Surface Structures of CsSnI3(001) Films on Au(111)

Although vacancies in perovskite CsSnI3 have been widely investigated to reveal the stumbling block effects on its optoelectronic properties, information concerning its surface structures and defects is very rare so far. Here, the surface structures of CsSnI3 films are studied by scanning tunneling microscopy, together with density functional theory calculations. Three coexisting phases, zigzag, double-chain, and tetramer structures, are found at the CsI terminated (001) surface of the CsSnI3 films grown on Au(111). The zigzag phase should be assigned to a perfect CsI-termination surface. The latter two phases show quasi-square structures belonging to root 2 x root 2 reconstructions, which are due to the orderly Cs vacancies on the surface. Our DFT calculations further indicate that the Cs vacancies on the surface of CsSnI3 perovskite not only play an important role in surface reconstruction but also have an additive effect on reducing the band gap.