Solar cells driven by bacteria can convert light into energy even on cloudy days

The use of bacteria that convert light into energy allows solar energy to be more widely used on cloudy days. Image source: © FotoAndalucia / Fotolia

Researchers at the University of British Columbia have discovered a cheap and sustainable way to build solar cells using bacteria that convert light into energy.

Their batteries produce more current than similar devices previously, and are as effective in dim light as in strong light.

This innovation may be a step in the widespread adoption of solar energy in British Columbia and parts of Northern Europe, where cloudy days are common. With further development, these solar cells-known as biological sources because they are composed of living organisms-can become as efficient as the synthetic batteries used in traditional solar panels.

Vikramaditya Yadav, a professor in the Department of Chemistry and Bioengineering of UBCs who led the project, said: "We solved an ancient problem and made solar energy an important step in a more economical direction."

Solar cells are the cornerstone of solar panels. They are responsible for converting light into electricity. Previous efforts to establish bio-solar cells have focused on extracting natural pigments from bacteria for photosynthesis. This is an expensive and complicated process that involves toxic solvents and may cause dye degradation.

The solution for UBC researchers is to leave the dye in the bacteria. They genetically engineered E. coli to produce a large amount of lycopene-a pigment that can make tomatoes appear red-orange, which is particularly effective in converting light energy into energy. The researchers coated the bacteria with minerals that could be used as semiconductors, and applied the mixture to the glass surface.

The conceptual diagram shows that the anode of the solar cell is made of biological material, which is produced by orange spherical bacteria coated with titanium dioxide nanoparticles on the surface that can produce lycopene. (Photo / Vikramaditya Yadav)

Coated glass acts as an anode at one end of the battery, and they produce a current density of 0.686 milliamperes per square centimeter, which is an improvement from 0.362 milliamperes created by others in the field.

Yadav said: "We have recorded the highest current density of bio solar cells. The hybrid materials we are developing can be manufactured economically and sustainably. And after being fully optimized, they can operate with the efficiency of traditional solar cells."

The cost savings are difficult to estimate, but Yadav believes that this process can reduce the cost of pigment production to one-tenth of the original. Yadav said that the "Holy Grail" would be to find a way that does not kill bacteria, so that bacteria can produce pigment indefinitely.

He added that these biomaterials have other potential applications in mining, deep-sea exploration and other low-light environments.

By chance

Like many scientific discoveries in the past, this research was accidental. "Our initial motivation was to develop bacterial 'small factories' to produce large amounts of lycopene and other carotenoid molecules to make health supplements," Yadav said. "However, our team encountered challenges in storing the newly produced lycopene."

By storing lycopene in transparent glass bottles, they quickly degraded, so the researchers switched to opaque bottles. The problem was solved, but this discovery caused more scientific problems, and the researchers then opened up a new way of exploration. "In chemistry, degradation usually means the release of electrons, we thought: If the rate of electron release is high enough, can it produce a measurable current?" Yadav said.

"A student in the research group, after seeing the changes in lycopene in a transparent bottle, said aloud: 'Is lycopene so easily degraded in the sun? What if we put it in a solar cell? 'This issue has stimulated our interest in developing dye-sensitized solar cells, "Yadav recalled. "The decision to apply the mineral coating directly on the bacteria was a gamble, and this gamble finally paid off. The chance coincidence was a great ally of scientists, and we are very grateful for this unexpected discovery and the curious student because he asked A sentence 'Why can't you try it?' "

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