400-C 28 JANUARY 2022 • VOL 375 ISSUE 6579 science.org SCIENCE
RESEARCH
pollen precursor cells and grains
through the 26 days from the
beginning of meiosis to pollen
shed. These data reveal that
about halfway through pollen
development, the pollen grain’s
haploid genome wrests control
from the going-away supplies
left by the parental, diploid
genome. With this sporophyte-
to-gametophyte transition, the
foundations are set for the next
generation. —PJH
Science, abl7392, this issue p. 424
SOLAR CELLS
Inverted solar cells’
surface sulfidation
Perovskite solar cells (PSCs) with
high power conversion efficiency
(PCE) and stability have been
reported in regular n-i-p devices,
but inverted p-i-n PSCs that could
be easier to use in tandem solar
cells usually have lower PCEs
(22 to 23%). Li et al. sulfurized a
lead-rich layer with hexamethyl-
disilathiane, and the lead-sulfur
bonds shifted the Fermi level
of perovskite-transporter layer
interface to create an electric field
that enhanced electron extrac-
tion. The inverted PSCs had PCEs
24%, and the strong lead-sulfur
bonds helped to maintain >90%
of this efficiency during illumi-
nated operation for 1000 hours at
55°C and after dark aging at 85°C
for 2200 hours. —PDS
Science, abl5676, this issue p. 434
2D MATERIALS
Displacing the
Fermi surface
Electrons that contribute to
electrical conduction in a metal
typically occupy high energy
levels near the Fermi level. To
get electrons from lower bands
to join the flow, extremely large
electric fields would be needed.
In graphene and its superlat-
tices, Berdyugin et al. show that
small, experimentally accessible
fields are sufficient to achieve
this regime. The researchers
discerned the signatures of this
highly nonequilibrium state in
transport data. —JS
Science, abi8627, this issue p. 430