High-efficiency endothermic energy transfer in polymeric light-emitting devices based on cyclometalated Ir complexes

Abstract

We report polymeric light-emitting diodes (PLEDs) made from pinene-substituted iridium(III) phosphorescent dopants: tris(5-(4-difluoro phenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F-pppy)3] and tris(5-(2,4-difluorophenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir(F2-pppy)3]. The pinene substitution introduces steric hindrance to molecular structure of the dopant that reduces triplet-triplet annihilation between dopants and consequently enhances device performance. Via endothermic energy transfer from poly(vinylcarbazole) to Ir(F-pppy)3 and Ir(F2-pppy)3, a peak electroluminescent efficiency of 32.8cd∕A or 12.3cd∕A at 12wt% Ir(F-pppy)3 or 15wt% Ir(F2-pppy)3 doped and solution-processed PLEDs have been obtained. These values represent significant improvement in performance over previously reported endothermic energy-transfer based electrophosphorescent devices.

Phosphorescent Molecularly Doped Light‐Emitting Diodes with Blended Polymer Host and Wide Emission Spectra

“…The lower doped devices (1% and 2%) showed higher current density than the heavy doped devices (4% and 8%) at the same driving bias. The shift of current density-voltage curves to higher voltages as doping concentration increasing could be attributed to charge-trapping effect [ 19 ]. When more iridium complex was doped in host material, more trapping center formed for the free carriers because the HOMO and LUMO level of (tpbi) 2 Ir(acac) were between that of PFO and PBD blended host, so that the current density of device became lower at the same driving voltage when increasing the doping concentration.…”

Study on triplet exciton diffusion length of mCP in phosphorescent organic light-emitting devices using electroluminescent spectra

“…The efficiency of OLED has been considerably increased thanks to the utilization of phosphorescent materials, which can harvest both singlet and triplet excitons leading to nearly 100% internal quantum efficiency [2,3], as two types of excitons, singlet and triplet, can be originated from the recombination zone using doping phosphor into host materials [4,5].…”