A group of scientists at the Okinawa Institute of Science and Technology (OIST) in Japan has created a high-quality version of one of the most promising halide perovskites – the α-formamidinium lead iodide known as α-FAPbI3 — for applications in absorber layers of solar cells.
The researchers explained that this perovskite material is fabricated by combining lead(II) iodide (PbI2) and formamidinium iodide (FAI) and that the reaction between them produces FAPbI3. “But this method is far from perfect,” they also specified. “There are often leftovers of one or both of the original materials, which can impede the efficiency of the solar cell.”
The Japanese group applied what it describes as a more precise powder engineering method consisting of adding formamidinium acetate (FAAc) and hydroiodic acid (HI) to PbI2, heating the mixture to 90 degrees Celsius, and then dissolving and filtering out impurities or unreacted materials. “When the perovskite’s absorber layer was formed from the original reaction, it was stable at high temperatures,” it further explained. “However, at room temperature, it turned from brown to yellow, which wasn’t ideal for absorbing light. The synthesized version was brown even at room temperature.”
This perovskite powder was used to build a small-area solar cell with a power conversion efficiency of over 23.5% and a lifespan of more than 2,000 hours. With this cell, the academics were also able to build a 5 x 5 cm2 small-sized module with an efficiency of around 14%. “Our next step is to make a solar module that is 15 x 15 cm2 and has an efficiency of more than 15%,” said research co-author Guoqing Tong. “One day I hope we can power a building at OIST with our solar modules.”
The technique to fabricate the special perovskite powder is presented in the study “Removal of residual compositions by powder engineering for high efficiency formamidinium-based perovskite solar cells with operation lifetime over 2000 h,” published in Nano Energy.
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