Published on August 21st, 2014 | by Tina Casey9
Solar Cell Breakthrough: “Artificial Leaf” Beats Photosynthesis At Its Own Game
August 21st, 2014 by Tina Casey
When a research team from Germany puts a microorganism from Japan to work in a solar cell, you’re either looking at the next iteration of the Godzilla series or a significant solar cell breakthrough. If you guessed solar cell that would be it. The new solar cell is described as an “artificial leaf” that mimics the electron transfer of photosynthesis, at a much faster rate than observed in nature.
The key to the whole thing is a protein complex called photosystem 1 (PS1). If PS1 hasn’t crossed your radar since AP Bio, before we tell you all about that microorganism from Japan let’s get reacquainted with PS1.
Photosystem 1 And The Next Solar Cell Breakthrough
PS1 owes its name to a quirk of history. For some plants and algae there are two sequential protein systems that enable the electron transfer at the heart of photosynthesis. The flow of electrons actually starts at a system called photosystem 2.
The question is why the second system in the series get to be called #1, and the answer is that it was discovered first.
Researchers have been tinkering around with PS1 as a substitute for silicon, as a pathway to leaner, cheaper solar cells. The renewability of the protein is also a plus for reducing the lifecycle footprint of next-generation solar cells.
Putting PS1 To Work Is Harder Than You Think
Back in 2012, CleanTechnica noted that MIT was dipping a toe in the biophotovoltaics (that’s fancyspeak for artificial leaf) field with a “paintable” solar cell using PS1.
That same year a multinational research team from Germany and Israel came up with a way to measure photocurrents in PS1, demonstrating proof of concept for integrating the protein complex into solar cells.
One of the challenges facing researchers is that PS1 is a complex system with both hydrophilic (water-attracting) and hydrophobic (water-resistant) properties, which means that it is not amenable to sitting still.
This is where the new German solar cell breakthrough part comes in. Late last year our sister site Green Building Elements reported that a research team from Ruhr-Universität Bochum (RUB) was developing a “bio-based” solar cell using both PS1 and PS2.
In the latest development, the team has announced that they’ve ramped up the efficiency of the original concept from nanowatts to microwatts. That’s still photovoltaics on the scale of implantable medical devices (the team suggests sensors implanted in contact lenses, in case you’re wondering how sunlight is supposed to get to an implanted medical device). However, the breakthrough was significant enough for the team to foresee application to the next generation of flexible, thin film solar cells.
The progress was accomplished by focusing on PS1. To accommodate the protein’s split hydro-personality, the team developed custom-made redox hydrogels, which are electron-conducting gels that connect enzymes to electrodes.
Like PS1, the tailored hydrogels are both hydrophopic and hydrophilic, but they can be tuned to the hydrophobic aspect of PS1 by shifting the pH.
When the team embedded PS1 in the new hydrogels, the magic happened:
This purpose-built environment provides the optimal conditions for PS1 and overcomes the kinetic limiting steps, which are found in natural leaves. This procedure yields the highest photocurrents observed to date for semi-artificial bio-photoelectrodes while the electron transfer rate exceeds by one order of magnitude the one observed in nature.
Based on their observation of the photocurrents, the team predicts that one order of magnitude is peanuts compared to the potential for even higher electron transfer rates.
About That Bacteria From Japan…
No, we did not forget about that bacteria from Japan. The PS1 used by the German research team came from a type of thermophilic (heat-loving) cyanobacteria found in a hot spring in Japan.
If cyanobacteria rings a bell, you are probably thinking of the stuff commonly referred to as blue-green algae, which has been making a big splash in algae biofuel circles . Cyanobacteria, as its moniker indicates, is not actually an algae as in plant life. It’s a bacteria, but whatevs.
The takeaway is that one of Earth’s most ancient life forms is beginning to play a key role in the high tech, clean tech world of the future.
Also, we didn’t forget about that “other” artificial leaf we’ve been following. A project of Harvard (formerly MIT) professor Daniel Nocera, this low-cost photochemical device is designed to use solar power to split water (even dirty water) into hydrogen, which can then be stored and used in a fuel cell to produce electricity.
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