Defects
at the grain boundary provide sites for nonradiative recombination
in halide perovskite solar cells (PSCs). Here, by polymerization and
fluorination of a Lewis acid of 4,4-bis(4-hydroxyphenyl)pentanoic
acid, a fluorinated oligomer (FO-19) is synthesized and applied to
passivate these defects in methlyammonium lead iodide (MAPbI3). It is demonstrated that the carboxyl bond of FO-19 was coordinated
with Pb ions in the perovskite films to achieve a wrapping effect
on the perovskite crystals. The defects of perovskite film are effectively
passivated, and the undesirable nonradiative recombination is greatly
inhibited. As a result, FO-19 gives a power conversion efficiency
of 21.23% for the inverted MAPbI3-based PSCs, which is
among the highest reported values in the literature. Meanwhile, the
corresponding device with FO-19 exhibits significantly improved humidity
and thermal stability. Therefore, this work offers insights into the
realization of high-efficiency and stable PSCs through fluorinated
additive engineering.
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