This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The bulk photovoltaic effect (BPVE), a photoelectric effect that generates photocurrent without a p–n junction, can persist even when a material's average crystal structure remains centrosymmetric, a study from Institute of Science Tokyo has found. Researchers demonstrated this in CuCrP2S6, a van der Waals material that transitions from a noncentrosymmetric to a centrosymmetric average structure.
The finding challenges the conventional view of BPVE and suggests a new strategy for enhancing photoelectric conversion. Conventional solar cells generate photocurrent by separating and transporting light-generated charge carriers, typically through structures such as p–n junctions. This approach has a fundamental theoretical efficiency limit, known as the Shockley–Queisser limit.
For an ideal single-junction silicon solar cell, this limit is about 33%. The bulk photovoltaic effect (BPVE) offers an alternative way of generating photocurrent that is not subject to the same Shockley–Queisser limit. In BPVE, light interacts with a material to generate photocurrent without requiring a p–n junction.
BPVE has traditionally been associated with noncentrosymmetric crystal structures. A team of researchers led by former graduate student Ryoga Murata and associate professor Takao Sasagawa from Institute of Science Tokyo (Science Tokyo), Japan, has now demonstrated BPVE in a material whose time-averaged crystal structure becomes centrosymmetric at room temperature. They found that dynamic changes in atomic positions can sustain BPVE even when the material appears symmetrical over longer timescales.
The study is published in the journal Advanced Functional Materials. "According to conventional theory, the BPVE should vanish in the room-temperature phase because inversion symmetry is restored. Surprisingly, our experiments revealed that a clear zero-bias photocurrent persists at room temperature and is even enhanced to approximately 1.5 times the magnitude observed in the low-temperature phase," says Sasagawa.
The effect was observed in copper chromium thiophosphate (CuCrP2S6) (CCPS) crystals, a layered van der Waals material. CCPS transitions from a noncentrosymmetric structure at low temperatures to a centrosymmetric structure at higher temperatures. At low temperatures, the copper ions (Cu+) occupy slightly displaced positions within sulfur octahedra.
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