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Summary Accelerating the experimental cycle for new materials development is vital for addressing the grand energy challenges of the 21st century. We fabricate and characterize 75 unique perovskite-inspired compositions within a 2-month period, with 87% exhibiting band gaps between 1.2 and 2.4 eV, which are of interest for energy-harvesting applications. We utilize a fully connected deep neural network to classify compounds based on experimental X-ray diffraction data into 0D, 2D, and 3D structures, more than 10 times faster than human analysis and with 90% accuracy. We validate our methods using lead-halide perovskites and extend the application to lead-free compositions. The wider synthesis window and faster cycle of learning enables the realization of a multi-site lead-free alloy series, Cs3(Bi1-xSbx)2(I1-xBrx)9. We reveal the non-linear band-gap behavior and transition in dimensionality upon simultaneous alloying on the B-site and X-site of Cs3Bi2I9 with Sb and Br.

The mechanism and elemental composition that form the basis for the improved optical and electronic properties in mixed-ion lead halide perovskite solar cells are still not well understood compared...

Pure metal-organic framework (MOF) layers deposited on porous supports are important candidates for molecular sieving membranes, but their performance usually deviates from theoretical estimations. Here, we combine step-wise scanning electron microscopy imaging, time-resolved synchrotron X-ray scattering, terahertz infrared spectroscopy, and density functional theory calculation to investigate the ZIF-8 membrane formation on two types (polydopamine and TiO2) of functionalized porous supports. Though molecular sieving of ZIF-8 membranes for smaller gases (He, H2, and CO2) can be achieved with both types of functionalized supports, we unravel that the strong interaction between MOF and polydopamine can disrupt the formation of "perfect" MOF crystals at the interface, leading to a "contracted" MOF structure with partially uncoordinated imidazolate ligands. This further affects the low-frequency dynamical parameters of the framework and inhibits the effective seeded growth. Eventually, it leads to an unexpected loss of selectivity for the bulkier gases (N2 and CH4) for ZIF-8 on polydopamine-functionalized supports. This work links the dynamical aspects of MOFs with their gas transport behavior and highlights the importance of regulating the interfacial weak forces to preserve the ideal molecular sieving efficiency of MOF membranes, which also provides guidance for defect engineering of MOF film fabrication for sensing and electronic devices beyond membranes.

A key debate involving mixed-cation lead mixed-halide perovskite thin-films relates to the effects of process conditions on film morphology and local performance of perovskite solar cells. In this contribution, we investigate the influence of precursor concentration on the film thickness, grain size, and orientation of these polycrystalline thin-films. We vary the molar concentration of the perovskite precursor containing Rb, Cs, MA, FA, Pb, I, and Br from 0.4 to 1.2 M. We use optical and electrical probes to measure local properties and correlate the effect of crystallographic orientation on the inter- and intragrain charge-carrier transport. We find that, with increasing precursor concentration, the grain size of the polycrystalline thin-films becomes larger and more faceted. Films with small grains show mostly random grain orientation angles, whereas films with large grains are oriented with {100} planes around an angle of 20° relative to the surface normal. These films with oriented large grains also ...

After reaching a device efficiency level comparable to silicon, perovskite solar cell's next big challenge is to tackle its environmental instability issue. To solve this problem, researchers have started incorporating a buffer layer called ‘capping layer’, consisting of low dimensional (LD) perovskite, sandwiched between perovskite absorber and hole transport layer. However, there is no conclusive agreement on how to select capping layer material that best extends the stability. By using feature importance rank on the regression models, we can start to see which molecular properties on capping layer have significant impact in suppressing degradation.

