Triphenyl phosphine oxide and carbazole-based polymer host materials for green phosphorescent organic light-emitting diodes

Abstract

Four novel polymers, poly(3,6-9-decyl-carbazole-alt-1,3-benzene) (PB13CZ), poly(3,6-9-decyl-carbazole-alt-bis(4-phenyl) (phenyl) phosphine oxide) (PTPPO38CZ), poly(3,6-9-decyl-carbazole-alt-2,4-phenyl(diphenyl) phosphine oxide) (PTPPO13CZ) and poly(3,6-9-decyl-carbazole-alt-bis(3-phenyl) (phenyl) phosphine oxide) (PTTPO27CZ) were synthesized, and their thermal, photophysical properties and device applications were further investigated to correlate the chemical structures with the photoelectric performance of bipolar host materials for phosphorescent organic light emitting diodes. All of them show high thermal stability as revealed by their high glass transition temperatures and thermal decomposition temperatures at 5% weight loss. These polymers have wide band gaps and relatively high triplet energy levels. As a result, the spin coating method was used to prepare the green phosphorescent organic light emitting diodes with polymers PTPPO38CZ, PTPPO13CZ and PTTPO27CZ as the typical host materials. The green device of polymer PTPPO38CZ as host material shows electroluminescent performance with maximum current efficiency of 2.16 cd·A−1, maximum external quantum efficiency of 0.7%, maximum brightness of 1475 cd·m−2 and reduced efficiency roll-off of 7.14% at 600 cd·m−2, which are much better than those of the same devices hosted by polymers PTTPO27CZ and PTPPO13CZ.