Conductive behavior of cross-linked electropolymeric films formed by ‘star-shaped’ multifunctional precursors

Abstract

Electropolymeric films must simultaneously achieve high planarity and high conductivity to fully realize the advantages of their superior processing techniques for a wide range of semiconductor applications. In the promising electrodeposition organic light-emitting diode (OLED) technology, the primary hole transport layer, 4,4′,4′′-tri(N-carbazolyl)triphenylamine (TCTA) electropolymeric films, exhibits high planarity but hole mobility of 0.38 × 10⁻⁷  cm²  V⁻¹ s⁻¹, which constrains device brightness and efficiency. Investigations into the electrochemical, spectroelectrochemical, and electrical properties reveal that TCTA electropolymeric film consists of a crosslinked network formed by twisted, non-conjugated linkages between conjugated oligomer segments, rather than a long-range conjugated conductive polymer. TCTA represents a class of “star-shaped” multifunctional electropolymeric precursors, with the electropolymeric groups serving as the primary charge-transporting units. The twisted configurations of these electro-crosslinked polymers significantly impede carrier transport, despite the films' high planarity. However, these structures confer substantial electrochemical activity. For example, TCTA electropolymerized films exhibit a high specific capacitance of 349.8 F cm⁻³@15.2 A cm⁻³ and a high specific capacity of 19.4 mA h cm⁻³@15.2 A cm⁻³. Accordingly, such materials are not well-suited for use as functional layers in electrodeposited organic semiconductors, but may offer promise for applications in electrochemically active systems.