Classic Fluorophores With a Horizontal Alignment for Enhancing Light Outcoupling Efficiency (≈30%) and External Quantum Efficiency (≈7%) of Near Ultraviolet (λ<sub>max</sub> < 400 nm) Organic Light‐Emitting Diodes
Jian Haur Lee, Jian Haur Lee, Jing‐Xiang Huang, Chia‐Hung Chen, Chia‐Hung Chen, Yi‐Ting Lee, Chin‐Yiu Chan, Yi‐Chung Dzeng, Po‐Wen Tang, Chi Chen, Chi Chen, Chihaya Adachi, Tien‐Lung Chiu, Jiun‐Haw Lee, Jiun‐Haw Lee, Chin‐Ti Chen, Chin‐Ti Chen
Abstract
Abstract Based on the classic 1,1′:4′,1″‐terphenyl fluorophore, a novel near‐ultraviolet (NUV) fluorescent BB4Ph (4,4″′‐bis(2,3,4,5‐tetraphenylphen‐1‐yl)(1,1′:4′,1″‐terphenyl) is designed, synthesized, and characterized. BB4Ph exhibits a NUV fluorescence with a λ max of 373 and 380 nm in solution and as a thin film, respectively. The grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals BB4Ph having a high value of order parameter ( S GIWAXS ) of 0.59 for a molecular layer array normal to the substrate; the angle‐dependent photoluminescence (ADPL) measurement shows Θ (horizontal–dipole ratios) as high as 95% with the neat film. The non‐doped BB4Ph organic light‐emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with 1931 Commission Internationale de l’ Eclairage coordinates (CIE x,y ) of (0.16, 0.04), a NUV electroluminescence. With 4P‐Cz (9,9′‐(1,1′:4′,1″:4″,1′″‐quaterphenyl‐4,4′″‐diyl)dicarbazole) as a dopant emitter, doped BB4Ph OLEDs show the highest EQE of 6.99% and a NUV 1931 CIE x,y (0.16, 0.04). The photoluminescence quantum yield is measured for the thin film of BB4Ph and 4P‐Cz:BB4Ph as 68% and 96%, respectively. Hence, the low limits of light outcoupling efficiency (η out ) of the two individual OLEDs are estimated as 31% and 29%, respectively.