Impact of Dielectric Environment on Trion Emission from Single-Walled Carbon Nanotube Networks

Abstract

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymersorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.

Photo-Activated, Solid-State Introduction of Luminescent Oxygen Defects into Semiconducting Single-Walled Carbon Nanotubes

“…Before illumination, all as-deposited SWCNT networks (see Figure a) exhibited PL spectra with characteristically narrow excitonic E 11 emission at 1.232 eV and weak, red-shifted sideband features as commonly observed in networks of (6,5) SWCNTs. The sideband contributions to the PL signal increased from nonpolar BCB to polar substrates and from nonreactive to reactive oxide surfaces, as expected. , These sidebands have been assigned to momentum-forbidden dark excitons coupling to phonons and to shallow extrinsic defects of the (6,5) SWCNT lattice due to interaction with reactive groups on mostly polar surfaces. − The additional feature observed at 1.051 eV for the TiO x sample most likely corresponds to SWCNT trion (charged exciton) emission due to slight p-doping by the oxide . The relatively strong sideband for (6,5) SWCNTs even on BCB-passivated samples probably results from the low network density.…”

“…An 850 nm long-pass filter in front of the spectrometer entrance slit blocked scattered excitation laser light (640 nm, continuous-wave laser diode; OBIS, Coherent). All spectra were averaged over an area of 800 μm 2 through expansion of the laser beam using a plano-convex lens (focal length f = 125 mm) in front of the near-infrared-optimized 20× Olympus objective and vertical binning to remove spot-to-spot variations, as reported elsewhere . Temperature-dependent PL measurements were carried out in a closed-cycle liquid helium-cooled cryostat (Montana Cryostation s50) at high vacuum (<10 –5 mbar) using a long-working distance, NIR-optimized 50× objective (N.A.…”

Near‐Intrinsic Photo‐ and Electroluminescence from Single‐Walled Carbon Nanotube Thin Films on BCB‐Passivated Surfaces

“…Hence, this approach enables an unambiguous and detailed analysis of the trion peak, which was previously complicated by E11 sidebands. [64] For gate voltage-dependent PL spectra in hole and electron accumulation regimes for samples without and with BCB, see the Supporting Information, Figure S19 and S20.…”

Multimodular Wide-Band Capturing Nanohybrids: Role of Carbon Nanotubes in Slowing Charge Recombination in Supramolecular C60-BisstyrylBODIPY-(Zinc Porphyrin)2 Donor–Acceptor Molecular Cleft

“…The former electron transfer route would yield P • + -SWCNT • – , while the latter route would yield P • – -SWCNT • + radical ion pairs . Direct excitation of SWCNT is known to produce excitons and, in some instance, trions. − , Due to relatively high binding energy and short lifetime, the exciton/trion dissociation to promote electron transfer to the LUMO level of P is rarely observed . Often, the produced radical ion pairs in “simple” P-SWCNT have been short-lived due to the proximity of donor–acceptor entities and the involvement of excitonic peaks, making the spectral interpretation tedious.…”