[font face=Serif]2017/01/24
[font size=5]Foundation for new type of solar cell[/font]

[font size=4]Using hot polarons to harvest sunlight[/font]

[font size=3]An interdisciplinary team of researchers has laid the foundations for an entirely new type of photovoltaic cell. In this new method, infrared radiation is converted into electrical energy using a different mechanism from that found in conventional solar cells. The mechanism behind the new solid-state solar cell made of the mineral perovskite relies on so-called polaron excitations, which combine the excitation of electrons and vibrations of the crystal lattice. The scientists from the research groups of Prof. Christian Jooss at the University of Göttingen, Prof. Simone Techert, Leading Scientist at DESY, Professor at the University of Göttingen and head of a research group at the Max Planck Institute for biophysical Chemistry in Göttingen, and Prof. Peter Blöchl at the Technical University of Clausthal-Zellerfeld present their work in the journal Advanced Energy Materials.

“In conventional solar cells, the interaction between the electrons and the lattice vibrations can lead to unwanted losses, causing substantial problems, whereas the polaron excitations in the perovskite solar cell can be created with a fractal structure at certain operating temperatures and last long enough for a pronounced photovoltaic effect to occur,” explains the main author of the paper, Dirk Raiser, from the Max Planck Institute for Biophysical Chemistry in Göttingen and DESY. “This requires the charges to be in an ordered ground state, however, corresponding to a sort of crystallisation of the charges, which therefore allows strong cooperative interactions to occur between the polarons.”

The perovskite solar cells studied by the team had to be cooled in the laboratory to around minus 35 degrees Celsius, in order for the effect to take place. If this effect is to be used in practical applications, it will be necessary to produce ordered polaron states at higher temperatures. “The measurements so far were made in a carefully characterised reference material, in order to demonstrate the principle of the effect. For this purpose, the low transition temperature was accepted,” explains co-author Techert.

Material physicists at Göttingen are trying to modify and optimise the material in order to achieve a higher operating temperature. “Also, we might be able to achieve the cooperative state temporarily through the cunning use of additional light to produce the excitation,” says Techert. If one of these strategies proves successful, future solar cells or photochemical energy sources could be made using perovskite oxide compounds, of which an abundant supply exists.

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