Synthesis, Characterization, and Growth Mechanism of n-Type CuInS2 Colloidal Particles

We report on the growth of CulnS(2) n-type semiconductive particles, prepared Using a modified Czekelius's colloidal method, its well its their chemical and electrochemical properties. Solid state Raman spectroscopy revealed two crystalline phases: chalcopyrite and the so-called copper-gold phase. Increasing the annealing temperature of the particles favors the formation of the chalcopyrite phase. As shown by XPS, EDX, and ICP-AES, an excess of indium wits obtained, which wits greater at the surface (CuIn1.45S1.9 at 450 degrees C) than in the bulk (CuIn1.45S1.74 at 450 degrees C). UV-visible measurements showed that the n-type CuInS2 possesses a direct bandgap energy of 1.45 eV. Two organic redox couples in nonaqueous media were used to perform the capacitance measurements carried out by EIS on a CUInS2 film: 5-mercapto-1-methltetrazolate (T-),/di-5-(1-methyltetrazole) disulfide (T-2) and 5-trifluoromethyl-2-mercapto-1,3,4-thiadiazolate (G(-))/5,5 '-bis(2-trifluoromethyl-1,3,4-thiadiazole) disulfide (G(2)). Fermi levels of -3.95 eV and -3.64 eV and majority charge carrier densities of 4.1 x 10(18) and 1.8 x 10(18) cm(-3) were determined, respectively, using these redox couples. On the basis of the CuInS2/electrolyte energy level diagrams, the G(-)/G(2) redox couple is expected to lead to it more efficient device (greater photocurrent and photovoltage). In situ Raman spectroscopy measurements showed that the reactivity of copper with hexamethyldisilathiane is faster than with indium. This explains the excess of indium at the surface of the CuInS2 particles, as well as its n-type semiconductivity.