled the single cell and pointed out that the degradation was attributed to contact resistance and substrate leakage current. Additionally, Belghachi et al [6] have modeled micro-cells considering the perimeter effect and pointed out that the performance of small area solar cells were also reduced by the perimeter recombination.…”

“…The deterioration of arrays is mainly reflected in a greater drop in voltage and fill factor which will not only make it difficult to estimate the number of required units but also affect the output stability of the devices. Usually, this deterioration is attributed to the heterogeneity of single cell [3]. However, the existing studies only give the qualitative interpretation of this phenomenon and deep investigation on the output performance of array is not sufficient.…”

Perimeter recombination in thin film solar cells

“…piezoelectric require 70 to 100 volts to perform a reasonable amount of work on a microscopic basis [1]. Micro thin film solar cells are the best candidate for built-in power sources for this new generation of MEMS actuators.…”