Multiple exciton generation in chiral carbon nanotubes: Density functional theory based computation.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Chemistry

Background:

• Understanding photo-excited states in nanomaterials is crucial for optoelectronic applications.
• Multiple exciton generation (MEG) offers a pathway to overcome the Shockley-Queisser limit in solar energy conversion.
• Phonon-mediated relaxation and exciton dynamics play significant roles in the efficiency of nanomaterials.

Purpose of the Study:

• To investigate the time evolution of photo-excited states in nanoparticles, including phonon-mediated exciton relaxation and MEG processes.
• To compute the internal quantum efficiency (QE) of exciton generation from absorbed photons.
• To apply a theoretical framework to chiral single-wall carbon nanotubes (SWCNTs).

Main Methods:

• Utilized a Boltzmann transport equation (BE) to model the time evolution of photo-excited states.
• Employed Kadanoff-Baym-Keldysh many-body perturbation theory for computing BE collision integrals.
• Integrated density functional theory (DFT) simulations with exciton effects.

Main Results:

• Predicted efficient MEG in (6,2) and (6,5) SWCNTs within the solar spectrum.
• Identified MEG processes including exciton-to-biexciton multiplication and biexciton-to-exciton recombination.
• Achieved a quantum efficiency (QE) of approximately 1.6 at 3E_g, starting from the 2E_g energy threshold.

Conclusions:

• The developed theoretical approach accurately models exciton dynamics and MEG in SWCNTs.
• Chiral SWCNTs exhibit efficient MEG, making them promising candidates for advanced solar energy applications.
• The study provides a quantitative prediction of QE, guiding future experimental efforts.