High brightness stable white and yellow light-emitting diodes from ambipolar polyspirofluorenes with high charge carrier mobility

Abstract
We have used two polyspirofluorenes, spirodiethylhexyloxylpolyfluorene (spiro-diEHPF) and triphenylamine-grafted spirodiethylhexyloxylpolyfluorene (spiro-TPA50-diEHPF), which exhibit rather high chargemobilities in the order of 10 − 3 – 10 − 4 cm 2 ∕ V s . The light-emitting devices with rubrene-doped spiro-diEHPF show maximal luminances of 36 000 and 70 000 cd ∕ m 2 with maximal efficiencies 3.5 and 9 cd ∕ A for the white and yellow emissions, respectively. For rubrene-doped triphenylamine-grafted polymer, spiro-TPA50-diEHPF, the maximal luminances and efficiencies are 56 000 cd ∕ m 2 and 9 cd ∕ A for white-emitting devices and 72 000 cd ∕ m 2 and 14 cd ∕ A for yellow emission. Furthermore, the electroluminescence profiles of the investigated devices show nearly independent of the applied voltages.