Suppression of Excimer Formation via Conjugation‐Driven Interactions in Crosslinked Hole Transport Layer for Efficient Blue Quantum Dot Light‐Emitting Diodes

Abstract

Abstract Blue quantum dot light‐emitting diodes (QLEDs), underperforming relative to red and green counterparts, shoulder the critical responsibility for full‐color displays. Crosslinked 9,9′‐([1,1′‐biphenyl]‐4,4′‐diyl)bis(3‐ethenyl‐9H‐carbazole) (CBP‐V), owning a deep HOMO level (∼−5.9 eV), is a promising hole transport layer (HTL) candidate for blue QLEDs. However, π–π interactions and molecular rotatability in CBP‐V promote parallel stacking and electron cloud overlap. This gives rise to excimer formation, which exacerbates the energy‐level disorder in crosslinked CBP‐V and thus degrades its hole mobility. Herein, 2,6‐bis(3‐(9H‐carbazol‐9‐yl)phenyl)pyridine (26DCzPPy) and 4,4′,4″‐tris(carbazol‐9‐yl)‐triphenylamine (TCTA), featuring analogous phenylcarbazole structural fragments, are incorporated into CBP‐V to suppress excimer formation via a conjugate‐interaction‐driven strategy. The asymmetric configuration of 26DCzPPy and the branched architecture of TCTA enable modulation of molecular stacking behavior and suppress parallel stacking of CBP‐V during the crosslinking process. This realizes spatial segregation of CBP‐V and thus eliminates the prerequisite for excimer formation. Resultantly, suppression of excimer allows HTL to achieve a tenfold enhancement of hole mobility from 5.37 × 10 −4 to 5.97 × 10 −3  cm 2 ·V −1 ·s −1 . Target QLEDs gain prominent enhancements in external quantum efficiencies for deep‐blue emission (456 nm) from 11.48% to 22.92% and pure‐blue emission (470 nm) from 13.39% to 24.12%, with maximum brightness values of 29735 and 91268 cd m −2 .