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

TL;DR

This study investigates how different dielectric environments affect trion and exciton emissions in single-walled carbon nanotube networks, revealing that charge trapping properties influence emission characteristics more than dielectric polarizability.

Contribution

It demonstrates that dielectric charge trapping, rather than polarizability, governs trion and exciton emission variations in doped SWCNT networks, challenging previous assumptions.

Findings

Charge trapping reduces exciton quenching and causes emission blue-shift.

Trion to exciton emission ratio is not a reliable doping metric.

Dielectric properties influence emission through charge localization, not polarizability.

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 polymer-sorted (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.