Green solution-processed thermally activated delayed fluorescence OLEDs with improved performance by using interfacial exciplex host

Abstract To achieve green solution-processed thermally activated delayed fluorescence (TADF) organic light emitting diodes (OLEDs) with low turn-on voltages and high power efficiencies (PEs), an interfacial exciplex system 4,4′-N,N′-dicarbazolylbiphenyl (CBP)/(1,3,5-triazine-2,4,6-triyl)tris(benzene-3,1-diyl)tris(diphenylphosphineoxide) (PO-T2T) was used as the host to sensitize TADF emitters. Due to barrier-free hole-electron injection and effectively energy transfer, green solution-processed OLED with interfacial CBP:PO-T2T host exhibits a low turn-on voltage of 3.0 V and maximum current efficiency (CE), PE and external quantum efficiency (EQE) of 53.4 cd/A, 41.9 lm/W and 16.2% by using our previous reported TADF molecule 2’-(10H-phenoxazin-10-yl)-[1,1’:3′,1″-terphenyl]-4,4″,5′-tricarbonitrile (oPTBC) as the emitter. And the compared OLEDs based on the bulk CBP:PO-T2T host and single CBP host exhibit relatively high turn-on voltages of 4.3 and 3.7 V and low maximum PEs of 20.8 and 33.0 lm/W. Moreover, the OLED based on classic green TADF emitter 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) achieves high performance with an ultralow turn-on voltage of 2.9 V and high maximum CE, PE and EQE of 67.2 cd/A, 62.1 lm/W and 20.0%, respectively. These results are remarkable among the reported green solution-processed TADF-OLEDs and demonstrate the superiority of interfacial exciplex host in solution-processed OLEDs.