Colored PV modules based on Interference Filters

Abstract

Building Integrated Photovoltaics (BIPV) has the potential to play a major role in the ongoing transition towards nearly zero energy buildings. However, the BIPV market is still a niche market, representing only 1% of the global PV share. One of the main barriers that hinder the deployment of BIPV is the lack of aesthetic flexibility. Architects and designers are often reluctant to embed PV systems in buildings due to their unsuitable color.
In this thesis, the use of interference filters (IFs) as color coating solution for PV modules is proposed. IFs are optical devices designed to selectively reflect a narrow portion of the visible solar spectrum while transmitting the remaining part. The structural coloration provided by the filter is highly dependent on the angle of incidence of the light. This angular dependence could be an issue for BIPV applications, since color homogeneity is often an important requirement. The objective of this work is to model, fabricate and assess the opto-electrical performance of colored crystalline silicon (c-Si) PV modules based on interference filters, with the final goal of increasing the aesthetics of this technology.
First, the angular resilience challenge is addressed. Simulation results show that texturing the glass surface significantly improves the color stability, thanks to diffuse reflection of light. Very high angular resilience up to 80º can be achieved with a double-side texture profile made of hemispherical grooves. Secondly, five interference filters deposited on different glass substrates are used to fabricate 10 x 10 cm² c-Si colored mini-modules. The optical characterization of the demonstrators
allows to partially validate the optical model and confirm the good angular resilience of the textured surfaces. Finally, the electrical performance of the mini-modules is evaluated. I-V measurements show that IFs only affect the short-circuit current of the mini-modules due to optical losses. Depending on the color and the topology of the surface, absolute efficiency losses range from 0,95% to 4,6%.