Scientists make an exciton organic PV discovery

Researchers at the U.S. Department of Energy’s Lawrence Berkeley Laboratory have found a mechanism for creating a charge in molecular materials. The findings, say the team, could lead to new approaches in the design of PV devices.

A team at the Lawrence Berkeley National Laboratory made the breakthrough observation.

Image: The Regents of the University of California, through the Lawrence Berkeley National Laboratory

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Scientists working for the United States Department of Energy have used X-ray spectroscopy to observe, at an atomic scale, how electricity is generated from light.

Working with a model material based on a metal-organic heterojunction that comprised copper phthalocyanine and a fullerene based layer, the scientists were able to observe the way excitons –quasiparticles which carry energy but no charge – moved through the material and separated into charges useful for generating electricity.

Observing the migration through the material on a picosecond – trillionth of a second – timescale, the researchers found that the slower moving, lower energy excitons which form in the bulk of the copper layer contributed more to the charge generated, on a time averaged basis.

The results of the study have been published in the paper Efficient charge generation from triplet excitons in metal-organic heterojunctions, in the American Physical Society journal Physical Review B. The paper also provides absolute benchmark values for the design of copper phthalocyanine/fullerene heterojunctions.

Scientists working on such devices will be able to use the new findings to focus their efforts on getting more charge out of the materials from the slower mechanism, rather than converting faster moving excitons created at the junction between the two layers.

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