Investigating Work Function Tunable Hole-Injection/Transport Layers of Electrodeposited Polycarbazole Network Thin Films

Abstract

Electrochemical doping properties and morphology changes of electropolymerized poly(N-vinylcarbazole) (PVK) thin films were investigated toward improved hole-injection/transport properties in polymer light emitting diode (PLED) devices. The conjugated network polycarbazole thin films (resulting from a poly(N-carbazole) (PCz) network) were prepared by electrodeposition of PVK and/or N-vinylcarbazole comonomer via precursor route and were investigated in situ by electrochemical-surface plasmon resonance spectroscopy (EC-SPS). Distinct doping-dedoping properties and morphology transitions were observed with different compositions of PVK and Cz. By electrochemical doping of the cross-linked conjugated polycarbazole units, the electrochemical equilibrium potential (Eeq), which correlates to Fermi level (Ef) or the work function (φw) of the film, was adjusted in the vicinity of the anode electrode. The conjugated network PCz films were then used as a hole-injection/transport layer in a two layer device. Remarkable enhancement of PLED properties was observed when optimal electrochemical doping was done with the films. Important insight was gained on charge transport phenomena between polymer materials and conducting oxide substrates.