Enhanced Optical Property with Tunable Band Gap of Cross‐linked PEDOT Copolymers via Oxidative Chemical Vapor Deposition

Abstract

Highoptical transmittance conjugated‐polymers with electrical conductivity are garnering much attention for the applications in organic optoelectronic devices including organic field‐effect‐transistors and solar cells. Polymers based on PEDOT are particularly promising candidates with high conductivity, uniform surface planarity and excellent ductility. In this work, homopolymer PEDOT deposited using oxidative chemical‐vapor‐deposition(oCVD) show the maximum conductivity of ≈3500 S/cm. However, their utility is limited due to the relatively low transmittance and abrupt decrease near the red edge in the visible regime. Here, the significantly improved optical properties achieved via tuning the bandgap of cross‐linked PEDOT copolymers using oCVD, offering a single‐step process for the synthesis and deposition of copolymer films, is reported. The cross‐linking monomers of biphenyl or anthracene are simultaneously evaporated with EDOT monomer and an oxidant(FeCl3) during the deposition. Poly(anthracene‐co‐EDOT)[p(ANTH‐co‐EDOT)] shows the superior transmittance (≈93%) to homopolymer PEDOT (≈80%) and poly(biphenyl‐co‐EDOT)[p(BPH‐co‐EDOT)] (≈88%). Additionally, copolymers show no transmission decay in the red edge regime unlike homopolymer PEDOT that presents an abrupt transmission falloff. An improvement in optical transmittance is in agreement with an increase in bandgap of materials (p(ANTH‐co‐EDOT), ≈2.3eV vs PEDOT, ≈1.8 eV). oCVD‐processed bandgap‐tunable PEDOT copolymers with enhanced transmittance may, therefore, have applications in organic optoelectronic devices that require high optical transparency.