Transparent film heaters using multi-walled carbon nanotube sheets

• Heating performance of the MWCNT sheet was investigated and characterized.
• The thermal characteristics of the MWCNT sheet were highly depended on thickness of the sheets.
• Temperature dependence of the MWCNT sheets was examined; although MWCNT has metal property, semiconductive temperature behavior was observed in the MWCNT sheet.

This paper presents carbon nanotubes (CNTs) used as transparent heaters, which offer great advantages in miniaturization, high efficiency, low power consumption, and rapid response. Previously proposed transparent single-walled carbon nanotube (SWCNT) based heaters used to replace indium tin oxide (ITO) heaters were fabricated either by dielectrophoresis or the piece-wise alignment of read-out electronics around randomly dispersed CNTs. These methods require steps for purification, separation, and dispersion in a liquid or polymer in order to improve their electrical and optical properties. We studied a transparent film used for heating, fabricated by employing a multi-walled carbon nanotube (MWCNT) sheet. The sheet was made from a super-aligned MWCNT forest; the heater was fabricated by direct coating onto a glass substrate. The characteristics of the MWCNT sheet, i.e. a high transmittance of ∼90% and a sheet resistance of ∼756 Ω/sq, are comparable to previously reported SWCNT-based transparent films. These properties are directly applicable to applications such as window tinting and defrosters in production vehicles.