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Spin‐Coated Highly Efficient Phosphorescent Organic Light‐Emitting Diodes Based on Bipolar Triphenylamine‐Benzimidazole Derivatives
Author(s) -
Ge Ziyi,
Hayakawa Teruaki,
Ando Shinji,
Ueda Mitsuru,
Akiike Toshiyuki,
Miyamoto Hidetoshi,
Kajita Toru,
Kakimoto Masaaki
Publication year - 2008
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.200700913
Subject(s) - triphenylamine , homo/lumo , oled , materials science , phosphorescence , photochemistry , benzimidazole , molecule , amine gas treating , spin coating , optoelectronics , thin film , nanotechnology , organic chemistry , chemistry , fluorescence , physics , optics , layer (electronics)
A new series of star‐shaped bipolar host molecules, tris(4′‐(1‐phenyl‐1 H ‐benzimidazol‐2‐yl)biphen‐yl‐4‐yl) amine (TIBN), tris(2′‐methyl‐4′‐(1‐phenyl‐1 H ‐benzimida zol‐2‐yl)biphenyl‐4‐yl)amine (Me‐TIBN), and tris(2,2′‐dimethyl‐4′‐(1‐phenyl‐1 H ‐benzimidazol‐2‐yl)biphenyl‐4‐yl)amine (DM‐TIBN), that contain hole‐transporting triphenylamine and electron‐transporting benzimidazole moieties are designed based on calculations using density functional theory and successfully prepared. The theoretical calculation of energy levels of TIBN derivatives affords helpful ideas to design molecules with a favorable localization of highest occupied/lowest unoccupied molecular orbital (HOMO/LUMO) levels and a predefined enhancement of the triplet energy gap. The TIBN derivatives are employed as hosts to fabricate phosphorescent organic light‐emitting diodes (OLEDs) by the two methods of spin‐coating and vacuum deposition. Notably, the spin‐coated Me‐TIBN and DM‐TIBN devices exhibit a much better performance than the vacuum‐deposited ones, in which the spin‐coated DM‐TIBN device (47 500 cd m −2 , 27.3 cd A −1 , 7.3 lm W −1 ) is outstanding with respect to other seminal work for solution‐processed OLEDs. More importantly, the new concept of localizing HOMO and LUMO levels for bipolar molecules is illustrated, and a facile strategy to tailor the energy levels by breaking the conjugation of hole‐ and electron‐transporting moieties is demonstrated.