A First-Principles Investigation of the Optical Properties of Two-dimensional Si Thin Films
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.
Jingsong Huang, Oak Ridge National Laboratory
Primary Advisor's Department
Chemical and Materials Engineering
Stander Symposium, School of Engineering
Institutional Learning Goals
"A First-Principles Investigation of the Optical Properties of Two-dimensional Si Thin Films" (2023). Stander Symposium Projects. 2909.
Presentation: 1:15-2:30 p.m., Kennedy Union Ballroom