Researchers at France's National Solar Energy Institute (INES) – an arm of the French Alternative Energies and Atomic Energy Commission (CEA) –have developed a perovskite solar cell on a flexible substrate with an efficiency of 19.2%.
The scientists explained that the same cell had achieved an efficiency of 20.2% for a cell with a size of 11cm2 based on a rigid glass substrate and that the cell technology was transposed onto a flexible substrate by adapting the thickness of the active layer to the optical specificities of the substrate made of indium tin oxide (ITO) and polyethylene terephthalate (PET).
The flexible single-junction solar cell has an area of 0.33cm² and is built with a double layer of cesium and formamidinium, which the researchers said offers promising stability results compared to technologies using a methylammonium type cation, which is more thermally unstable.
The cell was tested through a damp heat test, which is an accelerated environmental aging test that determines the ability of a PV device to withstand long-term exposure to high temperature and penetration of humidity. It showed that the perovskite cell can retain around 90% of its initial efficiency after 800 hours.
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The scientists specified that the achieved conversion efficiency is not the highest for this perovskite cell technology, which in previous research has reached up to 21%, although with smaller cell surfaces, but they stated it is the first time a very strong performance has been obtained with a low-cost substrate such as PET. “Our technology combines simplicity and performance,” they affirmed.
The cell is being developed under the EU-funded Apolo research project. CEA-INES and other partners are working on advanced materials, from cell to encapsulant, to develop flexible, fully printable perovskite cells with an efficiency of at least 22% and 80% of initial performance after relevant accelerated-test standards.
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Have they tested the device at damp heat for 800 hours and obsereved a 90% retention, or is the 800 hours figure the extrapolated period under normal operating conditions? If the former, how does this correspond to rates of performance degredation at various operating humidity and temperature profiles?