Impurities in Vacuum Chamber and OLED Lifetime
The OLED lifetime is influenced by contamination of impurities present in a vacuum chamber, depending on the duration of organic deposition process. The impurities are identified by LC-MS analysis: Chemicals typically used for resin additives and/or organic compounds previously evaporated in the chamber.
Left figure:Outcome from the joint research with Sumika Chemical Analysis Service, Ltd.
Right figure:H. Fujimoto, et al., Scientific Reports 6, 38482 (2016).
Evaluation of Chamber Cleanliness by Contact Angle Measurement
①A lower Γs leads to a hydorophobi”c surface.
②A substance with a low surface tension leads to a small intermolecular force and tends to be volatile in vacuum.
③The contact angle is a measure of vacuum chamber contamination.
Correlation between Chamber Cleanliness and OLED Lifetime
The correlation between the contact angle and the OLED lifetime reveals that the impurities in vacuum chamber have a significant impact on the OLED lifetime. As a proof, the OLEDs fabricated with a clean new vacuum chamber, which is free from the above mentioned impurities, indeed shows two times longer lifetime.
H.Fujimoto, et al., AIP Advances 8, 085025 (2018).