Tuning the electronic band gap of Cu₂O via transition metal doping for improved photovoltaic applications

Cu2O is a widely known p-type semiconductor with a band-gap value suitable for photovoltaic applications. However, due to its parity-forbidden nature of the first interband transition and high carrier recombination currents, Cu2O has failed to reach commercial application. Hybrid density functional theory has been used to study the effect of transition metal dopants on the electronic and optical properties of Cu2O. Substitutional transition metal dopants, incorporated on the copper site, allow band-gap tunability by creating a range of defect states in the electronic structure, from shallow levels to deep intermediate bands. The preferred position of the dopants is in the vicinity of copper vacancies, which are naturally found in Cu2O and are responsible for its p-type conductivity. Impurity levels created via extrinsic transition metal dopants increase substantially the capacity of Cu2O to absorb light, reaching values close to 10%. First row transition metal dopants thus show potential for considerable improvement of the overall photovoltaic performance of Cu2O.