Ultrafast self-powered CsPbCl3 ultraviolet photodetectors with choline chloride for surface passivation and charge transport regulation

Abstract

The emerging wide-bandgap and chemically stable CsPbCl₃ perovskites are of significant interest by virtue of their broad application prospects in high-precision ultraviolet (UV) detection. Although many fabrication techniques have been developed to improve the quality of CsPbCl₃ polycrystalline films for their use in self-powered UV photodetectors, the high intrinsic trap density in the surface and grain boundaries of the films restricts the improvement of the device performance. Herein, organic choline chloride (ChCl) is introduced to passivate the surface and grain boundary defects of the evaporated CsPbCl₃ films. Systematic experimental characterization and theoretical calculations validate that the bond formation between the ChCl and uncoordinated positively charged Pb²⁺ cations helps to alleviate the Cl⁻ vacancy defects and Pb–Cl antisite substitution defects as well as enhance the structural stability of CsPbCl₃ perovskites. The ChCl modification can also tailor the band alignment and expand the built-in potential of the device, conducive to the charge extraction and suppression of the non-radiative recombination loss. Thus, the ChCl-modified photodetectors exhibit a pronouncedly augmented UV detection performance compared to their non-modified counterparts. The best-performing photodetector achieves a fast UV response speed of 1.85 μs, a high on/off ratio of up to 3.91 × 10⁵ and an excellent specific detectivity of 8.64 × 10¹² Jones in a self-driven mode. In addition, the ChCl-modified device presents superior comprehensive stability when exposed to consecutive UV light soaking, humidity and heat, conspicuously promoting the practical applications of CsPbCl₃-based UV detectors.