Dion-Jacobson Lead Bromide Perovskites with 1,4-Butanediammonium Cations: Lattice Dynamics, Phase Transitions, Dielectric Switching, and Optical Properties.

Hybrid lead halides incorporating diammonium cations have attracted wide attention due to their excellent optoelectronic properties. We report the crystal structures and vibrational, dielectric, and optical properties of three bromides comprising 1,4-butanediammonium (BDA2+) cations, namely, n = 1 BDAPbBr4, and n = 3 (BDA)(MA)2Pb3Br10 and (BDA)(EA)2Pb3Br10 (MA+ = methylammonium; EA+ = ethylammonium). The studies show that the phase transitions in (BDA)(MA)2Pb3Br10 and (BDA)(EA)2Pb3Br10 are associated with a pronounced change in the BDA2+ conformation and counterintuitive shortening of the interlayer distance in the high-temperature phases. (BDA)(MA2)Pb3Br10 exhibits bistable dielectric switching, and (BDA)(EA)2Pb3Br10 is a rare example of a tristable dielectric switch. Both compounds emit narrow-band purplish-blue photoluminescence (PL). BDAPbBr4 exhibits both narrowband and broadband PL, attributed to free (FEs) and self-trapped excitons (STEs), respectively. The intensity ratio of these PL bands shows a pronounced change on cooling, leading to PL color tuning from blue at 295 K to yellow at 80 K. Most importantly, in the 160-195 K range, the emission color appears as near-neutral white, and at 155 K, the emission color is very similar to light generated by the tungsten bulb. The crystal structures reveal that the different optical properties of the studied perovskites can be related to different n values, Pb-Br bond lengths, and distortion of the octahedral layers.