Progress in next-generation organic electroluminescent materials:material design beyond exciton statistics  

作　　者：YAO Liang YANG Bing MA YuGuang 

机构地区：[1]State Key Laboratory of Supramolecular Structure and Materials, Jilin University [2]State Key Laboratory of Luminescent Materials and Devices, South China University of Technology

出　　处：《Science China Chemistry》2014年第3期335-345,共11页中国科学（化学英文版）

基　　金：financially supported by the National Science Foundation of China(51073069,51273078);the National Basic Research Program of China(2013CB834801)

摘　　要：Exciton(or spin)statistics is a physical principle based on the statistics of spin multiplicity.In electroluminescence,injected electrons and holes have randomized spin states,and usually form singlet or triplet excitons in the ratio of 1:3.Exciton statistics determines that the upper limit of internal quantum efficiency is 25%in fluorescent devices,since only singlet exciton can decay radiatively.However,both experimental and theoretical evidence indicate that the actual efficiency can exceed the exciton statistics limit of 25%by utilizing materials with special electronic structure and optimized device structures.These results bring light to break through the exciton statistics limit and develop new-generation fluorescent materials with low cost and high efficiency.Recently,the exciton statistics,which has attracted great attention in the past decade,is being rejuvenated due to the discovery of some fluorescent materials with abnormally high efficiencies.In view of their significance in theoretical research of organic semiconductors and developing new-generation OLED materials,such materials are widely investigated in both academic institutions and industry.Several key issues still require further clarification for this kind of materials,such as the molecular design concepts.Herein,we review the progress of the materials with efficiency exceeding the exciton statistics limit,and the routes to improve exciton utilization efficiency.In the end,we present an innovative pathway to fully harvest the excitons in fluorescent devices,namely,"hot exciton"model and relevant fluorescence material with hybridized local and charge-transfer(HLCT)excited state.Exciton（or spin）statistics is a physical principle based on the statistics of spin multiplicity.In electroluminescence,injected electrons and holes have randomized spin states,and usually form singlet or triplet excitons in the ratio of 1：3.Exciton statistics determines that the upper limit of internal quantum efficiency is 25%in fluorescent devices,since only singlet exciton can decay radiatively.However,both experimental and theoretical evidence indicate that the actual efficiency can exceed the exciton statistics limit of 25%by utilizing materials with special electronic structure and optimized device structures.These results bring light to break through the exciton statistics limit and develop new-generation fluorescent materials with low cost and high efficiency.Recently,the exciton statistics,which has attracted great attention in the past decade,is being rejuvenated due to the discovery of some fluorescent materials with abnormally high efficiencies.In view of their significance in theoretical research of organic semiconductors and developing new-generation OLED materials,such materials are widely investigated in both academic institutions and industry.Several key issues still require further clarification for this kind of materials,such as the molecular design concepts.Herein,we review the progress of the materials with efficiency exceeding the exciton statistics limit,and the routes to improve exciton utilization efficiency.In the end,we present an innovative pathway to fully harvest the excitons in fluorescent devices,namely,＂hot exciton＂model and relevant fluorescence material with hybridized local and charge-transfer（HLCT）excited state.

关 键 词：organic light-emitting device（OLED） exciton statistics reverse intersystem crossing（RISC） hybridized local and charge-transfer（HLCT） hot exciton 

分 类 号：TN104.3[电子电信—物理电子学]