The role of metallic dopants in improving the thermal stability of the electron transport layer in organic light-emitting diodes

Chang-Min Keum, Nils Michael Kronenberg, Caroline Murawski, Kou Yoshida, Yali Deng, Cordelia Berz, Wenbo Li, Mengjie Wei, Ifor D. W. Samuel, Malte C. Gather

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)
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Abstract

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 (Tg) 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 Tg 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.
Original languageEnglish
Article number1800496
JournalAdvanced Optical Materials
VolumeEarly View
Early online date25 Jun 2018
DOIs
Publication statusE-pub ahead of print - 25 Jun 2018

Keywords

  • Organic light-emitting device
  • Thermal stability
  • Molecular doping
  • Crystallization
  • Atomic layer deposition

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