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

Abstract 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 π─π 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 (V turn‐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).