Highly effective III-V solar cells by controlling the surface roughnesses

Abstract

An advanced approach to minimize the light loss was discussed for III-V solar cells, by controlling the roughnesses of the device surface. Adhesives with different viscosities were applied to bond the III-V solar cells with the supporting substrate before the epitaxial lift-off process. The surface roughness of the III-V solar cells with epoxy adhesive (Rrms = 15.4 nm) is one order of magnitude higher than that with acrylic adhesive (Rrms = 1.6 nm), due to the differences in viscosity, resulting from the spreadability while being hardened. This roughness has increased the reflectance in the wavelength between 650 and 900 nm, implying that this reflectance is influenced by the rear surface of the solar cell. The device performance of the double-junction solar cells (Ga0.5In0.5P- and GaAs- based) also reflects the effect of the reflectance. The solar cell with the epoxy adhesive exhibited ~2% increase of the conversion efficiency than that with the acrylic adhesive, mainly due to the increased current density. The integrated current density from the external quantum efficiency (EQE) also exhibited ~2% increase only in the bottom (GaAs-based) cell, corresponding to the higher reflectance for red and near-infrared wavelength ranges.