Structural and thermoelectric properties of optically transparent thin films based on single-walled carbon nanotubes

Thin films have been produced via a spray method from commercially available single-walled carbon nanotubes (SWCNTs). A SWCNT film thickness has ranged from $\sim$10 to $\sim$80 nm. The SWCNT diameter has accepted values of 1.6–1.8 nm. The existence of SWCNTs longer than 10 $\mu$m is established. The optimal thickness of a SWCNT thin film is found to be $\sim$15 nm at which the transmittance exceeds 85%. The specific resistance of SWCNT thin films goes from $\sim$1.5 $\times$ 10$^{-3}$ to $\sim$3 $\times$ 10$^{-3}$ Ohm cm at room temperature. The pioneering study of the temperature dependences of the Seebeck coefficient and surface resistance is performed for this type of SWCNT. A surface resistance is found to increase with rising temperature. Furthermore, the Seebeck coefficient of SWCNT thin films weakly depends on temperature. Its value for all samples is evaluated to be $\sim$40 $\mu$V/K. According to the sign of the Seebeck coefficient, thin films exhibit hole-type conductivity. Moreover, the power factor of a 15-nm thin SWCNT-film decreases with a temperature increase to 140$^\circ$C from the value of approximately $\sim$120 to $\sim$60 $\mu$W m$^{-1}$ K$^{-2}$. A further rise in temperature has led to a gain in the power factor.