Li Doped CuO Film Electrodes for Photoelectrochemical Cells

Li is known for its ability to increase the conductivity of CuO films. Li doped CuO nanoparticles prepared by flame spray pyrolysis and followed by spin coating for the film preparation were studied at dopant concentrations of 0.5 at %, 2 at %, 3.5 at % and 5 at %. The photocurrent density and photon-to-hydrogen conversion efficiency increased by a factor of five to ten when introducing Li into CuO. This is attributable to the increase in the electrical conductivity of the film by almost two orders of magnitude, i.e. from 2 × 10−6 ∼ 4 × 10−6 S/cm to 7 × 10−5 ∼ 3 × 10−4 S/cm, and thus the increase in the lifetime of the photogenerated charge carriers. The best photocurrent density and photon-to-hydrogen conversion efficiency was 1.69 mA/cm2 and 1.3%, respectively, corresponding to the film prepared by 2.0 at % Li-CuO sintered at 450°C for 1 hr with the thickness 1.7 μm at bias voltage of −0.55 V vs. Ag/AgCl in 1M KOH and under 1 sun illumination. Furthermore, the charge carrier density was estimated based on the Mott-Schottky plot to be 4.2 × 1021 cm−3 which is almost double the charge carrier densities obtained by other doping conditions. The high carrier charge density was also confirmed by the higher photocurrent density.