Danish researchers develop color-tunable BIPV foil

Danish researchers have developed color-tunable foil technology made in a roll-to-roll process for building integrated PV (BIPV) modules.

In two recent papers the researchers detailed an optimization algorithm and process to structure the surface of a polymer foil, dubbed Colorfoil, which inserted between the encapsulation layer and crystalline silicon (c-Si) solar cells in PV panels enables color-matching panels with low iridescence.

“Colorfoil was born to develop structural colored interlayers with low iridescence that can be deposited by roll-to-roll magnetron sputtering on top of a flexible polymer foil, and that can be easily incorporated in the PV laminate, in front of the photovoltaic cell, to tune its coloration with minimal efficiency loss, regardless of the size or geometry,” corresponding author of the research, Catarina G. Ferreira, told pv magazine, pointing out several unique aspects of research.

“On the one hand, the concept of Colorfoil is itself innovative, as the currently existing solutions in the color BIPV market either rely on absorptive pigments, which strongly affects the PV efficiency, or apply structural colored layers directly on the glass superstrate, severely limiting the flexibility and adaptability to different PV module sizes,” said Ferreira.

“On the other hand, there is novelty in the combination of nanoimprinting lithography and magnetron sputtering, both carried out in roll-to-roll (R2R) manufacturing lines, to fabricate large-volume of colored foils with low iridescence, which has had limited research so far,” she said.

The researchers noted that distributed Bragg reflectors (DBRs) were considered due to a “simple periodic design and color tunability spanning a broad gamut of hues,” but DBRs were limited in producing certain colors and it was not possible to customize color hues on demand.

“By modelling and optimizing the optical response of a periodic multilayer systems, we demonstrate that we can not only match almost any target color contained in the sRGB color space but, more importantly and innovatively, we can do so while minimizing iridescence significantly. Finally, we have a close match between modelling and the experimental results using full scale R2R manufacturing tools,” said Ferreira.

Indeed, the researchers demonstrated red-colored silicon PV mini-modules that mimic the color of clay rooftiles characteristic of Danish architecture with a low efficiency loss of “approximately 18%” and “remarkable color matching.”

“In fact, such clay red mini-modules were able to maintain more than 80% of the PV performance compared to an equivalent bare c-Si PV mini-module, without any coloring interlayer element, of the same area and with the same bill of materials,” said the researchers.

The work is detailed in “Colored Planar Multilayers with Minimal Angular Color Dependence for Building Integrated Photovoltaics,” published in Nano Energy.

In a complementary study, Structural Colored Planar Multilayers with Minimal Angular Color Dependence for Building Integrated Photovoltaics, published in Solar RRL, an alternative methodology for low iridescence optimization was detailed.

An alternative “optimization-based inverse design methodology” was used to identify “simple planar multilayer configurations with a relatively low number of layers and capable of reflecting selected target colors with minimal angular variation.”  The team assessed it as not increasing design complexity with potential for use in large-scale manufacturing of PV modules.

The research was led by University of Southern Denmark with researchers from Technical University of Denmark and Stensborg A/S participating.

Looking ahead, the researchers aim to investigate large-scale implementation and the application of the optical optimization methodology to find the ideal trade-off between color matching and efficiency. “A third and very significant topic is to demonstrate the durability of the foil within the laminate to ensure long-last colored PV modules, enabling aesthetically pleasing energy producing facades,” said Ferreira.

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