Influence of the Nature of A Cation on Dynamics of Charge Transfer Processes in Perovskite Solar Cells

The electronic processes occurring within the perovskite solar cells (PSCs) are strongly influenced by the nature of the organic A cations present within the inorganic framework. In this study, the impact of FA (CH(NH₂)₂⁺) and Cs⁺ cations on the intrinsic and interfacial properties in the FAPbBr₃ and CsPbBr₃ PSCs is investigated. The analysis of current density ( J _SC) and photovoltage ( V _OC) as a function of illumination intensity establishes that the interfacial charge transport is more rapid in FAPbBr₃ devices. Small perturbation measurements including intensity modulated photocurrent and photovoltage spectroscopy are applied to explore the resistive and capacitive elements. Furthermore, electrochemical impedance spectroscopy measurements are found to correlate well with the photovoltaic characteristics of FAPbBr₃ and CsPbBr₃ PSCs. Overall, the in‐depth analysis of various phenomena occurring within the bromide PSCs allows to underline the working principle, which provides a key to optimize the device performance. The present protocol is not only valid for PSCs but can also be extended to devices based on alternative light harvesters.     

Reinforcement of SC-15 epoxy with CNT/CNF under high magnetic field: an investigation of mechanical and thermal response

We report here reinforcement of SC-15 epoxy matrix with 1.0 wt% loading of carbon nanotubes (CNTs)/carbon nanofibers (CNFs), and cured under a high (28 T) magnetic field. The improvement in mechanical properties such as compressive strength and stiffness was phenomenal with CNT inclusion, about 126% and 166% increase in strength and modulus, respectively. Enhancement in the glass transition (T _g) and thermal decomposition temperatures was also significant, by about 30 and 23 °C, respectively. Although the degree of anisotropy introduced by the magnetic field was not significant, it was observed that almost half of the improvement was due to magnetic flocculation. In the following is described the results of initial experiments conducted in the National High Magnetic Field Laboratory (NHMFL). Enhanced properties of the nanocomposites strongly suggest improved ordering of nanoparticles within the matrix.     

Fatigue crack growth and life prediction of foam core sandwich composites under flexural loading

Fatigue crack growth of foam core sandwich beams loaded in flexure has been investigated. Sandwich panels were manufactured using an innovative co-injection resin transfer molding process. S2-glass fiber with epoxy resins was used as face sheets over a PVC foam core. Testing was performed in a three-point flexure mode utilizing a newly designed fixture such that the localized indentation damage was minimal. Extensive fatigue data were generated for the S–N diagram and crack growth was monitored to develop a model for life prediction. The first visible sign of damage initiation was a core–skin debond parallel to the beam axis. This debond propagated slowly along the top interface and eventually kinked into the core as shear crack and then grew in an unstable manner resulting in total specimen collapse. A fatigue model based on this crack growth has been developed and validated with experiments.     

Low‐Cost and Highly Efficient Carbon‐Based Perovskite Solar Cells Exhibiting Excellent Long‐Term Operational and UV Stability

Today's perovskite solar cells (PSCs) mostly use components, such as organic hole conductors or noble metal back contacts, that are very expensive or cause degradation of their photovoltaic performance. For future large‐scale deployment of PSCs, these components need to be replaced with cost‐effective and robust ones that maintain high efficiency while ascertaining long‐term operational stability. Here, a simple and low‐cost PSC architecture employing dopant‐free TiO₂ and CuSCN as the electron and hole conductor, respectively, is introduced while a graphitic carbon layer deposited at room temperature serves as the back electrical contact. The resulting PSCs show efficiencies exceeding 18% under standard AM 1.5 solar illumination and retain ≈95% of their initial efficiencies for >2000 h at the maximum power point under full‐sun illumination at 60 °C. In addition, the CuSCN/carbon‐based PSCs exhibit remarkable stability under ultraviolet irradiance for >1000 h while under similar conditions, the standard spiro‐MeOTAD/Au based devices degrade severely.     

