Scientists from the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) plan to build a thermochromic photovoltaic window to generate power and reduce the need for air conditioning.
The scientists presented their findings in “Reversible multicolor chromism in layered formamidinium metal halide perovskites,” which was recently published in Nature Communications. The new “thermochromic photovoltaic” window technology is based on a thermochromic solar window developed in an earlier study by the same NREL scientists in 2017. This window darkens as the sun heats its surface, producing electricity through perovskite film embedded within the material.
“The first-generation solar window was able to switch back and forth between transparent and a reddish-brown color, requiring temperatures between 150 F (65.6 C) and 175 F to trigger the transformation,” the research team explained. “The latest iteration allows a broad choice of colors and works at 95 F to 115 F, a glass temperature easily achieved on a hot day.”
They improved the color transformation via different chemical compositions and materials. They also sped up this process from around three minutes to just seven seconds. A formamidinium metal halide perovskite (MHP) – an inherently thermochromic material exhibiting significant optical changes – was embedded between two layers of glass, and vapor was then injected into the layers.
“We synthesize composite films composed of layered formamidinium-based MHPs of the general formula FAn+1PbnX3n+1 (X = I, Br) and their mixed-halide compositions,” the scientists said.
The vapor triggers a reaction that makes the perovskite arrange itself by taking on different shapes. “The colors emerge with the changing shapes,” the scientists explained. “Lowering the humidity returns the perovskite to its normal transparent state.”
The NREL group said that it will develop the first window prototype within a year. It will conduct additional research to determine the number of times the thermochromic window can be cycled into an electricity-generating operating mode.
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