arXiv subjects

Deyan Mihaylov

Publications and source records attributed to Deyan Mihaylov.

3 recordsLinked to original sources

arXiv2020

Biexciton State Energies from Many-Body Perturbation Theory Based on Density Functional Theory Simulation

We develop a method for computing self-energy of a biexciton state in a semiconductor nanostructure using many-body perturbation theory (MBPT) based on the density functional theory (DFT) simulation. We compute energies of low-energy biexciton states composed of singlet excitons in the chiral single-wall carbon nanotubes (SWCNT), such as (6,2), (6,5) and (10,5). In all cases we find a small decrease in the biexciton gap: -0.045 $eV$ in (6,2), which is 4.59\% of the non-interacting biexciton gap; -0.041 $eV$ in (6,5), which is 4.47\% of the non-interacting gap and -0.036 $eV$ in (10,5), which is 4.31\%.

cond-mat.mes-hall↗

arXiv2017

Multiple Exciton Generation in Chiral Carbon Nanotubes: Density Functional Theory Based Computation

We use Boltzmann transport equation (BE) to study time evolution of a photo-excited state in a nanoparticle including phonon-mediated exciton relaxation and the multiple exciton generation (MEG) processes, such as exciton-to-biexciton multiplication and biexciton-to-exciton recombination. BE collision integrals are computed using Kadanoff-Baym-Keldysh many-body perturbation theory (MBPT) based on density functional theory (DFT) simulations, including exciton effects. We compute internal quantum efficiency (QE), which is the number of excitons generated from an absorbed photon in the course of the relaxation. We apply this approach to chiral single-wall carbon nanotubes (SWCNTs), such as (6,2), and (6,5). We predict efficient MEG in the (6,2) and (6,5) SWCNTs within the solar spectrum range starting at the $2 E_g$ energy threshold and with QE reaching $\sim 1.6$ at about $3 E_g,$ where $E_g$ is the electronic gap.

cond-mat.mes-hall↗

arXiv2017

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

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.

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