When people think of solar cells, they mostly imagine large panels placed in installations on hillsides or in fields. However, researchers have been building smaller and smaller solar cells to power individual devices, allowing for mobile, battery-free power from a renewable source of energy.
To this end, researchers at Binghamton University have created one of the smallest micro-scale solar cells packing the biggest energy punch for its size yet, with a micro-scale biological solar cell (micro-BSC) that generates a higher power density for longer than any existing cell of its kind.
The cell—a microfluidic lab-on-a-chip system that generates its own power is essential—can be used as power for stand-alone, independent, self-sustainable point-of-care diagnostic devices limited-resource and remote regions, said Seokheun Choi, an electrical and computer science assistant professor at Binghamton, who led the research.
“Miniaturized biological solar cells can be the most suitable power source for those lab-on-a-chip applications because the technique resembles the earth’s natural ecosystem--living organisms work in conjunction with non-living components of their environment to create a self-assembling and self-maintaining system,” he told Design News. “Micro-BSCs can continuously generate electricity from microbial photosynthetic and respiratory activities over day-night cycles, offering a clean and renewable power source with self-sustaining potential.”
So far, the promise of this type of technology hasn’t been realized for practical applications because of its relatively low power, Choi said. He along with PhD candidate Lin Liu were able to overcome this limitation by developing a high-performance, self-sustaining, long-life micro-BSC by using breakthroughs in device architectures and electrode materials, he said.
Researchers published a paper about their work in the journal Lab on a Chip.
Researchers at Binghamton University have created one of the smallest solar cells packing the biggest energy punch yet with the design of a micro-scale biological solar cell (micro-BSC) that generates a higher power density for longer than any existing cell of its kind. The microfluidic lab-on-a-chip system can be used as power for stand-alone, independent, self-sustainable point-of-care diagnostic devices limited-resource and remote regions, said Seokheun Choi, an electrical and computer science assistant professor at Binghamton who led the research. (Source: Binghamton University)
In it, the team describes how they created a 3D conductive polymer-coated anode and a gas-permeable configuration in a well-controlled, tightly enclosed micro-chamber.
“The 3D porous anode ensured a large surface area for the bacterial attachment and efficient mass transfer to and from the anode, increasing the power,” Choi explained. Meanwhile, the gas-permeable microfluidic system enabled sustaining electricity generation for a longer period, he said.
“Once the bacterial cells were injected into the microfluidic chamber, they penetrated through the 3D anodic layer and accumulated on each conductive fiber, forming a conformal biofilm,” Choi said. “Continuous gas supply through the [polymer] membrane and light-energy transfer through the transparent top layers enabled photosynthesis of the bacterial cells inoculated in the anode, harvesting electrons via the bacterial photosynthetic electron-transfer chain.”
At the same time as this process occurs, the bacterial respiration produces all the energy-consuming activities of the bacterial cells, which can transfer electrons even at night and on cloudy days, Choi said. An external electrical circuit transfers the generated electrons to the anode and cathode, creating a potential difference between them, he said.
“During those reactions, protons are released and diffused to the cathode, where they re-combine with the electrons that traveled from the anode and oxygen supplied from the air, forming water,” Choi explained.
All of this means that the micro-BSC can generate maximum power density of 43.8µW·cm-2 and a sustained consistent power production of ~18.6µW·cm-2 during the day, and ~11.4µW·cm-2 at night for 20 days, he said.
“This is the highest and longest reported success of any existing micro-scale bio-solar cells,” Choi said, adding, however, that this performance is not even comparable to typical semiconductor solar cells.
Still, the micro-BSC technology is useful for low-power applications like environmental sensors deployed in remote and resource-limited field locations, he said.
In addition to its practical application, the work provides a deeper understanding “of the interplay between photosynthetic bacteria and miniature device architectures and establishes fundamental knowledge critical to enabling much higher power production in a more sustainable way,” Choi said.
The team plans to continue to study gas transfer and bacterial growth to further develop and improve the technology, he added.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.