Awards Database

Scialog: Collaborative Teams - 2013

Stephen Bradforth

Chemistry, University of Southern California

Richard Brutchey

Chemistry, University of Southern California

Frank Osterloh

Inorganic Chemistry, University of California, Davis

Investigation into Interfacial States in Hybrid Polymer: Nanocrystal Solar Cells – Finding a Path to High Efficiencies

Organic Photovoltaic (OPV) technology holds out the promise of providing an extremely cheap, lightweight and flexible source of clean, renewable electricity generated directly from sunlight. But there is a bottleneck to overcome. It is the subject of a research project being conducted by Frank Osterloh, a professor of inorganic chemistry at UC Davis, and his colleagues, Stephen Bradforth, professor of physical chemistry, and Richard Brutchey, an associate professor of inorganic chemistry, both at USC. The OPV bottleneck seems to occur at the initial “charge-transfer” stage, the moment when an electron, energized by absorbing light, moves from its home molecule – called an electron donor—toward a second molecule, the electron acceptor. The donor layer of the OPV solar panel is made of plastic polymers – essentially the stuff of grocery bags—while the acceptor layer is usually composed of a material called fullerene, a unique form of carbon also known as “buckyballs.” Because something appears to be going wrong at this stage, OPVs are only about 7-8 percent efficient when converting sunlight to electricity (versus roughly 20 percent for today’s leading – and much more expensive – silicon technology). OPV researchers suspect the fault lies in the acceptor side of the charge-transfer process. Furthermore, the general thinking seems to be that the donor side of process already may be nearing its optimum potential. So Osterloh, Bradforth and Brutchey intend to study the feasibility of replacing the OPV’s fullerene acceptor with a more tunable semiconductor nanocrystal material. “Nanocrystal” refers to incredibly tiny (nano) structures – much smaller than the width of a human hair—whose atoms or molecules are arranged in a highly repetitive (crystalline) pattern. Initially the researchers will investigate a promising acceptor material, cadmium selenide, CdSe. It is a yellow-orange solid that exhibits interesting properties at the nanoscale. One such property, the “quantum confinement effect,” results when the electrons in a material are confined to a very small volume. For various reasons, electrons trapped in tiny particles seem to be more easily excited by photons streaming in from sunlight or some other source. The researchers’ ultimate goal is to lay the groundwork for inexpensive solar panels with much higher efficiencies that can be printed almost as easily as newspapers.

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