Detection and relevance of ion conduction in hybrid organic-inorganic halide perovskites for photovoltaic applications

In recent years, hybrid organic-inorganic halide perovskites have attracted much attention with respect to their potential use as sensitizers in solar cells.[1] These materials show many outstanding properties, such as high absorption coefficients, ideal bandgap for solar light absorption (1.5 eV), long electron-hole recombination lengths and high charge carrier mobilities[1-3], that leads to a photo-conversion efficiency of hybrid-perovskite-containing devices exceeding 20%.[4] However, anomalous behaviors have been reported for these materials, such as high apparent dielectric constants at low AC frequencies or photocurrent hysteresis of solar cell devices during operation.[5] In this study[6] we measure the electrical transport properties of CH3NH3PbI3, by means of DC galvanostatic polarization, AC impedance spectroscopy and open circuit voltage measurements in electrochemical cells. By using ion-blocking electrodes, we detect a clear stoichiometric polarization behavior, from which we can separate electronic and ionic contributions to the total conductivity. We show that, under certain conditions, ionic conductivity can substantially exceed electronic conductivity and we assess the nature of the migrating ions (iodine ions). It is noteworthy that such ionic conductivity can naturally explain the above mentioned anomalies (Figure 1). Moreover, from the experimental data, a strong trapping of the electronic carriers due to ionic defects is ascertained. As a natural follow-up to better understand the defect chemistry of such materials, conductivity response to different atmospheres (I2, O2) has been measured and acceptor doping has been successfully applied. Please click Additional Files below to see the full abstract

Non-stoichiometry and ion transport in halide perovskites: Equilibrium situation and light effects

In recent years, hybrid halide perovskites have been attracting great attention due to their exceptional photo-electrochemical properties.[1-2] When used as light-harvesters in solar cells, device efficiencies exceeding 22% can be realized. We showed that a deeper understanding of (i) functionality, (ii) stability, as well as (iii) the possibility to improve the performance require a thorough insight into non-stoichiometry and ion transport.[3-5] In this contribution, we study the nature of the ionic conductivity in methylammonium lead iodide (MAPbI3), the archetypal halide perovskite, by means of a great number of electrochemical and nuclear magnetic techniques.[4] To aid the experimental investigation, we include detailed defect chemical modelling describing the effects of iodine partial pressure (Fig. 1a), doping and interaction with oxygen.[5] We also discuss results that show the significance of ion redistribution phenomena for relevant interfaces. By extending this study to the situation under illumination, we observe a striking enhancement of ionic conductivity by more than 2 orders of magnitude in MAPbI3, alongside the expected increase in electronic conductivity.[6] We provide a mechanistic explanation of this astonishing phenomenon and discuss its relevance for future light-triggered ionic devices (“opto-ionics”, see Fig. 1b). Please click Additional Files below to see the full abstract

THE EFFECTS OF WEARING SPANDEX WEAR WITH COMPRESSION BAND ON MUSCLE ACTIVITY DURING A GOLF SWING

The purpose of this study was to determine how spandex wear with compressive band affects muscle activities during a golf swing. This study showed that average and maximum nEMG (normalized EMG) values of left AO (external abdominal oblique) were less in EG (experimental group) compared with CG (control group) during back swing, whereas those of left PM (pectoralis major) in EG were greater than CG. It is more likely that EG performed effectively golf swing without excess muscle activity. Thus, the spandex wear with compressive band played an important role in improving swing performance with injury prevention. This has led to suggestions of the need for further kinetic and kinematic analyses to evaluate its function

THE EFFECTS OF WEARING SPANDEX GARMENT WITH COMPRESSION BAND ON KINEMATIC VARIABLES DURING A GOLF SWING

The purpose of this study was to investigate how spandex garment with compressive band affects kinematic variables during a golf swing. The X-factor and angular velocity of the club in EG were increased during the down swing phase, whereas the significant changes of other kinematic variables were not found in this study. Thus, the effects of wearing spandex garment with compression band cannot be explained as a function of the kinematic variables of interest. It is clear that wearing spandex garment with compressive band may enhance joint stability, which in turn may affect joint kinetics and muscle activation. This has led to suggestions of the need for further kinetic and EMG analyses to evaluate its function

Differences in Clinical Features According to Boryoung and Karp Genotypes of Orientia tsutsugamushi

Scrub typhus is an infectious disease caused by Orientia tsutsugamushi. The differences in virulence of O. tsutsugamushi prototypes in humans are still unknown. We investigated whether there are any differences in the clinical features of the Boryoung and Karp genotypes.Patients infected with O. tsutsugamushi, as Boryoung and Karp clusters, who had visited 6 different hospitals in southwestern Korea were prospectively compared for clinical features, complications, laboratory parameters, and treatment responses. Infected patients in the Boryoung cluster had significantly more generalized weakness, eschars, skin rashes, conjunctival injection, high albumin levels, and greater ESR and fibrinogen levels compared to the Karp cluster. The treatment response to current antibiotics was significantly slower in the Karp cluster as compared to the Boryoung cluster.The frequency of occurrence of eschars and rashes may depend on the genotype of O. tsutsugamushi

