n-Type Transparent Conducting Films of Small Molecule and Polymer Amine Doped Single-Walled Carbon Nanotubes

In this report, we investigate the electrical and optical properties of thin conducting films of SWNTs after treatment with small molecule and polymeric amines. Among those tested, we find hydrazine to be the most effective n-type dopant. We use absorbance, Raman, X-ray photoelectron, and nuclear magnetic resonance spectroscopies on thin conducting films and opaque buckypapers treated with hydrazine to study fundamental properties and spectroscopic signatures of n-type SWNTs and compare them to SWNTs treated with nitric acid, a well-characterized p-type dopant. We find that hydrazine physisorbs to the surface of semiconducting and metallic SWNTs and injects large electron concentrations, raising the Fermi level as much as 0.7 eV above that of intrinsic SWNTs. Hydrazine-treated transparent SWNT films display sheet resistances nearly as low as p-type nitric-acid-treated films at similar optical transmittances, demonstrating their potential for use in photovoltaic devices as low work function transparent electron-collecting electrodes.