The influence of treatment by a low energy hydrogen ions on degradation of the spectral response, diffusion length of minority carriers (L-D) and efficiency (eta) of silicon p-n junction photodiodes ( solar cells without antireflective coatings) under the effect of electron irradiation has been investigated. Evaluation of the radiation hardness was made by subjecting the unhydrogenated and hydrogenated photodiodes to 1 MeV electron irradiation with doses of (0.1 divided by 3) x 10(15) cm(-2). The measurements have shown that pre-hydrogenation of the silicon p-n junction devices significantly decreases the degradation rate of LD and. thereby improving their radiation hardness. (C) 2005 Springer Science + Business Media, Inc.