25 research outputs found
Competition between Polar and Antiferrodistortive Modes and Correlated Dynamics of the Methylammonium Molecules in MAPbI from Anelastic and Dielectric Measurements
The mechanisms behind the exceptional photovoltaic properties of the
metallorganic perovskites are still debated, and include a ferroelectric (FE)
state from the ordering of the electric dipoles of the organic molecules. We
present the first anelastic (complex Young's modulus) and new dielectric
measurements on CHNHPbI, which provide new insight on the
reorientation dynamics of the organic molecules, and the reason why they do not
form a FE state. The permittivity is fitted within the tetragonal phase with an
expression that includes the coupling between FE and octahedral tilt modes,
indicating that the coupling is competitive and prevents FE ordering. The onset
of the orthorhombic phase is accompanied by sharp stiffening, analogous to the
drop of permittivity, due to the hindered molecular dynamics. On further
cooling, an intense anelastic relaxation process without a dielectric
counterpart suggests the reorientation of clusters of molecules with strong
antiferroelectric correlations.Comment: accepted in J. Phys. Chem. Let
Stability of Cubic FAPbI from X-ray Diffraction, Anelastic, and Dielectric Measurements
Among the hybrid metal-organic perovskites for photovoltaic applications
FAPbI_3 (FAPI) has the best performance regarding efficiency and the worst
regarding stability, even though the reports on its stability are highly
contradictory. In particular, since at room temperature the cubic alpha phase,
black and with high photovoltaic efficiency, is metastable against the yellow
hexagonal delta phase, it is believed that alpha-FAPI spontaneously transform
into delta-FAPI within a relatively short time. We performed X-ray diffraction
and thermogravimetric measurements on loose powder of FAPI, and present the
first complete dielectric and anelastic spectra of compacted FAPI samples under
various conditions. We found that alpha-FAPI is perfectly stable for at least
100 days, the duration of the experiments, unless extrinsic factors induce its
degradation. In our tests, degradation was detected after exposure to humidity,
strongly accelerated by grain boundaries and the presence of delta phase, but
it was not noticeable on the loose powder kept in air under normal laboratory
illumination. These findings have strong implications on the strategies for
improving the stability of FAPI without diminishing its photovoltaic efficiency
through modifications of its composition
Titanium and Ruthenium Phthalocyanines for NO2 Sensors: A Mini-Review
This review presents studies devoted to the description and comprehension of phenomena connected with the sensing behaviour towards NO2 of films of two phthalocyanines, titanium bis-phthalocyanine and ruthenium phthalocyanine. Spectroscopic, conductometric, and morphological features recorded during exposure to the gas are explained and the mechanisms of gas-molecule interaction are also elucidated. The review also shows how X-ray reflectivity can be a useful tool for monitoring morphological parameters such as thickness and roughness that are demonstrated to be sensitive variables for monitoring the exposure of thin films of sensor materials to NO2 gas
Spectroscopic and Morphological Studies of Metal-Organic and Metal-Free Dyes onto Titania Films for Dye-Sensitized Solar Cells
We have investigated the spectroscopic behavior of three different sensitizers adsorbed onto titania thin films in order to gain information both on the electron transfer process from dye to titania and on the anchorage of the chromophore onto the semiconductor. We have examined by UV-Vis and fluorescence spectroscopy the widely used ruthenium complex cis-di(thiocyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylato)ruthenium(II) (N719), the more recently developed organic molecular 3-(5-(4-(diphenylamino)styryl)thiophen-2-yl)-2-cyanoacrylic acid (D5), and a push-pull zinc phthalocyanine sensitizer (ZnPc). Three type of titania films with different morphology, characterized by SEM and FT-IR measurement, were considered: a mesoporous transparent film deposited by spin-coating (TiMS), a semiopaque film deposited by doctor-blade from mesoporous titania (TiMS_DB) and a semiopaque film deposited by doctor-blade form commercial P25 titania (P25_DB). The use of TiMS is responsible for the adsorption of a higher amount of dye since the mesoporous structure allows increasing the interfacial area between dye and titania. Moreover, the fluorescence emission peak is weaker when the sensitizers are adsorbed onto TiMS. These findings suggest that mesostructured films could be considered the most promising substrates to realize photoanodes with a fast electron transfer process
Consigli pratici per il corretto utilizzo del catetere vescicale in pediatria
Urinary catheters are invasive devices, frequently employed in hospitals and nursing home settings to maintain urine output in patients, both for diagnostic and therapeutic
aspects. There are many Guidelines concerning their use and application in adults, but specific indications for children are not actually available. The aim of the present paper is to identify medical recommendations to understand better how, when and why to use them, in order to help paediatricians in their prescription and nurses in their positioning.
Moreover, two clinical final case reports show the possible onset of complications due to
their invasive positioning procedure. However, risks are not enough to restrict their use
when necessary
Competition between Polar and Antiferrodistortive Modes and Correlated Dynamics of the Methylammonium Molecules in MAPbI<sub>3</sub> from Anelastic and Dielectric Measurements
The
mechanisms behind the exceptional photovoltaic properties of
the metallorganic perovskites are still debated and include a ferroelectric
(FE) state from the ordering of the electric dipoles of the organic
molecules. We present the first anelastic (complex Young’s
modulus) and new dielectric measurements on CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub>, which provide new insight into the reorientation
dynamics of the organic molecules and the reason why they do not form
a FE state. The permittivity is fitted within the tetragonal phase
with an expression that includes the coupling between FE and octahedral
tilt modes, indicating that the coupling is competitive and prevents
FE ordering. The onset of the orthorhombic phase is accompanied by
sharp stiffening, analogous to the drop of permittivity, due to the
hindered molecular dynamics. On further cooling, an intense anelastic
relaxation process without a dielectric counterpart suggests the reorientation
of clusters of molecules with strong antiferroelectric correlations
Metal–organic green dye: chemical and physical insight into a modified Zn-benzoporphyrin for dye-sensitized solar cells
A novel green benzoporphyrin has been synthesized, characterized, studied by theoretical methods and tested in DSSC devices. Ab initio simulations predict the actual charge displacement during S0 → S1 excitation.</p