Light Out-Coupling for High-Performance Quantum Dot Light-Emitting Diodes by π-π Oriented PEDOT: PSS

Breaking the theoretical limits of external quantum efficiency (EQE) and obtaining quantum dot light-emitting diodes (QLEDs) with high brightness, high efficiency, and low operating voltage is the basis of commercial applications in display and illumination. Devices with an EQE of over 20% can be realized by carrier equilibrium injection and light out-coupling enhancement. However, it is difficult to synergistically enhance the performance of QLEDs by combining the light out-coupling and the hole enhancement injection. In this paper, the injection enhancement of holes and the light out-coupling are realized simultaneously only by nano-imprint lithography (NIL). The pi & horbar;pi bonds of the PEDOT: PSS film treated by NIL demonstrate a molecular orientation perpendicular to the substrate, which improves the injection of the hole. The PEDOT: PSS patterned by NIL further presents improved light out-coupling. Consequently, the EQE of red-QLED is 30.42% with a synergistic enhancement factor of 61%, accompanying the maximum brightness increased by 8% to 125 200 cd m(-2) at 4.6 V (Vturn-on, 1.74 V). The EQE and brightness of green-QLED increased by 38.9% and 34.3% to 24.16% and 279 700 cd m(-2), respectively. Therefore, NIL will provide new insights into synergistically enhancing light out-coupling and internal quantum efficiency to break through the performance of electroluminescence (EL).