Reduced efficiency roll-off in electrophosphorescent devices by a short-living rhenium emitter with well-matched energy levels

We demonstrated reduced efficiency roll-off in electrophosphorescent devices based on a rhenium [Re(I)] complex, {9, 9-Di-[9′-(4″-phenoxybutyl)-9′H-carbazyl]-9-H-4,5-Diazafluorene Re(CO)3Br} (Re-PCDF). The devices based on Re-PCDF exhibited the peak luminance of 7888 cd/m2 and the maximum efficiency of 7.41 cd/A, respectively. Remarkably, the devices exhibited very small efficiency roll-off with only ca. 28%, which is much better than the reported Re(I) complexes based devices. Such excellent performances could be ascribed to the short luminescent lifetime of Re-PCDF and well-matched energy levels between the singlet host and the triplet emitter. The detailed mechanisms of such small efficiency roll-off were also investigated.