Electrochemical Synthesis of Uniform Cu2O Film and Its Photoelectrochemical Properties

Cu2O films as photocathodes were synthesized using direct current electrodeposition method. Utilizing a cyclic voltammetry (CV) test before potentiostatic electrodeposition increased the uniformity and transparency of the Cu2O film. The optical band gap of the Cu2O film obtained through electrodeposition for 7200 s was 2.1 eV, while the one electrodeposited for 1000 s showed a blue shift (2.4 eV). The high transparency of the Cu2O film electrodeposited after the CV test and increased thickness of the electrodeposited film for 7200 s did not affect the value of the photocurrent density. The photocurrent density of the electrodeposited films for time periods more than 200 s did not change considerably. The thickness of the Cu2O film electrodeposited for 200 s was measured to be 70 nm. Electrodeposition for above 200 s resulted in Cu2O films with thicknesses greater than the electron collection length, i.e. 20–100 nm, which was the reason why the photocurrent density was not improved. Electrochemical impedance spectroscopy (EIS) was used to explain charge transfer characteristics of the Cu2O photocathode. The Nyquist plot showed two semicircles, which can be attributed to the charge transfer process across the electrode/electrolyte interface and inside the electrode. The EIS data was fitted with an equivalent circuit and the parameters value was derived. Using the Mott–Schottky plot, the flat band potential and the carrier density were obtained to be 0.19 V vs. Ag/AgCl and 1.3 × 1018 cm–3, respectively.