A molecule that glows in clusters just helped push solar cell efficiency past 26%
In organic solar materials, crowding is usually the enemy. Pack the molecules too tightly, and they stop glowing — bleeding off energy as heat instead of converting it into electricity. That quirk has quietly capped how efficient perovskite-organic tandem solar cells can get, leaving researchers chasing a voltage gap that conventional materials struggle to close.
Now a molecule engineered to do the opposite — one that actually glows brighter as it clusters together — may offer an unexpected way through.
The voltage gap that has held back tandem solar cells
Perovskite-organic tandem solar cells stack two light-absorbing layers — a perovskite top cell and an organic bottom cell — to capture a broader slice of the solar spectrum than either material could alone. That architecture makes them strong candidates for pushing efficiency beyond what single-junction cells can reach.
These molecules emit more efficiently when clustered, not less — because molecular geometry restricts the internal motion that would otherwise waste absorbed energy.
The problem sits in the organic half. These sub-cells consistently lose more voltage than theory says they should. Researchers call this the open-circuit voltage (VOC) deficit, and it directly cuts into the energy the tandem device can deliver.
The root cause is non-radiative recombination — electrons and holes meet, annihilate, and produce neither useful current nor light. The energy simply escapes as heat. The more recombination happens this way, the wider the voltage gap grows.
Two metrics help researchers track the problem: photoluminescence quantum yield (PLQY), which measures how efficiently a material re-emits absorbed light, and electroluminescence quantum efficiency (EQEEL), which measures the same under electrical excitation. Low numbers on both scales signal heavy non-radiative losses.
Why conventional organic molecules glow less as they pack together
Most modern organic solar cells rely on non-fullerene acceptor molecules. Strong absorption, good charge transport — but a real structural liability: when these materials pack tightly into films, as they must in any real device, their luminescence collapses.
This is aggregation-caused quenching, or ACQ. Molecular crowding opens pathways for energy to bleed away non-radiatively, dragging PLQY down and worsening recombination losses.
The contrast with aggregation-induced emission (AIE) materials is stark. These molecules emit more efficiently when clustered, not less — because molecular geometry restricts the internal motion that would otherwise waste absorbed energy. Despite that advantage, AIE materials have remained largely unexplored in photovoltaics, with most research concentrated in bioimaging and sensing. Bringing them into solar cell design represents a genuine conceptual shift.
Designing TPE-BTA3: A rotor-shaped molecule built to shine in a crowd
The molecule at the center of this work, TPE-BTA3, was rationally designed with a three-dimensional rotor-stereo configuration — and that architecture is the key to everything.
In flat, planar molecules, close packing lets energy transfer between neighbors and escape without emission. TPE-BTA3’s three-dimensional shape physically disrupts that pathway. When the molecules cluster, their rotors become restricted, and that restriction forces energy out as light instead of heat.
The result is a PLQY of 68% — exceptional compared to typical non-fullerene acceptors, which tend to score far lower once packed into films. The AIE-active design means TPE-BTA3 performs best under the dense conditions found in real solar cell layers — precisely the opposite of what ACQ materials do.
What Happens When TPE-BTA3 Joins the Solar Cell Blend
Rather than replacing the existing organic blend entirely, the researchers used a ternary strategy: TPE-BTA3 was added as a third component to a binary organic bulk-heterojunction, letting it work alongside established materials without requiring a complete redesign.
The addition produced two measurable benefits. It dramatically boosted the PLQY of the alloy-acceptor system, reducing non-radiative losses and lifting the open-circuit voltage. It also strengthened the cell’s ability to absorb near-infrared photons, raising the short-circuit current.
That second benefit matters especially in a tandem architecture. The wide-bandgap perovskite top cell handles higher-energy visible light, while the organic bottom cell’s job is to capture what passes through — primarily near-infrared photons. Better absorption there means more current from the part of the spectrum that would otherwise go to waste.
A certified 25.8% efficiency and what it means for solar research
The combined improvements pushed the perovskite-organic tandem cell to a power conversion efficiency of 26.5%. Independent certification confirmed 25.8% — placing this device among the highest-performing cells of its type.
The tandem pairs the optimized organic bottom cell with a wide-bandgap perovskite top cell operating at 1.85 eV, a combination designed to maximize complementary light absorption across the spectrum.
Beyond the headline number, the result points toward something broader: luminescence-focused molecular engineering could become a mainstream strategy for reducing energy losses in next-generation solar technologies. AIE design has spent years on the margins of photovoltaics research. Whether TPE-BTA3’s approach can extend to other material systems, scale up, and eventually reach manufacturable devices remains the central question.
You can check the complete study here: Li, X., Du, M., Wang, Z. et al. Aggregation-induced emission luminogen in ternary organic bulk-heterojunction for efficient perovskite-organic tandem solar cells. Nat Commun 17, 7019 (2026). https://doi.org/10.1038/s41467-026-73743-4
Daniel García is an Editor-in-Chief with strong expertise in structural work and engineering principles. He combines this technical foundation with deep knowledge of energy, spatial design, and emerging technologies, bringing a forward-thinking and analytical approach to editorial leadership.