The Significance of Ion Conduction in a Hybrid Organic-Inorganic Lead-Iodide-Based Perovskite Photosensitizer

The success of perovskite solar cells has sparked enormous excitement in the photovoltaic community not only because of unexpectedly high efficiencies but also because of the future potential ascribed to such crystalline absorber materials. Far from being exhaustively studied in terms of solid-state properties, these materials surprised by anomalies such as a huge apparent low-frequency dielectric constant and pronounced hysteretic current-voltage behavior. Here we show that methylammonium (but also formamidinium) iodoplumbates are mixed conductors with a large fraction of ion conduction because of iodine ions. In particular, we measure and model the stoichiometric polarization caused by the mixed conduction and demonstrate that the above anomalies can be explained by the build-up of stoichiometric gradients as a consequence of ion blocking interfaces. These findings provide insight into electrical charge transport in the hybrid organic-inorganic lead halide solar cells as well as into new possibilities of improving the photovoltaic performance by controlling the ionic disorder

Thermally Tunable Dynamic and Static Elastic Properties of Hydrogel Due to Volumetric Phase Transition

The temperature dependence of the mechanical properties of polyvinyl alcohol-based poly n-isopropyl acrylamide (PVA-PNIPAm) hydrogel was studied from the static and dynamic bulk modulus of the material. The effect of the temperature-induced volumetric phase transition on Young’s Modulus, Poisson’s ratio, and the density of PVA-PNIPAm was experimentally measured and compared with a non-thermo-responsive Alginate hydrogel as a reference. An increase in the temperature from 27.5 to 32 °C results in the conventional temperature-dependent de-swelling of the PVA-PNIPAm hydrogel volume of up to 70% at the lower critical solution temperature (LCST). However, with the increase in temperature, the PVA-PNIPAm hydrogel showed a drastic increase in Young’s Modulus and density of PVA-PNIPAm and a corresponding decrease in the Poisson’s ratio and the static bulk modulus around the LCST temperature. The dynamic bulk modulus of the PVA-PNIPAm hydrogel is highly frequency-dependent before the LCST and highly temperature-sensitive after the LCST. The dynamic elastic properties of the thermo-responsive PVA-PNIPAm hydrogel were compared and observed to be significantly different from the thermally insensitive Alginate hydrogel

Spatial Decomposition of a Broadband Pulse Caused by Strong Frequency Dispersion of Sound in Acoustic Metamaterial Superlattice

An acoustic metamaterial superlattice is used for the spatial and spectral deconvolution of a broadband acoustic pulse into narrowband signals with different central frequencies. The operating frequency range is located on the second transmission band of the superlattice. The decomposition of the broadband pulse was achieved by the frequency-dependent refraction angle in the superlattice. The refracted angle within the acoustic superlattice was larger at higher operating frequency and verified by numerical calculated and experimental mapped sound fields between the layers. The spatial dispersion and the spectral decomposition of a broadband pulse were studied using lateral position-dependent frequency spectra experimentally with and without the superlattice structure along the direction of the propagating acoustic wave. In the absence of the superlattice, the acoustic propagation was influenced by the usual divergence of the beam, and the frequency spectrum was unaffected. The decomposition of the broadband wave in the superlattice’s presence was measured by two-dimensional spatial mapping of the acoustic spectra along the superlattice’s in-plane direction to characterize the propagation of the beam through the crystal. About 80% of the frequency range of the second transmission band showed exceptional performance on decomposition

Photocatalytic Methylene Blue Degradation of Electrospun Ti–Zn Complex Oxide Nanofibers

Photocatalysts are the most important technology in air pollution removal and the detoxification of organic materials. Doping and complexation are among the most used methods to improve the efficiency of photocatalysts. Titanium dioxide and zinc oxide nanomaterials are widely used materials for photocatalysts and the degradation of toxic materials. Their mixed structure can be fabricated by many methods and the structure affects their properties. Nanofibers are efficient materials for photocatalysts due to their vertically formed structure, which improves the charge separation of photoelectrons. We fabricated them by an electrospinning process. A precursor consisting of titanium 4-isopropoxide, zinc acetate dihydrate and polyvinylpyrrolidone was used as a spinning solution for a mixed structure of titanium dioxide and zinc oxide with different molar ratios. They were then calcined, crystallized by heat treatment and analyzed by thermogravimetric-differential thermal analysis (TG-DTA), X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM) and energy-dispersive spectroscope (EDS). After annealing, the average diameters of the Ti–Zn complex oxide nanofibers were 237.6–278.6 nm with different salt ratios, and multiple crystalline structures were observed, namely TiO2, ZnO, ZnTiO3 and Zn2TiO4. We observed the photocatalytic performance of the samples and compared them according to the photodegradation of methylene blue. The methylene blue concentration decreased to 0.008–0.650 after three hours, compared to an initial concentration of 1, with different metal oxide structures