Inversion Symmetry Broken For Efficient Optoelectronics

Light-emitting, energy-harvesting, and sensing technologies could all benefit from optoelectronic materials that can convert light energy into electricity and light. However, devices leveraging these materials are notoriously inefficient, wasting a considerable amount of valuable energy in heat. New light-electricity conversion principles can break the present efficiency restrictions. Inversion symmetry is a physical property that restricts engineers’ control over electrons in the material and their ability to develop unique or efficient devices. It is a limitation for many materials with efficient optoelectronic features.

For the first time, a team of materials scientists and engineers employed a strain gradient to break the inversion symmetry of molybdenum disulfide (MoS2), resulting in a novel optoelectronic phenomenon.

The scientists placed a vanadium oxide (VO2) wire underneath a sheet of molybdenum disulfide. Because MoS2 is a flexible material, it deformed its original shape to follow the curve of the VO2 wire, creating a gradient within its crystal lattice. The gradient breaks the material’s inversion symmetry, allowing the manipulation of electrons traveling within the crystal.

It is the first time such an effect in this material has been demonstrated. Because vanadium oxide is extremely temperature sensitive, the researchers demonstrated that the flexo-photovoltaic effect caused temperature dependence at the interface of the MoS2 and VO2 materials, resulting in a change in the lattice gradient. This discovery suggests a novel principle that could be used in remote thermal sensing.

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