# Singlet Fission in Chiral Carbon Nanotubes: Density Functional Theory Based Computation

## TL;DR

This study uses density functional theory and many-body perturbation theory to analyze singlet fission in chiral carbon nanotubes, revealing how surface functionalization can enhance multiple exciton generation efficiency within the solar spectrum.

## Contribution

It provides the first detailed computational analysis of singlet fission rates in specific chiral SWCNTs and shows how surface functionalization can improve MEG performance.

## Key findings

- Singlet fission rates in SWCNTs are around 10^{14}-10^{15} s^{-1} within the solar spectrum.
- Biexciton-to-exciton recombination is significantly weaker than fission rates.
- Surface functionalization with Cl atoms can enhance MEG by modifying low-energy electronic states.

## Abstract

Singlet fission (SF) process, where a singlet exciton decays into a pair of spin one exciton states which are in the total spin singlet state, is one of the possible channels for multiple exciton generation (MEG). In chiral single-wall carbon nanotubes (SWCNTs) efficient SF is present within the solar spectrum energy range which is shown by the many-body perturbation theory (MBPT) calculations based on the density functional theory (DFT) simulations. We calculate SF exciton-to-biexction decay rates ${\rm R}_{1\to 2}$ and biexciton-to-exction rates ${\rm R}_{2\to1}$ in the (6,2), (6,5), (10,5) SWCNTs, and in (6,2) SWCNT functionalized with Cl atoms. Within the solar energy range, we predict ${\rm R}_{1\to2}\sim 10^{14}-10^{15}~s^{-1}$, while biexciton-to-exction recombination is weak with ${\rm R}_{2\to 1}/{\rm R}_{1\to 2}\leq 10^{-2}.$ SF MEG strength in pristine SWCNTs varies strongly with the excitation energy, which is due to highly non-uniform density of states at low energy. However, our results for (6,2) SWCNT with chlorine atoms adsorbed to the surface suggest that MEG in the chiral SWCNTs can be enhanced by altering the low-energy electronic states via surface functionalization.