Artificial Photosynthesis In Solar Cells

One of mankind’s greatest challenges is to find ways to replace the diminishing fossil fuel supply. The most obvious energy source is the sun, origin of almost all the energy found on Earth. The surface of the Earth receives solar radiation energy at an average of 81,000 terawatt – exceeding the whole global energy demand by a factor of 5,000. Yet, we are still figuring out a cost-effective way of harnessing it. Plants have been doing it for billions of years without issues and now man has succeeded in recreating a solar cell inspired by the photosynthetic cycle of the leaves.

Picture Courtesy Millennium Prize website

The 2010 Millennium Prize Laureate Michael Grätzel scientist and professor of photonics and interfaces at the École Polytechnique Fédérale de Lausanne in Switzerland is the father of third generation dye-sensitized solar cells. Grätzel cells, which promise electricity-generating windows and low-cost solar panels, have just made their debut in consumer products.

According to the Millennium Prize committee “Dye Sensitized solar cells or ‘Grätzel cells’ are likely to have an important role in low-cost, large-scale solutions for renewable energy. Besides photovoltaics, the concepts of Grätzel cells can also be applied in batteries and hydrogen production, all important components of future energy needs.”

DSC cells are third generation photovoltaic technology. The technology often described as ‘artificial photosynthesis’ is a promising alternative to standard silicon photovoltaics. It is made of low-cost materials and does not need an elaborate apparatus to manufacture. ‘Grätzel cells’ use Phthalocyanine an organic dye atop titanium dioxide to capture sunlight instead of the traditional silicon approach.  Phthalocyanine is an intensely colored macrocyclic compound that is widely used in dyeing.

Source of pic solarisnano

DSC cells separate light harvesting from charge carrier transport, mimicking the principles of solar energy conversion that natural photosynthesis has successfully adopted over the last 3.5 billion years. We can think plant leaves as tiny factories in which sunlight absorbed in the leaf by chlorophyll converts carbon dioxide and water into oxygen and glucose, providing energy for the plant. In DSC cells’ ‘artificial photosynthesis,’ the leaf structure is replaced by a porous titanium oxide nanostructure, and the chlorophyll is replaced by dye molecules.

  • The timeline of development of the DSC cells:
    • 1970 First attempts to construct DSC cells (Oil embargo etc… alternative energy research sets off)
    • 1988 Grätzel’s team tests the first dye-sensitized mesoscopic titanium oxide material on solar cells (oil at 5$ a barrel! Alternative energy future looks pretty distant)
    • 1991 Grätzel’s landmark Nature paper on dye-sensitized solar cells is published
    • 2009 Mass production of DSC cells begins

    Of all renewable energy sources, solar power is one of the most easily exploitable. The only constraint is its price. Using dye sensitized solar cells, grid parity – the point at which photovoltaic electricity is equal to or cheaper than grid power – is much closer. Michael Grätzel displays a fabric-like sheet of flexible DSC-panel. “This panel is cut with scissors from the production line.”  Grätzel sometimes still gives a Grätzel cell show to high school students. Using simple demonstration kit, students have the opportunity to be involved in cutting-edge, green chemistry research. Blackberries or raspberries are used as a light-harvesting sensitizer molecule. All the chemicals are mixed and put between glass plates. Exposed to light it produces current enough to power a small fan!! Students are as happy as Grätzel and his colleagues were 20 years ago.

  • What makes DSCs Attractive?
    • Dye-sensitized solar cells show similar performance under real life working conditions.
    • DSC cells capture power in low light or even rainy conditions.
    • DSCs are the only solar cells that can be made truly transparent their color depending on the choice of the sensitizer. By selecting dyes that absorb only in the near IR and UV region it is possible to produce even colorless transparent windows.
    • Dye-sensitized solar cells are low in cost, and can work on a broad scale.
    • Graetzel cells do not require a large setup to manufacture; would be considerably less expensive than standard silicon solar cell designs.
    • DSCs are mechanically robust and can be engineered into flexible sheets. They also require no protection from minor elements such as tree strikes or hail.
    • DSCs can be prepared on flexible, non-fragile and light weight substrates such as metal sheets or plastic foils.
    • DSC panel can be manufactured in a low-cost, roll-to-roll process and the production equipment is similar to manufacturing lines used by the printing, coating and packaging industries.

    Today, solar power accounts for only 0.54% of global energy usage. The average annual market growth of the photovoltaic industry has been 35–40 % for several years, and, for example, in 2007, grid-connected PV was the fastest growing source of energy with its 83% increase.

    Building-integrated photovoltaics (BIPV) are one of the fastest growing segments of the photovoltaic industry. Photovoltaic materials may be used to replace conventional building materials in parts of the building envelope such as the roof, skylights, or facades.

    In 2009 one of the DSC license holders, G24 Innovations, announced the first ever commercial shipment of DSC photovoltaic modules. The first consumer product, backpacks coated with the cheap and flexible DSC solar cell, for on-the-go recharging of portable gadgets, hit the shelves in January 2010.

    Though DSC cells are still in relatively early stages of development, it shows great promise as a reasonably priced substitute to costly silicon solar cells and an attractive candidate for a new renewable energy source. Dye Sensitized Solar Cells could be a large part of the future of alternative renewable energy. Solar is Green!
    Check out the stunning video on Gratzel DSCs, simply amazing! Watch the students use berries (you can even see one licking his fingers 🙂 ) Science at work!!

  • Sources: Millennium Prize Finland
    Wikipedia -Dye Sensitized Solar Cell
    DailyTech
  • You might find this interesting too Solar Cells use Poke Berry

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