24-1: Device Stability Enhancement In TADF OLEDs

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• 作者：Daniel P.K. Tsang ; Toshinori Matsushima and Chihaya Adachi
• 刊名：SID Symposium Digest of Technical Papers
• 出版年：2016
• 出版时间：May 2016
• 年：2016
• 卷：47
• 期：1
• 页码：290-293
• 全文大小：428K
• ISSN：2168-0159

文摘

Organic light-emitting diodes (OLEDs) under constant current operation suffer from a decrease of luminance accompanied by an increase of driving voltage. We report a way to greatly improve the stability of OLEDs having a green emitter exhibiting thermally activated delayed fluorescence (TADF), (4s,6s)-2,4,5,6-tetra(9Hcarbazol- 9-yl) isophthalonitrile (4CzIPN), by introducing ultrathin (1 to 3 nm) interlayers of 8-hydroxyquinolinato lithium (Liq) between hole-blocking layer and its surrounding emissive and electron-transport layers. Under constant current operation starting at a luminescence of 1,000 cd/m², the time to reach 90% of initial luminance (LT₉₀) increased eight times, resulting in LT₉₀ = 1,380 hours after insertion of the interlayers. Combining this new concept and mixed host system, LT₉₅ was further extended to 1315 hours that is 16 times of reference device. This is the best value reported for TADF-based OLEDs and is comparable to the operational lifetimes of well-established phosphorescence-based OLEDs. Thermally stimulated current measurements showed that the number of deep charge traps was reduced with the insertion of the ultrathin Liq interlayer, indicating that reducing the number of deep traps is important for improving the operational lifetime and that exciton-polaron annihilation may be a source of the device degradation.