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Abstract

Their high ambipolar charge carrier mobilities and narrowband emission in the near-infrared make semiconducting single-walled carbon nanotubes (SWCNTs) a promising material for optoelectronic devices. The controlled low-level decoration of SWCNTs with covalently bound sp3 defects gives rise to red-shifted luminescence and single-photon emission, thus strongly expanding their application potential. While the spectroscopic properties of sp3-functionalized SWCNT dispersions under optical excitation are already well-understood, little research efforts have been directed at the impact of luminescent defects on charge transport as well as defect population and emission in thin films and under electrical excitation. A fundamental understanding of these aspects is a prerequisite for the realization of light-emitting devices based on functionalized SWCNTs.

This thesis demonstrates high ambipolar charge carrier mobilities and red-shifted defect-state electroluminescence in light-emitting field-effect transistors with randomly oriented networks of functionalized SWCNTs as active layers. The results imply that luminescent defects act as shallow trapping potentials for charge carriers that still allow for fast detrapping at room temperature, thus explaining the moderate decrease in network mobilities upon functionalization. Time-resolved terahertz spectroscopy corroborates the impact of these defects on the intrinsic nanotube conductivity and provides further evidence that charge transport in semiconducting SWCNT networks, as opposed to the widespread belief, is not solely determined by the inter-nanotube junctions.

To achieve better control over the spectroscopic properties of SWCNT thin films deposited on surfaces, substrate passivation with a cross-linked polymer is demonstrated to reduce peak broadening and suppress sideband emission that is assigned to the uncontrolled formation of lattice defects through nanotube–substrate interactions. The realization of pristine and sp3-functionalized SWCNT network transistors with near-intrinsic electroluminescence on passivated substrates showcases the compatibility of the developed method with standard semiconductor processing steps and device fabrication. Moreover, the selective introduction of luminescent defects with a larger spectral red-shift pushes the electroluminescence from SWCNT networks further towards telecommunication wavelengths and highlights their potential for optoelectronic applications such as electrically-pumped single-photon sources.