Spectroscopic Signatures of Doping in Thin Films of Semiconducting Single-Walled Carbon Nanotubes

Semiconducting single-walled carbon nanotubes (SWCNTs) have unique optical, electronic, and mechanical properties that enable a wide range of applications. Changing and controlling the charge carrier density in thin films of SWCNTs by chemical, electrochemical, or electrostatic doping lies at the heart of many (opto-)electronic devices, such as thermoelectric generators, electrochromic cells, or field-effect transistors. The accumulation of charge carriers (holes or electrons) also affects the optical properties of nanotubes, especially their visible to far-infrared absorption, near-infrared fluorescence and electroluminescence as well as their Raman modes. The related spectral changes give insights into the interaction of charge carriers with SWCNTs on a fundamental level but also enable quantification and spatial resolution of carrier densities in operating devices. Here we review the current understanding of various spectroscopic signatures of doping in thin films of semiconducting SWCNTs, how they can be used to explore carrier concentration-dependent properties, and how they are applied in optoelectronic devices.