| 초록 |
Phosphorescence dye doped light emitting device (PhOLED) in polymer host shows lower efficiency than in small molecule host. To find out the origin of the lower efficiency in the polymer host, we have investigated the optical properties of phosphorescence dye doped film using Ir(ppy)3 as a dopant and CBP and PVK as hosts. Absolute photoluminescence (PL) efficiency measurement and time resolved technique were employed for the purpose. PL efficiency of Ir(ppy)3 doped CBP film (Ir(ppy)3 :CBP) decreases monotonically from 100% with increasing doping concentration. In contrast, PL efficiency of Ir(ppy)3 doped PVK film (Ir(ppy)3 :PVK) increases with doping concentration when the doping concentration was low, reaches the maximum efficiency of 70% at the doping concentration of 6%, and decreases monotonically with further increment of the doping concentration. The PL efficiency of Ir(ppy)3 :PVK is lower than Ir(ppy)3 :CBP for whole range of doping concentration. This low PL efficiency may be the reason of the lower efficiency of polymer based PhOLED than small molecule PhOLED. The origin of the lower efficiency of polymer PhOLED is investigated using time resolved spectroscopy technique and will be discussed from the view point of triplet energy level and the exciton dynamics in polymer and organic molecules. |
