The properties of GaAs/AlGaAs solar cells irradiated with 40, 70, 100 and 170 keV protons have been studied. Current-voltage (IV) measurement showed that the worst degradation was found in the cells irradiated by 100 keV protons. The degradation was found defect dependent. Defect pro. le was obtained by the stopping and range of ions in matter (SRIM) simulation and deep-level transient spectroscopy (DLTS) measurement. In order to obtain the deep-level defect profile in depletion layer by DLTS measurement, the traditional calculation formula of defect concentration has been modified. DLTS measurement showed good agreement with that of the SRIM simulation. (C) 2009 Elsevier B. V. All rights reserved.