Enhanced Multiple Exciton Generation in Amorphous Silicon Nanoparticles

TL;DR

This study uses many-body perturbation theory to show that amorphous silicon nanoparticles exhibit enhanced multiple exciton generation compared to crystalline structures, promising improved solar energy conversion.

Contribution

It provides a detailed theoretical analysis of MEG in amorphous silicon nanostructures, highlighting the role of structural disorder in enhancing quantum efficiency.

Findings

Amorphous silicon nanoparticles show QE of 1.3 to 1.8 at 3E_g.

Crystalline nanostructures have QE around 1.

Amorphous structures exhibit electron localization that boosts MEG.

Abstract

Multiple exciton generation (MEG) in nanometer-sized hydrogen-passivated silicon nanowires (NWs), and quasi two-dimensional nanofilms strongly depends on the degree of the core structural disorder as shown by the many-body perturbation theory (MBPT) calculations based on the density functional theory (DFT) simulations. Working to the second order in the electron-photon coupling and in the screened Coulomb interaction we calculate quantum efficiency (QE), the average number of excitons created by a single absorbed photon, in the ${\rm Si}_{29}{\rm H}_{36}$ quantum dots (QDs) with crystalline and amorphous core structures, simple cubic three-dimensional arrays constructed from these QDs, crystalline and amorphous NWs, and quasi two-dimensional silicon nanofilms, also both crystalline and amorphous. Efficient MEG with QE of 1.3 up to 1.8 at the photon energy of about $3E_g$, where $E_g$ is the electronic gap, is predicted in these nanoparticles except for the crystalline NW and crystalline film where $QE\simeq 1.$ MEG in the amorphous nanoparticles is enhanced by the electron localization due to structural disorder. Combined with the lower gaps, the nanometer-sized amorphous silicon NWs and films are predicted to have effective carrier multiplication within the solar spectrum range.