Highly efficient and bright red quantum dot light-emitting diodes with balanced charge injection

Improving hole injection to get better charge balance is a critical issue for achieving high performance quantum dot light-emitting diodes (QLEDs) because the hole injection is generally more difficult than the electron injection in QLEDs. In this work, we report an effort to develop a useful and easy processing bilayer hole injection layer (HIL) that consists of UV-ozone-treated graphene oxide (partially reduced graphene oxide, rGO) and PEDOT:PSS. We have successfully demonstrated that such a hybrid bilayer HIL possesses the advantages of high conductivity, staircase energy-level alignment, and high quality interface contact, which effectively promotes hole injection efficiency in the solution-processed QLEDs. Highly efficient and bright red solution-processed QLEDs have been realized based on the rGO/PEDOT:PSS bilayer stepwise HIL, exhibiting maximum brightness of 89157 cd m(-2), current efficiency of 25.0 cd A(-1) and power efficiency of 10.9 lm W-1, respectively. Importantly, both high external quantum efficiency (EQE) (>10%) and brightness (>30000 cd m(-2)) have been attained simultaneously; the peak EQE of the QLEDs reached 17.3% with a brightness of similar to 60108 cd m(-2), showing a great potential for high-power lighting applications.