Optimizing the Charge Balance of Fluorescent Organic Light‐Emitting Devices to Achieve High External Quantum Efficiency Beyond the Conventional Upper Limit

The external quantum efficiencies (EQEs) of fluorescent light emitting devices are drastically improved by optimizing the charge balance. When N,N′-di(naphthalene-1-yl)- N,N′-diphenylbenzidine (NPD) is used as a hole-transporting layer (HTL) and Alq3 as an electron-transporting layer (ETL) with the green dopant 2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-10-(2-benzothiazolyl)quinolizino-[9,9a,1gh]coumarin (C545T), the EQE is observed to be approximately 3%. However, when the HTL and ETL materials are optimized, a 7.5% external quantum efficiency (EQE) in a green-emitting device and an 8.2% EQE in a blue-emitting device are achieved at 100 cd m−2. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.