Strain-promoted double-click cross-linking enables robust charge transport networks for high-performance quantum dot light-emitting diodes

Abstract

Cross-linked charge transport layers are critical for achieving solvent-robust, solution-processed quantum dot light-emitting diodes (QLEDs). However, existing cross-linking strategies rely on harsh thermal or photochemical conditions that introduce residual catalysts, trap states, and structural defects, ultimately limiting device efficiency and operational stability. Here, a strain-promoted double-click (SPDC) cross-linking strategy is developed to construct robust hole transport layers (HTLs) for high-performance QLEDs under mild conditions. Using dibenzo[a,e]cyclooctadiyne (DIBOD) as a catalyst-free cross-linker and an azide-functionalized polymer, poly(9,9-dioctylfluorene-co-4-(6-azidohexyl)-N,N-diphenylaniline) (TFB-N-3), an optimized cross-linked HTL containing 7 wt% DIBOD (TFB-N-3-7) is achieved, exhibiting complete solvent resistance while simultaneously enhancing molecular ordering and reducing energetic disorder. These improvements suppress interfacial charge transfer and trap formation, leading to improved charge balance in the device. As a result, green QLEDs based on TFB-N-3-7 deliver a maximum external quantum efficiency of 28.34% and a current efficiency of 115.16 cd A(-1), among the highest reported for cross-linked HTL-based devices. In addition, the devices show substantially improved stability, with estimated half-lifetimes of approximate to 4800 h at 1000 cd m(-2) and approximate to 297,500 h at 100 cd m(-2). This work demonstrates SPDC cross-linking as an effective molecular engineering strategy for simultaneously achieving efficient charge transport, high efficiency, and long-term operational stability in QLEDs.