Improved performance of all-solution-processed quantum dot light-emitting diodes with TFB/PVK double-hole transport layers using 1,2-dichloroethane

High-performance quantum dot light-emitting diodes (QD-LEDs) require balanced electron and hole injection into the QD emissive layer-an especially difficult task when using all-solution processes. One effective strategy for achieving this balance is to create a stepwise hole injection pathway <i>via</i> double-hole transport layers (D-HTLs). Poly(9-vinylcarbazole) (PVK) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-<i>co</i>-(4,4'-(<i>N</i>-(4-<i>sec</i>-butylphenyl)diphenylamine))] (TFB) are commonly employed in D-HTLs because of their favorable energy level alignment and suitable hole mobilities. However, constructing TFB/PVK D-HTLs demands careful attention to solvent orthogonality, as both polymers often dissolve in the same solvent. Thus, identifying a solvent system that enables the formation of TFB/PVK D-HTLs without damaging the TFB layer is crucial. In this study, we systematically investigate the solvent orthogonality of TFB/PVK and demonstrate high-performance QD-LEDs fabricated entirely by solution processes. We examine various PVK solvents-evaluating their polarity, solubility, and potential to damage the TFB layer-and identify 1,2-dichloroethane (1,2-DCE) as optimal for forming TFB/PVK D-HTLs with minimal damage. The resulting all-solution-processed QD-LEDs exhibit a 1.5-fold increase in external quantum efficiency compared to devices employing a single HTL. Furthermore, 1,2-DCE also proves effective in inverted QD-LED architectures, protecting the QD emissive layer during PVK deposition and demonstrating its versatility across multiple device architectures.