Doping-Free Phosphorescent and Thermally Activated Delayed Fluorescent Organic Light-Emitting Diodes with an Ultra-Thin Emission Layer

Eun Bi Jang, Geun Su Choi, Eun Jeong Bae, Byeong Kwon Ju, Young Wook Park

Research output: Contribution to journalArticlepeer-review

Abstract

We report the electroluminescence (EL) characteristics of blue ultra-thin emissive layer (U-EML) phosphorescent (PH) organic light-emitting diodes (OLED) and thermally activated delayed fluorescence (TADF) OLED. A variety of transport layer (TL) materials were used in the fabricated OLEDs. The well-known FIrpic and DMAC-DPS were used with a thickness of 0.3 nm, which is relatively thicker than the optimal thickness (0.15 nm) of the blue phosphorescent ultra-thin emissive layer to ensure sufficient energy transfer. While FIrpic showed overall high efficiency in various TLs, DMAC-DPS exhibited three times lower efficiency in limited TLs. To clarify/identify low efficiency and to improve the EL, the thickness of DMAC-DPS was varied. A significantly higher and comparable efficiency was observed with a thickness of 4.5 nm, which is 15 times thicker. This thickness was oriented from the TADF itself, which reduces quenching in a triplet–triplet annihilation compared to the PH process. The thinner optimal thickness compared with ~30 nm of fluorescent OLEDs suggests that there still is quenching taking place. We expect that the efficiency of TADF U-EML OLEDs can be enhanced through further research on controlling the exciton quenching using multiple U-EMLs with spacers and a novel material with a high energy transfer rate (ΔES-T).

Original languageEnglish
Article number2366
JournalNanomaterials
Volume13
Issue number16
DOIs
Publication statusPublished - 2023 Aug

Bibliographical note

Funding Information:
This research was funded by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2020R1C1C1013567), and by a National Research Foundation of Korea (NRF) grant funded by the Ministry of Education (MOE) (2021RIS-004).

Publisher Copyright:
© 2023 by the authors.

Keywords

  • organic light-emitting diodes
  • phosphorescent
  • thermally activated delayed fluorescence
  • ultra-thin emissive layer

ASJC Scopus subject areas

  • General Chemical Engineering
  • General Materials Science

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