Dye-sensitized solar cells incorporating a "liquid" hole-transporting material

We present the first application of an amorphous "liquid" organic semiconductor in an optoelectronic device, demonstrating that it is highly suited for use as a hole-transporting material in nanostructured dye-sensitized solar cells. For such devices, we obtain power conversion efficiencies of up to 2.4% under simulated air mass 1.5 solar spectrum at 100 mWcm(-2), and incident photon-to-electron quantum efficiencies in excess of 50%.     

Subsurface plastic deformation in machining 6Al-2Sn-4Zr-2Mo titanium alloy

The effect of cutting speed and tool geometry on the plastic deformation in the surface region of 6242 titanium alloy machined orthogonally under lubricated and unlubricated conditions is determined using the grid technique and metallography.The results show that the magnitude of the plastic deformation in the surface region and the depth of the work-hardened layer increase with an increase in the cutting speed or the tool wear land length.The presence of the lubricant in the cutting region results in a considerable reduction in the subsurface damage.     

Dynamic compression of cellular cores: temperature and strain rate effects

Cross-linked polyvinyl chloride closed-cell foams were examined under quasi-static and high strain rate compression loading using a servo-hydraulic testing machine and a modified split Hopkinson pressure bar apparatus consisting of polycarbonate bars for strain rates up to 1900 s⁻¹. Three foam densities were examined viz. 75, 130, and 300 kg/m³. Each core density has been subjected to compressive loading at room and elevated temperatures. A reverse trend in failure modes was observed when moving from room to elevated temperatures at high strain loading, which was not found in quasi-static testing at elevated temperatures. Accordingly, post-impact tests were conducted to evaluate the residual strength of the foam cores subject to elevated temperatures and HSR. Results of the post-impact test revealed that the foam cores are still capable of taking some loading. The residual strength of cores was fairly constant regardless of temperature therefore recovery of volume does not signify an increase in residual strength of cores.     

Reactivity of high-valent iron-oxo species in enzymes and synthetic reagents: a tale of many states

The Account discusses the phenomenon of two-state reactivity (TSR) or multistate reactivity (MSR) in high-valent metal-oxo reagents, projecting its wide-ranging applicability starting from the bare species, through the reagents made by Que, Nam, and collaborators, to the Mn(V)-oxo substituted polyoxometalate, all the way to Compound I species of heme enzymes. The Account shows how the behaviors of all these variegated species derive from a simple set of electronic structure principles. Experimental trends that demonstrate TSR and MSR are discussed. Diagnostic mechanistic probes are proposed for the TSR/MSR scenario, based on kinetic isotope effect, stereochemical studies, and magnetic- and electric-field effects.     

Effect of reinforcement of sustainable β‐CaSiO3 nanoparticles in bio‐based epoxy resin system

The β‐CaSiO₃ nanoparticles (NPs) were prepared using calcium carbonate from egg shells and silica as precursors. These NPs were incorporated (1–4 wt %) into bio‐based epoxy resin to fabricate nanocomposites. Thermal and mechanical tests were carried out on these composites. The results of dynamic mechanical analysis showed significant improvement in the storage modulus of 1 and 2 wt % composites. The thermomechanical analysis data revealed ～19 and 20% of reduction in coefficient of thermal expansion for 1 wt % of CaSiO₃ before and after glass transition as compared to the neat epoxy system. Thermogravimetric analysis results also showed delayed thermal degradation of the composites by significant amounts (17–35°C) for 5% of decomposition, a proportional increase in residues corresponding to the loading concentrations. The flexure tests showed significant improvements in strength (17–36%), modulus (5–33%), and toughness for 1–4 wt % of reinforcement of β‐CaSiO₃ NPs. Theoretical calculations of the reinforcement effect on the flexure modulus of the composites agree well with the experimental values. The scanning electron micrograph of the fractured surfaces revealed better interfacial interactions in the composites and enhancements in crack path deflections over the neat specimen. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40867.