PPO27 is a host material developed for highly efficient thermally activated delayed fluorescence (TADF) devices. It has a bipolar structure of electron rich phenylcarbazole core with two electron deficient diphenylphosphine oxide units.
A maximum external quantum efficiency (EQE) of 24.2% was achieved by using PPO27 as the bipolar host and 4CzIPN as the green dopant. This was possible because due to the effective energy transfer from the host to the dopant. The TADF emitter 4CzIPN interacted strongly with the PPO27 host as the latter has strong polarity, and a significant redshift in the electroluminescence spectrum was observed at higher doping concentrations.PPO27 is a typical alcohol soluble bipolar host material which is soluble in isopropyl alcohol (IPA) and possesses a high triplet energy of 2.81 eV for application as a host for sky blue (FIrpic) and deep blue (FCNIrpic) phosphorescent triplet emitters. Smooth surface morphologies with low surface roughness less than 0.30 nm were observed in the PPO27:FIrpic and PPO27:FCNIrpic films spin coated from their IPA solutions.