Two-step colloidal synthesis of micron-scale Bi2O2Se nanosheets and their electrostatic assembly for thin-film photodetectors with fast response

Recently discovered bismuth oxychalcogenide (Bi2O2Se) has aroused great interest due to its ultrahigh carrier mobility, tunable band gap and good environmental stability, making it a promising candidate for high-performance electronics and optoelectronics. Their synthesis by colloidal approaches represents a cost-effective alternative to well-established chemical vapor deposition methods, and the resulting electronic-grade inks are important for large-area printed or wearable electronics. However, it is still challenging to control the colloidal growth of Bi2O2Se nanosheets in solution in addition to their assembly into high-performance thin films. Here, we report a two-step colloidal synthesis of Bi2O2Se nanosheets by separating the seeding and growth steps, thereby achieving controllable production of nanosheets with a lateral size of 1.4 mm and a thickness of 10 nm at optimized reaction conditions. These Bi2O2Se nanosheets are electrostatically assembled into large-area thin films, from which a photodetector is fabricated with a responsivity of 6.1 A/W and a short response time of 368 ms under the 520-nm laser illumination. The device exhibits fast response to modulations as high as 100 kHz, along with a -3 dB bandwidth of 1 kHz. This work provides an important understanding of the controlled colloidal synthesis of Bi2O2Se nanosheets, and demonstrates their potential applications in fast photodetectors. (C) 2021 Chinese Chemical Society and Institute of Materia Medica, Chinese Academy of Medical Sciences. Published by Elsevier B.V. All rights reserved.