A Better Way to Tap the Sun

Controlled Electron Transfer in Hydrogen-Bonded Systems

The amount of solar radiation that reaches the Earth’s surface in only one hour provides enough power to satisfy our energy demands for a whole year. Unfortunately, we are unable to take advantage of this energy, due to the high cost of solar cells.

During the last decade, conjugated polymers have emerged as an inexpensive alternative material for solar cell design. They have several advantages over traditional solar cell design: they’re easily synthesized and processed, their electronic band-gaps can be readily manipulated and they produce solar cells in the form of flexible films.

Despite all these advantages, however, the commercialization of organic solar cells is limited by their low photovoltaic efficiency. The main factors that lead to this decreased performance are their inefficient charge separation and unwanted charge recombination.

To improve solar cell efficiencies, Dr. Ksenija Glusac’s research group is focusing on finding ways to make charge separation long-lived. Particularly, they want to learn how to take advantage of hydrogen bond (H-bond) dynamics to control the electron flow in molecular systems.

To do so, they’re working along two chief lines of inquiry. First, they’re exploring ways to use H-bond dynamics to produce long-lived charge-separated states. To achieve this goal, they’re experimenting with specific H-bonded D/A systems in which the initial charge separation induces proton motion along an H-bonded surface. This in turn can make the charge recombination thermodynamically and/or kinetically inefficient — in essence, making the H-bonded surface act as a unidirectional gate for the electron flow. With this goal in mind, the research group is studying H-bonded D/A systems using femtosecond VIS and mid-IR laser spectroscopy.

A second line of inquiry involves developing new ways to take advantage of H-bonds’ potential to produce nanoscale materials using self-assembly. By chemically designing conjugated polymers to assemble using H-bonds, solar cells with nano-scale heterojunctions can be produced, which will lead to more efficient splitting of the excitons into charge-separated states.

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