Influence of grain boundaries and interfaces on the electronic structure of polycrystalline CuO thin films

Abstract

Abstract CuO thin films were grown by reactive magnetron sputtering and analyzed with respect to their structural, chemical, optical, and electrical properties. The films are strongly p‐type with carrier concentrations of cm −3 . Carrier accumulation at grain boundaries is evident from temperature and gas phase dependent conductivity measurements. The films show high absorption coefficients with a band gap of approximately 1.5 eV. Interface formation with TiO 2 and Au was studied by photoelectron spectroscopy. Regarding the TiO 2 /CuO interface, a strong band bending in the TiO 2 substrate and a valence band offset of eV were observed. The TiO 2 conduction band is therefore approximately midgap of CuO at the interface. CuO is chemically reduced upon Au deposition but an ideal ohmic contact is formed with a Fermi level at the valence band maximum of CuO. Solar cell device structures were prepared of fluorine‐doped SnO 2 /TiO 2 substrates and Au back contacts, revealing open circuit voltages of <0.15 V and photocurrent densities of <0.1 mA/cm 2 . The photoactivity of the structures is ascribed mostly to the TiO 2 substrate.