Enhanced multiple exciton generation in amorphous silicon nanowires and films

ABSTRACT

Multiple exciton generation (MEG) in nanometer-sized hydrogen-passivated silicon nanowires (NWs), and quasi two-dimensional nanofilms depends strongly on the degree of the core structural disorder as shown by the perturbative many-body quantum mechanics calculations based on the density functional theory 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 Si₂₉H₃₆ 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 ranging from 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 ≃ 1. MEG in the amorphous nanoparticles is enhanced by the electron localisation 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.

KEYWORDS:

• Multiple exciton generation
• density functional theory
• silicon nanowire
• amorphous silicon nanoparticle
• silicon quantum dot

Acknowledgements

Andrei Kryjevski acknowledges use of computational resources of the Center for Computationally Assisted Science and Technology (CCAST) at North Dakota State University. Authors are grateful to Kirill Velizhanin for a fruitful discussions. Dmitri Kilin acknowledges the South Dakota Governor's Office of Economic Development and NSF award EPS-0903804 for financial support, and DOE, BES-Chemical Sciences and NERSC No. DE-AC02-05CH11231, allocation Award 88777 ‘Computational Modeling of Photo-catalysis and Photo-induced Charge Transfer Dynamics on Surfaces’ 86185 for providing computational resources. Resources of high-performance computing systems at the University of South Dakota, operated by the Research Computing Manager, Doug Jennewein are gratefully acknowledged. The authors acknowledge financial support for method development from the NSF grant CHE-1413614.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Andrei Kryjevski acknowledges financial support from the US Department of Energy [grant number DE-FG52-08NA28921]; ND EPSCOR NSF Fund [EPS-0814442]. Dmitri Kilin acknowledges the South Dakota Governor's Office of Economic Development; NSF award [EPS-0903804] for financial support. The authors acknowledge financial support for method development from the NSF [grant number CHE-1413614].