Novel lead-free bismuth-based perovskite-like (BrC 5 H 13 N) 3 Bi 2 Br 9 : synthesis, structural investigations and optoelectronic properties

Lead-free organic-inorganic hybrid perovskites have attracted increasing attention owing to their advantages of reduced toxicity, photo-detectability, switchable dielectric device application, ferroelectric properties and distinctive optical characteristics. Despite their promising features, the chemical engineering of hybrid perovskites remains a challenge, as identifying the appropriate strategies is essential to achieve the desired properties such as controlled bandgap energy and phase transition behaviours. Numerous approaches have been explored to optimize these characteristics. In this study, we employed halogenation of the organic component as a targeted strategy to enhance the stability and performance of hybrid perovskite materials. This approach enabled the successful synthesis of a non-centrosymmetric halobismuthate (BrC₅H₁₃N)₃Bi₂Br₉ compound (BrC₅H₁₃N⁺: (2-bromoethyl)trimethylammonium), which exhibited excellent optic and electric properties and crystallized in the non-polar P2₁2₁2₁ space group. The inorganic framework was precisely arranged with [Bi₂Br₉]^3- polyhedra that were face-shared and separated by organic cations, resulting in an A₃B₂X₉-type structure. Additionally, the compound (BrC₅H₁₃N)₃Bi₂Br₉ possessed an indirect band gap of 2.58 eV, which suggests this material's semiconductor character. Photoluminescence (PL) studies revealed that the compound exhibited a broad band emission at about 730 nm. The electrical properties as a function of frequencies and temperatures showed the contribution of the grain and grain boundary to conduction, and AC conductivity confirmed the semiconductor behaviour. The activation energy suggested the combination of ionic and electronic conduction. These findings enrich the understanding on the behaviour of A₃B₂X₉-type low-dimensional hybrids and holds promise in extending the application of lead-free hybrids to the field of ferroelectric, electric and optic materials.