Changhee Lee, Hyo‐Bin Kim, Ryungyu Lee, Yunjae Shin, Tae‐Hyeon Kim, Joon Song, Hojin Lee
ABSTRACT In solution‐processed organic light‐emitting diodes (OLEDs), carrier injection imbalance and interfacial quenching persist as major hurdles, primarily due to the hole‐dominated transport in polymer‐based emitters. Here, we introduce a simple but highly effective post‐fabrication strategy for enhancing charge balance and device performance by chemically modifying ZnO nanoparticles (ZnO‐NPs) through acetone immersion. This treatment selectively passivates oxygen vacancy–related trap states at the ZnO NPs surface, resulting in improved electron injection and restored hole‐blocking behavior, without disrupting the device structure or layer interfaces. Comprehensive analyses, including X‐ray photoelectron spectroscopy (XPS), photoluminescence (PL), and transient electroluminescence (EL) measurements, confirm the defect passivation mechanism and its impact on charge injection dynamics. Acetone‐treated OLEDs exhibit reduced turn‐on voltage, significantly higher luminance (exceeding 44 000 cd/m 2 ), and enhanced efficiency across all RGB subpixels, while maintaining spectral purity. Furthermore, this method enables scalable fabrication of ultra‐high‐resolution RGB pixel arrays on a large scale without requiring additional functional layers.