Research On Photoelectric Properties Of CsPbX₃ Nanocrystals Regulated By Inorganic Additives

In recent years,cesium lead halide perovskite nanocrystals（CsPbX₃（X=Cl,Br,I）NCs）,as the novel type of semiconductor light-emitting materials,have attracted much attention due to their excellent photoelectric properties such as high photoluminescence quantum yield,adjustable band gaps,large absorption cross section and strong carrier transmission capacity.They were widely applied in photodetectors,light-emitting diodes（LED）and solar cells.However,the defects of perovskite will inevitably occur in the growth process due to the soft ion lattice,which is easy to collapse the lattice structure of perovskite.At the same time,the photoelectric properties and stability of perovskite will be limited.Generally,the introduction of inorganic and organic additives can effectively resolve these problems.Compared to organic additives,the inorganic additives have more advantages in passivating defects,improving photoelectric properties and stability of perovskite.Firstly,the inorganic additives are easy to form a strong interaction with the perovskite,secondary,the inorganic additives with simple structure and small radiu can be synergistic,last but not at least,the inorganic additives exhibit robust conductivity.Therefore,inorganic additives can effectively passivate the defects,enhance the photoelectric properties and stability of perovskite.In view of this,the photoelectric properties and stability of CsPbX₃nanocrystals modified by inorganic additives are researched in this word.The specific research results are as follows:（1）Theα-CsPbI₃ NCs（cubic）with high photoluminescence quantum yield and excellent stability,were prepared by the passivation of MgI₂.The introduced MgI₂ passivated the surface of CsPbI₃NCs（Mg-CsPbI₃ NCs）,eliminated the vacancies of Pb²⁺and I^-,inhibited the non-radiative recombination of carriers,resulting the increase of photoluminescence quantum yield for Mg-CsPbI₃ NCs（93%）.When the colloidal solution of Mg-CsPbI₃ NCs was exposed to 365 nm ultraviolet irradation for 20 h,heated at 80°C for 150 mins and heated at 130°C for 12 mins,respectively,the photoluminescence quantum yield of the Mg-CsPbI₃ NCs can maintain about 85%of the initial value.In addition,the performance of LED based on Mg-CsPbI₃ NCs was significantly improved than that based on the pristine CsPbI₃ NCs,which exhibits the maximum luminance of 10461 cd m^-2,the maximum external quantum efficiency of 10.2%and the half-lifetime of 49.6 mins,and increased by 32%,37%and 86%,respectively.This indicates the effectiveness of MgI₂ passivation in enhancing the stability and luminous intensity of CsPbI₃ NCs.（2）Inorganic additives not only can enhance the photoelectric properties and stability ofα-CsPbI₃NCs by passivation of defects,but also can advance the properties of CsPbI₃ NCs by suppressing lattice distortion and maintaining the high lattice symmetry.Based on this,we develop the synergistic stratagy of NO₃^-passivation and Ca²⁺doping to passivate the surface defects along with modification of the lattice symmetry in CsPbI₃ NCs.As results,theα-CsPbI₃ NCs exhibit excellent photoelectric properties and stability.On the one hand,the introduced NO₃^-can passivate the I^-vacancies.On the other hand,the long-chain oleamine ions（RNH₃⁺）can be anchored on the surface of perovskite to increase its surface steric hindrance,which finally promotes the formation ofα-CsPbI₃ NCs with high lattice symmetry.Besides,the Ca²⁺doping can improve the lattice symmetry of CsPbI₃ NCs by adjusting the tolerance factor.As results,theα-CsPbI₃ NCs exhibit excellent photoluminescence quantum yield（96.6%）,conductivity and stability.Especially,when theα-CsPbI₃ NCs was stored in ambient for 270 days,under ultraviolet irradition for 32 h,and heated at 140°C for 15 mins,the fluorescence emission intensity of theα-CsPbI₃ NCs can remaine about 90%of its initial value,and the work stability of LED based on theα-CsPbI₃ NCs is up to18 h.This is the most stable unencapsulatedα-CsPbI₃ NCs comparing with the documented works so far.（3）Although we have improved the stability of the CsPbX₃ NCs,their ionic properties make it difficult to regulate their anisotropy.Based on this,we prepared the one-dimensional Cs Pb Cl₃NWs with the cooperative passivation strategy of Ln³⁺and Ac O^-.Then take the Cs Pb Cl₃ NWs regulated by Eu（Ac O）₃ as an example.Based on theoretical calculation and experimental research,we proposed the formation mechanism of the Cs Pb Cl₃ NWs.After adding Eu（Ac O）₃,the Ac O^-adsorbs on the（002）crystal facet and inhibits the growth,while the Eu³⁺tends to adsorb on the（200）crystal facet and introduce more Cl^-to active the crystal facet.In addition,the Eu³⁺will compete with RNH₃⁺to reduce the steric hindrance on the perovskite surface and promotes the growth of Cs Pb Cl₃ NWs along[200]direction.As results,the Cs Pb Cl₃ NWs exhibit low defect density,high photoluminescence quantum yield and excellent carrier transmission and separation capability.On this basis,we fabricated the ultraviolet self-powered photodetector based on the Cs Pb Cl₃ NWs,which displays high responsivity(398 m A W^-1),detectivity(3.3×10¹¹ Jones),as well as fast response speed（24 ms）.This work provides an inspiration to promote the practical application of the one-dimensional CsPbX₃ materials.