Kai Zang's (PhD '17) paper published in Nature Communications describes how nanotextured silicon can absorb more photons, furthering the effectiveness of solar cells. This research also resulted in a second discovery – improving the collision-avoidance technology in vehicles.
Professor Jim Harris said he always thought Zang's texturing technique was a good way to improve solar cells. "But the huge ramp up in autonomous vehicles and LIDAR suddenly made this 100 times more important," he says.
The researchers figured out how to create a very thin layer of silicon that could absorb as many photons as a much thicker layer of the costly material. Specifically, rather than laying the silicon flat, they nanotextured the surface of the silicon in a way that created more opportunities for light particles to be absorbed. Their technique increased photon absorption rates for the nanotextured solar cells compared to traditional thin silicon cells, making more cost-effective use of the material.
After the researchers shared these efficiency figures, engineers working on autonomous vehicles began asking whether this texturing technique could help them get more accurate results from a collision-avoidance technology called LIDAR, which is conceptually like sonar except that it uses light rather than sound waves to detect objects in the car's travel path.
In their Nature Communications paper, the team reports that their textured silicon can capture as many as three to six times more of the returning photons than today's LIDAR receivers. They believe this will enable self-driving car engineers to design high-performance, next-generation LIDAR systems that would continuously send out a single laser pulse in all directions. The reflected photons would be captured by an array of textured silicon detectors, creating moment-to-moment maps of pedestrian-filled city crosswalks.
Harris said the texturing technology could also help to solve two other LIDAR snags unique to self-driving cars – potential distortions caused by heat and the machine equivalent of peripheral vision. The Harris Group research website.
Excerpted from "A new way to improve solar cells can also benefit self-driving cars," Stanford Engineering, October 2, 2017.