Electrochemical reductions Of C-60 fullerene films were studied in the presence of Bronsted acids to form hydrogenated fullerenes. It was established that a simple electrochemical treatment, reversible reduction and oxidation of the films formed such structurally rearranged layers that could be transformed to HnC60 (where n depended on the acid, on the concentration of the acid and on the electrode potential). Hydrogenated fullerene films were shown to behave as semiconductors with very much increased photoefficiency. (C) 2003 Elsevier Science B.V. All rights reserved.