Study On Luminescence And Threshold Properties Based On Copper(Ⅰ) Ternary Halides And Their Flexible Composites

Recently,copper cation has attracted huge attention in replacing poisonous lead to produce high-efficiency lead-free halides.Among them,all-inorganic and non-toxic copper（I）-based ternary halides with high ambient stability and excellent optical properties have become potential candidates in producing stable and high-efficiency optoelectronic devices.This thesis employed simple strategies of liquid-phase synthesis at room temperature,surface functionalization and flexible polymer encapsulation to improve the fluorescence efficiency of copper（I）-based ternary halides,and develop various flexible devices to broaden their applications in full-color displays,solid-state lighting,flexible wearable electronics,energy harvesting and data storage.The research results are as follows:（1）Lead-free,air-stable and yellow light-emitting CsCu₂I₃ microplatelets（MPs）with well-defined smooth surface were synthesized by anti-solvent method at room temperature.The morphology characterization of CsCu₂I₃ MPs confirmed that the introduction of oleic acid（OA）ligand could effectively inhibit the surface pinholes caused by Kirkendall effect,thus improving the luminescence performance of CsCu₂I₃ MPs.It was found that while OA-free CsCu₂I₃ MPs exhibited yellow emission centered at 580 nm with photoluminescence quantum yield（PLQY）as low as 1.57%,the PLQY of the CsCu₂I₃ MPs was dramatically enhanced to 7.85%by capping OA ligands.In addition,the CsCu₂I₃ MPs showed high air-stability towards exposure of the ambient air environment.（2）Multi-color copper（I）-based ternary halides of Cs₃Cu₂I₅、Cs₃Cu₂Cl₅ and CsCu₂I₃ were prepared by a simple anti-solvent method.Stretchable multi-color composite films were developed by embedding the copper（I）-based ternary halides to flexible polymer for light-emitting diodes（LEDs）and triboelectric nanogenerators.In detail,ideal white light emission composite films,with Commission Internationale de L’Eclairage（CIE）coordinates of（0.33,0.34）,were generated successfully by using mixtures of the Cs₃Cu₂I₅and CsCu₂I₃powders.Furthermore,multi-color blue,green,yellow and cool white LEDs were fabricated by combining UV LED chips（310 nm）and the multi-color composite films,with CIE coordinates of（0.15,0.11）,（0.24,0.52）,（0.46,0.50）and（0.29,0.29）,respectively.Besides,the composite film was applied to single-electrode-mode triboelectric nanogenerator with an open-circuit voltage of 28 V and short-circuit current of 170 n A.（3）CsCu₂I₃ thin film was prepared by anti-solvent-assisted spin-coating method and assembled in the structure of Ag/PMMA/CsCu₂I₃/ITO to produce a threshold switching device.The device had low threshold voltage and high air-stability.In addition,the threshold voltage can be reduced from 0.54 V to0.23 V by UV illumination.Multilevel threshold switching behavior can be realized through the modulation of either compliance current or scan rate.Based on the electrode size-and temperature-dependent threshold switching behavior,a mechanism dominated by iodine vacancy filaments was proposed to explain the threshold switching phenomenon.Flexible transparent threshold switching device with outstanding mechanical stability and electrical reliability was also demonstrated.The environment-friendly and flexible threshold switching device based on the CsCu₂I₃ thin film provides a useful exploration for solving crosstalk problem of crossbar array and realizing long-term and low-power applications.