The difference on the physical properties between CsPbX3 and Cs2PbX6: A comparative study

A complete theoretical investigation is performed to study the physical properties of all-inorganic halide perovskites CsPbX3 and Cs2PbX6 (X ​= ​Cl, Br, I). The various physical properties are compared and discussed. The results show that the bond length Pb−X of Cs2PbX6 is shorter than that of CsPbX3. Six compounds are ductile materials and mechanically stable. According to the phonon spectrum calculations, Cs2PbCl6 and Cs2PbBr6 are dynamically stable, while Cs2PbI6 is unstable. The band gap of CsPbX3 is larger than that of Cs2PbX6. The strong spin−orbit coupling effect is found for CsPbX3, while it has little influence on the band structure of Cs2PbX6. The mobility between the electron and hole varies from CsPbX3 to Cs2PbX6. The different in physical properties mainly results from the different valence states of lead. The results further indicate that Cs2PbBr6 has an ideal band gap value and shows a stronger light absorption than that of CsPbI3 between 450 and 800 ​nm, which is expected to be a promising candidate for perovskite solar cells. Therefore, our study can provide further interest for exploring the potential of all-inorganic stable lead-based double perovskites in optoelectronic devices.