Acquire Photovoltaic Properties from WSe2 and BP

Researchers have discovered a method that could obtain polarity characteristics and photovoltaic properties from certain non-photovoltaic 2D tungsten diselenide (WSe₂) and black phosphorus (BP). It is reported that the effect produced by this method is different from the common photovoltaic effect in solar cells, and may even better.

Solar energy is considered a key technology to get rid of fossil fuels. Researchers dedicate to innovate more effective methods to obtain solar energy. Many innovations come from the field of materials research. Recently, Toshiya Ideue, an assistant researcher from the Department of Applied Physics, University of Tokyo, and his team have shown a keen interest in the photovoltaic properties of 2D materials and the interface when these materials meet.

Ideue pointed out: "Usually, the interface of multiple 2D materials exhibits different properties to a single crystal. We have found that two special materials that usually do not exhibit a photovoltaic effect will also produce when stacked in a very special way."

These two materials are tungsten diselenide and black phosphorus, and they both have different crystal structures. The two materials are non-polar and will not generate photocurrent under light. However, Ideue and his team found that by stacking the sheets of WSe₂ and BP in the correct way, the sample exhibited polarization, generating an electric current when light is projected onto the material. This effect occurs even if the illuminated area at both ends of the sample is far from the electrode.

The key to this behavior is the way tungsten diselenide and black phosphorus run together. The crystal structure of black phosphorus has reflection symmetry on a plane, while the crystal structure of tungsten diselenide has three mirror symmetry. When the symmetry lines of the material are aligned, the sample acquires polarity. This layering is a delicate task, but it also reveals new characteristics and functions to researchers, which cannot be predicted by observing the ordinary forms of the material.

Ideue said: "The maximal challenge we face is to find a good combination of 2D materials with higher power generation efficiency and to study the effect of changing the stacking angle. It is very worthwhile to find the emergent properties of materials that have never been seen before." Hope the research of acquiring photovoltaic properties from WSe₂ and BP could improve solar panels in the promising future.

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