The effects of proton irradiation on strained InAsxP1-x/InP-based quantum well solar cells (QWSCs) have been investigated by the electron beam induced current (EBIC) and cathodoluminescence (CL) techniques. From analysis of the EBIC data, capture rates within the quantum well region have been estimated, from which the open circuit voltages of the cells were calculated and shown to agree well with the measured values. Diffusion lengths have been estimated from analysis of both the EBIC and CL measurements. The location of the energy levels of proton-induced defects and their effectiveness as nonradiative recombination centers have been determined from Arrhenius plots of the total CL intensity emitted from the quantum wells following irradiation. The results suggest that deeper and narrower quantum wells increase the sensitivity of QWSCs to radiation damage. © 2001 American Institute of Physics.