Dion-Jacobson Lead Bromide Perovskites with 1,4-Butanediammonium Cations: Lattice Dynamics, Phase Transitions,...

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.