First-principles study on the electronic properties of atom passivating CsPbI2Br surface

The electronic properties of the bulk CsPbI2Br and the passivation of CsPbI2Br (110) surface states are calculated by using first-principles calculations. It is found that the band gap of CsPbI2Br is 1.42eV by using the generalized gradient approximation of the Perdew-Burke-Ernzerhof function. The band gap is about 1.96eV by using the more complex Heyd-Scuseria-Ernzerhof mixed functional, which is closer to the experimental value of 1.92eV. The valence band top of CsPbI2Br bulk is mainly contributed by I-5p orbital and Br-4p orbital, and the conduction band bottom is mainly contributed by Pb-6p orbital. Through the calculation of CsPbI2Br (110) surface states passivated by Cl, F and H atoms, it is found that H atom has the best passivation effect. Its adsorption energy value fluctuates less, it is less sensitive to the adsorption position, and the adsorption is stable. Followed by F atom, its passivation effect is worse than that of H atom, but better than that of Cl atom. Although the passivation position has a certain influence on it, it has little effect. The Cl atom is most affected by the passivation position. The different positions of passivated atoms have a significant impact on adsorption energy. The adsorption stability is poor, and the passivation effect is also poor. Through analyzing the charge density difference and Bader charges, it is found that the H atom gets more electrons from the I atom, which is beneficial to passivate surface states. The electron-acquiring ability of the F atom is inferior to that of the H atom and is superior to that of the Cl atom. The electron-acquiring ability and passivation ability of Cl atom are the weakest among the three elements.