Polymer-Controlled Growth and Wrapping of Perovskite Single Crystals Leading to Better Device Stability and Performance.

A commodity-scale polymer is used for controlling the nucleation and growth of single crystals of organolead halide perovskite. The polymer [polystyrene (PS)] cross-links and strongly interacts with PbI2 and MAI (MAPbI3 perovskite precursors) resulting in the control of the crystallization process. The PS concentration modulates the nucleation time, crystal size, and the number of perovskite single crystals. In addition, the PS-based MAPbI3 crystals show an enhanced performance as well as improved thermal and environmental stability. Specifically, the PS-MAPbI3 crystals show 3 times higher photocurrent than plain MAPbI3 crystals and maintain a stable structure for more than 50 days (1200 h) under continuous 0.1 sun illumination in the air with a relative humidity of 40-45%. The improved performance and stability are attributed to the direct interaction between the PS and perovskite, which greatly reduces the ion migration, defect traps, and charge recombination and improves the carrier mobility and lifetime.

Self-Powered Photodetector Based on Electric-Field-Induced Effects in MAPbI3 Perovskite with Improved Stability.

A monolith photodetector is presented that utilizes the material properties of MAPbI3 perovskite for self-powered operation and achieves improved stability by composting with polystyrene. The self-powered operation makes this device suitable for remote applications and in smart systems. Improved stability of more than 20 days, with performance maintained by over 80% under ambient conditions, is achieved by incorporating polystyrene without additional fabrication steps. A plain MAPbI3 device in comparison shows a performance degradation of 70-85% within 4 days of operation. The incorporation of polystyrene also improves the current detectivity of the device by over 70 times compared to plain perovskite.

A Light Harvesting, Self-Powered Monolith Tactile Sensor Based on Electric Field Induced Effects in MAPbI3 Perovskite.

Organolead trihalide perovskite MAPbI3 shows a distinctive combination of properties such as being ferroelectric and semiconducting, with ion migration effects under poling by electric fields. The combination of its ferroelectric and semiconducting nature is used to make a light harvesting, self-powered tactile sensor. This sensor interfaces ZnO nanosheets as a pressure-sensitive drain on the MAPbI3 film and once poled is operational for at least 72 h with just light illumination. The sensor is monolithic in structure, has linear response till 76 kPa, and is able to operate continuously as the energy harvesting mechanism is decoupled from its pressure sensing mechanism. It has a sensitivity of 0.57 kPa-1 , which can be modulated by the strength of the poling field. The understanding of these effects in perovskite materials and their application in power source free devices are of significance to a wide array of fields where these materials are being researched and applied.

Structural Studies of Multifunctional SrTiO3 Nanocatalyst Synthesized by Microwave and Oxalate Methods: Its Catalytic Application for Condensation, Hydrogenation, and Amination Reactions.

The present study deals with the synthesis of SrTiO3 (STO) nanocatalysts by conventional oxalate and microwave-assisted hydrothermal methods. Thorough characterization of the nanocatalysts synthesized has been done by using various techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy, N2 physisorption, transmission electron microscopy, total acidity by pyridine adsorption method, and acidic strength by n-butylamine potentiometric titration, respectively. Structural parameters were estimated by Rietveld refinement analysis from XRD data which confirms cubic structure of SrTiO3. Traces of impurities such as TiO2 and SrCO3 were found in conventional catalysts, whereas these are absent in microwave catalyst. Brunauer-Emmett-Teller (BET) surface area of the microwave catalyst was enhanced 14-folds compared to conventional catalyst. Increase in Lewis acid sites and their strength were also observed in STO microwave catalyst. Catalytic performance of the catalysts was evaluated for various reactions, such as Knoevenagel condensation of benzaldehyde, catalytic transfer hydrogenation of nitrobenzene, and amination of benzaldehyde. Catalytic results reveal that microwave-synthesized catalyst showed 100% conversion and selectivity (>99% yield) for the chosen reactions than the conventional catalyst. Excellent catalytic activity of the STO microwave catalyst was due to high BET surface area, pore volume, and acidity of the catalyst, as compared to conventional catalyst. The present study marks the first-time application of perovskite-based SrTiO3 as a potential multitasking cost-effective catalyst for the above reactions and synthesized using environment friendly microwave synthesis method.

Bio-inspired interlocking random 3-D structures for tactile and thermal sensing.

