Almost all commercial solar panels today rely on single-junction solar cells, which convert sunlight into electricity. For decades physics has set a precise limit on this conversion: according to the Shockley-Queisser limit, such a cell cannot turn more than 33.7% of the light it receives into usable energy. According to the source, the figure has been treated as established fact since its definition in 1961.
Now a group at the Institut de Ciències Fotòniques (ICFO) in Barcelona claims to have found a way around that ceiling. The team, led by Professor Jordi Martorell, works on a simple but counterintuitive principle: reducing the photon emissions of the cell itself. A cell absorbs light but then re-emits it in all directions, and in doing so loses potential energy. The researchers turned the cell into a specially designed optical cavity: it still receives sunlight, but has a smaller opening through which energy can escape.
According to Francisco Bernal Texca, author of the team's scientific article, this approach could allow solar cells to reach efficiencies close to 43%. Bernal Texca also stresses that the cavity design adds no extra fabrication complexity, unlike many other methods being explored to surpass the Shockley-Queisser limit. The work, however, is still experimental.
From the lab to the rooftop
The value of such an improvement is clear: more efficient panels produce more electricity from the same area and materials. Martorell summarises it this way: higher efficiency translates directly into a lower cost per watt and more efficient use of land and materials. But the distance from the market remains large. Many panels on sale today do not exceed 25% efficiency, due to physical limits, large-scale manufacturing, light reflection and shading. Reaching the 33% ceiling is already difficult, and according to the article the new theoretical maximum of 43% will be equally rare in the field.
The result, for now, does not change installations on rooftops. It does, however, point to a different route from the simple race for new materials: intervening on the physics by which the cell loses energy. If the method survives the test of production, household panels working at 40% or above could become reality, but for now the figure remains a laboratory promise.
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