Engineering the properties of NiO thin films by copper incorporation for optoelectronic applications

Abstract

In the present work, nickel oxide (NiO) thin films were successfully deposited on glass substrates using the spray pyrolysis technique. The effect of copper (Cu) doping on the structural, optical, and electrical properties of the films was systematically investigated. All Cu doped NiO thin films exhibited a cubic crystal structure with a preferred orientation along the (111) plane. The minimum crystallite size of 22.45 nm was obtained at a Cu concentration of 6 at.%. This indicates improved crystallinity and enhanced structural ordering compared with the other films. The average optical transmittance varied between 67% and 87% in the visible region. The band gap energy decreased from 3.43 to 3.60 eV and the Urbach energy increased from 0.523 to 0.935 eV, as the Cu doping increased from 0 to 12 at.%. This indicates that the observed behavior can be attributed to the formation of impurity levels and defect states within the band gap, which facilitate optical transitions at lower energies. Electrical measurements showed a maximum conductivity of 2.916 (Ω.cm)–1 at 12 at.% Cu, indicating improved charge carrier transport. However, the enhancement in structural, optical, and electrical properties suggests that Cu doped NiO thin films are promising candidates for optoelectronic applications, particularly as window layers in solar cells.