SusChEM: Next-Generation Dye-Sensitizers: Beyond the Shockley-Queisser Limit

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Technical Description: Organic dye sensitizers derived from plants are being investigated for their potential to provide two or more charge carriers per incident photon when used as sensitizers of titanium dioxide nanoparticles. The goal of the project is to determine the molecular basis for devices in which the efficiency of solar-energy conversion can exceed the 31% limit. Working with betalain plant pigments previously found to give high yields for converting photons to electrons in dye-sensitized solar cells, the principal investigator and her students use spectroscopic methods to reveal the mechanistic details of carrier multiplication and the molecular basis for enhanced light-harvesting (spectral broadening) of betalain dyes on titanium dioxide. Spectroelectrochemical measurements and time-resolved spectroscopy measurements are applied to determine the possibility of simultaneous two-electron oxidation, current multiplication, and singlet fission. The role of heterogeneous dye binding, co-sensitization and dye-aggregation in enhancing the light-harvesting of betalain pigments on titanium dioxide is examined using resonance Raman spectroscopy of purified dyes and dye-cocktails adsorbed on shape-tailored semiconductor nanoparticles.Non-technical Description: Results from this research benefit society by revealing how the efficiency of solar-energy conversion can be improved in a variety of photovoltaic devices, including those that are potentially cheaper and more environmentally friendly than current-generation solar cells. Broader impacts include the training of graduate and undergraduate students in research that fosters sustainable energy generation. Graduate students in the principal investigator's lab receive technological training in spectroscopy, electrochemistry and nanotechnology and contribute to two outreach programs that engender excitement about science and alternative energy in middle-school and high-school students. The Imagine Tomorrow competition builds relationships between prospective future scientists and faculty, while allowing both to showcase the results of their research in alternative energy. Graduate students are designing a Cougar Quest summer enrichment camp for Grades 7-12, which will allow campers to contribute to the project while learning about solar energy conversion.