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 measurements show that the dopant is unlikely to be the primary origin of the device degradation. Instead, UPS measurements 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.
|Journal||Applied Surface Science|
|Publication status||Published - 2023 Feb 15|
Bibliographical noteFunding Information:
This work was supported by the National Research Foundation of Korea [NRF- 2020R1A2C2014644, 2018M3D1A1058793, 2022M3D1A2083799, and 2017R1A5A1014862 (SRC program: vdWMRC center)], the Graduate School of YONSEI University Research Scholarship Grants, Samsung Display Company, KIST Institutional Program (Project No. 2V09352), and an Industry-Academy joint research program between Samsung Electronics and Yonsei University.
© 2022 Elsevier B.V.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physics and Astronomy(all)
- Surfaces and Interfaces
- Surfaces, Coatings and Films