Hybrid Charge-Transfer Semiconductors: (C7H7)SbI4, (C7H7)BiI4, and Their Halide Congeners

Hybrid metal halides yield highly desirable optoelectronic properties and offer significant opportunity due to their solution processability. This contribution reports a new series of hybrid semiconductors, (C 7 H 7 )MX 4 (M = Bi 3+ , Sb 3+ ; X = Cl - , Br - , I - ), that are composed of edge-sharing MX 6 chains separated in space by π-stacked tropylium (C 7 H 7 + ) cations; the inorganic chains resemble the connectivity of BiI 3 . The Bi 3+ compounds have blue-shifted optical absorptions relative to the Sb 3+ compounds that span the visible and near-IR region. Consistent with observations, DFT calculations reveal that the conduction band is composed of the tropylium cation and valence band primarily the inorganic chain: a charge-transfer semiconductor. The band gaps for both Bi 3+ and Sb 3+ compounds decrease systematically as a function of increasing halide size. These compounds are a rare example of charge-transfer semiconductors that also exhibit efficient crystal packing of the organic cations, thus providing an opportunity to study how structural packing affects optoelectronic properties.