Environmental stability of perovskite solar cells (PSCs) has been improved by trial-and-error exploration of thin low-dimensional (LD) perovskite deposited on top of the perovskite absorber, called the capping layer. In this study, a machine-learning framework is presented to optimize this layer. We featurize 21 organic halide salts, apply them as capping layers onto methylammonium lead iodide (MAPbI3) films, age them under accelerated conditions, and determine features governing stability using supervised machine learning and Shapley values. We find that organic molecules’ low number of hydrogen-bonding donors and small topological polar surface area correlate with increased MAPbI3 film stability. The top performing organic halide, phenyltriethylammonium iodide (PTEAI), successfully extends the MAPbI3 stability lifetime by 4 ± 2 times over bare MAPbI3 and 1.3 ± 0.3 times over state-of-the-art octylammonium bromide (OABr). Through characterization, we find that this capping layer stabilizes the photoactive layer by changing the surface chemistry and suppressing methylammonium loss., The stability of perovskite solar cells can be improved by using hybrid-organic perovskites capping-layers atop the active material. Here the authors use machine learning to optimize capping layers by monitoring time to degradation of differently capped lead-halide perovskite solar cells.

Process optimization of photovoltaic devices is a time-intensive, trial-and-error endeavor, which lacks full transparency of the underlying physics and relies on user-imposed constraints that may or may not lead to a global optimum. Herein, we demonstrate that embedding physics domain knowledge into a Bayesian network enables an optimization approach for gallium arsenide (GaAs) solar cells that identifies the root cause(s) of underperformance with layer-by-layer resolution and reveals alternative optimal process windows beyond traditional black-box optimization. Our Bayesian network approach links a key GaAs process variable (growth temperature) to material descriptors (bulk and interface properties, e.g., bulk lifetime, doping, and surface recombination) and device performance parameters (e.g., cell efficiency). For this purpose, we combine a Bayesian inference framework with a neural network surrogate device-physics model that is 100× faster than numerical solvers. With the trained surrogate model and only a small number of experimental samples, our approach reduces significantly the time-consuming intervention and characterization required by the experimentalist. As a demonstration of our method, in only five metal organic chemical vapor depositions, we identify a superior growth temperature profile for the window, bulk, and back surface field layer of a GaAs solar cell, without any secondary measurements, and demonstrate a 6.5% relative AM1.5G efficiency improvement above traditional grid search methods.

Lead halide perovskites (LHPs) are promising semiconductors for optoelectronic applications. In LHP solar cells, the focus thus far has been mainly on compositional optimization of the MHP layer, without much understanding of the effects of compositional mixing on structure and texture. This is a serious gap in our knowledge because research has shown that texture underlies the mechanisms of charge carrier and ionic transport. Therefore, it is essential to understand the mechanisms that drive changes in texture in LHPs. This work examines the effect of moisture and composition on the structure and texture of LHPs and their impacts on optoelectronic properties. Exposure to moisture is shown to induce a crystallographic reorientation in the polycrystalline films, which is also dependent on the amount of organic cation material present at the surface. For films with an excess of organic halide, moisture was shown to induce texture in the (001) plane contributing to the enhancement of photocurrents and long-Term device stability. This work shows the importance of texture for the electronic properties of LHPs with a special emphasis on charge carrier extraction in optoelectronic devices.

In previous research, sucrose and citric acid were used to synthesize an eco-friendlyplywood adhesive. Herein, further research was performed to determine the optimal hot-pressingconditions and curing behavior of a sucrose-citric acid (SC) adhesive. The results of dry and wetshear strength measurements showed that the optimal hot-pressing temperature, hot-pressing time,and spread rate of plywood samples bonded by the SC adhesive were 190 &deg, C, 7 min, and 140 g/m2,respectively. When plywood was bonded at the optimal hot-pressing conditions, the wet shearstrength met the requirements of the China National Standard GB/T 9846-2015. Thermal analysisshowed that the thermal degradation and endothermic reaction temperatures of the SC 25/75adhesive were lower than either sucrose or citric acid individually. In addition, the insoluble massproportion increased with the heating temperature and time. The Pyrolysis Gas Chromatographyand Mass Spectrometr (Py-GC/MS) analysis confirmed that the SC adhesive was cured by thereaction between furan compounds, saccharide, and citric acid, and the resulting polymer appearedto be joined by ether linkages.

