Managing excitons for high performance hybrid white organic light-emitting diodes by using a simple planar heterojunction interlayer

High performance hybrid white organic light-emitting diodes (WOLEDs) were fabricated by inserting a planar heterojunction interlayer between the fluorescent and phosphorescent emitting layers (EMLs). The maximum external quantum efficiency (EQE) of 19.3%, current efficiency of 57.1 cd A^-1, and power efficiency (PE) of 66.2 lm W^-1 were achieved in the optimized device without any light extraction enhancement. At the luminance of 1000 cd m^-2, the EQE and PE remained as high as 18.9% and 60 lm W^-1, respectively, showing the reduced efficiency-roll. In order to disclose the reason for such high performance, the distribution of excitons was analyzed by using ultra-thin fluorescent and phosphorescent layers as sensors. It was found that the heterojunction interlayer can efficiently separate the singlet and triplet excitons, preventing the triplet excitons from being quenched by the fluorescent emitter. The introduction of the heterojunction interlayer between the fluorescent and phosphorescent EMLs should offer a simple and efficient route to fabricate the high performance hybrid WOLEDs.