A InSn 2 S 6 ( A = K, Rb, Cs)─Layered Semiconductors Based on the SnS 2 Structure.

RbInSn 2 S 6 and CsInSn 2 S 6 are yellow two-dimensional (2D) semiconductors featuring anionic SnS 2 -type layers of edge-sharing (In/Sn)S 6 octahedra. These structures are directly derived from the parent structure of SnS 2 by replacement of Sn 4+ atoms with A + and In 3+ atoms. The compounds crystallize, isotypic to the ion-exchange material KInSn 2 S 6 . They adopt the triclinic space group R 3̅ m (no. 166). The compounds have similar indirect optical band gaps of 2.31(5) eV for Rb and 2.47(5) eV Cs. The measured work functions for each material are ∼5.38 eV. The density functional theory-calculated effective mass values exhibit strong anisotropy due to the 2D nature of the crystal structures and in the case of CsInSn 2 S 6 for hole carriers along the a , b , and c crystallographic directions are 0.30 m 0 , 0.34 m 0 , and 2.54 m 0 , respectively, while for electrons are 0.06 m 0 , 0.07 m 0 , and 0.47 m 0 , respectively.