A new sunbeam in the solar race

When in July 2015 the prestigious Scientific American magazine carried an article titled ‘Outshining Silicon’, it was an indication that the time of ‘perovskite’ was fast approaching. The authors Varun Sivaram, Henry Snaith and Samuel Stranks said right in the blurb that the “upstart material” could make solar cells that are cheaper and more efficient than silicon.

The trick (and money) in solar energy is ‘efficiency’. If you make a solar cell that produces more electricity from sunlight, but also lasts long, you are the winner. Higher efficiency implies cheaper power.

In the last three years, a mineral called ‘perovskite’, a lot cheaper than silicon, has been knocking about in solar labs and the efficiency levels in lab tests have reached 20 per cent-levels that conventional silicon cells took two decades to get to.

Are perovskites, then, the wonder material that will accelerate mainstreaming of solar? Opinion is divided.

Sivaram, 26, who advises the Governor of New York on renewable energy, expects perovskites’ efficiency in labs to exceed silicon in two years. Few disagree. As pure technology, the ‘perovskite solar cell’ is the long-awaited breakthrough. Among the ‘third generation’ solar cells (after crystalline silicon, and thin-film) perovskites have proven to be better than ‘dye-sensitised’ and ‘organic’ cells. “I can categorically affirm that perovskites are the most exciting,” says Sivaram, who has worked on all the three.

Technical challenges However, perovskites have technical challenges to overcome. They ‘degrade’ in air and contain lead, a toxic metal. “Making Perovskite modules as durable as silicon modules requires technological advances that have yet to be demonstrated,” says Keith Emery, Research Director at the National Renewable Energy Laboratory in the United States (US).

Sivaram, a perovskite-backer, agrees that “a good deal of product development and engineering will be required to bring perovskite cells to market. However, while Emery feels it is “premature to talk of perovskites in the market” until the technical problems are solved, Sivaram believes the problems to be “serious concerns, but not deal-breakers.” Any technology hatching in the lab will need to leap across the ‘valley of death’ to reach the markets, because the already heavily-invested incumbents will fight the newcomers.

Experts believe that commercialising perovskites are out of the range of start-up companies and venture funds, but could happen if the large solar companies get into the act.

These companies could make strategic investments for scaling up production of perovskite solar cells for high-value niche applications, such as for the military, because these cells are of high efficiency, light-weight and flexible.

Sivaram says perovskites can be “chemically tweaked” for various applications, and large solar companies could make it happen. “These (perovskites) could potentially be used for decorative, building-integrated windows that can make power,” says Prof Nitin Padture, Institute for Molecular and Nanoscale Innovation of the Brown University, US.

Perhaps, the first step is to combine perovskite and the conventional cells. Pointing to “a viable path to commercialisation”, Sivaram says smaller perovskite firms could partner with silicon companies to add a perovskite layer to the silicon solar panel. Such ‘tandem’ cells, according to Oxford Photovoltaics, a company co-founded by Henry Snaith, can produce 20 per cent more energy than just silicon cells, and the additional costs will be paid back in five years.

Energy payback An important factor that weighs in favour of perovskites is energy payback, or the time it takes to offset the energy that went into producing a material. If you take into account all the energy that went into the manufacture of a silicon solar cell—from mining and purifying silicon to baking it into ingots and cutting wafers out of it—you would find it takes three years for a silicon cell to save (or payback) that much of energy. In contrast, perovskites give back in just three months, according to scientists at the Northwestern University of the US.

The solar cell user industry is keeping a sharp eye on the unfolding developments in perovskites. "It is an interesting technology and we are very keenly following the progress of perovskites," says Pashupathy Gopalan, who heads Asia-Pacific operations of US solar major, SunEdison.

What is Perovskite?

Perovskite is a mineral composed of calcium titanate, used for making solar cells. The mineral was discovered in the Ural Mountains of Russia by Gustav Rose in 1839 and is named after Russian mineralogist Lev Perovski.

Correction

This article has been modified to correct Varun Sivaram's age to 26, from 21.

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