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Amorphous Diphenylaminofluorene‐Functionalized Iridium Complexes for High‐Efficiency Electrophosphorescent Light‐Emitting Diodes
Author(s) -
Wong W.Y.,
Zhou G.J.,
Yu X.M.,
Kwok H.S.,
Tang B.Z.
Publication year - 2006
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.200500523
Subject(s) - iridium , phosphorescence , materials science , dopant , oled , homoleptic , quantum efficiency , photochemistry , amorphous solid , electroluminescence , acetylacetone , carbazole , optoelectronics , fluorescence , crystallography , doping , optics , nanotechnology , chemistry , inorganic chemistry , organic chemistry , catalysis , physics , layer (electronics) , metal , metallurgy
Two new phosphorescent iridium( III ) cyclometalated complexes, [Ir(DPA‐Flpy) 3 ] ( 1 ) and [Ir(DPA‐Flpy) 2 (acac)] ( 2 ) ((DPA‐Flpy)H = (9,9‐diethyl‐7‐pyridinylfluoren‐2‐yl)diphenylamine, Hacac = acetylacetone), have been synthesized and characterized. The incorporation of electron‐donating diphenylamino groups to the fluorene skeleton is found to increase the highest occupied molecular orbital (HOMO) levels and add hole‐transporting ability to the phosphorescent center. Both complexes are highly amorphous and morphologically stable solids and undergo glass transitions at 160 and 153 °C, respectively. These iridium phosphors emit bright yellow to orange light at room temperature with relatively short lifetimes (< 1 μs) in both solution and the solid state. Organic light‐emitting diodes (OLEDs) fabricated using 1 and 2 as phosphorescent dopant emitters constructed with a multilayer configuration show very high efficiencies. The homoleptic iridium complex 1 is shown to be a more efficient electrophosphor than the heteroleptic congener 2 . Efficient electrophosphorescence with a maximum external quantum efficiency close to 10 % ph/el (photons per electron), corresponding to a luminance efficiency of ∼ 30 cd A –1 and a power efficiency of ∼ 21 lm W –1 , is obtained by using 5 wt.‐% 1 as the guest dopant.