Colorful photovoltaics using thickness-modulated thin film optical filters

Abstract

Colorful photovoltaics have long been appealing to consumers for applications such as rooftop, building-integrated, and electric vehicle-integrated solar cells, among others. Achieving vibrant colors involves reflecting specific wavelengths of visible light. But energy capture in the visible range is crucial, as it often provides optimal external quantum efficiency. Therefore, it is essential to enhance the reflection of solar irradiance to achieve color while minimizing photocurrent loss. Researchers have explored various bottom-up approaches, such as modulating the thickness of single or dual-layer antireflective coatings (ARCs) or adding layers to existing standard ARCs. However, this often leads to broader reflection peaks and substantial photocurrent loss. While photonic crystal structures and metasurfaces show promise for color rendering, they require significant development before mass production. We explored various design strategies to develop two innovative methods for optical filter design that enhance both aesthetic appeal and photovoltaic efficiency while using fewer layers. Our first method employs a top-down strategy utilizing OptiLayer and MATLAB to design optical filters consisting of 2-6 layers. This approach results in narrower reflection peaks and achieves optimal colors (blue, green, red) while maintaining a photocurrent loss of only 5-10%, a notable improvement over previously proposed solutions. We investigated various combinations of materials to identify the optimal range of material pairs for this specific application. Our designs were validated through fabrication with three material pairs and two deposition techniques (CVD and PVD), and feedback from our experimental understanding was incorporated into our design method to make it robust.

Our second approach uses a custom MATLAB code to design an optimal filter based on selected layer numbers and materials, specified by the manufacturers. The thesis includes details on design methods, deposition and characterization techniques, comparisons of spectral responses, and images of the colors produced by the fabricated filters.