Nitrogen-Doped CuO Thin Films for Photovoltaic Applications

Cuprous oxide (CuO) is a p-type semiconductor with high optical absorption and a direct bandgap of about 2.1 eV, making it an attractive material for photovoltaic applications. For a high-performance photovoltaic device, the formation of low-resistivity contacts on CuO thin films is a prerequisite, which can be achieved by, for instance, nitrogen doping of CuO in order to increase the carrier concentration. In this work, nitrogen-doped p-type CuO thin films were prepared on quartz substrates by magnetron sputter deposition. By adding N gas during the deposition process, a nitrogen concentration of up to 2.3 × 10 atoms/cm in the CuO thin films was achieved, as determined from secondary ion mass spectroscopy measurements. The effect of nitrogen doping on the structural, optical, and electrical properties of the CuO thin films was investigated. X-ray diffraction measurements suggest a preservation of the CuO phase for the nitrogen doped thin films, whereas spectrophotometric measurements show that the optical properties were not significantly altered by incorporation of nitrogen into the CuO matrix. A significant conductivity enhancement was achieved for the nitrogen-doped CuO thin films, based on Hall effect measurements, i.e., the hole concentration was increased from 4 × 10 to 3 × 10 cm and the resistivity was reduced from 190 to 1.9 Ω⋅cm by adding nitrogen to the CuO thin films.