Turning the energy channel of side-chain TADF polymers by monomer optimization for high-efficiency solution-processed white OLEDs

Abstract

Suppressing non-radiative channel in luminescent polymer is the key factor for high device efficiency of organic light-emitting diodes (OLEDs). In this paper, we synthesized three side-chain TADF polymers, PTRZ-TRZ, PTRZ-TPA and PTRZ-Cz, to deeply investigate the relationship between energy transfer and molecular structure. The photophysical measurements show that the copolymerized monomer has significant effect on the exciton deexcitation process of TADF fragment. The rigid carbazole unit can efficiently separate the TADF units to inhibit the aggregation-caused quenching (ACQ) of polymer, while electron-donating triphenylamine unit will induce the severe charge transfer state to form low energy exciplex, which lead to severe energy leakage of the excited TADF. Moreover, according to the single-charge devices test, the ideal separation unit also can improve the capability of charge injection and carrier balance. As a result, the solution-processed OLEDs host with PTRZ-Cz achieved the external quantum efficiency (EQEmax) of 14.2%, which was much higher than that of PTRZ-TPA and PTRZ-TRZ. By doping red phosphorescent emitter Ir(MDQ)2(acac), the hybrid white OLED devices (T-P WOLEDs) based on PTRZ-Cz achieved the maximum current efficiency (CEmax), power efficiency (PEmax) and EQEmax of 46.8 cd/A, 32.6 lm/W and 20.7%, respectively, with a high CRI of 80.6. The outcomes obtained in this study can provide useful insights into the structure−property relationship for further development of efficient TADF polymer hosts for solution-processable OLEDs.