Long-Term Stability of Emitter Orientation in Organic Light-Emitting Diodes at Temperatures in the Range of the Active Layer Glass Transition

Research output: Contribution to journalResearch articleContributedpeer-review


Controlling the alignment of emitter molecules in the active layer of organic light-emitting diodes has become a main approach to maximize the device efficiency when emitter molecules with luminescence quantum yields approaching 100% are used. In order to guarantee stable device performance, the initial molecular orientation should not change over time. In this work, we study this property for a time frame of 1.5 years and storage temperatures up to 80 °C which may be reached in displays exposed to direct sun light. For the studied material systems, this temperature is close to the glass transition at which drastic morphological changes occur and a randomization of the molecule arrangement is expected. We compare two different phosphorescent emitter molecules and, additionally, investigate the impact of the substrate temperature during evaporation. Concluding this long-term study, we prove experimentally that the emitter orientation remains unchanged under those device-critical storage conditions. On the contrary, the fatal potential of heat-induced reorientation is revealed by post-annealing experiments that show a strong change of the emitter orientation at about 20 K above the glass transition temperature.


Original languageEnglish
Pages (from-to)9221-9227
Number of pages7
JournalChemistry of materials
Issue number20
Publication statusPublished - 6 Oct 2022

External IDs

Scopus 85139564616
Mendeley 53c5da9a-2d1b-359e-ad48-9115ac538985
unpaywall 10.1021/acs.chemmater.2c02314
WOS 000875685300001



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