Deep-blue high-efficiency triplet-triplet annihilation organic light-emitting diodes using hydroxyl-substituted tetraphenylimidazole-functionalized anthracene fluorescent emitters

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Vol. 1; no. 27; pp. 9968 - 9979
• Main Authors: Li, Wan, Chasing, Pongsakorn, Nalaoh, Phattananawee, Chawanpunyawat, Thanyarat, Chantanop, Nuttapong, Sukpattanacharoen, Chattarika, Kungwan, Nawee, Wongkaew, Praweena, Sudyoadsuk, Taweesak, Promarak, Vinich
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 14.07.2022
• Subjects: Anthracene; Current efficiency; Efficiency; Electroluminescence; Emitters; Excitons; Fluorescence; Hole mobility; Organic light emitting diodes; Polyvinyl alcohol; Quantum efficiency; Spectral emittance; Substitutes; Thin films
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d2tc01406h

Herein, two new triplet-triplet annihilation (TTA) molecules, namely HO-PIAC and PIAC , as deep-blue emitters for high-efficiency TTA-OLEDs were designed and synthesized. HO-PIAC and PIAC contain 4-( N -phenylcarbazol-3-yl)phenylanthracene as a blue emissive core directly functionalized with hydroxyl-substituted tetraphenylimidazole and tetraphenylimidazole, respectively. Their structural, physical, and photophysical properties were experimentally and theoretically examined. Both molecules exhibited deep-blue color emissions in solution and neat films, with decent hole mobility and high thermal and electrochemical stabilities. Intense TTA emissions were seen in their thin films (2 wt% doped in poly(4-bromostyrene) (PBS) films covered by a polyvinyl alcohol (PVA) film). The two molecules were effectively utilized as emitters in OLEDs and both devices displayed deep-blue electroluminescence (EL) spectra (CIE y ≤ 0.08) with a narrow full width at half maximum of ≤59 nm, low turn-on voltages (3.0-3.3 V), and TTA characteristics. In particular, the HO-PIAC -based device attained a superior EL performance with a maximum luminance ( L max ) of 7042 cd m −2 , a maximum external quantum efficiency (EQE max ) of 6.43%, a maximum current efficiency (CE max ) of 2.64 cd A −1 , and a singlet exciton utilization ( η s ) of 38%. A new triplet-triplet annihilation-OLED exhibits deep-blue electroluminescence (CIE y 0.08) with a narrow full width at half maximum of 59 nm, high external quantum efficiency of 6.43%, low turn-on voltage, and singlet exciton utilization of 38%.