Hierarchical nanostructures are tailored and used routinely in nature to accomplish tasks with high performance. Their formation in nature is accomplished without the use of any patterning process. Inspired by the performance of such structures, we have combined 2-D nanosheets with 1-D nanorods for functioning as electronic skin. These structures made in high density without any patterning process can be easily assembled over large areas. They can sense pressures as low as 0.4 Pa, with a response time in milliseconds. Further, these structures can also detect temperature changes with a non-linear response in the 298-400 K range, which is similar to skins perception of thermal stimuli. We illustrate this effect by showing that the device can differentiate between two 10 µl water droplets which are at room temperature and 323 K respectively.

Structure and Catalytic Activity of Cr-Doped BaTiO3 Nanocatalysts Synthesized by Conventional Oxalate and Microwave Assisted Hydrothermal Methods.

In the present study synthesis of BaTi1-xCrxO3 nanocatalysts (x = 0.0 ≤ x ≤ 0.05) by conventional oxalate and microwave assisted hydrothermal synthesis methods was carried out to investigate the effect of synthesis methods on the physicochemical and catalytic properties of nanocatalysts. These catalysts were thoroughly characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 physisortion, and total acidity by pyridine adsorption method. Their catalytic performance was evaluated for the reduction of nitrobenzene using hydrazine hydrate as the hydrogen source. Structural parameters refined by Rietveld analysis using XRD powder data indicate that BaTi1-xCrxO3 conventional catalysts were crystallized in the tetragonal BaTiO3 structure with space group P4mm, and microwave catalysts crystallized in pure cubic BaTiO3 structure with space group Pm3̅m. TEM analysis of the catalysts reveal spherical morphology of the particles, and these are uniformly dispersed in microwave catalysts whereas agglomeration of the particles was observed in conventional catalysts. Particle size of the microwave catalysts is found to be 20-35 nm compared to conventional catalysts (30-48 nm). XPS studies reveal that Cr is present in the 3+ and 6+ mixed valence state in all the catalysts. Microwave synthesized catalysts showed a 4-10-fold increase in surface area and pore volume compared to conventional catalysts. Acidity of the BaTiO3 catalysts improved with Cr dopant in the catalysts, and this could be due to an increase in the number of Lewis acid sites with an increase in Cr content of all the catalysts. Catalytic reduction of nitrobenzene to aniline studies reveals that BaTiO3 synthesized by microwave is very active and showed 99.3% nitrobenzene conversion with 98.2% aniline yield. The presence of Cr in the catalysts facilitates a faster reduction reaction in all the catalysts, and its effect is particularly notable in conventional synthesized catalysts.

Synthesis of Eu³âº-activated BaMoO4 phosphors and their Judd-Ofelt analysis: Applications in lasers and white LEDs.

Eu(3+)-activated BaMoO4 phosphors were synthesized by the nitrate-citrate gel combustion method. The Rietveld refinement analysis confirmed that all the compounds were crystallized in the scheelite-type tetragonal structure with I41/a (No. 88) space group. Photoluminescence (PL) spectra of BaMoO4 phosphor reveals broad emission peaks at 465 and 605 nm, whereas the Eu(3+)-activated BaMoO4 phosphors show intense 615 nm ((5)D0→(7)F2) emission peak. Judd-Ofelt theory was applied to evaluate the intensity parameters (Ω2, Ω4) of Eu(3+)-activated BaMoO4 phosphors. The transition probabilities (AT), radiative lifetime (τrad), branching ratio (ß), stimulated emission cross-section (σe), gain bandwidth (σe×Δλeff) and optical gain (σe×τrad) were investigated by using the intensity parameters. CIE color coordinates confirmed that the BaMoO4 and Eu(3+)-activated BaMoO4 phosphors exhibit white and red luminescence, respectively. The obtained results revealed that the present phosphors can be a potential candidate for red lasers and white LEDs applications.

Facile synthesis of PbWO4: applications in photoluminescence and photocatalytic degradation of organic dyes under visible light.

Stolzite polymorph of PbWO4 catalyst was prepared by the facile room temperature precipitation method. Structural parameters were refined by the Rietveld analysis using powder X-ray data. PbWO4 was crystallized in the scheelite-type tetragonal structure with space group I41/a (No. 88). Field emission scanning electron microscopy revealed leaf like morphology. Photoluminescence spectra exhibit broad blue emission (425 nm) under the excitation of 356 nm. The photocatalytic degradation of Methylene blue, Rhodamine B and Methyl orange dyes were measured under visible illumination. The 100% dye degradation was observed for MB and RhB dyes within 60 and 105 min. The rate constant was found to be in the decreasing order of MB>RhB>MO which followed the 1st order kinetic mechanism. Therefore, PbWO4 can be a potential candidate for blue component in white LEDs and also acts as a catalyst for the treatment of toxic and non-biodegradable organic pollutants in water.