Solution‐Processed F4TCNQ‐Doped Polymeric Hole Injection Layers Enabling Highly Efficient and Stable Inverted Organic Light‐Emitting Diodes

ABSTRACT Molecular doping is an effective strategy for optimizing electroluminescent device performance. Herein, we developed a solution‐processable triarylamine–fluorene copolymer (YM3) as a high‐efficiency p‐dopable host for inverted organic light‐emitting diodes (i‐OLEDs). Blending YM3 with 5–10 wt.% F4TCNQ induces quantitative integer charge transfer, evidenced by complete bleaching of neutral F4TCNQ absorption, emergence of F4TCNQ − and polymer polaron bands in ultraviolet–visible–near infrared spectroscopy, CN‐stretch downshift ‌from Fourier transform infrared spectroscopy, strong polymer radical electron paramagnetic resonance signal, and results from UV photoelectron spectroscopy, X‐ray photoelectron spectroscopy, and liquid and solid‐state nuclear magnetic resonance characterizations. The doped YM3:F4TCNQ composite forms ultra‐smooth, homogeneous hole‐injection layers, elevating the electrode's effective work function to 4.83 eV and ensuring excellent solvent orthogonality with the underlying emissive layer. Fully solution‐processed blue i‐OLEDs with 20‐nm YM3:F4TCNQ hole‐injection layer exhibit low turn‐on voltage (∼3.00 V), deep‐blue emission (CIE: 0.14, 0.12), maximum external quantum efficiency of 5.72%, current efficiency of 6.30 cd A − 1 , reduced roll‐off, and improved operational stability. These results demonstrate that the YM3:F4TCNQ system, with superior solubility, suppressed dopant aggregation, and efficient work‐function tuning, provides an acid‐free, neutral, and industrially feasible hole‐injection solution for high‐performance fully solution‐processed printable i‐OLEDs.