High-Efficiency Electrophosphorescent Copolymers Containing Charged Iridium Complexes in the Side Chains

摘要

A convenient approach to novel charged Ir polymers for opto electronic devices to achieve red emis sion was developed.2-(Pyridin-2-yl)- benzimidazole units grafted into the side chains of macroligands (PFCz and PFP) served as ligands for the forma tion of charged Ir complex pendants with 1-phenylisoquinoline (1-piq).The charged Ir polymers (PFPIrPiq and PFCzIrPiq) showed exclusive Ir(1-piq)2{N-[2-(pyridin-2-yl)benzimida-zole]hexyl}~+BF_4~-(IrPiq) emission,with the peak at 595 nm.The best device performances were obtained from PFCzIrPiq4 with the device configuration of ITO/PEDOT:PSS/PFCzIr-Piq4+PBD (30 wt%)/TPBI/Ba/Al (PBD: 5-(4-tert-butylphenyl)-2-(bi-phenyl-4-yl)-l,3,4-oxadiazole;TPBI:l,3,5-tris-(2-A7-phenylbenzimidazolyl)-benzene).A maximum external quantum efficiency (EQE) of 7.3% and a luminous efficiency (LE) of 6.9 cd A~(-1) with a luminance of 138 cdm~2 were achieved at a current density of 1.9 mA cm~(-2).The efficiencies remained as high as EQE=3.4% and LE=3.3 cd A~(-1) with a luminance of 3770 cd m~(-2) at a current density of 115 mA cm~(-2).The single-layer devices based on charged Ir polymers also showed high efficiency with the high work-function metal Ag as cathode.The maximum external quantum efficiencies of the devices were 0.64 % and 0.66% for PFPIrPiq2 and PFPIrPiq10,respectively.A possible mechanism of an electrochemical cell associated with its electrochemical redox pathway for single-layer devices has been proposed.The results showed that the charged Ir polymers are promising candidate materials for polymer optoelectronic devices.