Charge Balance in Red QLEDs for High Efficiency and Stability via Ionic Liquid Doping

Abstract Colloidal quantum dot light‐emitting diodes (QLEDs) simultaneously exhibiting high external quantum efficiency (EQE) and operation stability are achieved via a simple solution processing. A silver bis(trifluoromethane‐sulfonyl)imide treatment that is used to chemically dope the poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) hole injection layer (HIL) is proposed. The ionic liquid salt acts as an effective p ‐dopant for high charge concentrations; and it raises the work functions and surface potentials of the PEDOT:PSS HIL for an interface energy band alignment. Benefiting from a raised hole mobility and a better charge mobility balance, the processing‐simple colloidal red QLEDs yielded the highest EQE of up to 17.4%. In particular, a very broad plateau of EQE values over 16.5% in the brightness of 400–10 000 cd m −2 is obtained. Moreover, the packaged QLEDs exhibit an excellent operation stability in ambient air. The T 95 (time for the device brightness to decrease to 95% of its initial brightness) at an initial brightness of 1000 cd m −2 is 4160 h. The work highlights a promising ionic liquid strategy to guide the development of high‐performance and cost‐effective QLEDs.