A hole transport material with low cross-linking temperature for high-performance blue quantum dot light-emitting diodes

Inefficient hole injection poses a major challenge in the realization of stable and economically feasible solution-processed blue quantum dot light-emitting diodes (QLEDs). The advancement of hole transport materials (HTMs) for the realization of high-performance blue QLEDs has demonstrated considerable challenges, primarily attributed to their intrinsic low hole mobility and mismatched energy levels. Herein, two vinyl-based cross-linkable HTMs, 4,4′-bis(3-vinyl-9H-carbazol-9-yl)-1,1′biphenyl (CBP-V) and 2,8-bis(3-vinyl-9H-carbazol-9-yl)dibenzo[b,d]thiophene (KSP-V), are designed and synthesized. Compared with CBP-V, KSP-V possesses a relatively low cross-linking temperature of 190 °C with a nearly 100% solvent resistance. Moreover, KSP-V exhibits exceptional hole transport properties, with a notable 4.2-fold enhancement in hole mobility. By substituting thiophene groups for biphenyl groups, the highest occupied molecular orbital level of KSP is reduced to −5.92 eV. When applying KSP to solution-processed blue QLEDs [Commission Internationale de l'Eclairage coordinates of (0.15, 0.03)], the devices exhibit excellent properties. Particularly, the maximum luminance of 27 036 cd m−2 and external quantum efficiency of 15.69%. Our work provides important guidance for the rational design of cross-linkable HTMs for solution-processed blue QLEDs.