Researchers at the Massachusetts Institute of Technology (MIT) and Stanford University are reporting an advance in solar cell technology that could significantly improve the efficiency of photovoltaic cells in harvesting the sun’s energy. The researchers reported in the journal Applied Physics Letters that their prototype solar cell has the potential to surpass 35 per cent efficiency. The current maximum efficiency for photovoltaic cells is around 25 per cent. The power efficiency is the percentage of sunlight’s energy that is converted to electricity. The solar-to-electricity conversion efficiency is the technical variable that most strongly influences silicon photovoltaic module costs, the researchers write.
The MIT cell is made with a layer of silicon, as is common in solar panels, but adds a transparent layer of perovskite, creating a tandem solar cell in which the two different layers absorb different portions of sunlight. Perovskite, the researchers say, absorbs higher-energy particles of sunlight. Unlike an earlier model, in which the two layers operated, and had to be wired, independently of each other, the new version operates like a single silicon cell, with a single electrical control circuit.
Increasing the power efficiency of the prototype remains the major challenge, as it is limited by the capacity of the lesser of the two layers. The proof-of-concept solar cell was able to achieve a power output of “about the same” as would be produced by a conventional solar cell, about 13.7 per cent. While this leaves much to be desired, the researchers say they have already identified ways of increasing that output to 30 per cent, and ultimately to 35 per cent.
Another major challenge lies in the perovskite itself, a crystalline organometal mineral that is abundant in geological deposits around the world, and can be produced inexpensively in the lab. A statement from MIT on the new work explains that the material degrades quickly in open air and must therefore be modified to improve its durability or encapsulated to prevent exposure to air. This must be done without adding to manufacturing costs or compromising performance.