Abstract
Because of its high conductivity and intrinsic stability, poly(3,4-ethylenedioxythiophene (PEDOT) has gained great attention both in academic research and industry over the years. In this study, we used the oxidative molecular layer deposition (oMLD) technique to deposit PEDOT from 3,4-ethylenedioxythiophene (EDOT) and a new inorganic oxidizing agent, rhenium pentachloride (ReCl5). We extensively characterized the properties of the films by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectroscopy (EDS), Raman, and conductivity measurements. The oMLD of polymers is based on the sequential adsorption of the monomer and its oxidation-induced polymerization. However, oMLD has been scarcely used because of the challenge of finding a suitable combination of volatile, reactive, and stable organic monomers applicable at high temperatures. ReCl5 showed promising properties in oMLD because it has high thermal stability and high oxidizing ability for EDOT. PEDOT films were deposited at temperatures of 125–200 °C. EDS and XPS measurements showed that the as-deposited films contained residues of rhenium and chlorine, which could be removed by rinsing the films with deionized water. The polymer films were transparent in the visible region and showed relatively high electrical conductivities within the 2–2000 S cm–1 range.
Highlights
Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the best-known conjugated conductive polymers that has been extensively studied for decades.[1]
Inspired by the MoCl5-based process, we explored oxidizers, which have been previously used for oxidation of thiophene monomer derivatives in chemical vapor deposition (CVD) such as Br2, SbCl5, and VOCl3.36,38,39 Rhenium pentachloride (ReCl5) was identified as another potential oxidizer based on its similar properties and structure to MoCl5
In the initial experiments besides ReCl5, bromine, antimony pentachloride, vanadium oxytrichloride, and ozone were used as oxidizers, but only ReCl5 led to PEDOT deposition
Summary
Poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the best-known conjugated conductive polymers that has been extensively studied for decades.[1]. Compared to the other conductive polymers, PEDOT has attracted lots of attention because of its high and stable electrical conductivity. Electrical conductivities up to 8797 S cm−1 and 7520 S cm−1 have been reported for single crystals[5] and thin films,[6] respectively. These conductivity values are just 1 order of magnitude lower than those of the most conductive metals such as silver and copper.[7] Conductive polymers are often highlighted for their mechanical, electrical, optoelectronic, thermoelectric, photovoltaic, and lighting properties both academically and industrially. The significant importance of PEDOT is acknowledged through the high number of applications in thermoelectricity, photovoltaics, lighting, sensing, technical coatings, transparent electrodes, bioelectronics, and so forth.[8−14]
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