Dynamics of Charge Transfer and Multiple Exciton Generation in the Doped Silicon Quantum Dot-Carbon Nanotube System: Density Functional Theory-Based Computation.

We use the Boltzmann transport equation (BE) to study time evolution of a photoexcited state, including phonon-mediated exciton relaxation, multiple exciton generation (MEG), and energy-transfer processes. BE collision integrals are derived using Kadanoff-Baym-Keldysh many-body perturbation theory (MBPT) based on density functional theory (DFT) simulations, including exciton effects. We apply the method to a nanostructured p- n junction composed of a 1 nm hydrogen-terminated Si quantum dot (QD) doped with two phosphorus atoms (SiPH) adjacent to the (6, 2) single-wall carbon nanotube (CNT) with two chlorine atoms per two unit cells adsorbed to the surface.

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

We use a 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 based on density functional theory 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.

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 calculations based on the density functional theory simulations. We calculate SF exciton-to-biexciton decay rates R and biexciton-to-exciton rates R in the (6,2), (6,5), (10,5) SWCNTs, and in the (6,2) SWCNT functionalized with Cl atoms.

Photoinduced Single- and Multiple-Electron Dynamics Processes Enhanced by Quantum Confinement in Lead Halide Perovskite Quantum Dots.

Methylammonium lead iodide perovskite (MAPbI) is a promising material for photovoltaic devices. A modification of MAPbI into confined nanostructures is expected to further increase efficiency of solar energy conversion. Photoexcited dynamic processes in a MAPbI quantum dot (QD) have been modeled by many-body perturbation theory and nonadiabatic dynamics.

Abrupt Size Partitioning of Multimodal Photoluminescence Relaxation in Monodisperse Silicon Nanocrystals.

Intrinsic constraints on efficient photoluminescence (PL) from smaller alkene-capped silicon nanocrystals (SiNCs) put limits on potential applications, but the root cause of such effects remains elusive. Here, plasma-synthesized colloidal SiNCs separated into monodisperse fractions reveal an abrupt size-dependent partitioning of multilevel PL relaxation, which we study as a function of temperature. Guided by theory and simulation, we explore the potential role of resonant phonon interactions with "minigaps" that emerge in the electronic density of states (DOS) under strong quantum confinement.

Theoretical predictions on efficiency of bi-exciton formation and dissociation in chiral carbon nanotubes.

Efficient multiple exciton generation (MEG) in chiral single-wall carbon nanotubes (SWCNTs) is present within the solar spectrum range as shown by the many-body perturbation theory calculations combined with the density functional theory simulations. To describe the impact ionization process, we calculate exciton-to-biexciton decay rates R and biexciton-to-exciton rates R in the (6,2) and (10,5) SWCNTs. Within the solar energy range, we predict R ∼ 10 s, while biexciton-to-exciton recombination is weak with R/R ≤ 10.