Chalcopyrite p-type quaternary CuInxAl1-xSe2 (x=0.44-0.74) semiconductor photoelectrodes are prepared on various substrates via the reactive selenization of radio-frequency-sputtered Cu-In-Al metal precursors. The influence of the aluminum content in the quaternary CuInxAl1-xSe2 photoelectrodes on the structural, optical and photoelectrochemical properties of CuInxAl1-xSe2 samples is investigated. Xray diffraction patterns and energy-dispersive analysis of X-rays results reveal that the metal precursors can be converted into the tetragonal CuInxAl1-xSe2 phase after the selenizations process under a Se atmosphere at a temperature of 570 degrees C for 1 h. The energy band gaps of samples are tuned by varying the aluminum content in samples. The direct energy band gap of samples increases from 1.25 to 1.8 eV when the [AI]/[Al+In] molar ratio in samples increases from 0.26 to 0.56. The mobility and carrier density of samples are in the ranges of 1.06-5.86 cm(2) V-1 s(-1) and 8.23 x 10(16)-2.34 x 10(19) cm(-3), respectively. The sample with an [Al]/[Al+In] molar ratio of 0.34 has the highest photoelectrochemical performance in aqueous H2SO4 solution with the applied bias photon-to-current efficiency (ABPCE) and photo-enhanced ABPCE of 8.99% and 3.61% at an applied voltage of -1.0 V vs. an Ag/AgCl electrode, respectively. Crown Copyright (C) 2016 Published by Elsevier B.V. All rights reserved.