Constructing Effective Hole Transport Channels in Cross-Linked Hole Transport Layer by Stacking Discotic Molecules for High Performance Deep Blue QLEDs.

The inadequate hole injection limits the efficiency and lifetime of the blue quantum dot light-emitting diodes (QLEDs), which severely hampers their commercial applications. Here a new discotic molecule of 3,6,10,11-tetrakis(pentyloxy)triphenylene-2,7-diyl bis(2,2-dimethylpropanoate) (T5DP-2,7) is introduced, in which the hole transport channels with superior hole mobility (2.6 × 10 -2 cm 2 V -1 s -1 ) is formed by stacking. The composite hole transport material (HTM) is prepared by blending T5DP-2,7 with the cross-linked 4,4'- bis(3-vinyl-9H-carbazol-9-yl)-1,1'biphenyl (CBP-V) which shows the deep highest occupied molecular orbital energy level. The increased hole mobility of the target composite HTM from 10 -4 to 10 -3 cm 2 V -1 s -1 as well as the stepwise energy levels facilitates the hole transport, which would be beneficial for more balanced carrier injection. This composite hole transport layer (HTL) has improved the deep-blue-emission performances of Commission International de I'Eclairage of (0.14, 0.04), luminance of 44080 cd m -2 , and external quantum efficiency of 18.59%. Furthermore, when L 0 is 100 cd m -2 , the device lifetime T 50 is extended from 139 to 502 h. The state-of-the-art performance shows the successful promotion of the high-efficiency for deep blue QLEDs, and indicates that the optimizing HTL by discotic molecule stacking can serve as an excellent alternative for the development of HTL in the future.