Photo-Crosslinking Hole Transport Layer for Solution Processed Quantum Dot Light-Emitting Diodes

Quantum dots (QDs) have recently attracted many researchers' interest as promising materials for lighting. Despite much progress in QD light-emitting diodes (QD-LEDs), the performance of environmental-friendly QD-LEDs still lags behind that of heavy metal-based devices. In addition, since QD-LEDs are multilayer devices, an effective method of minimizing the underlying layer erosion by subsequent solution process is required for solution-processed QD-LEDs, which is significant for the cost-effective manufacture of large-area QD displays. Here, we demonstrate high-performance solution-processed Indium phosphide (InP) QD-LEDs via photo-crosslinking of the hole transport layer (HTL) with an efficient photo-crosslinker. Photo-crosslinking of hole transport materials (TFB and PVK) using an azide-based crosslinker allows a robust HTL minimizing the damage that may occur when the QD emissive layer is deposited onto the HTL in the solution process. The solvent resistance of photo-crosslinked HTL enables fabricating high-performance green InP QD-LED through the solution process. Optimizing the photo-crosslinked TFB layer, the maximum current efficiency of crosslinked TFB-based QD-LEDs is improved by about five times compared to pristine TFB-based ones. Also to investigate the effect of photo-crosslinking on the electrical properties of HTL, we analyze pristine and crosslinked TFB based hole-only devices by using an orthogonal solvent. Furthermore, double HTLs in the conventional QD-LEDs are implemented through photo-crosslinking to reduce the hole injection barrier, resulting in efficient hole injection.