High-efficiency solution-processed green thermally activated delayed fluorescence OLEDs using a polymer-small molecule mixed host

Abstract

The development of suitable host materials for application to an emitter is of significant importance for high-efficiency organic light-emitting diodes (OLEDs). In this study, we successfully synthesized poly(9,9-diphenyl-10-(4-vinylbenzyl)-9,10-dihydroacridine) (P(Bn-DPAc)) as a polymer donor and 2-(4'-(tert-butyl)-[1,1'-biphenyl]-4-yl)-4,6-diphenyl-1,3,5-triazine (tPTRZ) as a small-molecule acceptor. A blend of P(Bn-DPAc) and tPTRZ was used as the host material in solution-processed green thermally activated delayed fluorescence OLEDs (TADF-OLEDs). The P(Bn-DPAc)-tPTRZ blend showed a new red-shifted peak in the photoluminescence spectrum, suggesting the possibility of exciplex formation. The polymer-mixed host film showed a fine surface morphology, a well-formed exciplex in the bulk state, and good charge balance. The OLED fabricated with the as-prepared mixed host (P(Bn-DPAc) : tPTRZ = 1: 1 wt ratio) and 2,4,5,6-tetra(3,6-di-tert-butylcarbazol-9-yl)-1,3-dicyanobenzene (t4CzIPN) emitter exhibited a high current efficiency of 107.3 cd A(-1) and a maximum external quantum efficiency (EQE) of 31.2%. The OLED fabricated with the mixed host demonstrated better performance compared to the device with a unipolar host P(Bn-DPAc).