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High‐Performance Red, Green, and Blue Electroluminescent Devices Based on Blue Emitters with Small Singlet–Triplet Splitting and Ambipolar Transport Property
Author(s) -
Wang Kai,
Zhao Fangchao,
Wang Chenguang,
Chen Shanyong,
Chen Dong,
Zhang Hongyu,
Liu Yu,
Ma Dongge,
Wang Yue
Publication year - 2013
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.201202981
Subject(s) - homo/lumo , ambipolar diffusion , materials science , oled , photochemistry , singlet state , electroluminescence , phosphorescence , fluorescence , optoelectronics , molecule , nanotechnology , excited state , electron , chemistry , optics , atomic physics , physics , organic chemistry , layer (electronics) , quantum mechanics
Two coordination complex emitters as well as host materials Be(PPI) 2 and Zn(PPI) 2 (PPI = 2‐(1‐phenyl‐1 H ‐phenanthro[9,10‐ d ]imidazol‐2‐yl)phenol) are designed, synthesized, and characterized. The incorporation of the metal atom leads to a twisted conformation and rigid molecular structure, which improve the thermal stability of Be(PPI) 2 and Zn(PPI) 2 with high T d and T g at around 475 and 217 °C, respectively. The introduction of the electron‐donating phenol group results in the emission color shifting to the deep‐blue region and the emission maximum appears at around 429 nm. This molecular design strategy ensures that the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) HOMO and LUMO of Be(PPI) 2 and Zn(PPI) 2 localize on the different moieties of the molecules. Therefore, the two complexes have an ambipolar transport property and a small singlet–triplet splitting of 0.35 eV for Be(PPI) 2 and 0.21 eV for Zn(PPI) 2 . An undoped deep‐blue fluorescent organic light‐emitting device (OLED) that uses Be(PPI) 2 as emitter exhibits a maximum power efficiency of 2.5 lm W −1 with the CIE coordinates of (0.15, 0.09), which are very close to the National Television Standards Committee (NTSC) blue standard (CIE: 0.14, 0.08). Green and red phosphorescent OLEDs (PhOLEDs) that use Be(PPI) 2 and Zn(PPI) 2 as host materials show high performance. Highest power efficiencies of 67.5 lm W −1 for green PhOLEDs and 21.7 lm W −1 for red PhOLEDs are achieved. In addition, the Be(PPI) 2 ‐based devices show low‐efficiency roll‐off behavior, which is attributed to the more balanced carrier‐transport property of Be(PPI) 2 .