Fabrication of Monolithic Integrated Series-Connected GaAs Photovoltaic Cells for Concentrator Applications

Abstract

Aiming at reducting in Joule energy loss of a photovoltaic cell under sunlight concentration, monolithic integration of GaAs cells has been realized, in which five subcells were connected in series and the total surface area of the cells occupied over 80% of the whole chip area. Using plasma etching with Cl2, a sufficiently sharp mesa for device isolation was obtained. Insulation between etched mesa sidewalls and interconnect electrodes proved to be the most significant issues for the purpose of eliminating shunt resistance and securing a reasonable fill factor; the SiO2 layer deposited by sputtering was much superior to polyimide as an insulator. The fabricated test device showed a short circuit current density of 20.7 mA/cm2 and an open circuit voltage of 4.79 V, which were consistent with the values for a single subcell.