A First-Principles Investigation of the Optical Properties of Two-dimensional Si Thin Films

A First-Principles Investigation of the Optical Properties of Two-dimensional Si Thin Films

Presenter(s)

Nicholas Saunders

Comments

Presentation: 1:15-2:30 p.m., Kennedy Union Ballroom

Description

Recent experimental studies suggest that thin-film crystalline silicon is viable as a high-efficiency material for energy conversion in solar cells. A theoretical study on the optical properties of two-dimensional (2D) silicon thin films is needed to gain insights into the structure-property correlation of this material. In our project, we made Density Functional Theory calculations of multiple 2D silicon thin films of different structures. We first constructed their model structures from bulk silicon by cutting it along the (100), (110), and (111) low-Miller-index faces, varying the number of silicon atomic layers from two to eight layers, and exposing the bare surfaces or terminating them with hydrogen atoms. We then relaxed the atomic coordinates and in-plane lattice vectors of the 2D films. Next, we calculated the surface energies for the thin films with bare surfaces and modelled the octahedral crystal habit of silicon. From electronic structure calculations, we found that the 2D films with bare surfaces possess metallic in-gap states near the Fermi level, whereas hydrogen termination on the surfaces can render semiconducting thin films suitable for optical applications. Finally, we calculated the optical properties of the semiconducting thin films from the complex dielectric function at different levels of approximation, giving frequency-, face-index-, and thickness-dependent absorption coefficients. We found that the absorption coefficients increase with increasing thicknesses, asymptotically approaching that of the bulk structure. Among the three face indices studied, the (111) films have the lowest surface energy and achieve the highest absorption coefficients, making (111) the most favorable face index for thin-film silicon solar cell applications.

Publication Date

4-19-2023

Project Designation

Independent Research

Primary Advisor

Jingsong Huang, Oak Ridge National Laboratory

Primary Advisor's Department

Chemical and Materials Engineering

Keywords

Stander Symposium, School of Engineering

Institutional Learning Goals

Scholarship

A First-Principles Investigation of the Optical Properties of Two-dimensional Si Thin Films

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