Positive Aging‐Free Quantum Dot Light‐Emitting Diodes Enabled by Single‐Source Chloride‐Doped ZnMgO Electron Transport Layers

), which mitigates oxygen vacancy (OV)-related defect signatures. Time-dependent X-ray photoelectron spectroscopy, single-carrier device measurements, and steady-state/time-resolved QD photoluminescence show that undoped ZnMgO undergoes gradual defect passivation during storage, whereas Cl-doped ZnMgO remains nearly time-invariant. As a result, devices with Cl-doped ZnMgO reach peak EQE at day 0 and maintain it during storage, while devices with undoped ZnMgO require several days to reach peak efficiency. In addition, as-fabricated QD-LEDs employing Cl-doped ZnMgO exhibit ≈1.8× higher peak EQE and ≈1.3× longer operational lifetime than undoped controls, with negligible positive aging signatures. This intrinsic ETL stabilization enables day-0 calibration, improves uniformity and yield, and removes the need for storage-driven conditioning-identifying single-source chloride doping as a practical route to robust ZnMgO ETLs for display applications.