Solar Cells Achieve 'Impossible' 130% Efficiency Through Energy Multiplication Breakthrough

Researchers have achieved a solar cell efficiency rating of 130 percent — a figure that sounds physically impossible but refers to an energy multiplication effect in which a single absorbed photon triggers the release of more than one electron, effectively extracting more usable energy from incoming light than the photon itself carried.

The breakthrough, published in the journal Science, was achieved by a team at the University of Michigan using organic photovoltaic cells incorporating so-called spin-flip metal complexes — compounds in which the absorption of a single photon causes the molecule to enter an excited state that rapidly splits into two lower-energy excited states, each capable of driving a separate electron through the photovoltaic circuit. The process, known as singlet fission, was first theorized in the 1960s but has only recently been demonstrated in practical device geometries with conversion efficiencies high enough to be commercially relevant.

Conventional silicon solar cells are bounded by the Shockley-Queisser limit, which predicts a maximum theoretical efficiency of about 33 percent for a single-junction device. The best commercial silicon panels currently achieve roughly 22 to 24 percent under laboratory conditions and around 18 to 20 percent in field deployment. Tandem cells, which stack multiple semiconductor layers optimized for different parts of the light spectrum, have pushed laboratory efficiencies above 47 percent, but at costs that remain too high for widespread deployment.

The 130 percent figure reported by the Michigan team does not mean the device produces more energy than it receives — that would violate the law of conservation of energy. Rather, it means the device converts 130 percent of the photons in the wavelength range it is optimized for into electron-hole pairs, by using the singlet fission effect to split the energy of high-energy photons into two charges instead of wasting the excess energy as heat. Combined with conventional absorption of lower-energy photons, the overall power conversion efficiency of the best devices in the study reached 29 percent, approaching but not yet exceeding the Shockley-Queisser limit for the full solar spectrum.

Researchers said the true commercial potential of the technique lies in its possible integration with existing silicon cell manufacturing. Because the spin-flip organic layer can be deposited as a thin film on top of a conventional silicon cell, the technology could potentially be added to existing production lines as an upgrade rather than requiring an entirely new manufacturing process.