Video: Sunflowers inspire light-tracking solar material

Many plants can orient themselves toward a light source to maximize the energy they absorb. Young sunflowers, for example, tilt their heads to follow the sun throughout the day, a result of their stems growing asymmetrically. Now, researchers at the University of California, Los Angeles, and Arizona State University have designed a material to mimic that behavior (Nat. Nanotechnol. 2019, DOI: 10.1038/s41565-019-0562-3). The researchers made small cylinders from a combination of light-absorbing nanoparticles and a thermoresponsive polymer that contracts when heated. They call the cylinders SunBOTs. When light shines on the SunBOT from an angle, the side facing the light source absorbs light, heats up, and contracts, bending the cylinder toward the light beam. The researchers tested an array of the cylinders in a device that collects sunlight to generate steam, and they estimate that SunBOT-based systems could harvest up to twice as much energy as flat sunlight-absorbing surfaces.

Music:“Autumn” by Kevin Graham.

The following is a transcript of this video:

Kerri Jansen: Have you ever noticed how young sunflowers can tilt their heads to follow the sun? Their stems grow asymmetrically to help them absorb the maximum amount of light. Now, researchers at the University of California, Los Angeles, and Arizona State University have designed a material that replicates sunflowers’ ability to bend toward a light source. These small cylinders contain two components: a light-absorbing nanomaterial and a heat-responsive polymer that shrinks when it’s heated. The researchers call them SunBOTs.

When light hits a SunBOT on an angle, the cylinder heats up along one side and shrinks asymmetrically, bending toward the light beam. It holds the position until the light changes. A SunBOT can follow a beam of light through a wide range of angles. The researchers hope the material can improve the efficiency of devices that harvest solar energy to produce electricity or vaporize water. They made an array of SunBOTs to test in a light-harvesting device. The researchers estimate that at certain latitudes on Earth, SunBOT-based systems could harvest up to twice as much energy as flat energy-harvesting materials because they can automatically adapt to variations in the sun’s angle.

C&EN will be tracking this team's progress as it works to prove its new technology.