Direct Observation of Photoexcited Electron Dynamics in Organic Solids Exhibiting Thermally Activated Delayed Fluorescence via Time-Resolved Photoelectron Emission Microscopy

Yusuke Fukami, Masato Iwasawa, Masahiro Sasaki, Takuya Hosokai, Hajime Nakanotani, Chihaya Adachi, Keiki Fukumoto, Yoichi Yamada

Research output: Contribution to journalArticlepeer-review

Abstract

Solid-state films exhibiting thermally activated delayed fluorescence (TADF) can offer high internal electroluminescence (EL) quantum efficiency, even in a simplified device structure. However, the exciton dynamics in solid-state TADF films, particularly for the unexpected exciton loss processes such as concentration quenching, have not yet been clarified. The dynamics of photoexcited electrons in the TADF process of a 2,4,5,6-Tetra (9H-carbazol-9-yl) isophthalonitrile (4CzIPN) solid film are observed via time-resolved photoelectron emission microscopy (TR-PEEM) and the results are compared with the conventional time-resolved photoluminescence (TR-PL) technique. The initial decay process of the photoexcited electrons probed via TR-PEEM is thoroughly traced in the TR-PL signal, while unusual long-lived electrons are detected only through the use of TR-PEEM. These results indicate that the excitons of 4CzIPN spontaneously dissociate into free carriers within the exciton lifetime, which seems to be a common process that contributes to the exciton loss in polar organic solids.

Original languageEnglish
Article number2100619
JournalAdvanced Optical Materials
Volume9
Issue number19
DOIs
Publication statusPublished - Oct 4 2021

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics

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