Study of photoelectrochemical conductivity mechanism and electrochemical impedance spectroscopy of bulk CuInTe2 – Electrolyte interface

Abstract

CuInTe2 (CIT) thin films were electrochemically deposited in an aqueous electrolyte on fluorine doped tin oxide (FTO) coated glass substrates for potentials ranging from −0.6 V to −0.9 V at pH 4. Films were annealed at 400 °C for 15 min in air ambient. Both as-deposited and annealed layers were characterized by various characterization techniques. The conductivity type of the CIT layers was studied by photoelectrochemical (PEC) response and solid–electrolyte interface by impedance spectroscopy. As-deposited samples confirmed amorphous nature of CIT in contrast to that of polycrystalline films obtained upon annealing. Three prominent reflections (1 1 2), (2 2 0)/(2 0 4) and (3 1 2)/(1 1 6) of chalcopyrite CIT were obtained upon annealing. The optical band gap values ∼0.90 eV and 1.08 eV and ∼0.88 eV and 1.01 eV were estimated for as-deposited and annealed CIT layers deposited at −0.7 V and −0.8 V respectively. The most prominent A1 mode observed at 123 cm−1 in the Raman spectra of chalcopyrite CIT was shifted towards lower wavelengths due to the development of tensile strain. Very compact, well adhesive and void free globular layers were deposited at pH 4. The indium content was found to be increased with increasing the deposition potential which agrees well with the overpotential deposition of indium. Photoelectrochemical (PEC) study confirms the growth of p-type CIT layers. The negative resistance at higher frequency domain (3 MHz to 10 kHz) from electrochemical impedance spectroscopy (EIS) confirms the power/energy giving nature of CIT/electrolyte interface at higher frequency and diffusion mechanism of ionic species dominate at lower frequency region.