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Rhee SH, Kim SH, Kim HS, et al. Heavily Doped, Charge-Balanced Fluorescent Organic Light-Emitting Diodes from Direct Charge Trapping of Dopants in Emission Layer. ACS Appl Mater Interfaces. 2015;7(30):16750-9doi: 10.1021/acsami.5b04519.
Rhee, S. H., Kim, S. H., Kim, H. S., Shin, J. Y., Bastola, J., & Ryu, S. Y. (2015). Heavily Doped, Charge-Balanced Fluorescent Organic Light-Emitting Diodes from Direct Charge Trapping of Dopants in Emission Layer. ACS applied materials & interfaces, 7(30), 16750-9. https://doi.org/10.1021/acsami.5b04519
Rhee, Sang Ho, et al. "Heavily Doped, Charge-Balanced Fluorescent Organic Light-Emitting Diodes from Direct Charge Trapping of Dopants in Emission Layer." ACS applied materials & interfaces vol. 7,30 (2015): 16750-9. doi: https://doi.org/10.1021/acsami.5b04519
Rhee SH, Kim SH, Kim HS, Shin JY, Bastola J, Ryu SY. Heavily Doped, Charge-Balanced Fluorescent Organic Light-Emitting Diodes from Direct Charge Trapping of Dopants in Emission Layer. ACS Appl Mater Interfaces. 2015 Aug 05;7(30):16750-9. doi: 10.1021/acsami.5b04519. Epub 2015 Jul 21. PMID: 26151550.
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ACS Appl Mater Interfaces. 2015 Aug 05;7(30):16750-9. doi: 10.1021/acsami.5b04519. Epub 2015 Jul 21.

Heavily Doped, Charge-Balanced Fluorescent Organic Light-Emitting Diodes from Direct Charge Trapping of Dopants in Emission Layer.

ACS applied materials & interfaces

Sang Ho Rhee, Sung Hyun Kim, Hwang Sik Kim, Jun Young Shin, Jeeban Bastola, Seung Yoon Ryu

Affiliations

  1. ‡Department of Chemistry, College of Natural Sciences, Seoul National University, Seoul 151-747, Republic of Korea.

PMID: 26151550 DOI: 10.1021/acsami.5b04519

Abstract

We studied the effect of direct charge trapping at different doping concentrations on the device performance in tris(8-hydroxyquinoline) aluminum (Alq3):10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-(1)-benzopyropyrano(6,7-8-i,j)quinolizin-11-one (C545T) as a host-dopant system of a fluorescent organic light-emitting diode. With increasing C545T doping concentration, trap sites could lead to the promotion of hole injection and the suppression of electron injection due to the electron-transport character of Alq3 host for each carriers, as confirmed by hole- and electron-only devices. Direct charge injection of hole carriers from the hole transport layer into C545T dopants and the charge trapping of electron carriers are the dominant processes to improve the charge balance and the corresponding efficiency. The shift of the electroluminescence (EL) spectra from 519 nm to 530 nm was confirmed the exciton formation route from Förster energy transfer of host-dopant system to direct charge trapping of dopant-only emitting systems. Variation in the doping concentration dictates the role of the dopant in the fluorescent host-dopant system. Even though concentration quenching in fluorescent dopants is unavoidable, relatively heavy doping is necessary to improve the charge balance and efficiency and to investigate the relationship between direct charge trapping and device performance. Heavy doping at a doping ratio of 6% also generates heavy exciton quenching and excimer exciton, because of the excitons being close enough and dipole-dipole interactions. The optimum device performance was achieved with a 4%-doped device, retaining the high efficiency of 12.5 cd/A from 100 cd/m(2) up to 15,000 cd/m(2).

Keywords: charge balance; direct charge trapping; fluorescent OLEDs; hole-/electron-only devices; hole/electron injection; trap sites

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