Synergistic Interfacial Engineering With Self‐Assembled Molecules in PEDOT:PSS Composites for High‐Performance Deep‐Blue QLEDs

Insufficient hole injection remains a critical bottleneck hindering the commercialization of blue quantum dot light‐emitting diodes (QLEDs), making the optimization of hole transport behavior highly significant. Herein, (2‐(9 H ‐carbazol‐9‐yl)ethyl)phosphonic acid (2PACz) is incorporated into poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) to construct a composite hole injection layer (HIL). Within this composite layer, a portion of 2PACz anchors onto the ITO surface, while a portion engages in π – π interactions with hole transport layer (HTL) poly(9‐vinylcarbazole), giving rise to a synergistic dual‐interface modification effect that substantially enhances interfacial hole injection and transport. The overall hole mobility of the HIL/HTL stack increases markedly from 2.15 × 10 −7 to 7.84 × 10 −6 cm 2 V −1 s −1 . Meanwhile, the introduction of 2PACz raises the electrical conductivity of the HIL from 2.51 × 10 −4 to 5.35 × 10 −4 mS cm −1 and deepens its HOMO level from −5.15 to −5.48 eV, thereby further facilitating hole injection into the HTL. Consequently, deep‐blue QLEDs employing this composite HIL achieve a remarkable maximum luminance of 11,185.50 cd m −2 , a high external quantum efficiency of 22.61% with a CIE y coordinate of 0.0305, and an extended lifetime of 793.19 h ( T 50 @100 cd m −2 ), representing a significant improvement in optoelectronic performance.