Thermodynamically
induced tensile stress in the perovskite film
will lead to the formation of atomic vacancies, seriously destroying
the photovoltaic efficiency stability of the perovskite solar cells
(PSCs). Among them, cations and halide anions vacancies are unavoidable;
these point vacancies are considered to be a major source of the ionic
migration and perovskite degradation at the crystal boundary and surface
of the perovskite films. Here, we use choline bromide to modify the
perovskite film by occupying the atomic defects in the CsPbBr3 perovskite film. The results show that the zwitterion quaternary
ammonium ions and bromide ions in choline bromide can simultaneously
occupy the Cs+ cation and Br– anions
vacancies in the perovskite film by the ionic bonding effect, for
which the defect-state density on the surface of the perovskite film
can be significantly reduced, leading to the effective enhancement
of carrier lifetime. In addition, the residual stress at the crystal
boundary can be effectively reduced by lowering the Young’s
modulus in the CsPbBr3 perovskite film. As a result, the
optimized device achieves a photoelectric conversion efficiency (PCE)
of 9.06% with an increase of 41.1% compared to the control device
with a PCE of 6.42%. Most importantly, the newborn thermal stress
due to thermal expansion during heat working conditions can be transferred
from the polycrystalline perovskite to the carbon layer by the matched
Young’s modulus, thus resulting in improved stability perovskite
film under environmental conditions. The work provides new insights
for preparing high-quality perovskite films with low defect-state
density and residual stress.
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