Kinetics of Triplet Exciton Energy-Transfer Processes in Triplet Sensitizer-Doped Fluorescent Polymers

Triplet sensitization is an important aspect for enhancing the performance of organic light-emitting diodes (OLEDs). The triplet-triplet annihilation (TTA) process is known to increase the efficiency of OLEDs. In this case, the time scale of triplet diffusion is an important parameter. In this paper, we have studied the triplet energy-transfer process as a function of time scale and temperature in pure and phosphorescent molecule FIrpic (bis[2-(4,6-difluorophenyl)pyridinato-C2, N](picolinato)iridium(III))-doped F8BT (poly(9,9-dioctylfluorene- alt-benzothiadiazole)) films. We have investigated the dynamics of triplet energy-transfer processes by probing the corresponding delayed fluorescence (DF) spectra (of the F8BT host system) generated from TTA. We have noticed that the dynamics of DF depends on the diffusion kinetics of the triplet excitonic state. We find that the successful triplet transfer to the host polymer system is directly proportional to the triplet lifetime of the guest molecule. We have further implemented doped F8BT films in polymer LEDs (PLEDs). A high triplet absorption (TA) signal (of the host triplets, i.e., F8BT) has been observed in doped PLEDs under electrical excitation. The high TA signal of the host triplets indicates the successful triplet transfer process from the FIrpic guest molecule to the F8BT host polymer system.