Multinary Cu-In-Zn-S-based Quantum-Dot Electroluminescence and Implications on Device Designs

Currently, the performance of quantum-dot light-emitting diodes (QLEDs) based on environmental-friendly CuInZnS quantum dots (QDs) still lags far behind that of Cd-QDs-based devices. Here it is demonstrated that the unique trap-related recombination in CuInZnS QDs is mainly responsible for the low device efficiency. The luminous efficiency of CuInZnS-based QLEDs is rather sensitive to the temperature and hole-transporting layers (HTLs) due to the susceptible thermal-related trappingdetrapping processes of holes in radiative Cu-related traps. The holes in Cu-related traps can be quenched by escaping to the valence band of the QDs or/and transferring to the adjacent HTLs. An HTL with low highest occupied molecular orbitals is desired to enhance the hole injection and hinder the aforementioned hole transfer. As a result, a high device efficiency of 6.0 cd A-1 is achieved at room temperature, which is attributed to suppressed HTL-induced emission quenching and efficient valence-band-dominated hole injection from HTL to the QDs. The device efficiency is further increased to 13.2 cd A-1 at 150K by suppressing thermal-induced quenching. The electroluminescence mechanism of CuInZnS quantum dots (QDs) is demonstrated to be trap-related recombination. Hole transporting layers (HTL) with low highest occupied molecular orbital energy levels can suppress the hole transfer from QDs to the HTL. Consequently, quantum-dot light-emitting diodes with 2,2 '-bis(4-(carbazol-9-yl)phenyl)biphenyl as the HTL exhibit a higher efficiency of 6.0 cd A-1 due to efficient hole injection and limited back transfer of holes.image