2 research outputs found
Determination of Mobile Ion Densities in Halide Perovskites via Low-Frequency Capacitance and Charge Extraction Techniques
Mobile ions in perovskite photovoltaic devices can hinder
performance
and cause degradation by impeding charge extraction and screening
the internal field. Accurately quantifying mobile ion densities remains
a challenge and is a highly debated topic. We assess the suitability
of several experimental methodologies for determining mobile ion densities
by using drift-diffusion simulations. We found that charge extraction
by linearly increasing voltage (CELIV) underestimates ion density,
but bias-assisted charge extraction (BACE) can accurately reproduce
ionic lower than the electrode charge. A modified Mott–Schottky
(MS) analysis at low frequencies can provide ion density values for
high excess ionic densities, typical for perovskites. The most significant
contribution to capacitance originates from the ionic depletion layer
rather than the accumulation layer. Using low-frequency MS analysis,
we also demonstrate light-induced generation of mobile ions. These
methods enable accurate tracking of ionic densities during device
aging and a deeper understanding of ionic losses
Interface Modification for Energy Level Alignment and Charge Extraction in CsPbI<sub>3</sub> Perovskite Solar Cells
In perovskite solar
cells (PSCs) energy level alignment and charge
extraction at the interfaces are the essential factors directly affecting
the device performance. In this work, we present a modified interface
between all-inorganic CsPbI3 perovskite and its hole-selective
contact (spiro-OMeTAD), realized by the dipole molecule trioctylphosphine
oxide (TOPO), to align the energy levels. On a passivated perovskite
film, with n-octylammonium iodide (OAI), we created
an upward surface band-bending at the interface by TOPO treatment.
This improved interface by the dipole molecule induces a better energy
level alignment and enhances the charge extraction of holes from the
perovskite layer to the hole transport material. Consequently, a Voc of 1.2 V and a high-power conversion efficiency
(PCE) of over 19% were achieved for inorganic CsPbI3 perovskite
solar cells. Further, to demonstrate the effect of the TOPO dipole
molecule, we present a layer-by-layer charge extraction study by a
transient surface photovoltage (trSPV) technique accomplished by a
charge transport simulation