Deep Blue Fluorescent Material with an Extremely High Ratio of Horizontal Orientation to Enhance Light Outcoupling Efficiency (44%) and External Quantum Efficiency in Doped and Non-Doped Organic Light-Emitting Diodes

Jian Haur Lee; Hung-Yi Lin; Chia-Hsun Chen; Yi-Ting Lee; Tien-Lung Chiu; Jiun-Haw Lee; Chin-Ti Chen; Chihaya Adachi

doi:10.1021/acsami.1c07859

Deep Blue Fluorescent Material with an Extremely High Ratio of Horizontal Orientation to Enhance Light Outcoupling Efficiency (44%) and External Quantum Efficiency in Doped and Non-Doped Organic Light-Emitting Diodes

ACS Appl Mater Interfaces. 2021 Jul 28;13(29):34605-34615. doi: 10.1021/acsami.1c07859. Epub 2021 Jul 15.

Authors

Jian Haur Lee^{1

2

3}, Hung-Yi Lin⁴, Chia-Hsun Chen⁴, Yi-Ting Lee⁵, Tien-Lung Chiu⁶, Jiun-Haw Lee⁴, Chin-Ti Chen^{1

2}, Chihaya Adachi^{5

7}

Affiliations

¹ Sustainable Chemical Science and Technology, Taiwan International Graduate Program, Academia Sinica, Taipei 11529, Taiwan.
² Institute of Chemistry, Academia Sinica, Taipei 11529, Taiwan.
³ Department of Applied Chemistry, National Yang Ming Chiao Tung University, Hsinchu 30010, Taiwan.
⁴ Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, National Taiwan University, Taipei 10617, Taiwan.
⁵ Center for Organic Photonics and Electronics Research (OPERA), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan.
⁶ Department of Electrical Engineering, Yuan Ze University, Taoyuan 32003, Taiwan.
⁷ International Institute for Carbon Neutral Energy Research (WPI-I2CNER), Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan.

PMID: 34264644
DOI: 10.1021/acsami.1c07859

Abstract

A novel bis-4Ph-substituted 9,10-dipehnylanthracene deep blue [1931 CIE (0.15, 0.08)] fluorescent compound, AnB4Ph, has been synthesized and characterized for organic light-emitting diode (OLED) applications. Our experimental study of AnB4Ph excludes the possibility of triplet-triplet annihilation, hybridized local and charge transfer, or thermally activated delayed fluorescent characteristics of the material. Since the solid-state photoluminescence quantum yield of AnB4Ph was determined to be 48%, assuming a 100% for the charge recombination efficiency, the light outcoupling efficiency (η_out) of an AnB4Ph non-doped OLED achieving an external quantum efficiency (EQE) of 5.3% is at least 44%, which is more than twofold higher than 20% for conventional OLEDs. Both grazing incidence wide-angle X-ray scattering (GIWAXS) and angle-dependent photoluminescence (ADPL) measurements reveal AnB4Ph having a high value of order parameter (S_GIWAXS) of 0.61 for a ππ stacking along the normal direction and an orientation order parameter (S_ADPL) for a horizontal emitting dipole moment of -0.50 or Θ (horizontal-dipole ratios) of 100%, respectively. Otherwise, a refractive index (n) measurement provides a n = 1.80 for AnB4Ph thin films. Based on η_out = 1.2 × n^-2, the calculated η_out is 37%, which is also in accordance with the results of GIWAXS and ADPL. We have also fabricated the classical fluorescent DPAVBi-doped AnB4Ph OLEDs, which display a true blue [1931 CIE (0.15 and 0.16)] electroluminescence with a high efficiency (EQE = 6.9%), surpassing the conventional ∼5% EQE. Based on an η_out of 42% for DPAVBi-doped AnB4Ph OLEDs, our studies suggest that the extremely horizontally aligned AnB4Ph host material exerts the same horizontal alignment on the DPAVBi dopant molecules.

Keywords: deep blue OLEDs; fluorescence materials; horizontal orientation; light outcoupling efficiency; light-emitting diode; molecular orientation; non-doped OLEDs; transition dipole moment.