The NSF Sustainable Energy pathways (SEP) Program, under the umbrella of the NSF Science, Engineering and Education for Sustainability (SEES) initiative, will support the research program of Prof. Yanfa Yan and co-workers at the University of Toledo. The highly multi-disciplinary research team consists of experts in physics, materials science, engineering, chemistry, socioeconomics, environmental science, and education. The objective of the project is to develop the concepts, materials, and processes necessary to economically produce environmentally friendly thin-film solar cells from earth-abundant, environmentally benign (EAEB) materials including FeS2, Cu2S, CuO, Zn3P2 and Cu2ZnSnS4 (CZTS). To achieve high efficiency EAEB solar cells, the research team proposes two new concepts: (1) a bulk homojunction for EAEB inorganic materials that have low carrier mobility and low structural stability (e.g., for FeS2, Cu2S, and CuO) and (2) a hetero-homo dual-junction (HHDJ) for Zn3P2- and CZTS-based thin-film solar cells. The bulk homojunction concept will be realized by assembling nanocrystals (NCs) with surfaces that will be carefully engineered to contain cation-rich domains. Upon assembly, the NCs will form a three-dimensional interconnected network of electron and hole channels that can facilitate charge separation and transfer with minimal efficiency-robbing recombination due to the homojunction topology. The HHDJ will be achieved by accurate control of the junction chemistry using dedicated physical vapor deposition systems with in situ monitoring, including real-time electron impact emission spectroscopy and real-time spectroscopic ellipsometry. The HHDJ concept combines the benefits of the heterojunction and the homojunction: the homojunction minimizes efficiency-robbing recombination while the heterojunction enhances the charge separation and transfer, leading to optimal solar cell performance.
The research team will concomitantly develop and analyze the sustainability of our new solar cell systems and manufacturing processes through life cycle tools where life cycle costing (LCC), environmental life cycle assessment (LCA), and social life cycle assessment (SLCA) will be developed simultaneously to create a comprehensive life cycle sustainability assessment (LCSA). To implement LCSA, a new dynamic approach will be used whereby different scenarios will be iteratively modeled to identify the specific interactions of the parameters and, ultimately, the most sustainable scenarios. To address education/workforce development, the research team will target critical educational goals for students at all levels. The research team will also employ an integrative approach wherein students from widely varying backgrounds and fields of expertise will work together to solve complex real world problems. This approach will further reinforce synergy, broaden educational goals, and build a true team philosophy.
This project will yield at least two scientific impacts: (1) a thorough understanding of the fundamental science and engineering issues that are critical for realizing a sustainable solar energy pathway using non-toxic and earth-abundant materials, and (2) new science and education paradigms for designing economically, environmentally, and socially sustainable renewable energy and, specifically, solar electricity pathways. By directly integrating the needs of society and industry in developing the materials and engineering technology, this project should serve as a transformational model for the sustainable development of new renewable energy technologies.
