InGaN solar cell structures had a tapered GaN structure at GaN/sapphire interface that was fabricated through a laser decomposition process and a wet crystallographic etching process. A 51% backside roughened-area ratio was observed in the treated solar cell structure to increase the light scattering process at GaN/sapphire interface. The peak external quantum efficiency (EQE) and peak wavelengths of the photovoltaic properties were measured at 38.3% (at 392 nm) and 70.5% (at 396 nm) for the conventional and the treated solar cell structures, respectively. The cutoff wavelength of the relative transmittance spectra and the wavelength of the peak EQE values for the treated solar cell structure had the redshift phenomenon which was caused by increasing light reflectance at the tapered-GaN/sapphire interface and increasing light absorption at the InGaN layers. (C) 2012 Elsevier B.V. All rights reserved.