Physical and photoelectrochemical properties of p-CuInSe2 bulk material

CuInSe2 ingots were elaborated by direct reaction in evacuated quartz ampoule. The material is polycrystalline and crystallizes in the chalcopyrite structure (SG : 1 (4) over bar 2d). The chemical composition was determined by the energy dispersive spectroscopy and RBS technique. The analysis indicates a stoichiometric compound with small copper deficiency and a uniform bulk composition. A band gap at 0.94 eV was evaluated from the diffuse reflectance spectrum. The electrical properties were investigated and an activation energy of 23 meV was obtained in the heating direction from the Arrhenius type law. The thermal variation of the thermo power indicates p-type conduction with polaron hopping. The compound is stable in aqueous electrolyte with a dissolution rate of 8 mu mol cm(-2) month(-1). A corrosion potential of +0.20 V-SCE and an exchange current density of 0.318 mA cm(-2) were determined from semi logarithmic plot in KCl (1M). The current-potential characteristic gave a potential V-on of onset photocurrent of -0.60 V-SCE close to the flat band potential (V-fb = -0.58 V-SCE), determined by extrapolating the linear part to C-2 = 0 in the Mott Shottky plot. The doping density (N-A = 3.8 10(17) cm(-3)) was calculated from the slope. The Nyquist plot shows a semicircular arc whose center is localized below the real axis with an angle of 0.086 rad. This can be attributed to single barrier of the junction SC/electrolyte and single relaxation time of the electrical equivalent circuit. (c) 2007 Elsevier B.V. All rights reserved.