Colorful perovskites: Thermochromic window technologies
Research developments create faster changes at lower temperatures, more
colors

Date:
October 20, 2020
Source:
DOE/National Renewable Energy Laboratory
Summary:
Scientists report a breakthrough in developing a next-generation
thermochromic window that not only reduces the need for air
conditioning but simultaneously generates electricity.



FULL STORY ========================================================================== Scientists at the U.S. Department of Energy's National Renewable Energy Laboratory (NREL) report a breakthrough in developing a next-generation thermochromic window that not only reduces the need for air conditioning
but simultaneously generates electricity.


==========================================================================
Heat generated by sunlight shining through windows is the single
largest contributor to the need for air conditioning and cooling in
buildings. Because residential and commercial buildings use 74% of all electricity and 39% of all energy in the United States, the shading
effect from tinting windows helps buildings use less energy.

The technology, termed "thermochromic photovoltaic," allows the window
to change color to block glare and reduce unwanted solar heating when
the glass gets warm on a hot, sunny day. This color change also leads
to the formation of a functioning solar cell that generates on-board
power. Thermochromic photovoltaic windows can help buildings turn into
energy generators, increasing their contribution to the broader energy
grid's needs. The newest breakthrough now enables myriad colors and a
broader range of temperatures that drive the color switch. This increases design flexibility for improving energy efficiency as well as control
over building aesthetics that is highly desirable for both architects
and end users.

The research builds upon earlier work at NREL into a thermochromic window
that darkened as the sun heated its surface. As the window shifted
from transparent to tinted, perovskites embedded within the material
generated electricity.

Perovskites are a crystalline structure shown to have remarkable
efficiency at harnessing sunlight.

"A prototype window using the technology could be developed within
a year," said Bryan Rosales, a postdoctoral researcher at NREL and
lead author of the paper, "Reversible Multicolor Chromism in Layered Formamidinium Metal Halide Perovskites," which appears in the journal
Nature Communications. His co- authors from NREL are Lance Wheeler, who developed the first thermochromic photovoltaic window, Taylor Allen,
David Moore, Kevin Prince, Garry Rumbles, and Laura Schelhas. Other
authors are Laura Mundt from SLAC National Accelerator Laboratory,
and Colin Wolden from Colorado School of Mines.

The first-generation solar window was able to switch back and forth
between transparent and a reddish-brown color, requiring temperatures
between 150 degrees and 175 degrees Fahrenheit to trigger the
transformation. The latest iteration allows a broad choice of colors
and works at 95 degrees to 115 degrees Fahrenheit, a glass temperature
easily achieved on a hot day.

By using a different chemical composition and materials, the researchers
also were able to rapidly speed up the color transformation. The time was reduced to about seven seconds from the three minutes it took during the proof-of-concept thermochromic photovoltaic window demonstrated in 2017.

The scientists sandwiched a thin perovskite film between two layers of
glass and injected vapor. The vapor triggers a reaction that causes the perovskite to arrange itself into different shapes, from a chain to a
sheet to a cube. The colors emerge with the changing shapes. Lowering
the humidity returns the perovskite to its normal transparent state.


========================================================================== Story Source: Materials provided by
DOE/National_Renewable_Energy_Laboratory. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Bryan A. Rosales, Laura E. Mundt, Taylor G. Allen, David T. Moore,
Kevin
J. Prince, Colin A. Wolden, Garry Rumbles, Laura T. Schelhas,
Lance M.

Wheeler. Reversible multicolor chromism in layered formamidinium
metal halide perovskites. Nature Communications, 2020; 11 (1) DOI:
10.1038/ s41467-020-19009-z ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201020131401.htm

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