Performance Enhancement of Polymer Light-Emitting Diodes by Using Ultrathin Fluorinated Polyimide Modifying the Surface of Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate)

Abstract

Herein, an insulating fluorinated polyimide (F−PI) is utilized as an ultrathin buffer layer of poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in polymer light-emitting diodes to enhance the device performance. The selective solubility of F−PI in common solvents avoids typical intermixing interfacial problems during the sequential multilayer spin-coating process. Compared to the control device, the F−PI modification causes the luminous and power efficiencies of the devices to be increased by a factor of 1.1 and 4.7, respectively, along with almost 3-fold device lifetime enhancement. Photovoltaic measurement, single-hole devices, and X-ray photoelectron spectroscopy are utilized to investigate the underlying mechanisms, and it is found that the hole injection barrier is lowered owing to the interactions between the PEDOT:PSS and F−PI. The F−PI modified PEDOT:PSS layer demonstrates step-up ionization potential profiles from the intrinsic bulk PEDOT:PSS side toward the F−PI-modified PEDOT:PSS surface, which facilitate the hole injection. Moreover, the insulating F−PI layer at the PEDOT:PSS surface is also favorable for the hole injection by blocking the electrons and strengthening the local electric field at the interface.