Evaluation of Nitrogen Doping of Tungsten Oxide for Photoelectrochemical Water Splitting

Abstract

Thin films of tungsten oxide were fabricated by reactive RF magnetron sputtering for applications related to the direct solar splitting of water. To investigate band gap reduction by nitrogen doping, films were deposited with nitrogen introduced into the sputtering ambient at partial pressures in the range of 0−6 mTorr N2. For dilute doping (pN2 3 mTorr), the diffraction pattern shows the evolution of a new phase that shows an increase in scattering power relative to the pure WO3. For these samples, a reduction of the optical band gap to <2.0 eV is measured. However, the photocurrent density under AM1.5G illumination showed a degradation from 2.68 mA/cm2 for pure WO3 to 0.67 mA/cm2 for the nitrogen doped sample (6 mTorr). The poor photocurrent fo...