The development of eco-friendly adhesives is a major research direction in the wood-based material industry. Previous research has already demonstrated the mixture of sucrose and citric acid could be utilized as an adhesive for the manufacture of particleboard. Herein, based on the chemical characteristics of sucrose, a synthesized sucrose-citric acid (SC) adhesive was prepared, featuring suitable viscosity and high solid content. The investigation of synthesis conditions on the bond performance showed that the optimal mass proportion between sucrose and citric acid was 25/75, the synthesis temperature was 100 &deg, C, and the synthesis time was 2 h. The wet shear strength of the plywood bonded with SC adhesive, which was synthesized at optimal conditions and satisfied the China National Standard GB/T 9846-2015. The synthesis mechanism was studied by both 13C NMR analysis and HPLC, and the chemical composition manifesting caramelization reaction occurred during the synthesis process. The results of ATR FT-IR indicated the formation of a furan ring, carbonyl, and ether groups in the cured insoluble matter of the SC adhesive, which indicated dehydration condensation as the reaction mechanism between sucrose and citric acid.

The development of eco-friendly adhesives for wood composite products has been a major topic in the field of wood science and product engineering. Although the research on tannin-based and soybean protein-based adhesives has already reached, or at least nears, industrial implementation, we also face a variety of remaining challenges with regards to the push for sustainable adhesives. First, petroleum-derived substances remain a pre-requisite for utilization of said adhesive systems, and also the viscosity of these novel adhesives continues to limit its ability to serve as a drop-in substitute. Within this study, we focus upon the development of an eco-friendly plywood adhesive that does not require any addition of petroleum derived reagents, and the resultant liquid adhesive has both high solid contents as well as a manageably low viscosity at processing temperatures. Specifically, a system based on sucrose and ammonium dihydrogen phosphate (ADP) was synthesized into an adhesive with ~80% solid content and with viscosities ranging from 480&ndash, 1270 mPa&middot, s. The bonding performance of all adhesive-bound veneer specimens satisfied GB/T 9846-2015 standard at 170 &deg, C hot pressing temperature. To better explain the system&rsquo, s efficiency, in-depth chemical analysis was performed in an effort to understand the chemical makeup of the cured adhesives as well as the components over the time course of curing. Several new structures involving the fixation of nitrogen speak to a novel adhesive molecular network. This research provides a possibility of synthesizing an eco-friendly wood adhesive with a high solid content and a low viscosity by renewable materials, and this novel adhesive system has the potential to be widely utilized in the wood industry.

Inspired by the rapid rise in efficiencies of lead halide perovskite (LHP) solar cells, lead-free alternatives are attracting increasing attention. In this work, we study the photovoltaic potential of solution-processed antimony (Sb)-based compounds with the formula A3Sb2I9 (A = Cs, Rb, and K). We experimentally determine bandgap magnitude and type, structure, carrier lifetime, exciton binding energy, film morphology, and photovoltaic device performance. We use density functional theory to compute the equilibrium structures, band structures, carrier effective masses, and phase stability diagrams. We find the A-site cation governs the structural and optoelectronic properties of these compounds. Cs3Sb2I9 has a 0D structure, the largest exciton binding energy (175 ± 9 meV), an indirect bandgap, and, in a solar cell, low photocurrent (0.13 mA cm–2). Rb3Sb2I9 has a 2D structure, a direct bandgap, and, among the materials investigated, the lowest exciton binding energy (101 ± 6 meV) and highest photocurrent (1....

The mechanical properties of formamidinium lead halide perovskites (FAPbX3, X = Br or I) grown by inverse temperature crystallization have been studied by nanoindentation. The measured Young's moduli (9.7 - 12.3 GPa) and hardnesses (0.36 - 0.45 GPa) indicate good mechanical flexibility and ductility. The effects of hydrogen bonding were evaluated by performing ab initio molecular dynamics on both formamidinium and methylammonium perovskites and calculating radial distribution functions. The structural and chemical factors influencing these properties are discussed by comparison with corresponding values in the literature for other hybrid perovskites, including double perovskites. Our results reveal that bonding in the inorganic framework and hydrogen bonding play important roles in determining elastic stiffness. The influence of the organic cation becomes more important for structures at the limit of their perovskite stability, indicated by high tolerance factors.

