Improved performance of inverted quantum dots light emitting devices by introducing double hole transport layers

• A low turn-on voltage and highly efficient deep red QD-LEDs has been successfully fabricated.
• Through thermal treatment, the Von decreases from 4.8 V to 3.6 V and Lmax increases by 60% for single HTL QD-LEDs.
• The QD-LEDs with double HTLs exhibits low Von of 1.9 V, high CE and PE of 8.68 cd/A and 10.2 lm/W respectively.

Here we reported very bright and highly efficient deep-red quantum dot light-emitting devices (QD-LEDs) with inverted structure by introducing double hole transport layers (HTLs) consisting of 4,4′,4″-tri (N-carbazolyl)-triphenyl-amine (TCTA) and N,N′-bis (naphthalen-1-yl)-N,N′-bis (phenyl)-benzidine (NPB). The turn-on voltage of the optimized device was as low as 1.9 V, the maximum current efficiency and luminance were 8.68 cd/A and 15,000 cd/m2, respectively. However, for the best performance of QD-LED with single hole transport layer, the turn-on voltage reached up to 3.6 V, the peak current efficiency was only 3.84 cd/A and the maximum luminance was 7700 cd/m2. The enhancement of the performance is attributed to the stepwise HTL structure, which can decrease the hole-injection barrier from HTL to QD emitting layer and reduce the turn-on voltage of QD-LEDs. Besides, the lower highest occupied molecular orbital of TCTA can suppress the accumulation of electrons at the interface of QDs/HTL and separate the carrier accumulation zone from the exciton formation interface, which can balance the carriers transportation and enhance performance of QD-LEDs.

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