Intracation and Interanion-Cation Charge-Transfer Properties of Tetrathiafulvalene-Bismuth-Halide Hybrids

Tetrathiafulvalene (TTF) derivatives as promising hole transport materials in assembling hybrid halide perovskite solar cells have attracted great attention; however, electron transfer or charge-transfer (CT) between TTF and metal halides has been studied with less detail at the molecular level. Using molecular models, we herein report four new TTF-bismuth-halides assembled by methylated or protonated bis(4'-pyridyl)-tetrathiafulvalene cations, (MePy)₂TTF or (HPy)₂TTF, and bismuth-halide anions. Single crystal analysis showed that the cations are stacked to form a TTF column, and the bismuth-halide anions are inlaid between the TTF columns with anion-cation interactions. In these compounds, the main contribution to CT is the intracation CT, namely intramolecular CT (IMCT) from TTF moiety to pyridinium group. However, the anion to cation CT (ACCT) has a significant effect on the IMCT and physical properties. The different anion-cation interaction modes result in different synergistic effects of IMCT and ACCT, which modified the band gaps and photocurrent properties of the hybrids. The research gives a clear image of structure-property relationship and provides a perspective on the design of new perovskite materials at the molecular level.