Highly Efficient Orange-Red Organic Light-Emitting Diodes Based On Thermally Activated Delayed Fluorescence

Orange-red thermally activated delayed fluorescence(TADF)material is a challenge in organic light-emitting diodes(OLEDs).Compared to the high EQEs(close to 40%)of green and blue TADF-OLEDs,orange-red OLEDs suffer from significant non-radiative decay.Longer wavelength means a narrower energy gap from the triplet state(T1)to the ground state(S0),and the non-radiative decay process is significantly enhanced.Therefore,the development of efficient orange-red TADF materials become a challenge.First,two orange-red materials,3,6,11-triTPA-BPQ and 3,6,12-triTPA-BPQ,were synthesized by using BPQ with large plane-rigid structure as acceptor and TPA with small steric hindrance as donor.Different positions of the N atoms significantly influenced the OPL,ΔEST and device efficiencies.3,6,11-triTPA-BPQ and 3,6.12-triTPA-BPQ showed ΦPL of 94.0%and 78.4%,respectively.In addition,both materials exhibited high Θ//of 92%in CBP films.The device efficiencies based on 3,6,11-triTPA-BPQ were 30.3%,65.4 lm W-1,and 52.7 cd A-1 at 576 nm,while the device efficiencies based on 3.6,12-triTPA-BPQ were 19.9%,45.4 lm W-1,and 38.6 cd A-1 at 578 nm.This provides a novel way to boost the efficiency of orange-red OLEDs.Secondly,we selected PXZ and DMAC with stronger rigidity as donors and BP as acceptor to design and synthesize 1P2D and 2P2D.As expected,the wavelength was red-shifted due to the enhanced rigidity.Among them,the efficiencies of the doped devices based on 1P2D were 15.0%,22.1 lm W-1 and 21.1 cd A-1 at 610 nm.The device efficiencies based on 2P2D were 15.7%.35.7 lm W-1 and 32.5 cd A-1 at 582 nm.This result also illustrates the feasibility of the strategy.Finally,we aimed to explore the application of orange-red TADF material in other fields.We chose blue 3Ph2CzCzBN as the sensitizer and mCBP as the host,and mCBP:30 wt%3Ph2CzCzBN:1 wt%1P2D or 2P2D as the emitting layer to fabricate white OLEDs.Among them,these devices based on 1P2D obtained better performance with device efficiencies of 23.64%,39.60 lm W-1 and 40.39 cd A-1.These findings also illustrate the importance of orange-red TADF materials in other fields.