Effect of Π-Π Conjugation in Benzylammonium Cations on Crystal Structure, Morphology, Optical Properties, and Optoelectronic Performance of Bi-Based Perovskite

Bi-based organic halides have attracted widespread attention as potential substitutes for lead-based organic halide perovskites and have been explored and applied in many optoelectronic devices. The rational design of organic Bi-based halides is a popular research topic. In this work, we used benzylammonium (BA) cations to synthesize BA 3 Bi 2 I 9 (BBI) perovskite material and FA 3 Bi 2 I 9 (FBI, FA [formamidinium]) as control. We observe that the benzene rings in BA cations overlap with each other due to the benzene rings Π-Π conjugation in the crystal structure of BBI, which exhibits large interplanar spacing due to large BA ions. BBI has preferential orientation along the (020) crystal plane. Due to conjugation, scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS) mapping images indicate that the surface of the BBI thin film is smoother and more uniform than that of the FBI thin film. We fabricated the device by growing thin films of BBI and FBI on ITO interdigital electrodes. The photodetector based on BBI SC exhibits stability and regularity with turning on/off of the light at different intensities (10, 20, 30, and 40 W m −2 ) and wavelengths (386, 397, 405, and 433 nm). The ultraviolet–visible (UV–vis) absorption and reflection spectrum analysis shows that BBI has a slightly wider bandgap than FBI. This study can provide some ideas for the design Π-Π conjugation in organic metal halides.