High efficiency phosphorescence light-emitting diodes with conjugated polymer host

Abstract

Polymer hosted phosphorescent light-emitting diodes （PLEDs） were attractive because of their high efficiency light-emission and easy fabrication technology using solution process. For green phosphorescence PLEDs，non-conjugated polymer，such as poly （N-vinylcarbazole） （PVK），were often used as host；while conjugated polymer have been proved to quench phosphorescence emission because of their low-lying triplet energy level. In this article，high efficiency phosphorescent green-emission was obtained with conjugated polymer of poly （9，9-dioctylfluorene） （PFO） as host using the device structure of ITO/poly （ehtlenedioxythiophene）: poly （styrene sulfonic acid） （PEDOT: PSS） （50 nm）/PVK （40 nm）/emissive layer （EML） （80 nm）/Ba （4 nm）/Al （150 nm）. The EML were PFO doped with different concentration of fac-tris （2-phenylpyridine） iridium （Ⅲ） （Ir（ppy）3） in weight. The PLED with 2 wt% Ir（ppy）3 demonstrated the maximum luminous efficiency of 24.8 cd/A at current density of 4.65 mA/cm2 and power efficiency of 11 lm/w with the peak emission at 520 nm. The luminance reached 35054 cd/m2 at the current density of 265 mA/cm2. According to analyzsis，the hole transport layer PVK can play important role in obtaining highly efficient green light emissing，whose electrons blocking effect resulted in the interfacial emissing center, and then the interfacial PVK enhanced green emission through energy transfer due to its high triplet enery level.