Collecting solar energy and shift to electricity has been a very important issue. Materials Science Center of Peking University School of Physics, Quantum von economy in recent work, the strain construct so-called "solar funnel" to provide a fresh perspective on a topic. This work was published in "Nature - Photonics [Ji Feng, In Nature Photonics et al 6, 886-872 (2012); the doi: 10.1038/nphoton.2012.285].
Traditional materials can withstand a tensile elastic strain that usually does not exceed 0.2%. The recent emergence of a new class of low-dimensional materials, such as graphene, a single layer of molybdenum disulfide, able to withstand the huge elastic stretch. Von economy and its partners to consider how to use the elastic strain to bring unprecedented performance for material. They envision the probe top pressure suspended elastic film, constructed a nonuniform strain field. Elastic strain in the corresponding micro chemically stretch or compress, the change in the energy of the electrons (or carriers) in the material. Non-uniform strain distribution can lead to an effective electric field on the carrier. If stress concentrations in a device that is able to achieve the concentration of charge carriers through the stress field. It's like a "funnel" carrier. Feng Ji and his collaborators, the geometry of the device just a funnel-shaped (Figure).
Schematic diagram of the solar "funnel" (Image credit: Arend van der Zande, and James Hone)
As a concept demonstration, Feng Ji and collaborators to carry out numerical simulation for single-layer molybdenum disulfide. Single layer of molybdenum disulfide is a current concern of quantum materials. Feng solar cell Ji and Wang Enge previous cooperation, demo single layer of molybdenum disulfide has been known as the "Valley" quantum degrees of freedom, reflecting the the Valley circular dichroism selective and quantum transport characteristics [Ting Cao et al. Nature Communications 3, 887 (2012)]. Super strength elastic crystal film in addition to the specific optical properties, molybdenum disulfide, or one of only 0.6 nanometers thick, that can carry 11% of the elastic strain. Feng Ji and collaborators by the GW approximation, based on the density functional theory of solving the Bethe-Salpeter equation, derived molybdenum disulfide quasiparticle energy (electrons, holes and excitons). The calculations show that the quasi-particle energy of the molybdenum disulfide to the strain is very sensitive, and the exciton energy within the scope of the strength of the material can be changed as much as 0.7 eV. The combination of classical molecular dynamics calculations strain distribution, a the top depressed monolayer molybdenum disulfide Feng Ji and his collaborators demonstrated the feasibility of the design.
Strain and strain field at the quantum level has a profound impact on many of the performance of the material. Feng Ji's work has demonstrated the unique ability of the non-uniform strain field in the regulation of the carrier. Elastic strain has d (d +1) / 2 dimensions (d is the dimension of the material), the solar panel corresponding strain field is a d (d +3) / 2-dimensional continuous variables, material properties has a rich and varied regulation capacity. In the super strength materials budding, it is not difficult to foresee the elastic strain engineering will be a value of theoretical and technical research direction. James Hone of Columbia University Professor Feng economic work that commented on the same period in the News and Views of Nature - optical "[Nature Photonics 6, 804-806 (2012)], but also on the potential of the elastic strain engineering highly praised.
This work is the MIT Department of Materials and Nuclear Engineering Professor Li Ju, Dr. Qian Xiaofeng and Cheng-Wei Huang completed by the China Natural Science Foundation, the 973 plan, the U.S. NSF and the Air Force funding.