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

Abstract

A convenient approach to novel charged Ir polymers for optoelectronic devices to achieve red emission was developed. 2-(Pyridin-2-yl)benzimidazole units grafted into the side chains of macroligands (PFCz and PFP) served as ligands for the formation 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)benzimidazole]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/PFCzIrPiq4+PBD (30 wt %)/TPBI/Ba/Al (PBD: 5-(4-tert-butylphenyl)-2-(biphenyl-4-yl)-1,3,4-oxadiazole; TPBI: 1,3,5-tris-(2-N-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 cd m(-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.