Interfaces between Pb-Free Double Perovskite Cs 2 NaBiI 6 and MXenes Sc 2 CO 2 and Sc 2 C(OH) 2 .

First-principles calculations are used to explore the electronic properties of the interfaces between the Pb-free double perovskite Cs 2 NaBiI 6 and the MXenes Sc 2 CO 2 and Sc 2 C(OH) 2 . The effect of the termination group on the stability, ionization potential, electron affinity, and band alignment is investigated. We find a type II band alignment at the Cs 2 NaBiI 6 /Sc 2 CO 2 interface, which permits charge transfer, and a type III band alignment at the Cs 2 NaBiI 6 /Sc 2 C(OH) 2 interface, which results in electron-hole recombination. Sc 2 CO 2 turns out to be highly promising for solar cell applications due to an almost ideal ionization potential difference to Cs 2 NaBiI 6 .