Solvent treatment induced interface dipole and defect passivation for efficient and bright red quantum dot light-emitting diodes

Abstract Quantum dot light-emitting diodes (QLEDs) have been widely recognized as one of the potential candidates for next-generation displays. In QLEDs, unbalanced carrier distribution (lacking holes) is an essential factor limiting device efficiency. Herein, we propose the solvent treatment of hole transporting layer (HTL) and quantum dot (QD) emission layer (EML) to enhance hole injection from HTL and reduce the defects in QD EML. Scanning Kelvin probe microscopy measurements reveal that the surface potential of HTL is lowered by solvent treatment with dimethyl formamide (DMF), which is due to the formation of an interface dipole layer between QD EML and HTL, and thus the hole injection barrier from HTL to QD EML is reduced. Furthermore, steady and transient photoluminescence (PL) measurements reveal that the DMF treated QD film, in comparison with the standard QD film, exhibits higher PL intensity and reduced non-radiative recombination induced by the defects. These improvements result in a 25% boost in the current efficiency of the QLEDs with DMF treated QD EML as compared to the QLED with unmodified EML, leading to a high current efficiency of 14.81 cd/A and a maximum brightness of 113 373 cd/m2. Furthermore, the solvent treatment enables the QLEDs possessing sub-bandgap turn-on voltage, which is 1.8 V (the optical bandgap of 2.1 eV) for the QLEDs with DMF treated QD EML.