Enhanced On–Off Ratio Photodetectors Based on Lead‐Free Cs3Bi2I9 Single Crystal Thin Films

• Published in: Advanced functional materials Vol. 30; no. 12
• Main Authors: Li, Wen‐Guang, Wang, Xu‐Dong, Liao, Jin‐Feng, Jiang, Yong, Kuang, Dai‐Bin
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.03.2020
• Subjects: Carrier mobility; Charge transfer; Crystallization; Cs3Bi2I9; Diffusion length; Indium tin oxides; Lead compounds; Materials science; Metal halides; Optoelectronic devices; Perovskites; photodetectors; Photometers; single crystal thin films; Single crystals; stability; Thin films; Toxicity
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201909701

Hybrid organic–inorganic lead halide perovskite single crystal thin film (SCTF) recently has attracted enormous interest in the field of optoelectronic devices, since it efficiently resolves the trade‐off between thickness and carrier diffusion length. However, the toxicity of lead element and the instability induced by organic component still hinder its future developments. In this work, lead‐free all‐inorganic Cs3Bi2I9 SCTF with a high orientation along (00h) has been in situ grown on indium tin oxide (ITO) glass via a space‐limited solvent evaporation crystallization method. The trap density of Cs3Bi2I9 SCTF (5.7 × 1012 cm−3) is 263 folds lower than that of the polycrystalline thin film (PCTF) counterpart, together with a 5‐order‐of‐magnitude higher carrier mobility. These superior charge transfer properties enable a photoresponse on–off ratio as high as 11 000, which far surpasses that of the PCTF device by 460 folds, comparable to the lead halide perovskite. Furthermore, the Cs3Bi2I9 SCTF photodetector exhibits outstanding stability even without any encapsulation, whose initial performance is well maintained after aging 1000 h in humid air of 50% RH or continuous on–off light illumination for 20 h. This work will pave the way to produce new families of high‐performance, stable, and nontoxic perovskite SCTF for future optoelectronic applications. High‐quality Cs3Bi2I9 single crystal thin film (SCTF) with ≈1 µm in thickness and 4 mm in lateral size is grown via a space‐limited solvent evaporation crystallization method. The Cs3Bi2I9 SCTF–based photodetectors exhibit superior photodetecting performance such as a high on–off ratio of 104, low dark current, wide linear dynamic range, and fast response speed.