1 research outputs found
Interface-Dependent Ion Migration/Accumulation Controls Hysteresis in MAPbI<sub>3</sub> Solar Cells
Hysteresis
in the current–voltage characteristics of hybrid
organic–inorganic perovskite-based solar cells is one of the
fundamental aspects of these cells that we do not understand well.
One possible cause, suggested for the hysteresis, is polarization
of the perovskite layer under applied voltage and illumination bias,
due to ion migration <i>within the perovskite</i>. To study
this problem systemically, current–voltage characteristics
of both regular (light incident through the electron conducting contact)
and so-called inverted (light incident through the hole conducting
contact) perovskite cells were studied at different temperatures and
scan rates. We explain our results by assuming that the effects of
scan rate and temperature on hysteresis are strongly correlated to
ion migration within the device, with the rate-determining step being
ion migration at/across the interfaces of the perovskite layer with
the contact materials. By correlating between the scan rate with the
measurement temperature, we show that the inverted and regular cells
operate in different hysteresis regimes, with <i>different</i> activation energies of 0.28 ± 0.04 eV and 0.59 ± 0.09
eV, respectively. We suggest that the differences observed between
the two architectures are due to different rates of ion migration
close to the interfaces, and conclude that the diffusion coefficient
of migrating ions in the inverted cells is 3 orders of magnitude higher
than in the regular cells, leading to different accumulation rates
of ions near the interfaces. Analysis of <i>V</i><sub>OC</sub> as a function of temperature shows that the main recombination mechanism
is trap-assisted (Shockley-Read Hall, SRH) in the space charge region,
similar to what is the case for other thin film inorganic solar cells