Compositional engineering related to the organic and inorganic cations (A-site) in halide perovskites solar cells has helped improve efficiency and long-term durability. However, this compositional complexity can lead to phase segregation that weakens the optoelectronic performance. Here, we show the halide distribution and cation distribution by means of synchrotron-based nanoprobe x-ray fluorescence. We find that the halide distribution homogenizes upon the addition of CsI and RbI precursors. The halide homogenization coincides with long-lived charge carrier decays. Additionally, we observe Rb-rich areas that phase segregate within the film and the Rb aggregates are identified to be recombination active using X-ray and E-beam induced current microscopy.

This journal is © The Royal Society of Chemistry. Methylammonium lead iodide (MAPI) is a prototypical photoabsorber in perovskite solar cells (PSCs), reaching efficiencies above 20%. However, its hygroscopic nature has prompted the quest for water-resistant alternatives. Recent studies have suggested that mixing MAPI with lower dimensional, bulky-A-site-cation perovskites helps mitigate this environmental instability. On the other hand, low dimensional perovskites suffer from poor device performance, which has been suggested to be due to limited out-of-plane charge carrier mobility resulting from structural dimensionality and large binding energy of the charge carriers. To understand the effects of dimensionality on performance, we systematically mixed MA-based 3D perovskites with larger A-site cations to produce dimethylammonium, iso-propylammonium, and t-butylammonium lead iodide perovskites. During the shift from MAPI to lower dimensional (LD) PSCs, the efficiency is significantly reduced by 2 orders of magnitude, with short-circuit current densities decreasing from above 20 mA cm-2 to less than 1 mA cm-2. In order to explain this decrease in performance, we studied the charge carrier mobilities of these materials using optical-pump/terahertz-probe, time-resolved microwave photoconductivity, and photoluminescence measurements. The results show that as we add more of the low dimensional perovskites, the mobility decreases, up to a factor of 20 when it reaches pure LD perovskites. In addition, the photoluminescence decay fitting is slightly slower for the mixed perovskites, suggesting some improvement in the recombination dynamics. These findings indicate that changes in structural dimensionality brought about by mixing A-site cations play an important role in determining the measured charge carrier mobility, and in the performance of perovskite solar cells., NSF (grant no. CBET-1605495), Institute for Soldier Nanotechnology (ISN) (grant no. W911NF-13-D-0001), NASA (grant no. NNX16AM70H)

The mechanism and elemental composition that form the basis for the improved optical and electronic properties of perovskite solar cells are still not well understood. Here, we use synchrotron-based X-ray fluorescence to map the elemental distribution of ions in perovskite thin films with three different film thicknesses. To create a link to the electronic properties, we perform time-resolved photoluminescence spectroscopy and Kelvin probe force microscopy. We find that the elemental composition of the thin films is highly dependent on their thickness which resulted in different photoluminescence behaviors. In particular, we find that the I/Pb ratio is altered for single grains revealing the difference in grain composition. Our approach sheds light onto the fundamental properties occurring at the microscale which help to further engineer perovskite thin films and interfaces.

Characterization, material parameter extraction and subsequent optimization of solar cell devices is a highly time‑consuming and complex procedure. In this work, we propose a method for quick extraction of limiting material parameters in solar cell devices using a surrogate, physics-embedded, neural network model. This surrogate model, implemented by an autoencoder architecture trained with a physical numerical model, allows to quickly extract the device parameters of interest at a certain process condition by using only a small number of illumination dependent current-voltage (JV) measurements. Our surrogate model adequately links material parameters at a certain process condition to final device efficiency. The model provides physical insights about the location of the best performing and robust processing conditions in solar cell devices. We test our approach with GaAs and CH3NH3PbI3 (MAPbI) perovskite solar cells. The model allows to find a set of processing conditions that maximize the performance of both GaAs and MAPbI solar cells, and analogous processing conditions that minimize solar cell variability.

