Tuning a Weak Emissive Blue Host to Highly Efficient Green Dopant by a CN in Tetracarbazolepyridines for Solution‐Processed Thermally Activated Delayed Fluorescence Devices

• DOI: 10.1002/adom.201500016
• Publication Date: 2015-02-26T16:03:19Z
• Authors: Chao Tang; Tao Yang; Xudong Cao; Youtian Tao; Fangfang Wang; Cheng Zhong; Yan Qian; Xinwen Zhang; Wei Huang
• Keywords: 01 natural sciences; 0104 chemical sciences

For example, a maximum EQE of 8.1% for the most popular green emissive 2,4,5,6-tetra(carbazol-9-yl)-1,3-dicyanobenzene (4CzIPN) TADF dye and 18.2% for its tert -butyl substituent t4CzIPN were achieved in device structure of ITO/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)/PVK/ SiCz:TADF dopant/TSPO1/TPBI/LiF/Al. Different from the previous famous dicyanobenzene [ 7,13,14 ] containing TADF dyes, in this work, we expanded it to a new building block known as cyanopyridine, by introducing one cyano moiety to the electronwithdrawing pyridine ring for a new effi cient TADF material 2,3,5,6-tetracarbazole-4-cyano-pyridine (4CzCNPy). Simultaneously, our previously reported cyano-free high triplet blue phosphorescent host 2,3,5,6-tetracarbazole-pyridine (2,3,5,6-CzPy or 4CzPy) was selected as comparison. [ 22 ] The incorporation of a CN unit to pyridine greatly alters the optoelectronic properties. Compared to 4CzPy with weak blue emission which is quenched by n–π* transition, 4CzCNPy shows strong green– yellow donor–acceptor (D–A)-based intramolecular charge transfer emission, and a signifi cant decrease of singlet/triplet energy (0.84/0.6 eV). By using 4CzCNPy as TADF dopant, high triplet 4CzPy and 1,3-bis( N -carbazolyl)benzene (mCP) as host materials for solution-processable simple two-layer devices of ITO/PEDOT:PSS/host:4CzCNPy/1,3,5-tri(m-pyrid-3-ylphenyl) benzene (TmPyPB)/LiF/Al, maximum current effi ciencies as high as 35.4 and 38.9 cd A −1 were achieved, respectively, corresponding to EQE of 10.4% and 11.3%. Scheme 1 illustrates the chemical structures and synthetic routes for 4CzPy and 4CzCNPy. Both compounds can be Tuning a Weak Emissive Blue Host to Highly Effi cient Green Dopant by a CN in Tetracarbazolepyridines for Solution-Processed Thermally Activated Delayed Fluorescence Devices