Effects of the Dopant Site on the Absorption Properties of CsPb_1–<i>x</i>M_<i>x</i>I₂Br (M = Ge, Sn, Sr, and Cu): A First-Principles Investigation

Abstract

In order to find low-toxic light-absorbing materials for perovskite solar cells, the electronic structures and optical absorption spectra of doped perovskites CsPb1–xMxI2Br (M = Ge, Sn, Sr, and Cu) have been investigated with the first-principles method. Ge- and Sn-doped perovskites display monotonously decreased band gaps with increasing x, opposite to Sr- and Cu-doped ones. Different from group IV Ge and Sn elements, Sr and Cu dopants show distinct electronic characteristics, that is, weak interaction with halogens because of the d orbitals splitting in octahedral complexes and unique density of states and band-decomposed charge densities. Meanwhile, Ge, Sn, and Cu dopants prefer substituting Pb sites in the CsI-terminated surfaces based on thermodynamic consideration, and the dopants accumulating on surfaces will deteriorate the optical absorption of perovskites based on the comparison of the absorption spectra of various doped structures. Therefore, this study provides a theoretical insight into the declined absorption spectra with the increasing concentration of dopants in experimental observations.