Lead Halide Perovskite Nanocomposites:Controllable Construction And Their Optoelectronic Properties

In recent years,lead-halide perovskite nanocrystals have been widely used in optoelectronic devices and other fields due to their excellent optoelectronic properties,simple synthesis methods,and low cost.However,due to the ionic properties of perovskite nanocrystals and the dynamic binding of surface ligands,their unsatisfactory stability and device efficiency still need to be further improved and other problems still seriously restrict their rapid development and practical applications.At present,the construction of lead-halide perovskite nanocrystalline composite structure is one of the effective methods to improve its stability and optoelectronic properties.Although researchers have successfully prepared a series of heterojunction structures based on perovskite nanocrystals,there are still problems such as complex synthesis strategies and relatively single structures or components.Therefore,it is necessary to develop simple and reliable preparation methods and synthesize novel and efficient heterojunction structures.In this paper,starting from the controllable preparation of perovskite nanocrystals,various methods are designed to synthesize heterojunction structures based on perovskite nanocrystals.Its potential in optoelectronic devices,the specific research contents are as follows:1.The CsPbX₃/Pb₃（PO₄）₂ composite nanocrystals with uniform size and tunable composition were prepared by a simple room temperature reprecipitation method.The CsPbX₃ composite nanocrystals protected by a thin layer of Pb₃（PO₄）₂ exhibit excellent optical properties with an absolute quantum yield（PLQY）as high as 95%.In addition,the resistance of composite nanocrystals to water,oxygen and polar solvents is significantly improved.This work not only provides a reliable method for the preparation of composite nanostructures with excellent performance,but also opens up anew avenue for the composite of inorganic salts with lead halide perovskites.2.The CsPbBr3 nanocrystals were modified with larger A-site guanidine ions（GA⁺,C（NH₂）₃⁺）,and the morphology and structure of the perovskite nanocrystal products were finely regulated.Using GABr to treat CsPbBr3 nanocrystals can produce high-yield,monodisperse green nanosheets with lattice dislocations,and their PLQY is increased from 30%to 85%;CsPbBr3/Cs2GAPb2Br7 heterojunction structure can be obtained by GAOA post-treatment blue light nanorods.This is because GA⁺induces the generation of low-dimensional structures to form lattice dislocations or heterojunction structures.The introduction of GA⁺increases the exciton binding energy of perovskite nanocrystals,and also effectively suppresses the defects of the system.This work reveals the important role of mixed cations in tuning the photophysical properties of lead halide perovskites.3.The doping of GA⁺ on the A site of CsPbI₃ nanocrystals was successfully achieved by post-treatment with different concentrations of GAI.This work focuses on the influence of the introduction of GA⁺ ions on the properties of CsPbI₃ nanocrystals.The results show that GA⁺ helps to increase the radiation recombination ratio of pristine nanocrystals and effectively improves the film quality.When 25%GA⁺ was incorporated,the bottom of the valence band of CsPbI₃ nanocrystals moved up,successfully suppressing the carrier loss of the device.The nanocrystals were applied to solar cell devices and it was found that the photoelectric conversion efficiency（PCE）increased from 14.14%to 15.33%.This work provides a new direction for the modification of CsPbI₃ nanocrystals.