Break that symmetry, and the cancellation fails. Charge carriers can drift preferentially in one direction, and light falling on the crystal produces a measurable current without any junction.

This is why the new result is surprising. The material's average structure was symmetric — the kind of arrangement that should cancel everything out — yet the photocurrent survived.

What explains the persistence of the current?

The answer, according to the researchers, lies in atomic motion. The atoms in CuCrP2S6 do not sit frozen in place. Even when their time-averaged positions paint a centrosymmetric picture, the instantaneous, moment-to-moment arrangement of atoms can still lack a center of symmetry.

Think of a photograph versus a video. A long-exposure photograph of the vibrating crystal looks symmetric. But frame by frame, each snapshot is slightly lopsided — and those fleeting asymmetries, the study suggests, are enough to keep driving a photocurrent.

The finding reframes how scientists should think about BPVE. It is not only the static, average structure of a crystal that matters. The dynamics — how atoms actually move and oscillate within the lattice — can determine whether the effect appears or vanishes.

The researchers said their finding challenges the conventional view of BPVE and suggests a new strategy for enhancing photoelectric conversion.

Why does this matter for solar energy?

Conventional solar cells rely on p–n junctions and are bound by the Shockley–Queisser-style efficiency ceilings that come with junction-based design. BPVE materials, in principle, offer a different physical mechanism for converting photons into current, one that theorists have long discussed as a possible way past those limits.

Until now, the candidate pool for BPVE materials was restricted largely to crystals with static asymmetric structures. If atomic motion can sustain the effect in materials whose average structure is symmetric, the range of usable materials widens considerably.

Van der Waals materials such as CuCrP2S6 add another practical attraction. Their weakly bonded layers can be exfoliated, stacked and combined with other materials, giving engineers unusual freedom in device design.

How solid are the results?

Readers should treat this as a foundational physics finding rather than a ready-made technology. The study demonstrates the effect in one material, CuCrP2S6, under controlled laboratory conditions.

Several questions remain open:

• How large can the photocurrent from motion-driven BPVE become in an optimized device?
• Does the effect appear in other van der Waals materials with similar structural transitions?
• Can the mechanism operate efficiently at the temperatures and illumination levels found in real-world solar applications?

The Institute of Science Tokyo team has established the phenomenon; translating it into a competitive photovoltaic technology would require substantially more research.

The bigger picture

For decades, symmetry has served as a simple rule of thumb for spotting candidate BPVE materials: look for asymmetric crystals, ignore symmetric ones. That rule now looks incomplete.

By showing that a material's dynamic behavior — its atoms in motion — can carry photovoltaic function that its static structure hides, the Science Tokyo researchers open a new dimension in the search for better light-harvesting materials. The next step for the field will be testing whether this motion-driven mechanism can be strengthened and harnessed, rather than merely observed.

For now, the result stands as a careful, well-supported reminder: in solid-state physics, the averages do not always tell the whole story.