高稳定性、高量子产率CsPbBr_(3)@CsPb_(2)Br_(5)纳米晶体的可控合成及性能

Controllable synthesis and performance research of CsPbBr_(3)@CsPb_(2)Br_(5) nanocrystals with high stability and quantum yield

近年来,全无机铅卤钙钛矿材料(CsPbX_(3))因其优异的光学性能和相对于有机-无机杂化钙钛矿更好的稳定性等优势,从各类钙钛矿中脱颖而出,成为当前最具潜力的光电材料之一.本研究从提高全无机铅卤钙钛矿的稳定性出发,从材料的合成入手,采用创新方法:伪包晶法,利用溶液中的包晶反应实现对CsPbBr_(3)钙钛矿的同元素表面修饰;通过合理控制反应物的配比,制备出表面均匀分布CsPb_(2)Br_(5)相的CsPbBr_(3)@CsPb_(2)Br_(5)复合型钙钛矿.复合材料中同元素CsPb_(2)Br_(5)相的存在降低了CsPbBr_(3)的表面缺陷浓度,并对CsPbBr_(3)相起到一定的保护作用,提高了CsPbBr_(3)钙钛矿的发光和稳定性能.

In the past decade,all-inorganic lead halide perovskite nanocrystals have emerged as promising active materials for optoelectronics,such as photovoltaics,lasers,and photodetectors,owing to their size-tunable optical bandgaps,attractive light absorption,and extraordinary charge-transport properties.Besides these photoelectric applications,nanostructured lead halide perovskites have shown good wavelength tunability,high photoluminescence quantum yields(PLQYs),and high color purity with narrow full width at half maximum(FWHM),rendering them potential candidates for highperformance light-emitting diodes(LEDs).Unfortunately,despite the remarkable advancements of all-inorganic lead halide perovskite,the problem of their unsolved stability upon exposure to thermal and humid environments has greatly hampered their further practical and commercial applications.Thus,many researchers have been bent their mind to improve the water stability of perovskites from moist air or solutions,such as moisture-impermeable polymer embedding,water proof organic ligand coating,inorganic encapsulation,and superhydrophobic framework structures.CsPb_(2)Br_(5),which has an indirect band gap of 3.87 e Vand a two-dimensional structure with[Pb_(2)Br_(5)]–layers spaced by Cs+cations,has been reported to modify the stability of CsPbBr_(3).However,the arrangement of CsPbBr_(3) and CsPb_(2)Br_(5) phases,which is significant for both the improvement of the stability and the investigation of the mechanism,is still a bottleneck.In order to improve the stability of the all-inorganic lead halide perovskite,an innovative method—Pseudo-peritectic method,that is a peritectic reaction in the solution,was proposed to achieve the same element surface modification of the CsPbBr_(3) perovskite by reasonably controlling the ratio of reactants.In our experiment,the CsPbBr_(3) nanocrystals were synthesized by solvothermal method first,and then injected into the PbBr_(2) solution.The peritectic reaction between CsPbBr_(3) and PbBr_(2) occurred in the solution.The synthesized CsPb_(2)Br_(5) phase is excepted to disperse on the surface of the as-prepared CsPbBr_(3) phase.The study of the crystal structure,morphology,composition and photoluminescence of the prepared composite perovskite CsPbBr_(3)@CsPb_(2)Br_(5) were carried out.The X-ray diffraction(XRD)pattern and morphologies of the samples synthesized by the pseudo-peritectic method indicated that the composite perovskite CsPbBr_(3)@CsPb_(2)Br_(5) with uniformly distributed CsPb_(2)Br_(5) phase on the surface can be prepared by controlling the ratio of reactants.With the ratio of CsPbBr_(3):PbBr_(2) changing from 1:1 to 2.5:1,the CsPb_(2)Br_(5) phase increased.When the ratio of CsPbBr_(3):PbBr_(2) was 2.5:1,the CsPb_(2)Br_(5) phase well dispersed on the surface of the as-prepared CsPbBr_(3) phase.However,when the ratio increased to 3:1,even 5:1,the synthesized CsPb_(2)Br_(5) phase decreased.The photoluminescence spectroscopy and fluorescence quantum yield of the composite material showed that the presence of the same element phase CsPb_(2)Br_(5) greatly improved the stability and the photoluminescence(PL)properties.The uniformly distributed CsPb_(2)Br_(5) phase on the surface of the composite material reduced the surface defect concentration of CsPbBr_(3),and protected the CsPbBr_(3) phase to a certain extent,that improved the luminescence and stability of the CsPbBr_(3) perovskite.The method for synthesizing composites provides a new pathway to ensure a controllable surface modification structure,which would dramatically enhance the stability of CsPbBr_(3) nanocrystals in highly polar solvents such as water.The waterstable enhanced nanocrystals make it possible for long-term stable electronic applications in the atmosphere.