| Jan 17, 2024 |
Looking inside a solar cell
(Nanowerk News) In a ground-breaking study published in Nature Energy ("Charge-carrier-concentration inhomogeneities in alkali-treated Cu(In,Ga)Se2 revealed by conductive atomic force microscopy tomography"), researchers from the Nanostructured Solar Cells group have unveiled critical insights into the optimisation of thin-film solar cells, shedding light on methods to enhance their efficiency and pave the way for more cost-effective electricity generation.
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Photovoltaic power conversion utilising polycrystalline light-absorbing semiconductors has long been recognised for its potential to revolutionise solar energy. Among these technologies, polycrystalline CIGS (copper indium gallium selenide) stands out as a high-performing option, and recent advances have propelled its efficiency even further through an alkali-fluoride post-deposition treatment, which elevates the charge-carrier concentration.
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However, the team led by Sascha Sadewasser discovered a previously overlooked challenge in the application of this treatment – inhomogeneities in the conductivity of individual material grains, which they trace back to the charge-carrier concentration. This revelation has significant implications for the efficiency of solar cells and their overall performance.
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Using an emerging conductive atomic force microscopy tomography technique, the research team at INL literally scratched away material layer by layer, generating three-dimensional conductivity maps. A detailed analysis of these maps provided for a sub-micrometre scale visualisation of the carrier concentration grain by grain, allowing for a detailed look into the inside of the solar cell.
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In collaboration with the Centre for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) in Germany, the team has tested the alkali-fluoride post-deposition treatment with different elements. The study found that a lower efficiency solar cells treated with potassium-fluoride correlate with more pronounced inhomogeneity of charge-carrier concentration. In contrast, better performing solar cells treated with rubidium- and caesium-fluoride showcased narrower distributions at higher charge-carrier concentrations. Deepanjan Sharma, the PhD candidate conducting this study adds “the charge-carrier concentration of the p-type CIGS absorber layer was identified as a key factor directly influencing the open-circuit voltage of solar cell devices, thereby impacting overall device performance”.
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“These findings have immediate implications for the development of higher efficiency thin-film photovoltaics,” said Sascha Sadewasser. “By optimising the alkali-fluoride post-deposition treatment we can unlock the full potential of polycrystalline semiconductor materials and propel the advancement of clean energy technologies”.
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The researchers’ pioneering atomic force microscopy tomography and data analysis methods, showcased in this study, are not only applicable to CIGS thin-film solar cells but hold promise for a wide range of polycrystalline semiconductor and energy materials. This breakthrough opens new avenues for research and development across the renewable energy landscape.
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As the world seeks sustainable solutions to address the growing demand for clean energy, this research marks a significant step forward in harnessing the power of thin-film solar cells, bringing us one step closer to a greener and more sustainable future.
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