Self-Assembled Carbazole-Phosphonate Hole-Injection Layer with a Dual-Modification Mechanism Enables High Efficient and Stable Blue Quantum-Dot Light-Emitting Diode

Abstract

As a widely used hole-injecting material in quantum-dot light-emitting diodes (QLEDs), poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) remains limited by its acidity and hygroscopicity, which cause ITO corrosion and degrade the long-term stability of the devices. Herein, a carbazole-phosphonic acid, [2-(9H-carbazol-9-yl)ethyl]phosphonic acid (2PACz), is introduced as a substitute for PEDOT:PSS. As a result, the blue CdSe/ZnSe/ZnS QLEDs achieve a maximum external quantum efficiency (EQE), current efficiency, and luminance of 16.58%, 11.15 cd·A^–1, and 31,764 cd·m^–2, respectively. Notably, the T₅₀ lifetime of the devices is extended from 55 h in PEDOT:PSS-based QLEDs to 148 h in 2PACz-based counterparts at a constant current density of 20 mA·cm^–2. In our analysis, this enhancement is attributed to the dual-modification mechanism of 2PACz. On one hand, interaction between ITO and 2PACz modifies the work function, improves the film surface roughness, and ultimately reduces the interfacial traps of ITO. On the other hand, interaction between 2PACz and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-s-butylphenyl)diphenylamine)] (TFB) facilitates hole injection by optimizing the transport pathway through the π–π stacking, which effectively balances charge recombination.