Michael Wasielewski is the Clare Hamilton Hall Professor of Chemistry and executive director of the Institute for Sustainability and Energy at Northwestern University. Wasielewski is also director of the Center for Light Energy Activated Redox Processes, a U.S. Department of Energy Frontier Research Center. He spoke with MITEI following a recent seminar in which he discussed advancements in the study of molecular approaches to solar energy conversion.
Q: In your view, what are the best methods out there for improving solar cell efficiency? How can photosynthesis play a role?
A: The best methods for improving solar cell efficiencies will take advantage of understanding and applying new physical phenomena. For example, the absorption of blue light by solar cells results in most of that energy being lost as heat. The development of new materials that can be used with current solar cell technology to use blue light to generate charges instead of heat are important. These methods include multi-exciton generation in inorganic materials and singlet fission in organic materials. In both cases, absorption of blue light ultimately leads to formation of more than one electron-hole pair that can be used to provide extra current from the solar cell.
The primary light capture, charge generation and transport properties of photosynthesis give us a detailed picture of how the structural relationships between molecules can be exploited to optimize the efficiencies of these processes.
Q: What are some of the opportunities and challenges related to molecular-level approaches?
A: The biggest challenge for molecules is long-term stability. Fortunately, there are many molecules that are capable of enhancing solar cell performance that have been tested by industry in other applications, such as paint pigments, and have been optimized for long lifetime. An example of what is possible with good engineering is the organic light emitting diode, which began as a short-lived lab experiment about 20 years ago, and now is being incorporated into large screen displays, such as televisions, with estimated 100,000-hour lifetimes.
Q: Why is improving solar cell efficiency important for the industry?
A: Improving solar cell efficiency is important for the obvious reason that increasing solar cells’ power output can result in economic advantages as well as the ability to use smaller solar installations in locations that larger arrays that are less efficient would not be possible. In addition, it is important to develop solar cells that produce electrons and holes at higher potentials that can be used directly to carry out energy-demanding chemicals reactions for energy storage and chemical and/or materials synthesis.