High-efficiency light-emitting devices based on quantum dots with tailored nanostructures

We report a full series of blue, green and red quantum-dot-based light-emitting devices (QD-LEDs), all with high external quantum efficiencies over 10%. We show that the fine nanostructure of quantum dots-especially the composition of the graded intermediate shell and the thickness of the outer shell-plays a very important role in determining QD-LED device performance due to its effects on charge injection, transport and recombination. These simple devices have maximum current and external quantum efficiencies of 63 cd A(-1) and 14.5% for green QD-LEDs, 15 cd A(-1) and 12.0% for red devices, and 4.4 cd A(-1) and 10.7% for blue devices, all of which are well maintained over a wide range of luminances from 102 to 104 cd m(-2). All the QD-LEDs are solution-processed for ease of mass production, and have low turn-on voltages and saturated pure colours. The green and red devices exhibit lifetimes of more than 90,000 and 300,000 h, respectively.