First principles prediction of the carrier mobilities and optical properties of strained lead free perovskite Cs2SnX6(X=Cl, Br)

Cs2SnX6(X = Cl, Br) are non-toxic perovskites and fairly stable in air. However, the broad band gaps limit their applications. The strain is an effective way to regulate the photoelectrical properties. The calculation results show that unstrained Cs2SnCl6 and Cs2SnBr6 bulk are direct bandgap semiconductors with the band gap of 3.984 eV and 2.491 eV at Γ points. The band gap decreases under compressive strain and increases under tensile strain. Moreover, the electron and hole mobilities of unstrained Cs2SnCl6 are 288.33 and 0.007 cm2V−1s−1, the electron and hole mobilities of unstrained Cs2SnBr6 are 611.31 and 0.02 cm2V−1s−1. The carrier mobility is greatly enhanced by applying compressive strain. The reason is that the charge localization becomes weaker under compressive strain, resulting in better transmission. Besides, the compressive strains result in the band gaps to become smaller, making the absorption edges of Cs2SnX6 (X = Cl, Br) red shifted. Thus the strain can effectively tune the photoelectric properties and facilitate the application of Cs2SnX6(X = Cl,Br) perovskite.