Although methylammonium lead iodide (MAPI) perovskite solar cells have reached efficiencies above 20%, the material is environmentally unstable. Mixing MAPI with lower dimensional (LD) perovskites has been suggested to improve its stability in recent studies. However, the LD-mixed perovskites have lower device performance, likely as a result of limited charge-carrier mobility due to their decreased structural dimensionality. To understand this effect, we mixed large-A-site cation LD perovskites, tert-butylammonium lead iodide, with MAPI, and performed a device performance diagnostics. The results suggested although the charge-carrier lifetime was improved, the mobility decreased by a factor of 20. This contributed to a reduction in device efficiency by 2 orders of magnitude, indicating that mobility plays an important role in 3D/LD perovskite mixtures.

One of the key properties of lead-halide perovskites employed in solar cells is the defect tolerance of the materials, in particular regarding intrinsic point defects, which mainly form shallow traps. Considering that high luminescence yields and photovoltaic performance are obtained by simple solution processing from commercial chemicals, it is commonly anticipated that the defect tolerance-at least to a considerable degree-extends to grain boundaries and extrinsic defects, i.e. impurities, as well. However, the effect of impurities has hardly been investigated. Here, we intentionally introduce small quantities of bismuth (10 ppm to 2%) in solution to be incorporated in the perovskite films based on mixed cation mixed anion compositions. We observe that Bi impurities in the %-regime reduce charge carrier collection efficiency and, more importantly, that the open-circuit voltage decreases systematically with impurity concentration even in the ppm regime. This strong defect intolerance against Bi impurities comes along with reduced electroluminescence yields and charge carrier lifetimes obtained from transient photoluminescence experiments. Calculations based on molecular dynamics and density functional theory predict delocalized (≈0.16 eV) and localized deep (≈0.51 eV) trap states dependent on the structural arrangement of the surrounding atoms. Structural characterization supports the idea of Bi being present as a homogeneously spread point defect, which substitutes the Pb2+ by Bi3+ as seen from XPS and a reduction of the lattice parameter in XRD. Sensitive measurements of the photocurrent (by FTPS) and surface photovoltage (SPV) confirm the presence of tail states. Photoelectron spectroscopy measurements show evidence of a deep state. These results are consistent with the common idea of shallow traps being responsible for the reduced charge collection efficiency and the decreased fill factor, and deeper traps causing a substantial reduction of the open-circuit voltage. As Bi is only one potential impurity in the precursor salts used in perovskite solar cell fabrication, our findings open-up a research direction focusing on identifying and eliminating impurities that act as recombination centers-a topic that has so far not been fully considered in device optimization studies. Fil: Yavari, M.. École Polytechnique Fédérale de Lausanne; Suiza Fil: Ebadi, Firouzeh. École Polytechnique Fédérale de Lausanne; Suiza Fil: Meloni, Simone. Università di Roma; Italia Fil: Wang, Zishuai. École Polytechnique Fédérale de Lausanne; Suiza Fil: Yang, Terry Chien-Jen. École Polytechnique Fédérale de Lausanne; Suiza Fil: Sun, Shijing. Massachusetts Institute Of Technology; Estados Unidos Fil: Schwartz, Heidi. University Of Cologne; Alemania Fil: Wang, Zaiwei. École Polytechnique Fédérale de Lausanne; Suiza Fil: Niesen, Bjoern. École Polytechnique Fédérale de Lausanne; Suiza Fil: Durantini, Javier Esteban. Universidad Nacional de Río Cuarto. Facultad de Ciencias Exactas Fisicoquímicas y Naturales. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Tecnologías Energéticas y Materiales Avanzados; Argentina Fil: Rieder, Philipp. Julius Maximilian University Of Würzburg; Alemania Fil: Tvingstedt, Kristofer. Julius Maximilian University Of Würzburg; Alemania Fil: Buonassisi, Tonio. Massachusetts Institute Of Technology; Estados Unidos Fil: Choy, Wallace C.H.. The University Of Hong Kong; Hong Kong Fil: Filippetti, Alessio. Università Di Cagliari; Italia Fil: Dittrich, Thomas. Helmholtz Center Berlin For Materials And Energy; Alemania Fil: Olthof, Selina. University Of Cologne; Alemania Fil: Correa Baena, Juan Pablo. Massachusetts Institute Of Technology; Estados Unidos Fil: Tress, Wolfgang. École Polytechnique Fédérale de Lausanne; Suiza

