Physical, photoelectrochemical properties of CuIn3Se5 and relevance for hydrogen production

CuIn3Se5, prepared by the fusion technique crystallizes in the P-chalcopyrite structure and exhibits n-type conduction ascribed to indium excess. The electrical conductivity follows an Arrhenius-type law with activation energy of 0.35 eV and an electron mobility of 10−4 cm2 V−1 s−1 in conformity with small polaron hopping. The optical gap (1.19 eV), determined from the diffuse reflectance spectrum, is properly matched to the sun spectrum. CuIn3Se5 is chemically stable and a corrosion rate of only 1.2 μmol year−1 is found at neutral pH. The slope and the intercept to C−2 = 0 of the Mott Schottky plot gives respectively an electron density of 3.75 × 1016 cm−3 and a flat band potential of −0.22 VSCE. The conduction band (−0.74 VSCE) therefore lies below the potential of H2O/H2 couple and as application, H2 photo-production is successfully achieved over CuIn3Se5. The best performance is obtained in S2O32− solution (10−2 M, pH ∼ 7) with an evolution rate of 0.54 mL g−1 min−1. The conversion efficiency (0.13%) is due to the formation of small depletion width (230 nm) and a large diffusion length compared to a very large penetration depth (∼1 μm). Attempts have been made to improve the photoactivity and the hetero-system CuIn3Se5/WO3 is compared favorably with respect to CuIn3Se5. The photoactivity is ascribed to electrons transfer from the sensitizer CuIn3Se5-conduction band (CB), acting as electrons pump, to WO3-CB (−0.4 VSCE) resulting in the enhanced water reduction.