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The Role of Metallic Dopants in Improving the Thermal Stability of the Electron Transport Layer in Organic Light‐Emitting Diodes
Author(s) -
Keum ChangMin,
Kronenberg Nils M.,
Murawski Caroline,
Yoshida Kou,
Deng Yali,
Berz Cordelia,
Li Wenbo,
Wei Mengjie,
Samuel Ifor D. W.,
Gather Malte C.
Publication year - 2018
Publication title -
advanced optical materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.89
H-Index - 91
ISSN - 2195-1071
DOI - 10.1002/adom.201800496
Subject(s) - oled , materials science , dopant , doping , thermal stability , diode , phosphorescence , optoelectronics , crystallization , annealing (glass) , layer (electronics) , nanotechnology , chemical engineering , fluorescence , composite material , optics , physics , engineering
4,7‐Diphenyl‐1,10‐phenanthroline (BPhen) is widely used to create the electron transport layer (ETL) in organic light‐emitting diodes (OLEDs) because of its high electron mobility and good compatibility with alkali metal n‐dopants. However, the morphology of these ETLs is easily altered by heating due to the relatively low glass transition temperature ( T g ) of BPhen and this change often reduces the performance of OLEDs. Here, an enhancement in the thermal stability of OLEDs when doping their BPhen‐based ETLs with cesium (Cs) is reported. To investigate the role of the Cs dopant in the BPhen matrix, the crystallization features of Cs‐doped BPhen films with different doping concentrations are examined. Next, the electrical and optical properties of blue fluorescent and red phosphorescent OLEDs containing Cs‐doped BPhen ETLs are characterized after annealing the OLEDs at temperatures up to 100 °C. Cs plays a critical role in inhibiting the undesired crystallization of BPhen films, which enhances the thermal stability of OLEDs beyond the T g of neat BPhen. Finally, highly stable BPhen‐based OLEDs encapsulated via atomic layer deposition at 80 °C are demonstrated. This work may lead to a new strategy for enhancing the intrinsic thermal durability of organic devices and their compatibility with thermally demanding processes.