Nitrogen-Doped Cu₂O Thin Films for Photovoltaic Applications

Cuprous oxide (Cu₂O) 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 Cu₂O thin films is a prerequisite, which can be achieved by, for instance, nitrogen doping of Cu₂O in order to increase the carrier concentration. In this work, nitrogen-doped p-type Cu₂O thin films were prepared on quartz substrates by magnetron sputter deposition. By adding N₂ gas during the deposition process, a nitrogen concentration of up to 2.3 × 10²¹ atoms/cm³ in the Cu₂O 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 Cu₂O thin films was investigated. X-ray diffraction measurements suggest a preservation of the Cu₂O 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 Cu₂O matrix. A significant conductivity enhancement was achieved for the nitrogen-doped Cu₂O thin films, based on Hall effect measurements, i.e., the hole concentration was increased from 4 × 10¹⁵ to 3 × 10¹⁹ cm^-3 and the resistivity was reduced from 190 to 1.9 Ω⋅cm by adding nitrogen to the Cu₂O thin films.