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TAP TIMES -28- OCTOBER 2022

Solar material (from 27) by Xiaoqing Pan at UC Irvine uncovered
more evidence of CGB’s ferroelectricity: a

Through these calculations, which take “displaced” atomic structure offset by the
atomic structure and chemical species germanium center.
as input and can predict properties such
as the electronic structure and ferroelec- Switchable polarity
tricity, Griffin and her team zeroed in on Meanwhile, electrical measurement experi-
CGB, the only all-inorganic perovskite that ments carried out in the Ramesh lab by
checked off all the boxes on the research- Zhang and Eric Parsonnet, a UC Berkeley
ers’ ferroelectric perovskite wish list. physics graduate student researcher and
co-author on the study, revealed a switch-

Like a rhombohedran able polarity in CGB, satisfying yet another
Is it asymmetrical? Yes, its atomic struc- requirement for ferroelectricity.
ture looks like a rhombohedran, rect-
angle’s crooked cousin. Is it really a But a final experiment — photoconductiv-
perovskite? Yes, its chemical formula – Ce- ity measurements in Yang’s UC Berkeley
GeBr – matches the perovskite’s telltale lab — yielded a delightful result, and a
3
structure of ABX3. surprise.

The researchers theorized that the asym- Tunable light absorption
metric placement of germanium in the The researchers found that CGB’s light ab-
center of the crystal would create a poten- sorption is tunable — spanning the spec-
tial that, like an electric field, separates trum of visible to ultraviolet light (1.6 to
positive electrons from negative electrons 3 electron volts), an ideal range for coax-
to produce electricity. But were they right? ing high energy conversion efficiencies in
a solar cell, Yang said. Such tunability is
Tiny nanowires rarely found in traditional ferroelectrics, he
To find out, Zhang grew tiny nanowires noted.
(100 to 1,000 nanometers in diameter)
and nanoplates (around 200 to 600 nano- Yang says there is still more work to be
meters thick and 10 microns wide) of done before the CGB material can make
single-crystalline CGB with exceptional its debut in a commercial solar device, but
control and precision. he’s excited by the results so far. lbl.gov

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talline structure, a signal of ferroelectric- TAP TIMES taptimes.com
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