Residual Tetramethylammonium Hydroxide Limits ZnO Nanoparticle‐Based Quantum Dot Light‐Emitting Diode Performance

ABSTRACT Quantum dot light‐emitting diodes (QLEDs) are promising next‐generation display devices, with zinc oxide nanoparticle (ZnO NP) electron transport layers playing a central role in charge injection and device efficiency. However, factors beyond the intrinsic properties of ZnO NPs and the ZnO NP/quantum dot (QD) interface can also limit device performance. Here, precursor‐derived residual tetramethylammonium hydroxide (TMAH) was identified as a previously overlooked impurity source that induces emission quenching in ZnO NP‐based QLEDs. Fourier transform infrared spectroscopy and time‐of‐flight secondary ion mass spectrometry reveal that TMAH‐derived residues remain in purified ZnO NP films and diffuse into the adjacent QD emissive layer during thermal annealing. The diffused residues promote exciton quenching in the QD layer, as confirmed by steady‐state photoluminescence, time‐resolved photoluminescence, and time‐resolved electroluminescence analyses, reducing luminance and external quantum efficiency despite enhanced electron transport through the ZnO NP layer at elevated annealing temperatures. This TMAH‐induced degradation can be effectively suppressed by pre‐removing residual TMAH through thermal annealing above its decomposition temperature or by using TMAH‐free ZnO NPs synthesized with potassium hydroxide. These findings reveal that precursor‐derived impurities can substantially affect QLED operation depending on fabrication conditions and establish impurity management as an important strategy for improving QLED performance.