Positive Aging‐Free SnO ₂ ‐Based Quantum Dot Light‐Emitting Diodes With Average External Quantum Efficiency Exceeding 24%

Abstract SnO ₂ nanoparticles (NPs) have emerged as a promising electron transport material (ETL) for high‐performance and stable quantum dot light‐emitting diodes (QLEDs). However, their inherently high electron mobility and conductivity create a charge transport imbalance in QLEDs, ultimately limiting device performance. To address this challenge, a novel p‐type doping strategy is proposed to continuously decrease the electron mobility and conductivity of SnO ₂ NPs. As a result, the electron mobility and conductivity of Zn‐doped SnO ₂ NPs can be adjusted in a wide range owing to the substitution of Zn ²⁺ ions for Sn ⁴⁺ ions as the electron acceptors. The charge transportation balance in QLEDs can be realized by suppressing the electron transportation ability of Zn‐doped SnO ₂ nanocrystals and inserting a wide‐band‐gap CaMoO ₄ interface layer. Finally, QLED devices achieve an average external quantum efficiency (EQE) of 24.4% and a highest EQE of 27.1%, which are comparable to the state‐of‐the‐art ZnO‐based QLEDs. More importantly, the positive aging effect can be eliminated by using Zn‐doped SnO ₂ NPs as ETL, which provides a promising ETL material for the fabrication of high‐efficiency and stable QLEDs without positive aging effect.