4.2. Hysteresis and stability
Perovskite solar cells have achieved a great success with effi-
ciencies now exceeding 20%. However, a certain class of perovskite
solar cell, particularly organometal trihalide perovskites, exhibits
photocurrent hysteresis. Therefore, it is essential that the origins
and mechanisms of the I–V hysteresis are fully understood to
minimize or eradicate these hysteresis effects for practical applications.
This hysteresis has been tentatively attributed to the paraelectric
or ferroelectric properties of perovskites at room temperature
and above [144,145]. Simulations suggest that the internal
electrical fields associated with microscopic polarization
domains contribute to hysteretic anomalies in the current–voltage
response of PSCs due to variations in electron–hole recombination
in the bulk [144]. However, others would suggest that, because of
its low lattice energy, organometal halide perovskite tends to
possess strong ionic characteristics, which is sensitive to polarization
in an electric field [145]. Impedance study shows that a
high value of the dielectric constant at low frequencies resulting
from a combination of dipolar, ionic and electronic contributions is
the main reason for the J/V hysteresis [146].