Singlet fission: 130% quantum yield of panels

Breaking the Shockley-Queisser Limit: Singlet Fission with 130% Quantum Yield Solar Cells

A team from Kyushu University and Johannes Gutenberg University Mainz has achieved a record 130% quantum yield using a singlet fission system. This surpasses the traditional 100% barrier by capturing multiplied triplet excitons via a molybdenum emitter with spin-flip capability. The technology suppresses parasitic FRET and paves the way for high-efficiency solar panels without excessive heat buildup.

Physical Limits of Conventional Solar Cells

In silicon solar cells, photon absorption follows the "one-to-one" rule of the Shockley-Queisser limit. Low-energy infrared photons fail to generate charge carriers. High-energy photons (blue and UV range) lose excess energy as heat through parasitic thermalization.

Maximum efficiency for such systems is around 33%. The core challenge: converting a single photon into multiple excitons without losses.

Mechanism of Singlet Fission

Singlet fission (Singlet Fission) bypasses this limitation. A high-energy photon in an organic material (tetracene) generates a singlet exciton, which splits into two lower-energy triplet excitons.

The theoretical quantum yield limit is 200%. The practical hurdle: triplet excitons are prone to FRET—resonant energy transfer that competes with charge extraction.

• Singlet exciton: high energy, unstable state.
• Triplet excitons: two low-energy, spin-forbidden for direct emission.
• FRET: parasitic process that dissipates energy before capture.

Molybdenum Spin-Flip Emitter

The solution lies in a molybdenum metal complex that selectively captures triplet excitons. Upon energy absorption, the electron flips its spin, circumventing the spin selection rule.

The tetracene–molybdenum emitter system is precisely tuned energetically to suppress FRET. Result: 13 excited complexes from 10 photons (130% yield).

Associate Professor Yoiti Sasaki: "The energy acceptor ignores FRET and focuses exclusively on triplets right after fission."

Experiment and Results

Proof-of-concept was demonstrated in liquid solution. Quantum yield was measured spectroscopically: complete suppression of losses, efficient harvesting of triplets.

Comparison:

| Parameter | Standard System | With Singlet Fission |

|----------|---------------------|-----------------------|

| Quantum Yield | ≤100% | 130% |

| FRET Losses | Significant | Suppressed |

| Heat Generation | High (excess E) | Minimal |

Future Integration and Applications

Next step: transition to solid-state materials for real-world panels. Integrating molecular multipliers could boost efficiency without increasing panel area.

Additional applications:

• Ultra-bright OLED displays through efficient triplet harvesting.
• Quantum devices with controlled spin states.
• Hybrid photovoltaic systems with organic layers.

The project was initiated by student Adrian Zauer, uniting expertise from Japan and Germany.

Key Takeaways

• 130% quantum yield achieved via singlet fission and spin-flip emitter.
• Complete FRET suppression enables extraction of multiplied excitons.
• Technology applicable in solid-state solar cells and OLEDs.
• Proof-of-concept in solution; goal is integration into next-gen panels.
• Bypassing the Shockley-Queisser limit redefines fundamental photonic boundaries.

— Editorial Team