Characterization of copper indium ditelluride/electrolyte interface utilizing electrochemical impedance spectroscopy

Copper indium telluride (CIT) is a promising semiconductor material for use in thin film solar cells, especially photoelectrochemical solar cells (PESC). Impedance measurements were used to evaluate the relative band edge positions of polycrystalline n-CuInTe2 electrodes in various aqueous electrolytes, by measuring the extrapolated flat-band potentials, Vfb. By varying applied dc potential, frequency and pH of the electrolyte, the semiconductor-electrolyte interfaces are studied through capacitance measurements and Mott-Schottky analysis. The flat-band potential and carrier concentrations were determined from the Mott-Schottky plots. It was found that Vfb could be shifted depending on the pH of the electrolyte, while it is independent of the testing frequency. The changes in Vfb with pH could be due to surface states and other modifications through etching and polishing. The surface carrier concentrations were found to increase with pH. The different surface chemistry studied by X-ray photoelectron spectroscopy might account for this change.