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Source: Institute for Energy Economics and Financial Analysis

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Researchers at MIT and Princeton Universities have successfully demonstrated a new method for silicon solar cell design that could push efficiencies not just to record highs, but beyond what were theoretically thought possible.

Conventional silicon solar cells have a theoretical maximum efficiency of around 29 per cent, as there is a limit to how much sunlight can be converted into useful electricity within a silicon solar cell (dubbed the Shockley–Queisser limit).

Many commercially available cells achieve efficiencies in the order of 20-25 per cent, with higher efficiencies being a trade-off against the overall cost of the cell. But in a finding that may allow solar cells to surge beyond efficiencies that were previously thought possible, researchers at MIT have discovered a way of extracting even more energy out of the light that hits a solar cell, believing they can take silicon solar cell efficiencies to as high as 35 per cent.

Traditionally, photons have only been able to transfer their energy to a single “excited” electron as they pass through conventional silicon solar cells. However, some parts of the light spectrum, notably blue and green light, has enough energy to excite multiple electrons. Generally, this excess energy is converted into waste heat, and researchers have been searching for way to tap into this extra energy, seeing the potential to boost solar cell efficiencies.

In new research published in the journal Nature this week, researchers at MIT and Princeton Universities have demonstrated a method of doing exactly that, using photons (the light particles) to “excite” multiple electrons. By “exciting” multiple electrons, solar cells could produce more electric current using the same amount of light, boosting the efficiency of silicon solar cells by as much as 20 per cent. The proof of concept could lead to dramatic increases in the efficiencies of silicon solar cells, pushing beyond the 29% theoretical efficiency limit of current cells, to as high as 35%.

A wide range of research is currently underway for taking the efficiency of solar cells beyond 30%, with most techniques using a combination of silicon and organic solar cells “stacked” upon each other to maximise the amount of sunlight converted to electricity. But the MIT/Princeton research requires just a single silicon cell, which are most commonly used for commercially available solar cells.

More: Solar cell efficiency could get a dramatic boost, MIT team finds

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