Fig. 1: Sub-band gap operation of quantum dot light-emitting diodes with energy band discontinuity.
From: Surface state-induced barrierless carrier injection in quantum dot electroluminescent devices
a Energy level diagram for materials used in this study without taking the interface modification into consideration. The equation estimates the current threshold (VJ) of QLEDs under the assumption that series resistance is negligible. b Current density (J)–voltage (V) (open symbols) and c luminance (L)–voltage (closed symbols) characteristics of QLEDs employing 2TNATA (red circle), NPB (green triangle), and TCTA (blue square) HTLs. Grey shaded region indicates V > Eg /e (=1.97 V), where Eg is a bandgap of QDs. Inset shows a photographic image of 2TNATA-based QLEDs taken at an applied bias of 1.6 V. The pixel size of devices is 1.4 × 3.0 mm2. d VJ and luminance thresholds (VL) plotted to ECBM, ZnO − EHOMO, HTL, where ECBM, ZnO is the CBM of ZnO and EHOMO, HTL is a HOMO level of HTL. Dashed line indicates V = (ECBM, ZnO − EHOMO, HTL)/e for eye guidance. e EL spectra of QLEDs with different HTLs acquired at near VL.
