Passivating the vacancy defects of CsPbCl3 polycrystalline films by a Cl-containing ionic liquid for self-powered, charge-transport-layer-free UV photodetectors

Abstract

The emerging wide-bandgap CsPbCl₃ perovskite shows great potential for applications in ultraviolet (UV) detection due to its excellent UV response property and UV irradiation durability. However, the abundant Cl vacancies existing in CsPbCl₃ would cause severe charge recombination losses, significantly decreasing the detection performance of the photodetectors, especially for the self-powered ones. Herein, a Cl-containing ionic liquid (IL) of 1-butyl-2,3-dimethylimidazolium chloride ([BMMIm]Cl) is introduced to passivate the surface defects of the evaporated CsPbCl₃ polycrystalline films. Experimental characterizations and density functional theory calculations demonstrate that the electron-rich nitrogen and chlorine atoms in the [BMMIm]Cl layer can bond with the uncoordinated positively charged Pb²⁺ ions, effectively suppressing the Cl vacancy defects of the CsPbCl₃ films. The IL layer can also help to increase the structural stability of CsPbCl₃ and ameliorate the energy level alignment of the devices. These all contribute to a faster charge transport process with a lower non-radiative recombination rate, yielding a pronounced augmentation in the device performance. The best-performing [BMMIm]Cl-modified photodetector delivers an ultrafast response time of 1.74 μs, an excellent on/off ratio of 2.70 × 10⁵, and a high specific detectivity of 6.19 × 10¹² Jones at 0 V bias. Moreover, the as-fabricated CsPbCl₃ photodetectors exhibit salient stabilities under continuous UV illumination and thermal attacks at 85 °C in air. Since no charge transport layer is applied and carbon electrode is chosen to replace the noble metal electrode, the whole production costs of our devices are quietly low. Our work provides a feasible strategy for the scalable production of self-powered, low-cost, and high-performance UV photodetectors.