Development of a Highly Efficient Hybrid White Organic-Light-Emitting Diode with a Single Emission Layer by Solution Processing

Abstract

We use a mixed host, 2,6-bis[3-(carbazol-9-yl)phenyl]pyridine blended with 20 wt % tris(4-carbazoyl-9-ylphenyl)amine, to lower the hole-injection barrier, along with the bipolar and high-photoluminescence-quantum-yield (Φ_p= 84%), blue thermally activated delay fluorescence (TADF) material of 9,9-dimethyl-9,10-dihydroacridine-2,4,6-triphenyl-1,3,5-triazine (DMAC-TRZ) as a blue dopant to compose the emission layer for the fabrication of a TADF blue organic-light-emitting diode (BOLED). The device is highly efficient with the following performance parameters: maximum brightness (B_max) = 57586 cd/m², maximum current efficiency (CE_max) = 35.3 cd/A, maximum power efficiency (PE_max) = 21.4 lm/W, maximum external quantum efficiency (EQE_max) = 14.1%, and CIE coordinates (0.18, 0.42). This device has the best performance recorded among the reported solution-processed TADF BOLEDs and has a low efficiency roll-off: at brightness values of 1000 and 5000 cd/m², its CEs are close, being 35.1 and 30.1 cd/A, respectively. Upon further doping of the red phosphor Ir(dpm)PQ₂ (emission peak λ_max = 595 nm) into the blue emission layer, we obtained a TADF-phosphor hybrid white organic-light-emitting diode (T-P hybrid WOLED) with high performance: B_max = 43594 cd/m², CE_max = 28.8 cd/A, PE_max = 18.1 lm/W, and CIE coordinates (0.38, 0.44). This B_max = 43594 cd/m² is better than that of the vacuum-deposited WOLED with a blue TADF emitter, 10000 cd/m². This is also the first report on a T-P hybrid WOLED with a solution-processed emitting layer.