Doping effects on the optoelectronic properties and the stability of Cs3Sb2I9: Density functional theory insights on photovoltaics and light-emitting devices

In this work, we address a knowledge gap regarding how cation and anion doping affect the stability and optoelectronic properties of Cs3Sb2I9 perovskites. We have employed Density Functional Theory (DFT) to investigate structures doped with Ag, In, Mo, Nb, Sc, Bi, Br and Cl in both 0D hexagonal P63/mmc and 2D trigonal P 3¯ m1 Cs3Sb2I9 polymorphs. Our results show that doping with either Sc, Bi, or In leads to negative decomposition energy. Doping with Ag or In results in a reduced band gap while enhancing absorption, offering beneficial enhancements for LED and photovoltaic applications. Mo and Nb doping facilitate d-d transitions at lower energies, which is also significant for light emission applications. Conversely, halogen doping allows for fine-tuning the band gap with minimal changes in effective mass, accompanied by lattice parameter contraction yielding more stable Sb-X bonds. Additionally, our analysis demonstrates that the 0D polymorph allows for easier dopant incorporation, leading to improved stability compared to the 2D structure. The results from this study offer important directions to be explored by experimentalists in the development of efficient energy conversion materials.