Shockley-Queisser Limit Bypassed: 132% Quantum Yield

One photon, one electron. That rule capped solar energy for half a century. On March 25, 2026, a team from Japan and Germany published a result where one photon spawns 1.3 charge carriers. They did not break the rule — they routed around it with a quantum trick.

The Rule Nobody Could Break

In 1961, physicists William Shockley and Hans-Joachim Queisser calculated that a single-material silicon solar cell cannot convert more than 33,7% of incoming light into electricity. The reason is photon arithmetic.

Shockley-Queisser limit — the theoretical maximum efficiency for a solar cell made from one material. Photons below the energy threshold pass through. Photons above it lose excess energy as heat. Bottom line: one photon produces at most one electron.

Sunlight is a cocktail of photons carrying different energies. Silicon catches only those near its threshold (1.1 eV). Red photons are too weak — they fly through. Blue ones are too strong: silicon grabs exactly 1.1 eV and the surplus dissipates as heat. More than two-thirds of solar energy is lost.

Splitting an Exciton in Two

A team led by Yoichi Sasaki (Kyushu University, Japan) and Katja Heinze (Johannes Gutenberg University Mainz, Germany) found a way around this constraint. Their approach is called singlet fission — a process where one high-energy exciton splits into two.

Singlet fission — a quantum process in which one excited molecule shares its energy with a neighbor, producing two triplet excitons instead of one. Think of a billiard ball striking another so that both roll away at half speed.

The idea is not new — singlet fission was observed as far back as the 1960s. The problem has always been collection: a competing process called FRET (Förster resonance energy transfer) intercepts the energy before it can double.

A Molybdenum Filter

The key innovation is a molybdenum complex that acts as a «spin filter.» This molecule has a unique property: during its interaction with light, an electron inside it flips its spin state. Thanks to this behavior, the complex selectively captures triplet excitons (the fission products) while blocking unwanted FRET.

Spin-flip emitter — a molecule where an electron changes its spin state during an energy-level transition. This creates an energy «filter»: triplet excitons pass through, singlet ones do not.

The donor molecules were tetracene dimers with three different bridging groups. The best performer used a 2,5-methylphenylene bridge.

132%

The result: 132 ± 2% quantum yield for forming the excited doublet state of the molybdenum complex. For every 100 absorbed photons, the system generates 132 activated molecular complexes. One photon produces, on average, 1.3 carriers.

Three configurations delivered different yields:

• Phenylene bridge: 112 ± 6%
• 2,5-Methylphenylene bridge: 132 ± 2%
• p-Terphenylene bridge: 128 ± 4%

All three exceed 100%, confirming that fission genuinely doubles a fraction of the excitons.

The Caveat That Matters

132% is the quantum yield of one specific photophysical step, not the efficiency of a finished solar panel. Between a molecule in solution and a panel on a roof lies an enormous gap. All measurements were conducted in liquid media. Solid-state devices, stability under real sunlight, scaling — all of that remains ahead.

The work was published in the Journal of the American Chemical Society (JACS) on March 25, 2026 (DOI: 10.1021/jacs.5c20500) and underwent full peer review. The authors themselves describe the result as a «proof of concept, ” not a ready technology.

But if this molecular mechanism can be transferred to solid-state systems, the «one photon, one electron» rule stops being a ceiling. And the theoretical efficiency cap for solar cells rises from 33,7% toward 45%.

From Flask to Rooftop

Sasaki’s team has already outlined the next step: integration into solid-state films. By the most optimistic estimates, prototype modules incorporating singlet fission could emerge by 2028-2030. Mass production is a 2030s horizon.

Meanwhile, the industry is advancing a parallel route past the Shockley-Queisser limit — perovskite-silicon tandems, which have already reached pilot production. The two approaches do not compete; they complement each other. Tandems capture more of the spectrum. Fission extracts more from each photon.