Photoelectrochemical properties of Cu(In0.75Ga0.25)3Se5 ordered vacancy compound

Ordered vacancy compound Cu(In0.75Ga0.25)3Se5 was synthesized by the fusion technique. The starting elements were sealed in evacuated silica tube and submitted to programmed thermal treatment. The x-ray diffraction confirmed the formation of the phase which crystallizes in the chalcopyrite structure. The elemental composition (Cu = 13.45 at.%, In = 22.14 at.%, Ga = 8.42 at.%, Se = 56.0 at.%) was determined by the energy dispersive spectroscopy. The optical gap (Eg) was obtained from the diffuse reflectance spectrum through the Kubelka–Munk equation. The dependence of the absorption coefficient (α) on the photon energy (hν) near the band edge is characteristic of directly allowed optical transition with Eg value of 1.27 eV. The high temperature conductivity data were fitted to a small lattice type polaron hopping based on the strong electron–lattice interaction with an effective mass of 0.76 mo. The material exhibits an excellent chemical stability in basic solution with a corrosion rate of 0.87 µmol per month. The photoelectrochemical characterization was done in KOH (0.5 M) electrolyte and the n-type conductivity was confirmed by the anodic photocurrent. The flat band potential (−0.78 VSCE) and the donor's density (2.73 × 1019 cm−3) were derived respectively from the slope and intercept with the potential axis of the Mott–Schottky plot. The results showed the potentiality of Cu(In0.75Ga0.25)3Se5 for the photoelectrochemical hydrogen evolution.