Solar cells based on photoelectrochemical conversion of sunlight to electricity suffer from relatively narrow light absorption and cell degradation, which reduces device performance and lifetime. In nature, photosynthesis has solved many of these problems. Photosynthesis is a biologically-mediated photoelectrochemical process for conversion of sunlight into electrons. Natural photosynthesis has perfected robust molecular machineries that enhance photo-excitation energy collection using an array of chromophores that counteract the effect of photo-damage via self-regeneration. The current limitations of photoelectrochemical cells can be better understood and potentially improved by mimicking natural photosynthesis with artificial photosystems. The overall goal of this research is to develop general design rules to build artificial photosystems with improved overall photo-conversion efficiency and service lifetime.

This research seeks to mimic the photo-absorption/conversion and self-regeneration processes of natural photosynthesis with synthetic chromophore nanomaterials through biomolecular nanofabrication techniques. Specifically, photo-pigments and quantum wires will be reversibly assembled via programmable DNA molecular recognition techniques, forming photoelectrochemical nanostructures capable of panchromatic absorption and system repair. For example, DNA-based assembly of selective porphyrin chromophores on single-walled carbon nanotubes can interact with G-quadruplexes to facilitate charge transfer at the nanoscale. By this approach, a variety of synthetic photo-conversion nanostructures capable of mimicking the structure and function of natural photosystems will be developed, and their photo absorption and conversion processes will be studied using ultrafast pump-probe measurement of the energy and charge transport processes. This data will be analyzed to elucidate the thermodynamics and kinetics of photo-conversion processes, and generate design rules for constructing artificial photosynthetic units.

Broader Impacts

The proposed activities will couple the research efforts to educational and outreach activities designed to advance the public understanding of artificial photosynthesis. Specifically, hands-on modules for high-school students will be developed for Introduce a Girl to Engineering Day and Discovery Days hosted by Purdue University, and research outcomes will also be featured on nanoHUB, an NSF-funded, Purdue-based nanotechnology website. Female and underrepresented undergraduate students will be recruited for participation in the research through the Women in Engineering and Minority Engineering Programs at Purdue University.

Project Report

This research aimed at discovering fundamental scientific and engineering knowledge needed to demonstrate artificial photosynthetic nanosystems capable of efficient light harvesting and system regeneration, which are critical mechanisms in natural photosynthesis. The feasibility of such revolutionary bio-inspired concept was examined and demonstrated using all-synthetic, photo-electrochemically active, porphyrin chromophore/carbon nanotube assemblies. The outcomes of this research include (1) demonstration of DNA-based reversible assembly of photo-electrochemical complexes, (2) elucidation of molecular and photophysical interactions between porphyrins and carbon nanotubes, and (3) advanced understanding of charge transfer at the nanoscale. The regenerative light-harvesting strategies explored in this project could greatly benefit both scientific communities and photovoltaic industries, by providing new photosystems with adjustable efficiency and improved operation lifetime. In addition, biomolecular nanofabrication technologies could form the basis of new manufacturing approaches for energy materials and systems. The project activities included strong efforts integrating cutting-edge research with education and outreach. This project engaged 3 faculty investigators, 7 graduate students, and 5 undergraduate students who produced 1 book, 3 book chapters, and 4 journal papers. This research supported 2 PhD dissertations and 1 MS thesis, providing research opportunities for female and minority students: 1 graduate and 3 undergraduate students were female, while 1 student had underrepresented background. This project provided a unique multidisciplinary research environment where students of diverse backgrounds learn from each other and faculty investigators from Engineering, Chemistry, and Physics, becoming engineers and scientists of next generation to solve the challenges of our society. The project team developed a hands-on experimental outreach module called Glowing Grass: Observation of Photosynthetic Units and Processes for K-12 students, parents, and teachers. In this module, green leaves and grass are collected, grinded, and dissolved in ethanol by the participants who can then observe chlorophylls (pigments in plants) through optical visualization. This module helps K-12 students and teachers understand natural photosynthesis through simple hands-on experiments. The project team constructed portable units such that this module can be performed outside laboratory.

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Purdue University
West Lafayette
United States
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