Kim, Kiwoong Jae Chung, Won Lim, Junseop KYUJOON LEE Kim, Hong Hee Schultz, Thorsten Amsalem, Patrick 최원국 Kim, Hong Kyu Ahn, Jae Pyoung Lee, Hyunbok Yeob Lee, Jun Park, Soohyung Yi, Yeonjin 2024-01-12T02:32:53Z 2024-01-12T02:32:53Z 2022-11-24 2023-02 0169-4332 https://pubs.kist.re.kr/handle/201004/75831 Phosphorescent organic light-emitting diodes (PhOLEDs) have been considered potential candidates for high -efficiency blue emission. However, their short lifetime has been an issue, and much effort has been put into resolving this. Among such efforts, understanding energy level alignments (ELA) is one of the essential factors in understanding the degradation. However, ELA inside the actual PhOLED is rarely studied due to technical limitations. Here, we comprehensively investigate the degradation mechanism of blue PhOLEDs consisting of a cohost-dopant type emissive layer (EML). The blue PhOLEDs are aged with typical operating conditions until the luminance performance degrades. Ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) combined with a damage-free gas cluster ion beam (GCIB) etching and transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) unveil the buried interfaces inside the PhOLEDs. XPS and TEM-EDX measure-ments show that the dopant is unlikely to be the primary origin of the device degradation. Instead, UPS mea-surements show that the ELAs at the interfaces facing the EML are significantly altered unfavorably after device aging. This implies that the changes in the ELA are the leading cause of PhOLED degradation. Our results highlight the importance of retaining the ELAs during device operation to achieve long-lifetime blue PhOLEDs. English Elsevier BV Degradation-induced energy level mismatch in cohost-dopant blue phosphorescent OLEDs after device operation Article 10.1016/j.apsusc.2022.155753 1 Applied Surface Science, v.611 Applied Surface Science 611 N scie scopus 000906887900002 Chemistry, Physical Materials Science, Coatings & Films Physics, Applied Physics, Condensed Matter Chemistry Materials Science Physics Article LIGHT-EMITTING-DIODES EXTERNAL QUANTUM EFFICIENCY EXCITON-POLARON INTERACTIONS MOLECULAR AGGREGATION MECHANISMS INTERFACE STABILITY EXCIPLEX CARRIER GUEST Blue phosphorescent OLEDs Cohost-dopant system Energy level alignment Degradation Aging Molecular aggregation FIrpic UPS XPS GCIB Depth profile