载流子阶梯效应调控有机发光二极管三线态激子的解离和散射  

Carrier ladder effect regulated dissociation and scattering of triplet excitons in OLED

作　　者：保希 关云霞[1] 李万娇 宋家一 陈丽佳 徐爽 彭柯敖 牛连斌[1] Bao Xi Guan;Yun-Xia;Li Wan-Jiao;Song Jia-Yi;Chen Li-Jia;Xu Shuang;Peng Ke-Ao;Niu Lian-Bin(Chongqing Key Laboratory of Optical Engineering,Chongqing Key Laboratory of Optoelectronic Functional Materials,College of Physics and Electronic Engineering,Chongqing Normal University,Chongqing 400715,China)

机构地区：[1]重庆师范大学物理与电子程学院,重庆市光电功能材料重点实验室,重庆市高校光学工程重点实验室,重庆400715

出　　处：《物理学报》2023年第21期307-317,共11页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:61874016);重庆市自然科学基金(批准号:CSTC2020jcyj-msxmX0282,CSTC2021jcyj-msxmX0576);重庆市教育委员会科学技术研究计划(批准号:KJQN202200518)资助的课题。

摘　　要：三线态激子-电荷相互作用(triplet excition-charge interaction,TQI)有解离和散射两种形式,但至今仍未明确空穴注入层如何影响三线态激子的解离和散射以及磁电导(magneto-conductance,MC)正负之间的转变.本文采用能产生载流子阶梯效应的HAT-CN作为空穴注入层,运用磁效应作为工具对器件内部微观机理进行研究.结果表明,器件内部存在超精细、解离、散射三个特征磁场,利用Lorentzian和non-Lorentzian函数对MC进行拟合并得以验证.超精细场源于载流子自旋与氢核自旋间的超精细相互作用.随磁场增强,空穴注入层与空穴传输层界面产生载流子阶梯效应,提高了空穴注入效率,三线态激子被空穴解离后产生二次载流子.载流子阶梯效应也会导致注入电荷大量积累,载流子被三线态激子散射,使其迁移率降低,不利于激发态的形成和器件发光.MC由K_(S)/K_(T)(重组速率比)调制,电压较小时K_(S)>>K_(T),重组比相对较大,产生正MC;随电压增大K_(S)≈K_(T)=K,此时K_(S)/K_(T)趋近于1,出现负MC;尤其在低温下,MC均为负值.本工作为空穴注入层调控三线态激子的解离和散射及MC正负之间的转变提供新思路.Triplet exciton-charge interaction(TQI)has two forms:dissociation and scattering,However,it is still unclear how the hole injection layer affects the dissociation and scattering of triplet excition and the transition between positive and negative values of magneto-conductance(MC).In this paper,HAT-CN,which can produce carrier ladder effect,is used as hole injection layer(HIL),and magnetic effect is used as a tool to study it.The results show that there are three characteristic magnetic fields in the device:hyperfine,dissociation and scattering,which are verified by fitting the MC with Lorentzian and non-Lorentzian functions.The hyperfine characteristic magnetic field results from the magnetic field suppressing superfine field-induced charge-spin mixing.With the enhancement of magnetic field,hole injection layer/hole transport layer interface produces carrier ladder effect,which improves the hole injection efficiency.The triplet excitions are separated by the hole,then the secondary carriers are produced,which makes the device’s luminous brightness and efficiency reach to 43210 cd/m^(2) and 9.8 cd/A,respectively.The carrier ladder effect will also lead to a large accumulation of injected charges,resulting in the scattering of charge carriers by triplet excition,thereby reducing their mobility,which is not conducive to the formation of excited states nor device luminescence.The MC is modulated by K_(S)/K_(T)(recombination rate ratio),and when the electric field is small K_(S)≫K_(T),the recombination ratio is relatively large,resulting in positive MC.With the increase of electric field K_(S)≈K_(T)=K,K_(S)/K_(T) approaches 1 at this time,resulting in an MC,which is negative in a low temperature environment.This work provides a novel approach for regulating and effectively utilizing triplet excitons.

关 键 词：HAT-CN 有机发光二极管 空穴注入层 磁电导 

分 类 号：TN304.52[电子电信—物理电子学] TN383.1