Scientists are putting another piece of the puzzle on how the introduction of alkali metals into crystals of flexible thin film solar cells improves their efficiency – ScienceDaily


“When environmentally friendly, inexpensive, versatile and efficient solar cells are developed, all thermal and nuclear power plants will disappear and solar cells installed over the ocean or in space will power our world,” says Professor Dong-Seon Lee of the Gwangju Institute for science and technology in Korea. His extremely optimistic view of the future reflects the visions of many researchers involved in improving solar cells.

Over time, scientists have found that doping – distorting a crystal structure by introducing an impurity – creates polycrystalline solar cells, which are made by fusing crystals called CZTSSe with earth-rich and environmentally friendly alkali metals like sodium and potassium, increasing their efficiency in converting of light in electricity, while also leading to the creation of low cost, flexible thin film solar cells, which of course could find many applications in a society where portable electronics are becoming increasingly commonplace. Why doping improves performance is not yet known.

In a recent article in Advanced Science, Prof. Lee and his team reveal part of this unknown. Her revelations are based on her observations of the composition and electrical charge transport properties of CZTSSe cells doped with layers of sodium fluoride of various thicknesses.

When analyzing these doped cells, Prof. Lee and his team found that the amount of dopant determined the path that charge carriers took between the electrodes, making the cell either more or less conductive. With an optimal doping layer thickness of 25 nanometers, the charges flowed through the crystal via paths that enabled maximum conductivity. This in turn, the scientists suspected, influenced the cell’s “fill factor”, which indicates the efficiency of converting light into electricity. At 25 nanometers, a record fill factor of 63% was obtained, a remarkable improvement over the previous limit of 50%. Overall performance was competitive even with this amount of doping.

These results provide insights into CZTSSe and other polycrystalline solar cells and pave the way for their further improvement and the realization of a sustainable society. However, the competitiveness of the solar cell that has produced these results makes them more tangible to us normal people, as Prof. Lee explains, “We have developed flexible and environmentally friendly solar cells that will be useful in many ways real life, from building-integrated photovoltaics and solar roofing to flexible electronic devices. “And given Prof. Lee’s bold vision, a green economy may not be too far away.

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Materials provided by GIST (Gwangju Institute of Science and Technology). Note: The content can be edited by style and length.

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