In this paper, zinc oxide (ZnO) thin films as an antireflective (AR) coating layer have been successfully fabricated on GaAs solar cells by the sol-gel method. ZnO films were prepared chemically by spin coating the gel with an aqueous solution of zinc acetate and ethanolamine. The current-voltage measurements of the solar cells confirmed the increase of the short-circuit current induced by the AR effect. The open-circuit voltage and fill factor were also improved by the surface passivation. As a result, the conversion efficiency of the cells without an AR coating (8.2%) was significantly enhanced to 13.6%. The results indicate that the chemical deposition of ZnO was effective for the AR coating of GaAs solar cells. Additionally, we demonstrate that the cells coated with radiation resistant ZnO films exhibit less efficiency decay than the devices without such treatment. Under the maximum proton fluence of 10(13) cm(-2), the conversion efficiency decay was reduced to 69.8%, while the solar cells without ZnO films showed an efficiency decay of 83.1%. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3531937] All rights reserved.