This project supported by the Solid State and Materials Chemistry and Electronic and Photonic Materials Programs will develop solution-processable graphene quantum dots (QDs) with precisely controlled structures and study their electro-optical properties for thin-film photovoltaics. The goal is to exploit the unique properties of the graphene QDs, such as their broad, tunable absorption spectra, large extinction coefficient, and long hot-carrier lifetimes, to overcome some major difficulties in development of solution-processed solar cells. Soluble, well-defined graphene QDs will be synthesized and investigated so that their properties can be optimized for energy conversion. Since graphenes are made of abundant elements on Earth and are environmentally friendly, the proposed research could result in low-cost solar electricity with minimal adverse environmental impact, and thus lead to sustainable ways of using carbon for energy applications. The graphene QDs are synthesized through stepwise solution chemistry and therefore have precisely controlled structures and properties. The energy relaxation dynamics in the QDs will be investigated, which is an essential process for utilization of the photon energy absorbed. In addition, their properties, such as absorption spectra, redox potentials, electron transfer dynamics, and their interaction with metal oxides, will be optimized for dye-sensitized solar cells. The size, shape, and functionalization of the graphenes will be varied in a tightly controlled way, so that the parameters dictating their performance in the photovoltaic devices can be indentified and understood.
NON-TECHNICALSUMMARY The research proposed herein is to create a new type of carbon material that can be processed in simple ways for efficient thin-film solar cells. Because they are readily available and are environmentally friendly, the materials could lead to low-cost solar cells with minimal adverse environmental impact. The success of the proposed work could lead to a sustainable way of using carbon for energy, that is, instead of carbon-based energy sources(like coal) the carbon materials used in this project will be the active media that harvests and converts sunlight to electricity. The proposed research will be an excellent recruiting and training tool for young scientists, because it targets challenges that increasingly draw interest of students, and because of its interdisciplinary nature. For example, studies showed that interdisciplinary science programs tended to attract and retain more female students. Through undergraduate classroom and outreach programs, the research will have impact beyond the reach of traditional university teaching, and improve science literacy of the general public.
The research funded is to create solution-processable graphene quantum dots (QDs) with precisely controlled structures and to study their electro-optical properties for thin-film photovoltaics. The goal is to exploit the unique properties of the graphene QDs to overcome some major difficulties in development of solution-processed solar cells. Since graphenes are made of abundant elements on Earth and are environmentally friendly, the proposed research could result in low-cost solar electricity with minimal adverse environmental impact. Within the funding period, we have significantly advanced the synthesis of the GQDs to heteroatom-doped ones and large GQDs with unprecendented size, to tune their chemical and photophysical properties. Through spectroscopic studies we have identified some fundamental photophysical processes that are absent or inefficient in any other quatum dot systems. These could potentially lead to low-cost thin-film solar cells with efficiency exceeding the Shockley-Queisser limit. In addition, we have discovered unique electrocatalytic activities in doped GQDs for the oxygen reduction reaction, a key reaction in devices such as fuel cells. This could greatly expand and facilitate the renewable uses of abundant carbon materials in our society for energy-related applications. The proposed research has served as an excellent recruiting and training tool for young scientists, because it targets challenges that have sigificant societal impact and increasingly draw interest of students. Over the funding period we have trained five female graduate students and two African-American undergraduates for energy-related research. Through an outreach program, we have hosted a faculty member and three undergraduate students from a historically black college for summer research.