Deuterated Molecular Vibration Locking in Self‐Assembled Monolayers Enables Positive Aging‐Free SnO 2 ‐Based QLEDs With Over 30% External Quantum Efficiency

ABSTRACT The development of efficient and stable hole injection layers (HILs) remains a critical challenge for high‐performance quantum‐dot light‐emitting diodes (QLEDs), as the conventional PEDOT:PSS suffers from inherent acidity and hygroscopicity. Herein, we demonstrate a novel strategy of molecular vibration engineering by employing deuterated self‐assembled monolayers (SAMs) as an efficient alternative. The designed deuterated molecular backbone (Ph‐4PACzd10), featuring extended conjugated structures, not only delivers an enhanced molecular dipole moment to significantly deepen the work function of ITO, but also effectively suppresses high‐frequency C─H stretching vibrations through isotopic substitution, which promotes highly ordered molecular packing and superior film morphology, thereby minimizing interfacial energetic disorder and non‐radiative recombination losses. As a result, SnO 2 ‐based QLEDs utilizing Ph‐4PACzd10 achieve a record‐breaking external quantum efficiency (EQE) of 30.87%, markedly surpassing that of the conventional PEDOT:PSS‐based device (24.03%). Furthermore, the hydrophobic nature of the deuterated SAMs endows the devices with exceptional shelf and operational stability. Notably, the QLED device demonstrated excellent efficiency roll‐off characteristics, maintaining an EQE exceeding 20% at an ultra‐high luminance of 250 000 cd m −2 , with no positive aging effect observed. This work illustrates that isotopic engineering of molecular vibrations provides a compelling pathway to tailor interfacial energetics and advance the design principles for next‐generation QLEDs.