Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Slowed Recombination via Tunable Surface Energetics in Perovskite Solar
  Cells   Metal halide perovskite semiconductors have the potential to reach the
optoelectronic quality of meticulously grown inorganic materials, but with a
distinct advantage of being solution processable. Currently, perovskite
performance is limited by charge carrier recombination loss at surfaces and
interfaces. Indeed, the highest quality perovskite films are achieved with
molecular surface passivation, for example with n-trioctylphosphine oxide, but
these treatments are often labile and electrically insulating. As an
alternative, the formation of a thin 2D perovskite layer on the bulk 3D
perovskite reduces non-radiative energy loss while also improving device
performance. But, thus far, it has been unclear how best to design and optimize
2D/3D heterostructures and whether critical material properties, such as charge
carrier lifetime, can reach values as high as ligand-based approaches. Here, we
study perovskite devices that have exhibited power conversion efficiencies
exceeding 25% and show that 2D layers are capable of pushing beyond molecular
passivation strategies with even greater tunability. We set new benchmarks for
photoluminescence lifetime, reaching values > 30 {\mu}s, and perovskite/charge
transport layer surface recombination velocity with values < 7 cm s^{-1}. We
use X-ray spectroscopy to directly visualize how treatment with hexylammonium
bromide not only selectively targets defects at surfaces and grain boundaries,
but also forms a bandgap grading extending > 100 nm into the bulk layer. We
expect these results to be a starting point for more sophisticated engineering
of 2D/3D heterostructures with surface fields that exclusively repel charge
carriers from defective regions while also enabling efficient charge transfer.
It is likely that the precise manipulation of energy bands will enable
perovskite-based optoelectronics to operate at their theoretical performance
limits.

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The categories of this paper are: patt-sol
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The categories of this paper are: atom-ph
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The categories of this paper are: econ
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-lat
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The categories of this paper are: eess
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The categories of this paper are: funct-an
10
The categories of this paper are: q-bio
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: hep-ex
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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th