AsianScientist (Feb. 3, 2014) – Professor Michael Grätzel first became interested in alternative energy during the oil crisis of the 1970s, when petroleum-exporting Arab nations declared an oil embargo against countries that had supported Israel during the Yom Kippur War. As oil prices skyrocketed, he found himself unable to fill up his tank, he told Asian Scientist Magazine in an interview on the sidelines of the Global Young Scientists Summit 2014.
Prof. Grätzel, who directs the Laboratory of Photonics and Interfaces at the École Polytechnique Fédérale de Lausanne (EPFL), Switzerland, was awarded the 2010 Millennium Technology Prize for his invention of dye-sensitized solar cells, which are an efficient and low cost alternative to standard silicon photovoltaics. The prize has previously been won by Tim Berners-Lee, the inventor of the World Wide Web.
As the world’s population continues to grow, our global power supply gap is estimated to reach 14 terawatts by 2050, a giant figure equal to today’s entire energy consumption. Solar power has huge potential to fill this gap – the sun delivers about 120,000 terawatts to the surface of the Earth, 6,000 times our current energy consumption – but we are still working out cost-effective ways of harnessing this energy.
Green plants, of course, figured this out a long time ago, and dye-sensitized solar cells (also known as Grätzel cells) take a leaf out of their book. The cells use titanium dioxide nanoparticles coated with an organic dye sensitizer to capture sunlight and convert it into electricity – a technology often described as “artificial photosynthesis.” Compared to standard silicon cells, dye-sensitized solar cells are cheaper, easier, and more environmentally friendly to manufacture.
Just naïve chemists playing around in the lab
When Prof. Grätzel was embarking on his scientific career, his mentors advised him to stay away from the field of dye sensitization, which many physicists considered to be complex and full of pitfalls.
“We were lucky in the sense that, as a chemist, we didn’t know about all these objections the physicists had on their minds… we were just naive chemists,” he recalled in his plenary lecture.
His laboratory had been experimenting with colloidal particles (now called quantum dots), when they hit upon what would later form the basis of the dye-sensitized solar cells.
“First it was curiosity driven, playing around. Then I had a student, he did an experiment with one of those electrodes that has the particles coated on the surface… and we get this huge current. I knew immediately we had something special,” he told Asian Scientist Magazine.
At first, their results were met with skepticism.
“Initially nobody believed, we had to even show it to our colleagues, the experiment, or send our cells to be checked, because people were very skeptical,” said Prof Grätzel, adding that scientists should be careful not to be too dogmatic in their thinking.
They eventually published their findings in 1991 in a landmark Nature paper, which has to date garnered more than 12,000 citations.
The researchers continued to make improvements to the cells, developing a stable electrolyte that would not leak or evaporate even after hours of use in the heat of the Saudi Arabian desert.
More recent advances involve tweaking the molecular structure of the dye itself to improve its light harvesting properties. An engineered porphyrin molecule, for example, now works better than chlorophyll as a sensitizer. The group has also reached record high efficiency levels with cells that use the mineral perovskite as a light absorber.
Building integration and wearable technology
Dye-sensitized solar cells are translucent, come in many colors, and have a flexible configuration. These properties allow them to easily be incorporated into buildings, and even integrated into window glass, giving them a unique advantage over silicon-based cells. They also collect light from all directions, and can be used indoors or in diffused lighting conditions, such as on a cloudy day.
“It doesn’t look like a photovoltaic device – that’s the beauty of it,” said Prof. Grätzel.
The cells are increasingly being adopted in public spaces.
“I have to tell you the warm feeling I got when I got up to the departure level Sunday at Geneva airport, and seeing our panels there,” said Prof Grätzel.
EPFL’s new conference center, which is slated to open in April 2014, also has a colored glass façade composed of the cells.
The cells can also be incorporated into wearable devices. For example, Prof. Grätzel and his wife both own solar-powered backpacks – the cells in the backpack power a battery, which can then be used to charge the variety of gadgets we carry around today.
Electric or hybrid vehicles powered by the cells are also being developed. Considering the huge number of cars on the planet, this is one of the most promising applications for the cells, said Prof. Grätzel.
A unique advantage for the future
Describing workshops that teach high school students to make simple dye-sensitized solar cells using anthocyanin pigment extracted from blackberries, Prof. Grätzel said that it is critical to educate the next generation of scientists about the importance of developing new technologies to address our energy supply gap. If the crowd of students peppering Prof. Grätzel with questions when this correspondent arrived for the interview is any indication, there does seem to be great interest in this field among young researchers.
Going forward, a major barrier for the cells to be adopted is price, said Prof. Grätzel, adding that some companies have been drastically underpricing silicon-based cells in attempts to corner the market. But since this is clearly not a sustainable practice, he remains optimistic about the future.
“We feel it’s a very good chance that with these technologies, we can come down, way down in price.”
The versatility of the cells and their ability to be integrated into buildings and wearable devices also bodes well for the future.
“Silicon cells cannot compete there, there is no other technology that offers this… So we have a unique application,” said Prof. Grätzel.
Prof. Michael Grätzel was attending the Global Young Scientists Summit 2014, organized by the National Research Foundation of Singapore. The summit took place from January 19 to 24, 2014 at Nanyang Technological University.
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Copyright: Asian Scientist Magazine.
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