Photoelectrochemical water splitting using Cu(In,Al)Se₂ photoelectrodes developed via selenization of sputtered Cu-In-Al metal precursors

Chalcopyrite p-type quaternary CuIn_xAl_1-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 CuIn_xAl_1-xSe₂ photoelectrodes on the structural, optical and photoelectrochemical properties of CuIn_xAl_1-xSe₂ samples is investigated. X-ray diffraction patterns and energy-dispersive analysis of X-rays results reveal that the metal precursors can be converted into the tetragonal CuIn_xAl_1-xSe₂ phase after the selenizations process under a Se atmosphere at a temperature of 570 °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 [Al]/[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 cm² V^-1 s^-1 and 8.23×10¹⁶-2.34×10¹⁹ 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.