  Transparent and conductive films (TCFs) are of great technological
importance. The high transmittance, electrical conductivity and mechanical
strength make single-walled carbon nanotubes (SWCNTs) a good candidate for
their raw material. Despite the ballistic transport in individual SWCNTs,
however, the electrical conductivity of their networks is limited by low
efficiency of charge tunneling between the tube elements. Here, we demonstrate
that the nanotube network sheet resistance at high optical transmittance is
decreased by more than 50% when fabricated on graphene and thus provides a
comparable improvement as widely adopted gold chloride ($\mathrm{AuCl_3}$)
doping. However, while Raman spectroscopy reveals substantial changes in
spectral features of doped nanotubes, no similar effect is observed in presence
of graphene. Instead, temperature dependent transport measurements indicate
that graphene substrate reduces the tunneling barrier heights while its
parallel conductivity contribution is almost negligible. Finally, we show that
combining the graphene substrate and $\mathrm{AuCl_3}$ doping, the SWCNT thin
films can exhibit sheet resistance as low as 36 $\Omega$/sq. at 90%
transmittance.
