Optical Modeling of Black Silicon for Solar Cells Using Effective Index Techniques

• Published in: IEEE journal of photovoltaics 2017-11, Vol.7 (6), p.1556-1562
• Main Authors: Rahman, Tasmiat, Boden, Stuart A.
• Format: Article
• Language: English
• Subjects: Accuracy; Black Si; effective medium; Finite difference method; Finite difference methods; Finite difference time domain method; finite-difference time domain (FDTD); Mathematical models; Multiscale analysis; nanoscale; Nanoscale devices; Numerical methods; optics; Photovoltaic cells; Ray tracing; ray-tracing (RT); Silicon; Solar cells; Texturing; Time domain analysis; transfer matrix method (TMM)
• ISSN: 2156-3381; 2156-3403
• DOI: 10.1109/JPHOTOV.2017.2748900

Texturing the surface with both micro and nano scale features to form black silicon is a promising approach in improving solar cell efficiency. In optical modeling of such a surface, it is difficult to balance the accuracy and computational resource. In this work, we develop on a semianalytical model, effective index technique (EIT), which utilizes a finite-difference time domain (FDTD) method to represent the nanoscale texturing as an effective medium, and then apply this to microscale structures, which can then be modeled using the transfer matrix method and ray-tracing. We fabricate and model both periodic and random nanoscale textures, and analyze the accuracy of several effective index models against measured reflectivity. The limitations in the model are identified and coherency of the films is studied. The semianalytical method is shown to perform better than the other effective medium approaches for modeling black silicon and is applicable to modeling multiscale textures, whereas full numerical methods such as FDTD are not. However, although the EIT approach predicts the trends in antireflective performance of a texture, it remains inaccurate when compared with the experiment. Also, as with all effective medium approaches, the EIT does not account for light trapping through scattering.