Band Gap-Tunable, Chiral Hybrid Metal Halides Displaying Second-Harmonic Generation

The introduction of chirality in lead halide perovskites and related metal halide materials allows for an expansion of their unique and useful properties toward nonlinear optics. However, when synthesizing materials based on less toxic metals antimony and bismuth, the large variability in the crystal structures of their metalates and their tendency to form molecular or chain-like anion motifs can be a challenge when creating tunable materials. Here, we show that using a chiral amine template, we can synthesize an isomorphous family of compounds [(R)-1-(4-F)PEA]4[E2X10] ((R)-1-(4-F)PEA = (R)-1-(4-fluoro)phenylethylammonium; E = Sb and Bi; X = Cl, Br, and I) that combines multiple aspects: the compounds are not only chiral but also feature a trilayered arrangement of cations and anions that allows for facile cleavage and exfoliation. The different combinations of E and X allow for a variation of the onset of absorption between 3.35 and 2.09 eV. Using femtosecond laser spectroscopy, we show that our materials allow for efficient second-harmonic generation. Together with a simple synthesis and good stability, this makes these materials promising candidates for linear and nonlinear optical devices.