Band structure, optical properties, and band alignment of Cu-based delafossites

Recently, CuGaO₂ has been shown to hold great potential as inorganic hole transport layers (HTLs). In this work, we study the electronic band structure, optical properties and band alignment of all the Cu-based delafossites using the state-of-the-art GW-BSE approach. All the delafossites are shown to be indirect large band gap semiconductors with large exciton binding energies, varying from 0.24 to 0.44 eV, in consistent with experimental findings. Taking into consideration the exciton binding energy, the calculated band gap agrees quite well with experiments. Based on the GW band structure, we calculated the band alignment of the delafossites using the Anderson’s rule. By comparing the band alignment between the delafossites and MAPbI₃, we predict that, beside CuGaO₂, CuScO₂, CuYO₂, and CuCrO₂ are also suitable as HTLs in MAPbI₃ based solar cells. In addition, the suitability of CuCrO₂ as HTL has also been verified by our experimental collaborators.