Exploring the formation of intrinsic p-type and n-type defects in CuO

CuO (cupric oxide) is a well-known p-type semiconductor, suitable for solar cell photovoltaic applications. However, due to the easy formation of defects and Cu-rich layers at the copper(II) oxide heterointerface, commercial application is yet to be successfully implemented. Density functional theory calculations have been employed to study the formation of intrinsic defects and their effect on the electronic properties of CuO. Native impurities were observed, depending on the synthesis conditions, to render the conductivity to p-type or n-type at a low energetic cost, yet with states embedded deep in the electronic band gap. Respective defect pairs, effectively determining the majority charge carriers, were observed to cluster in near proximity of each other, lowering the formation energy substantially. Hydrogen passivation was illustrated to have a positive effect on deep defect states in p-type CuO, without affecting the n-type counterpart. Outlined results were found to support the experimentally observed low photoresponse of CuO and further illustrate some of the difficulties related with achieving high-performance samples.