Theoretical Study on Electronic Structure and Charge Transport Characteristics of Anthracene-based Host Material for Blue Organic Light-emitting Diode Application

초록

Organic light-emitting diodes (OLEDs) have received much attention for application the in next-generation display due to their many advantages. To increase the device performance of OLEDs, a host-dopant system in the emission layer has been used. In blue OLEDs, anthracene-based materials have been used as a host material. To understand the device behavior of OLEDs, a fundamental study on the electronic properties of organic semiconductors is necessary. In this study, theoretical calculations using density functional theory were performed to investigate the electronic structure and charge transport ability of 9,10-diphenyl-2-((3-trifluoromethyl)phenyl)anthracene (ATFP-Ph), 9,10-di([1,1’-biphenyl]-4- (trifluoromethyl)phenyl)anthracene (ATFP-BiPh), and 9,10-di(naphthalene-2-yl)-2-(3-(trifluoromethyl)phenyl)anthracene (ATFP-Naph). All molecules have similar lowest unoccupied molecular orbital and highest occupied molecular orbital energy levels, and thus their charge injection abilities from the adjacent layer to the host material are similar. However, ATFP-Ph has significantly lower hole and electron reorganization energy (λ) of 250 and 268 meV, compared to that of ATFP-BiPh which has hole and electron λ of 334 and 320 meV, and ATFP-Naph which has hole and electron λ of 324 and 361 meV, respectively. The origin of lower hole and electron λ is analyzed via charge distribution on the molecule. The change in charge on the phenyl moiety in ATFP-Ph during hole and electron injection is much smaller than the biphenyl moiety in ATFP-BiPh and the naphthyl moiety in ATFP-Naph, indicating low electron-phonon coupling. This low hole and electron λ of ATFP-Ph yield high hole and electron hopping rates, which result in the higher device performance of OLEDs.

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