We present a new approach to ubiquitous sensing for indoor applications, using high-efficiency and low-cost indoor perovksite photovoltaic cells as external power sources for backscatter sensors. We demonstrate wide-bandgap perovskite photovoltaic cells for indoor light energy harvesting with the 1.63eV and 1.84 eV devices demonstrate efficiencies of 21% and 18.5% respectively under indoor compact fluorescent lighting, with a champion open-circuit voltage of 0.95 V in a 1.84 eV cell under a light intensity of 0.16 mW/cm2. Subsequently, we demonstrate a wireless temperature sensor self-powered by a perovskite indoor light-harvesting module. We connect three perovskite photovoltaic cells in series to create a module that produces 14.5 uW output power under 0.16 mW/cm2 of compact fluorescent illumination with an efficiency of 13.2%. We use this module as an external power source for a battery-assisted RFID temperature sensor and demonstrate a read range by of 5.1 meters while maintaining very high frequency measurements every 1.24 seconds. Our combined indoor perovskite photovoltaic modules and backscatter radio-frequency sensors are further discussed as a route to ubiquitous sensing in buildings given their potential to be manufactured in an integrated manner at very low-cost, their lack of a need for battery replacement and the high frequency data collection possible., 16 pages, 3 figures

Development of a bio-based wood adhesive is a significant goal for several wood-based material industries. In this study, a novel adhesive based upon sucrose and ammonium dihydrogen phosphate (ADP) was formulated in hopes of furthering this industrial goal through realization of a sustainable adhesive with mechanical properties and water resistance comparable to the synthetic resins used today. Finished particleboards exhibited excellent mechanical properties and water resistance at the revealed optimal adhesive conditions. In fact, the board properties fulfilled in principle the requirements of JIS A 5908 18 type standard, however this occured at production conditions for the actual state of development as reported here, which are still different to usual industrial conditions. Thermal analysis revealed addition of ADP resulted in decreases to the thermal thresholds associated with degradation and curing of sucrose. Spectral results of FT-IR elucidated that furanic ring chemistry was involved during adhesive curing. A possible polycondensation reaction pathway was proposed from this data in an attempt to explain why the adhesive exhibited such favorable bonding properties.

In a search for lead-free materials that could be used as alternatives to the hybrid perovskites, (MA)PbX3, in photovoltaic applications, we have discovered a hybrid double perovskite, (MA)2KBiCl6, which shows strong similarities to the lead analogues. Spectroscopic measurements and nanoindentation studies are combined with density functional calculations to reveal the properties of this interesting system., F. Wei is a holder of an A*STAR international fellowship granted by the Agency for Science, Technology and Research, Singapore. G. Kieslich and A. K. Cheetham thank the Ras al Kaihmah Center for Advanced Materials for financial support. G. Kieslich further thanks the DFG for financial support (KI1870). S. Sun and Z. Deng would like to thank the Cambridge Overseas Trust and the China Scholarship Council. The calculations were performed at the Cambridge HPCS and the UK National Supercomputing Service, ARCHER. Access to the latter was obtained via the UKCP consortium and funded by EPSRC under Grant No. EP/K014560/1. All necessary computational data is included in the manuscript or ESI.† RUS facilities were established in Cambridge through grants to MAC from the Natural Environment Research Council (NE/B505738/1, NE/F017081/1) and the Engineering and Physical Sciences Research Council (EP/I036079/1).

