As all-inorganic perovskite (CsPbI3–x
Br
x
)
is prone to phase transition
from the α phase (black phase) to the δ phase (yellow
phase) in a humid environment or under heating, improving the phase
stability of all-inorganic perovskite of the black phase is one of
the urgent problems to solve. Herein, 1,2-dimethyl-3-acetylimidazolium
iodide (DMAII) is spin-coated onto the surface of CsPbI3–x
Br
x
perovskite for use
in p–i–n perovskite solar cells (PSCs). We find that
the DMAII coating has two effects on the CsPbI3–x
Br
x
perovskite film:
surface passivation and phase stabilization of perovskite. Traps in
the CsPbI3–x
Br
x
perovskite film can be reduced significantly by DMAII passivation,
resulting in enhanced hole extraction and suppressed charge recombination.
Consequently, the power conversion efficiency (PCE) is improved from
10.81 to 13.14%. Moreover, the DMAII coating can significantly inhibit
the phase transition from the α phase to the δ phase in
a humid environment or under heating, as characterized by the X-ray
diffraction pattern, UV–vis absorption spectrum, and film color.
After exposing the CsPbI3–x
Br
x
perovskite films to a humid atmosphere (relative
humidity = 40–60%) for 6 h, the PCE decreases dramatically
to only 0.12% of the initial PCE for the PSC without the DMAII coating,
while the PCE maintains 80% of the initial PCE for the PSC with the
DMAII coating. In addition, when the PSC devices are heated at 120
°C for 4 h, the control PSC shows a 96% decrease in PCE, while
the PCE decay is only 9% for the DMAII-coated PSC. These findings
indicate that carboxyl-substituted imidazolium iodide is a kind of
promising material to not only passivate traps but also stabilize
the black phase of all-inorganic perovskite.