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

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journal contribution
posted on 2009-08-25, 00:00 authored by Fabrice M. Courtel, Royston W. Paynter, Benoît Marsan, Mario Morin
We report on the growth of CuInS2 n-type semiconductive particles, prepared using a modified Czekelius’s colloidal method, as well as 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 was obtained, which was greater at the surface (CuIn1.45S1.9 at 450 °C) than in the bulk (CuIn1.04S1.74 at 450 °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-methyltetrazolate (T)/di-5-(1-methyltetrazole) disulfide (T2) and 5-trifluoromethyl-2-mercapto-1,3,4-thiadiazolate (G)/5,5′-bis(2-trifluoromethyl-1,3,4-thiadiazole) disulfide (G2). Fermi levels of −3.95 eV and −3.64 eV and majority charge carrier densities of 4.1 × 1018 and 1.8 × 1018 cm−3 were determined, respectively, using these redox couples. On the basis of the CuInS2/electrolyte energy level diagrams, the G/G2 redox couple is expected to lead to a 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.