Molecular engineering on hole injection self-assembled monolayers for superior RGB quantum dot light-emitting diodes

<p>Colloidal quantum dot light-emitting diodes (QLEDs) show strong performance dependence on efficient hole injection and balanced carrier injection. The widely used hole-injection layer (HIL) poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) suffers from inherent strong acidity, high cost and mismatched work function (WF) with transparent anodes in QLEDs. In this study, we propose herein molecular engineering on self-assembled monolayers (SAMs) as promising HILs to fabricate efficient red, green and blue QLEDs. Asymmetric conjugation extension and bromination on carbazole core strategically modulate the SAMs in dipole moment and interfacial modification of ITO’s WF. The 4-(10-bromo-7<i>H</i>-benzo[<i>c</i>]carbazol-7-yl)butyl)phosphonic acid (BCB-Br) constructs the optimal cascade energy level alignment for hole injection. SAMs based HILs with exceptional uniformity and conductivity afford significantly enhanced hole injection and reduced interfacial contact resistance in QLEDs. The BCB-Br HIL based red QLEDs contribute an impressive external quantum efficiency of 23.3% and a notably low turn-on voltage of 1.73 V. Moreover, the devices are endowed with commendable power efficiency of 47.0 lm/W and current efficiency of 30.4 cd/A, among the highest values across the critical QLEDs performance metrics in the literature. The university of SAMs as excellent HILs is further demonstrated by the superior electroluminescence (EL) performances in both green and blue QLEDs over PEDOT:PSS. These findings underscore the efficacy of molecular designed SAMs to boost the interface modification on transparent anodes, offering valuable insights for the development of new HILs for QLEDs.</p>