AbstractLight‐induced interfacial electron transfer from two p‐InP electrodes differing in the amount of majority carrier doping to a number of electron relays (R) dissolved in aqueous solution was investigated. The material with the lower carrier density (0.71 × 1018 cm−3) exhibited much better wavelength response and quantum yield for electron transfer than the electrode doped with 2.3 × 1018 cm−3 charge carriers. Using cobalt (III) sepulcrate, Co (sep)3+, as an electron relay a polychromatic light to electrical energy conversion efficiency of 18% was obtained. The potential of this relay for use in a regenerative photoelectrochemical cell is briefly discussed.