Ultrafast multiexciton kinetics in solar photovoltaics beyond the Shockley-Queisser limit

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Principal Investigator: Chee Wei WongNumber: 1438147The sun represents the most abundant potential source of pollution-free energy on earth. Solar cells for producing electricity require materials that absorb the sun's energy and convert its photons to electrons, a process called photovoltaics. To be competitive with fossil fuels, the cost of solar photovoltaic (PV) systems must be reduced, which is realized in part by increasing the solar energy conversion efficiency and by reducing the cost of solar PV materials. Recently, new photovoltaic materials have been discovered that harness the quantum physics behavior of inorganic semiconductor compounds ordered at the nanoscale to increase the solar energy conversion efficiency. The discovery of new and inexpensive materials for this next generation of photovoltaic devices is enabled by fundamental understanding of the interaction of light with these materials. The goal of this project is to develop a fundamental understanding of quantum physics processes in nanostructured photovoltaic materials which convert a single photon from light into multiple electrons, and thus surpass the single electron Shockley Queisser limit. The research will make use of advanced spectroscopic techniques which can probe multiexciton generation processes at ultrafast scales. Educational activities offered by the project focus on the development of a series of teaching and laboratory modules on solar energy, nanoscience, and sustainable energy, with content targeted separately to grade-school level students, low income, college-bound high school students in the New York City area, and undergraduate students at Columbia University.Technical DescriptionThe overall goal of this project is to develop a fundamental understanding of multi-exciton generation in nanostructured photovoltaic materials. The proposed research will study ultrafast multiexciton kinetics and generation in zero-dimensional and surface-modified nanostructures, as well as ultrafast multiexciton kinetics and collection in one-dimensional nanostructures and assemblies. This information will be used to harness multiexciton energy and electron transfer processes in nanostructured photovoltaics for improved solar energy conversion efficiency. Super-continuum ultrafast spectroscopy will be used to probe multiexciton kinetics and multiexciton efficiencies in semiconducting nanocrystals, nanorods, and nanostructures to elucidate the fundamental mechanisms. These studies will be extended to examine exciton and electron transfer of nanostructures in transparent high-mobility graphene electrode photovoltaics, using time- and spectrally-resolved studies and fast exciton quenching through blinking statistics of single nanostructures. Educational and outreach activities offered by the project focus on the development and delivery of a series of teaching and laboratory modules on solar energy, nanoscience, and sustainable energy, with content targeted separately to grade-school level students, low income, college-bound high school students in the New York City area, and undergraduate students at Columbia University.