Organic Spacer Cation Regulation Of Quasi-two-dimensional Perovskites And Performance Optimization Of Perovskite Light-emitting Diodes

Quasi-two-dimensional perovskites(（PEA&GA）₂（FA&Cs）_n-1Pbn Br_3n+1)have the advantages of high photoluminescence quantum yield,tunable emission color,and so on.The light-emitting diodes using them as the emitters（Q-2D Pe LEDs）are regarded as a potential candidate for the next generation of LEDs,with promising future applications.This thesis focuses bromine-based Q-2D Pe LEDs.In this thesis,we firstly optimized the hole transport layer（HTL）and perovskite layer of Q-2D Pe LEDs.Then,we investigated the effect of mixed or additive organic spacer cation salt of the perovskite on the performance of Q-2D Pe LEDs.The specific content of this thesis is as follows.（1）The HTL and the Q-2D perovskite layer were optimized to get high device performance.The HTL was optimized by the following strategies:1)The ratio of PSS-Na and PEDOT:PSS in m-PEDOT:PSS HTL was optimized to increase the highest occupied molecular orbital（HOMO）energy level of the HTL,thereby reducing the hole injection barrier.2)The solvents of PSS-Na solution were adjusted to improve the film quality of the HTL,leading to the smoothed surface,which improves the device performance.3)A Poly（9-vinylcarbazole）（PVK）layer was added to construct double HTLs for further reducing the hole injection barrier and improving the device performance.The Q-2D perovskite layer was optimized by the following strategies:1)As a basis,we firstly summarized the reported literature on green and blue Q-2D Pe LEDs,and analyzed the factors affecting the photon energy of quasi-2D perovskites.2)Based on the commonly used Q-2D perovskite composition,we adjusted the ratio of organic spacer cation,phenylethylamine（PEA⁺）,while its optimal addition ratio is 0.4.3)The ratio of the A-site cations,cesium（Cs⁺）and formamidinium（FA⁺）,were also adjusted.The device performs best at Cs⁺:FA⁺=0.9:0.1.4)The environmentally friendly anti-solvent ethyl acetate was used to replace toxic chlorobenzene,which was also more beneficial to the device performance.（2）The roles of guanidine hydrobromide（GABr）as an organic spacer cation salt and an additive in governing the film quality and device performance were explored,respectively.1)GA⁺was introduced together with PEA⁺as organic spacer cations to Q-2D perovskites.Phase impurities and large n phases defects were reduced.PEA⁺and GA⁺form a mixed phase in which the Ruddlesden–Popper（RP）phase and alternating cation in the interlayer space（ACI）phase coexist;at the same time,GA⁺can also form strong hydrogen bonds with halogen ions,thus reducing halogen vacancy defects.When the mixing ratio of PEABr and GABr is 1:3,the Q-2D Pe LED has the best performance,with the maximum luminance(L_max),current efficiency(CE_max),and external quantum efficiency(EQE_max)of 30168 cd/m²,34.9 cd/A,and 8.27%,respectively.2)GABr can also be incorporated into Q-2D perovskites as a Lewis acid additive.A small amount of GABr acts to passivate halogen vacancy defects without changing the phase distribution.When the GABr additive ratio is 0.05（compared with Pb）,the efficiency of the Q-2D Pe LED is the highest,with the CE_max and EQE_max of 36.5 cd/A and 10.9%,respectively.The function of GA⁺in affecting the film quality and device performance partially derive from its high solubility in the precursor solution.Herein,organic spacer ions with suitable solubility can tune the phase distribution from the crystallization process to fabricate high-efficiency Pe LEDs,which provides an idea for the optimization of Q-2D Pe LEDs.