New photonic material for self-aligning solar cells


Scientists from Tufts University have developed light-tracking solar cells based on a novel photonic crystal film.

The demonstrator devices feature a technology that the researchers refer to as “photonic sunflower.” The tech purportedly maintains a constant angle between the cell and the light source, which maximizes its efficiency as the light moves.

“Such wireless, light-responsive, heliotropic (sun-following) systems could potentially enhance light-to-energy conversion efficiency for the solar power industry,” the researchers said.

The photonic crystals in the cell feature an opal-like film made of silk fibroin, doped with gold nanoparticles (AuNPs) and an underlying substrate of polydimethylsiloxane (PDMS), which is a silicon-based polymer. The crystals were combined with an elastomeric composite that can be manipulated to respond to illumination. Elastomeric materials are able to regain their original shape when a load is removed from the material itself.

“In addition to remarkable flexibility, durability, and optical properties, silk fibroin is unusual in having a negative coefficient of thermal expansion (CTE), meaning that it contracts when heated and expands when cooled,” the academics said. “PDMS, in contrast, has a high CTE and expands rapidly when heated.”

They claimed that this combination makes one layer heat up faster than the other, so the material bends as one side expands.

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“With our approach, we can pattern these opal-like films at multiple scales to design the way they absorb and reflect light,” said researcher Fiorenzo Omenetto. “When the light moves and the quantity of energy that’s absorbed changes, the material folds and moves differently as a function of its relative position to that light.”

They used a water vapor treatment to design various film patterns and positioned stencils of various sizes on the surface of the films from the silicon monoxide (SIO) side.

“Then, the masked bilayer films were placed above a heated water surface (about 40 C) to directly expose the SIO surface to water vapor for a set of different durations,” the scientists said.

The solar cells have a three-junction tandem structure, an active area of 650 × 650 square micrometers, and are based on indium gallium phosphide (InGaP), gallium arsenide (GaAs), and indium gallium arsenide antimony nitride (InGaAsNSb). The scientists described the cells in “Light-activated shape morphing and light-tracking materials using biopolymer-based programmable photonic nanostructures,” which was recently published in Nature Communications.

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