Modeling of thin-film interference filters on structured substrates: microfacet-based BSDF versus ray tracing

Area of Science:

• Optics
• Materials Science
• Photovoltaics

Background:

• Photovoltaic (PV) modules can be colored using interference layers on cover glass.
• Understanding light scattering is crucial for predicting the optical appearance of these modules.
• Existing models need evaluation for accuracy and efficiency in describing complex optical phenomena.

Purpose of the Study:

• To compare two distinct ray optical modeling approaches for colored PV modules.
• To assess the suitability of a microfacet-based bidirectional scattering distribution function (BSDF) model versus ray tracing.
• To investigate the impact of structural parameters on color appearance and angle dependency.

Main Methods:

• Ray optical modeling was employed to simulate light interaction with PV module surfaces.
• A microfacet-based bidirectional scattering distribution function (BSDF) model was utilized to describe light scattering.
• Ray tracing was used as a comparative modeling technique.
• Structure inversion analysis was performed to identify critical geometric parameters.

Main Results:

• The microfacet-based BSDF model proved largely sufficient for the MorphoColor application structures.
• Significant deviations were observed only for extreme angles and very steep structures with correlated heights and surface normals.
• A structured layer system demonstrated a clear advantage over planar interference layers for angle-independent color appearance.

Conclusions:

• The microfacet-based BSDF model is a viable and efficient tool for simulating colored PV modules.
• Structured interference layers offer superior angle-independent color compared to planar layers combined with front-side scattering.
• Optimized layer design is key to achieving desired aesthetic and optical performance in PV modules.