Nonblinking Quantum-Dot-Based Blue Light-Emitting Diodes with High Efficiency and a Balanced Charge-Injection Process

Blue nonblinking (> 98% on time) ZnCdSe/ZnS//ZnS quantum dots (QDs) with absolute fluorescence quantum yield (QY) of 92% (lambda(peak) = 472 nm) were synthesized via a low temperature nucleation and high temperature shell growth method. Such bright nonblinking ZnCdSe/ZnS//ZnS core/shell QDs exhibit not only good emission tunability in the blue-cyan range with corresponding wavelength from 450 to 495 nm but also high absolute photoluminescence (PL) QY and superior chemical and photochemical stability. Highly efficient blue quantum dot-based light-emitting diodes (QLEDs) have been demonstrated by using nonblinking ZnCdSe/ZnS//ZnS QDs as emissive layer, and the charge-injection balance within the QD active layer was improved by introducing a nonconductive layer of poly(methyl methacrylate) (PMMA) between the electron transport layer (ETL) and the QD layer, where the PMMA layer takes the role of coordinator to impede excessive electron flux. The best device exhibits outstanding features such as maximum luminance of 14,100 cd/m(2), current efficiency of 11.8 cd/A, and external quantum efficiency (EQE) of 16.2%. Importantly, the peak efficiency of the QLEDs with PMMA is achieved at similar to 1,000 cd/m(2) and high EQE > 12% can be sustained in the range of 100 to 3,000 cd/m(2).