U.S. Air Force photo/Airman 1st Class Nadine Y. Barclay
In a finding that appears in the journal Nature Materials (original article here), researchers demonstrate efficient energy harnessing using a hybrid solar cell. Specifically, they show ultrafast energy transfer between an organic molecule (made up of carbon and hydrogen atoms) and an inorganic semiconductor (made of atoms other than carbon and hydrogen). Normally, absorption of one photon or particle of light by a solar cell produces one electron which can be used for electrical work, but here the authors show that their hybrid solar cell is able to absorb one photon of light and generate two electrons, which could theoretically double its efficiency in solar light harnessing.

Practically, there are other things to consider. The selection of the organic molecule to integrate with the semiconductor needs to be very specific in order to exploit more of the light energy for useful work rather than lose it to heat. The better matched the organic molecule and the semiconductor, the more efficient the solar cell, which is what the authors show here. This means that simply putting organic molecules on any current semiconductor solar cell will not necessarily produce more efficient solar cells. It also means that the solar cell enhances the efficiency for only a narrow range of the broad spectrum of visible light. Additionally, the thickness of the solar cell plays a large role in how efficient it can be. If it is too thick, more energy is lost to heat; if it is too thin, the organic layer cannot absorb as much light. Accordingly, the researchers show less than doubling in efficiency with their solar cell for the particular section of visible light spectrum they are working with. Yet their work is a milestone in a sought after goal among the solar cell community- to be able to efficiently transfer energy from an organic layer to an inorganic semiconductor, something that has long been predicted to be valuable for energy transport in solar cells, but slow to show with experiments.

Edited by SITN Waves Editor Ankita Shastri. Many thanks to Felipe Herrera and Robert Gustafson for their contributions, expertise and insight on the article. Robert Gustafson is a graduate student in the Applied Physics program. Felipe Herrera is a post-doc in the Chemistry and Chemical Biology program.

Check out the following SITN articles on solar energy:
Computational Chemistry Shines Light on Solar Energy Storage in Plants
Black Silicon
Special Edition on Sustainable Energy- Sustainable Energy

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