Universal electron transporting layers via mixing two homostructure molecules with different polarities for organic light-emitting diodes
- Authors
- Kim, K.J.; Lee, H.; Hwang, K.M.; Park, B.; Oh, H.Y.; Kim, Y.K.; Kim, Taekyung
- Issue Date
- Sep-2021
- Publisher
- Elsevier B.V.
- Keywords
- Electron transporting layer; Giant surface potential; OLED
- Citation
- Organic Electronics, v.96
- Journal Title
- Organic Electronics
- Volume
- 96
- URI
- https://scholarworks.bwise.kr/hongik/handle/2020.sw.hongik/15890
- DOI
- 10.1016/j.orgel.2021.106220
- ISSN
- 1566-1199
- Abstract
- In general, electron transport layer (ETL) in organic light-emtting diodes (OLEDs) consists of single component of electron transporting material (ETM) or a mixture with n-dopant such as 8-hydroxyquinolinolato-lithium (Liq). However, there exists a limit to controlling a wide range of carrier density in OLEDs according to the required characteristics of the devices due to electrically insulating property of Liq. Here, we suggest a universal strategy to construct an efficient ETL. We synthesized two ETMs, diphenyl-[4-(10-phenyl-anthracene-9-yl)-phenyl]-amine (An-Ph) and phneyl-[4-(10-phenyl-anthracene-9-yl)-phenyl]-pyridin-3-yl-amine (An-Py) that have the same core structures with different polarities in functional groups. The electrical characteristics of electron-only-devices (EODs) were investigated by space charge limited current (SCLC) modeling and impedance spectroscopy analysis. Interestingly, the homostructure type ETL composed of An-Ph and An-Py showed not only superior electron transporting capability, but also the possibility of controlling electron injection and transporting in a wide range compared to the heterostructure type ETL of An-Ph and Liq. Compared to the An-Ph-only EOD, the electron mobility in 75% An-Py-mixed homostructure EOD increased by almost 4 orders of magnitude. Such dramatic variation of electron mobility was achieved thanks to the molecular design strategy to separate charge injection and charge transport regions within a molecule, which consequently induced the giant surface potential (GSP) effect between the ETL/cathode interface. As a result, the external quantum efficiency (EQE) of blue fluorescent and phosphorescent OLEDs with the homostructure ETLs was enhanced by 28.6% and 34%, respectively, compared to that of each control device without manipulating outcoupling effects. © 2021 Elsevier B.V.
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