Electropolymerized Poly(3,4-ethylenedioxythiophene) Films as Hole-injection Layers for Organic Light-emitting Diodes

Electrodeposited organic light-emitting diode (OLED) technology requires a spin-coating-free hole-injection layer that simultaneously provides smooth surface morphology, stable energy levels, and compatibility with high-resolution pixel architectures. In this study, electropolymerization of 3,4-ethylenedioxythiophene (EDOT) in poly(styrene sulfonate) (PSS − ) surfactant-solubilized colloidal media is shown to afford poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films with robust surface uniformity and stable energy levels suitable for application as hole-injection layers in OLEDs. Systematic investigation reveals that the hole-injection properties of these films are governed primarily by the colloidal chemistry of EDOT/PSS − surfactant-solubilized systems, rather than by conventional electrochemical parameters. This colloidal regulation modulates the film work function over a practically useful range. Incorporation of optimized films into OLEDs leads to enhanced hole injection and improved device performance, with external quantum efficiency increasing from 2.2% to 7.4% and minimal roll-off. Overall, this work demonstrates a feasible example of realizing spin-coating-free hole-injection layers, offering a potential direction for the development of electrodeposited injection layers for OLEDs.