Solar cells using perovskite materials are inexpensive and easy to fabricate and the efficiency at which they convert photons to electricity has increased more rapidly than any other material to date, starting at 3% in 2009 and rising to 22% today. A team at the Molecular Foundry and the Joint Center for Artificial Photosynthesis, both at the Lawrence Berkeley National Laboratory (Berkeley, CA), used atomic force microscopy image of the surface of a perovskite solar cell to show a new path to much greater efficiency from manipulating the individual grain boundaries.
In the image (below) from the lab, the individual grains are outlined in black, low-performing facets are red, and high-performing facets are green. A big jump in efficiency could possibly be obtained if the material can be grown so that more high-performing facets develop.
Photoconductive atomic force microscopy allowed the researchers to map two properties on the active layer of the solar cell that relate to its photovoltaic efficiency. The maps revealed a bumpy surface composed of grains about 200 nanometers in length, with a huge difference in energy conversion efficiency between facets on individual grains. They found poorly performing facets adjacent to highly efficient facets, with some facets approaching the material’s theoretical energy conversion limit of 31%.
“If the material can be synthesized so that only very efficient facets develop, then we could see a big jump in the efficiency of perovskite solar cells, possibly approaching 31%,” says Sibel Leblebici, a postdoctoral researcher at the Molecular Foundry.