Benzimidazolium Lead Halide Perovskites: Effects of Anion Substitution and Dimensionality on the Bandgap

Abstract

We present the synthesis and structural characterization of a series of benzimidazolium‐based lead halide perovskites including (C 7 H 7 N 2 ) 2 PbCl 4 , (C 7 H 7 N 2 ) 2 PbBr 4 , (C 7 H 7 N 2 ) 2 PbI 4 , and (C 7 H 7 N 2 )PbI 3 , which serves as a platform to investigate the change in optical properties as a function of the halide and the dimensionality of the inorganic sublattice. The structural similarity of the layered systems with A 2 MX 4 stoichiometry was verified by single‐crystal X‐ray diffraction and solid‐state NMR spectroscopy. The optical properties were analyzed by absorption and photoluminescence (PL) measurements, confirming the decrease in bandgap when exchanging the chloride with its higher homologues Br and I. In addition, comparison of the layered compound (C 7 H 7 N 2 ) 2 PbI 4 with the known compound (C 7 H 7 N 2 )PbI 3 reveals an increase in bandgap on going from a 2D to a dimensionally reduced 1D topology. Besides, significant differences in the PL spectra of the halides are observed, which likely are due to recombination of self‐trapped excitons stabilized through lattice distortions or permanent lattice defects in the compounds featuring broad PL emission bands.