Highly stable lead-free Cs₃Bi₂I₉ perovskite nanoplates for photodetection applications

Lead halide perovskites have received tremendous attentions recently for their excellent properties such as high light absorption coefficient and long charge carrier diffusion length. However, the stability issues and the existence of toxic lead cations have largely limited their applications in optoelectronic area. Herein, we report the synthesis and investigation of highly stable and lead-free Cs₃Bi₂I₉ perovskite nanoplates for visible light photodetection applications. The Cs₃Bi₂I₉ nanoplates were synthesized through a facile solution-processed method, which is also applicable to various substrates. The achieved nanoplates present very good crystal quality and exhibit excellent long-term stability even exposed in moist air for several months. Photodetectors were constructed based on these high-quality perovskite nanoplates for the first time, and display a maximum photoresponsivity of 33.1 mA/W under the illumination of 450 nm laser, which is six times higher than the solution-synthesized CH₃NH₃PbI₃ nanowire photodetectors. The specific detectivity of these devices can reach up to 10¹⁰ Jones. Additionally, the devices exhibit fast rise and decay time of 10.2 and 37.2 ms, respectively, and highly stable photoswitching behavior with their photoresponse well retaining under alternating light and darkness. This work opens up a new opportunity for stable and low-toxic perovskite-based optoelectronic applications.