Abstract
UDC 544
The compound Cu(In0.6Ga0.4)3Se5 prepared by fusion in sealed tube is a wide band gap semiconductor; it crystallizes in the P-chalcopyrite structure with a direct transition of 1.42 eV. Its transport pro-perties exhibit a semi-conducting behavior, which seem to be not intrinsic but rather attributed to selenium vacancies, and the conductivity is well described by small-polaron hopping: σ = σ0exp{-29/kT}(Ω×cm)-1 with an effective mass of ~ 2 m0. The thermo-power is negative and changes little with temperature, suggesting that the conduction mechanism is mostly due to electron hopping. The analyzed material shows a chemical stability over a broad pH range; the semi-logarithmic plot in KOH solution displays an exchange current density of 27 µA×cm-2 and a corrosion potential of -0.204 VSCE. The capacitance measurement (C-2–V) exhibits a linear behavior, characteristic of n type conductivity, from which a flat band potential of -0.530 VSCE and an electron density of 3.49 ´ 1020 cm-3 are determined. The Nyquist plot shows a semicircle due to the predominance of the bulk contribution (= 127 Ω×cm2) and a low density of surface states. The centre is localized below the real axis with a depression angle of 12° ascribed to a constant phase element (CPE). The straight line in the low frequencies region is due to the Warburg diffusion.
Keywords: chalcopyrite Cu(In0.6Ga0.4)3Se5, small-polaron hopping, photoelectrochemical characterization, electrochemical impedance spectroscopy.