SCIENCE sciencemag.org 6 MARCH 2020 • VOL 367 ISSUE 6482 1088-C
role in regulating the develop-
ment of TEP cells. —AB
Sci. Immunol. 5 , eaax1036 (2020).
SOLAR CELLS
Tuning band gaps
with three halides
Tandem solar cells can boost
solar cell efficiency by using two
active layers to absorb the solar
spectrum more completely,
provided that the two cells are
current-matched. Inorganic-
organic perovskites tuned to
the appropriate wide band gap
(~1.7 electron volts) as top cells
that contained iodine and bro-
mine or bromine and chlorine
have short carrier diffusion
lengths and undergo photo-
induced phase segregation.
Xu et al. now report a method
for incorporating chloride that
allows for fabrication of stable
triple-halide perovskites with a
band gap of 1.67 electron volts.
Two-terminal tandem silicon
solar cells made with this mate-
rial had a power conversion
efficiency of 27%. —PDS
Science, this issue p. 1097
ELECTRON MICROSCOPY
Seeing single silicon
atom vibrations
Vibrational spectroscopy can
achieve high energy resolu-
tion, but spatial resolution of
unperturbed vibrations is more
difficult to realize. Hage et
al. show that a single-atom
impurity in a solid (a silicon
atom in graphene) can give
rise to distinctive localized
vibrational signatures. They
used high-resolution electron
energy-loss spectroscopy in a
scanning transmission electron
microscope to detect this signal.
An experimental geometry was
chosen that reduced the relative
elastic scattering contribution,
and repeated scanning near
the silicon impurity enhanced
the signal. The experimental
vibration frequencies are in
agreement with ab initio calcula-
tions. —PDS
Science, this issue p. 1124
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