Systematic Control of the Electrical Conductivity of Poly(3,4-ethylenedioxythiophene) via Oxidative Chemical Vapor Deposition

Systematic variation in the electrical conductivity of poly(3,4-ethylenedioxythiophene) (PEDOT) was achieved by oxidative chemical vapor deposition (oCVD). For oCVD, both the oxidant, Fe(III)Cl3, and 3,4-ethylenedioxythiophene (EDOT) monomer are introduced in the vapor phase. A heated crucible allows for sublimation of the oxidant directly into the reactor chamber operating at 150 mTorr. Spontaneous reaction of the oxidant with the monomer introduced though a feedback-controlled mass flow system results in the rapid (>200 nm thick film in 30 min) formation of π-conjugated PEDOT thin films directly onto a temperature-controlled substrate. As the substrate temperature is increased from 15 to 110 °C, increasing conjugation length, doping level, and electrical conductivity of the PEDOT chains are observed by UV−vis absorption spectroscopy (UV−vis), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. Concomitantly, the measured electrical conductivity of the PEDOT films increases systematically with an apparent activation energy of 28.2 ± 1.1 kcal/mol.