High efficiency and long lifetime fluorescent white organic light-emitting diodes by phosphor sensitization to strategically manage singlet and triplet excitons

Abstract

All fluorescent white organic light-emitting diodes (WOLEDs) have the advantages of low cost, low-efficiency roll-off, and good stability. However, how to utilize all singlet and triplet excitons for radiative emission through device structure design to effectively manage excitons in fluorescent WOLEDs is still a challenge. Here, we have successfully realized high efficiency, low-efficiency roll-off and long lifetime fluorescent WOLEDs by strategically controlling the position of the phosphor-sensitized fluorescent yellow emitter in the Bepp₂ layer so that singlet excitons are used for blue emission and triplet excitons for the yellow emission. The yellow emission layer is composed of the phosphor sensitizer Ir(ppy)₃ and yellow fluorescent emitter TBRb co-doped in Bepp₂. The resulting complementary-color fluorescent WOLEDs exhibited the maximum current efficiency of 46.8 cd A⁻¹, power efficiency of 56.5 lm W⁻¹ and external quantum efficiency of 15.2%; these efficiency values remained at 32.7 cd A⁻¹, 28.6 lm W⁻¹ and 10.9% at the luminance of 1000 cd m⁻². The operational lifetime LT₅₀ (decay to half of the initial luminance) of optimized WOLEDs was up to 1680 h at an initial luminance of 1000 cd m⁻². This strategy design proposes a potential route to achieve high-performance fluorescent WOLEDs for practical applications.