1702365 (1 of 7)
2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Reverse Bias Behavior of Halide Perovskite Solar Cells
Andrea R. Bowring, Luca Bertoluzzi, Brian C. O’Regan, and Michael D. McGehee*
solar cells have a breakdown voltage (V
at which current starts to ﬂow in reverse
bias. When current ﬂows in reverse bias,
the shaded cell dissipates power rather
than producing it, and this can cause local
heating, which damages the cell.
Silicon cells generally breakdown in
reverse bias by avalanche breakdown; the
carriers gain enough kinetic energy from
the applied electric ﬁeld to generate addi-
tional carriers through impact ionization.
s for silicon cells are typically >15 V. If
the pn junction is highly doped, the deple-
tion width can narrow enough to allow
tunneling in reverse bias. With either mech-
anism, breakdown current can get localized
by uneven doping, crystalline defects, trace
processing contaminants, etch sites, or
edge effects causing damaging hot spots.
CIGS and CdTe exhibit V
s < 10 V and a decrease in
under illumination. This has been attributed to tun-
neling through defects at the buffer layer/CIGS interface.
Partial shading has been shown to cause local current ﬂow
and the damage is exacerbated by the light dependence of
, which causes even more of the current to selectively
ﬂow through the illuminated region. This can cause localized
shunting those results primarily in a permanent decrease in ﬁll
Stability in reverse bias has not been explored for perovskite
solar cells, but there have been studies of MAPbI
which require biasing in both forward and reverse
directions, and photodetectors, which function in reverse bias.
Some memristors operate via the formation of metallic ﬁlaments
through the perovskite
and others seem to function based
on mobile defects in the perovskite.
Photodiodes of the
structure ﬂuorine-doped tin oxide (FTO)/porous TiO
Spiro-OMeTAD/Au show current multiplication in reverse bias,
which has been attributed to mobile ion accumulation.
ions have also been used to explain hysteresis in current–voltage
In most cells, preconditioning at lower volt-
ages makes cells worse, which is why scans from J
to give lower efﬁciencies. It has also been demonstrated that
mobile ions can cause band bending that can turn a symmetric
device with nonselective contacts into a diode that functions as a
Mobile ions likely also play an important role in the
behavior of perovskite solar cells in reverse bias.
In this paper, we ﬁrst present a phenomenological study
of reverse bias breakdown in halide perovskite solar cells.
We characterize cells that have been held at constant current
in the dark as they would be in a series connected module if
only one cell were completely shaded. We also provide constant
voltage measurements. We show how the reverse breakdown
The future commercialization of halide perovskite solar cells relies on
improving their stability. There are several studies focused on understanding
degradation under operating conditions in light, but little is known about the
stability of these solar cells under reverse bias conditions. Reverse bias sta-
bility is important because shaded cells in a module are put into reverse bias
by the illuminated cells. In this paper, a phenomenological study is presented
of the reverse bias behavior of halide perovskite solar cells and it is shown
that reverse bias can lead to a partially recoverable loss in efﬁciency, primarily
caused by a decrease in V
. A general mechanism is proposed, supported by
drift–diffusion simulations, to explain how these cells breakdown via tun-
neling caused by accumulated ionic defects and suggests that the reversible
loss in efﬁciency may be due to an electrochemical reaction of these defects.
Finally, the implications of these phenomena are discussed and how they can
possibly be addressed is also discussed.
Dr. A. R. Bowring, Dr. L. Bertoluzzi, Prof. M. D. McGehee
Department of Materials Science and Engineering
Stanford, CA 94305, USA
Dr. B. C. O’Regan
Berkeley, CA 94707, USA
The ORCID identiﬁcation number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/aenm.201702365.
Perovskite Solar Cells
Halide perovskite solar cells have experienced an extraordi-
nary rise in efﬁciency over the past few years, with record efﬁ-
ciencies for single junctions of 22.1%.
involving perovskites also exhibit impressive efﬁciencies of
23.6% for perovskite-on-silicon
and 19.0% for perovskite-
Halide perovskites are especially promising
because they are solution processed at low temperatures, which
could allow inexpensive manufacturing. One reason for the
high performance of these devices despite their polycrystallinity
is that the ionic defects that are likely to form have energies
near the band edges.
Now that high efﬁciencies have been achieved, the next con-
cern is whether these cells are stable under realistic operating
There have been promising reports of stable per-
formance over 1000 h at the maximum power point by changing
composition and contacts.
One important stability concern
that has not been addressed yet is stability in reverse bias. In a
solar cell module, a shaded cell ends up in reverse bias by being
forced to pass the photocurrent of its unshaded neighbors. All
Adv. Energy Mater. 2018, 8, 1702365