Photoimaging with Color-Sensing Abilities by Tuning the Band Gap of a Single-Crystal Lead-Free Perovskite

Photodetectors (PDs) composed of lead-free metal halideperovskiteshave been a shining topic in optoelectronics. However, it is debatablewhether perovskites are an n-type or p-type semiconductor with a director indirect band gap. Furthermore, to date, little research has beenconducted on lead-free metal halide perovskites with color-sensingabilities. Herein, for the first time, single-crystal MA(3)Bi(2)I(3x )Br(9-3x ) (x = 0, 1, 2, and 3) perovskiteswere systematically studied, and the results showed that MA(3)Bi(2)I(9) is a p-type direct-band-gap semiconductor,whereas MA(3)Bi(2)Br(9) is an n-type indirect-band-gapsemiconductor. Furthermore, the band gap of MA(3)Bi(2)I(3x )Br(9-3x ) (x = 0, 1, 2, and 3) perovskites can be systematicallytuned from 2.06 to 2.55 eV, affording it with color-sensing abilitiesfrom 450 to 580 nm, respectively. The representative Au-MA(3)Bi(2)I(9)-ITO (ITO = indium tin oxide) PD exhibitsa superior self-powered photodetecting performance with a high responsivity(15.8 mA W-1; 580 nm, 1.0 mW cm(-2)), detectivity (8.1 x 10(11) Jones), an on/off ratio(4231), LDR (72.5 dB) and a fast response speed (rise time of 2 mu sand decay time of 29 mu s). This study not only facilitates thetheoretical understanding of the band gap of perovskite materialsbut also sheds light on the application of lead-free perovskites inobject interaction and color perception.