The Influence Of Organic Biphenyl Liquid Crystalline Molecule On The Quasi-2D Perovskite Structure And The Performance Of Corresponding Light-emitting Diodes

In recent years,quasi-two-dimensional（2D）perovskite polycrystalline films have attracted wide attention in the field of light-emitting diodes（LEDs）because they possess the advantages of traditional three-dimensional（3D）perovskite materials,such as solution-processable fabrication,tunable bandgap,high color purity,high defect tolerance and high photoluminescence quantum yield（PLQY）.Meanwhile,the surface of quasi-2D perovskite films is protected by the hydrophobic organic amine spacer layers,which can effectively prevent the erosion of water and oxygen,hence greatly improving the film stability.Moreover,quasi-2D perovskite films have the typical multiphase microstructure,which can exhibit unique energy funneling effect,promoting the efficient energy transfer.Furthermore,exciton binding energy（E_b）can be modulated by the dielectric and quantum confinement effects in quasi-2D perovskite films,enhancing the carrier radiative recombination ratio.In quasi-2D perovskite films,the organic amine spacers play important roles in controlling the film properties.A large number of organic amine spacers have already been used in fabricating quasi-2D perovskite films and corresponding LED devices.It has been demonstrated that the introduction of these organic amine spacers can control the phase composition and distribution in quasi-2D perovskite films,exhibiting decent device performance.However,up to now,most of organic amine spacers are insulating and only contain one amino group.The introduction of such organic amine spacers can not only impede the carrier transport to a certain extent,but also affect the stability of perovskite crystal structure,thus reducing the carrier radiative recombination and lowering the operational stability of perovskite LEDs,hence seriously limiting their further commercialization.Therefore,in this thesis,two kinds of functional organic amine spacers,2-（4-aminophenyl）ethylamine（BPEA）with theπ-conjugated group and diethylenetriamine（DETA）with multi-amine groups,are introduced into the 3D perovskite lattice to prepare quasi-2D perovskite films for controlling the phase composition and distribution.On this basis,the high-efficient and stable quasi-2D perovskite LEDs are fabricated.The main contents are as follows:Firstly,BPEA is introduced into the 3D perovskite crystal lattice as the organic amine spacer for preparing quasi-2D perovskite polycrystalline films.The results show that the addition of BPEA can effectively inhibit the formation of low n phase and promote the energy transfer to 3D phase,thus facilitating the exciton radiative recombination in comparison with the quasi-2D perovskite films based on octylamine（OA）and phenethylamine（PEA）.Meanwhile,the inclusion of BPEA can effectively passivate defects and improve the PLQY of films.Based on the above results,corresponding quasi-2D perovskite LEDs are fabricated.It is found that the BPEA device deliver the peak external quantum efficiency（EQE）of 10.08%and maximal luminance of 3002.16 cd m^-2,which are higher than the OA device(2.34%,211.68 cd m^-2)and PEA device(8.21%,1957.98 cd m^-2).At the same time,the operational stability of the BPEA device is obviously improved compared to the OA and PEA devices.Furthermore,on the basis of the application of BPEA as organic amine spacer,the diethylenetriamine（DETA）with multi-amine groups is introduced as the second organic amine spacer into the quasi-2D perovskite films based on BPEA.It is revealed that the addition of DETA can further regulate the phase composition of quasi-2D perovskite films.As a result,the low n phases are concentrated at n=2 and n=3,and simultaneously the formation of n=1 is suppressed,which dramatically promote the energy transfer.As a consequence,the perovskite LEDs are fabricated by using the quasi-2D perovskite film based on BPEA and DETA organic amine spacer as the emissive layer,which provides the peak EQE of 13.43%and maximal luminance of5866.82 cd m^-2.In addition,the operational stability of such device is obviously improved.Our work provides a new strategy for the design and development of novel functional organic amine spacers to construct high-quality stable quasi-2D perovskite films,ultimately realizing efficient and stable quasi-2D perovskite LEDs.