Efficient multi-shell CuInS2/ZnS/ZnS quantum-dots based light-emitting diodes: Time-controlled synthesis of quantum-dots and carrier balance effects of PEI

CuInS2-based quantum-dots (QDs) have been highlighted as promising photoelectric materials for their low toxicity and color adjustable emissions as well as stability. Here, multi-shell CuInS2/ZnS/ZnS QDs with high PLQY of 76% were synthesized by employing a high temperature and long-time growth strategy while highly bright and efficient quantum-dot-light-emitting diodes (QLEDs) were fabricated by using these multi-shell QDs as an emission layer and polyethylenimine (PEI) as an insulating layer, respectively. By introducing PEI between the QDs and ZnO EML layers of the QLEDs, the balance of the carriers within the QDs layer injected from HTL and ETL was greatly improved. As a result, comparing to the QLEDs without PEI, the greatly improved efficiency (1.9 times as high as that of the QLEDs without PEI) has been achieved in the optimized QLEDs with PEI. These QLEDs exhibits an outstanding performance with the maximum EQE of 1.56% and the maximum brightness of 5825 cd/m(2).