We report that n-type single crystals of n-CuInSe2 in aqueous polysulfide solution exhibit high quantum efficiencies of 0.8–0.9 in the wavelength region between 600–1150 nm when used as photoanodes in photoelectrochemical cells. Photocurrents of 28 mA/cm2 were measured on a ’’winter’’ day in Rehovot (71 mW/cm2) which corresponds to 40 mA/cm2 under AM1 (Air Mass 1) conditions (100-mW/cm2 sunlight). Stability tests of n-CuInSe2 photoanodes (20 000-C/cm2 photocharge passage) at short circuit current densities of 40 mA/cm2 have shown no deterioration whatsoever of the measured photocurrents.