Formation of a Stable Guanidinium–Formamidinium Phase in Bismuth Chloride Perovskites with Broadband Emission

Lead-free zero-dimensional (0D) hybrid bismuth halide perovskites have aroused great interest due to their promising emission properties and good chemical stability. Herein, we report the design and synthesis of mixed-cation-phase 0D guanidinium–formamidinium bismuth chloride, [C(NH2)3]2[CH(NH2)2]3Bi2Cl11 (denoted as Gua2FA3Bi2Cl11), where an individual corner-sharing [Bi2Cl11]5– dimer is completely isolated and surrounded by the mixed Gua+ and FA+ organic cations. The corner-sharing connectivity mode in Gua2FA3Bi2Cl11 differs from that in pristine Gua3BiCl6, featuring an isolated [BiCl6]3– unit. Importantly, Gua2FA3Bi2Cl11 yields remarkable broadband emission spanning from 350 to 750 nm, different from the pristine Gua3BiCl6, showing distinct narrowband emission. Further investigation of photophysical properties reveals that the broadband emission has contributions from both free excitons and self-trapped excitons. Moreover, Gua2FA3Bi2Cl11 not only exhibits excellent photostability under continuous high-power UV lamp irradiation during 70 min but also is humidity stable for over 6 months under ambient conditions. This finding presents a novel molecular engineering strategy for the development of eco-friendly and stable 0D perovskite broadband emitters.