Organic–inorganic
lead trihalide perovskites have emerged
as an outstanding photovoltaic material that demonstrated a high 17.9%
conversion efficiency of sunlight to electricity in a short time.
We have found a giant dielectric constant (GDC) phenomenon in these
materials consisting on a low frequency dielectric constant in the
dark of the order of ε0 = 1000. We also found an
unprecedented behavior in which ε0 further increases
under illumination or by charge injection at applied bias. We observe
that ε0 increases nearly linearly with the illumination
intensity up to an additional factor 1000 under 1 sun. Measurement
of a variety of samples of different morphologies, compositions, and
different types of contacts shows that the GDC is an intrinsic property
of MAPbX3 (MA = CH3NH3
+). We hypothesize that the large dielectric response is induced by
structural fluctuations. Photoinduced carriers modify the local unit
cell equilibrium and change the polarizability, assisted by the freedom
of rotation of MA. The study opens a way for the understanding of
a key aspect of the photovoltaic operation of high efficiency perovskite
solar cells.
A new iridium complex, IrCp*Cl(PyPyz)[TFSI], has been synthesized and used as additive for the hole transporter material, spiro-OMeTAD, in perovskite solar cells. The cells prepared with this Ir additive present higher efficiency than reference cells, and similar to cells prepared with Co additive. We have determined that the presence of metal complexes as additives decreases the recombination rate, as it has been observed by impedance spectroscopy. Very interestingly, while the efficiency after 3 months decreases by 22% and 70% for reference cell and cell with Co additive, respectively, the efficiency of devices containing the Ir additive is only decreased by a 4%.
A {Tb(α-fur)3}n one-dimensional complex shows Single-Chain-Magnet (SCM) behavior at H = 0 in two different types of antiferromagnetic transverse chains (A and B), triggered by the existence of defects breaking the chains into segments with short-range order.
Determination of stable phases formed at the Fe/Si interface in (Fe/Si)n structure, grown by thermal evaporation in an ultrahigh vacuum system was performed using conversion electron Mössbauer spectroscopy (CEMS).
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