Abstract
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.
Highlights
O PTICAL enhancement is a key factor in achieving efficient performance in solar cells, in particular for materials that suffer from high reflectivity such as silicon (Si)
It should be clarified that whilst light trapping via scattering of incoming light by textured features is an important aspect of solar cell performance, none of the effective medium approaches takes this into account, and this work is limited to antireflection properties only
We present the use of an effective index technique (EIT) model which uses a cut-back approach with the finite-difference time domain (FDTD) method to calculate the refractive index of a semi-infinite NW array
Summary
O PTICAL enhancement is a key factor in achieving efficient performance in solar cells, in particular for materials that suffer from high reflectivity such as silicon (Si). RT can accurately model microscale features but is not valid for nanoscale features with dimensions below the ray optic limit In this work, this problem is studied by treating the nanoscale surface as a single film using various effective medium techniques and applying this to the microscale pyramidal surfaces. This problem is studied by treating the nanoscale surface as a single film using various effective medium techniques and applying this to the microscale pyramidal surfaces This multiscale hybrid structure can be modeled using a combination of RT and TMM with tools such as Sentaurus TCAD [13]. It should be clarified that whilst light trapping via scattering of incoming light by textured features is an important aspect of solar cell performance, none of the effective medium approaches (even EIT) takes this into account, and this work is limited to antireflection properties only
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