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New Solution‐Processable Electron Transport Materials for Highly Efficient Blue Phosphorescent OLEDs
Author(s) -
Ahmed Eilaf,
Earmme Taeshik,
Jenekhe Samson A.
Publication year - 2011
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.201100848
Subject(s) - materials science , oled , phosphorescence , iridium , quantum efficiency , common emitter , optoelectronics , cathode , nanopillar , quinoline , luminous efficacy , photochemistry , electron , diode , nanotechnology , chemistry , optics , nanostructure , physics , fluorescence , organic chemistry , layer (electronics) , quantum mechanics , catalysis
Several new solution‐processable organic semiconductors based on dendritic oligoquinolines were synthesized and were used as electron‐transport and hole‐blocking materials to realize highly efficient blue phosphorescent organic light‐emitting diodes (PhOLEDs). Various substitutions on the quinoline rings while keeping the central meta ‐linked tris(quinolin‐2‐yl)benzene gave electron transport materials that combined wide energy gap (>3.3 eV), moderate electron affinity (2.55‐2.8 eV), and deep HOMO energy level (<‐6.08 eV) with electron mobility as high as 3.3 × 10 −3 cm 2 V −1 s −1 . Polymer‐based PhOLEDs with iridium (III) bis(4,6‐(di‐fluorophenyl)pyridinato‐ N ,C 2′ )picolinate (FIrpic) blue triplet emitter and solution‐processed oligoquinolines as the electron‐transport layers (ETLs) gave luminous efficiency of 30.5 cd A −1 at a brightness of 4130 cd m −2 with an external quantum efficiency (EQE) of 16.0%. Blue PhOLEDs incorporating solution‐deposited ETLs were over two‐fold more efficient than those containing vacuum‐deposited ETLs. Atomic force microscopy imaging shows that the solution‐deposited oligoquinoline ETLs formed vertically oriented nanopillars and rough surfaces that enable good ETL/cathode contacts, eliminating the need for cathode interfacial materials (LiF, CsF). These solution‐processed blue PhOLEDs have the highest performance observed to date in polymer‐based blue PhOLEDs.