We report how mechanical and dynamical properties in formate-based perovskites can be manipulated by the preparation of an A-site solid-solution. In the series [NH3NH2]1−x[NH3OH]xZn(HCOO)3 with xmax = 0.48, the substitution of [NH3NH2]+ by [NH3OH]+ is accompanied by a series of complex changes in crystal chemistry which are analysed using PXRD, SCXRD, 1H solid state NMR, DSC and nanoindentation. NMR shows increased motion of [NH3NH2]+ in [NH3NH2]0.52[NH3OH]0.48Zn(HCOO)3, which results in a shift of the ferroelectric-to-paraelectric phase transition temperature from Tc = 352 K (x = 0) to Tc = 324 K (x = 0.48). Additionally, the loss of hydrogen bonds directly influences the mechanical response of the framework; the elastic moduli and hardnesses decrease by around 25% from E110 = 24.6 GPa and H110 = 1.25 GPa for x = 0, to E110 = 19.0 GPa and H110 = 0.97 GPa for x = 0.48. Our results give an in-depth insight into the crystal chemistry of ABX3 formate perovskites and highlight the important role of hydrogen bonding and dynamics.

Dense formate frameworks with a perovskite-like architecture exhibit multiferroic behavior and tunable mechanical properties. In such materials, interactions between the protonated amine and the metal–formate cavity have a large impact on the mechanical properties. We use complementary single-crystal X-ray diffraction and 1H solid state nuclear magnetic resonance spectroscopy to investigate amine–cavity interactions in [NH3NH2]Zn(HCOO)3. The results suggest that these interactions can be described as salt bridges similar to those in proteins and artificially synthesized helical polymers, where ionic interactions and hydrogen bonds are present at the same time. Nanoindentation and high-pressure single-crystal X-ray diffraction were used to study the mechanical properties of [NH3NH2]Zn(HCOO)3, yielding elastic moduli of E001 = 26.5 GPa and E110 = 24.6 GPa and a bulk modulus of K = 19 GPa. The mechanical properties suggest that, despite the relatively low packing density of [NH3NH2]Zn(HCOO)3, the amine–cavit...

Sucrose is one of the most abundantly available renewable chemicals in the world, and it is expected to be utilized as a raw material for wood-based material products. Herein, a novel adhesion system that was based on sucrose and ammonium dihydrogen phosphate (ADP) was synthesized into an adhesive with 80% solid content, and this eco-friendly was utilized on the fabrication of plywood. The effects of the synthesis conditions on the plywood bond performance and synthesis mechanism were investigated. The optimal synthesis conditions were as follows: the mass proportion between sucrose and ADP was 90/10, the synthesis temperature was 90 &deg, C, and the synthesis time was 3 h. The bonding performance of the plywood that was bonded by optimal SADP adhesive satisfied the GB/T 9846-2015 standard. The chemical analysis was performance tested by using High-Performance Liquid Chromatography (HPLC), Attenuated Total Reflection-Fourier Transform Infrared Spectra (ATR-FTIR), and Pyrolysis Gas Chromatography and Mass Spectrometry (Py-GC/MS) to understand the chemical transformation during the synthesis process. The chemical analysis results confirmed that the hydrolysis and conversation reaction of sucrose occurred in the synthesized SADP adhesive, and ADP promoted the pyrolysis efficiency of sucrose.

Tannin and sucrose (TS) can be used in a biomaterial-based wood adhesive that requires a higher hot pressing temperature and longer time than traditional resins. To solve these problems, hydrochloric acid and citric acid were utilized as a catalyst during the curing process to decrease energy costs (forming TSH and TSC adhesives, respectively). Thermal analysis revealed that the addition of hydrochloric acid and citric acid resulted in decreases to the thermal thresholds associated with degradation and curing. The resultant insoluble matter ratio verified that the polymerization reaction happened at a lower temperature than the adhesive without acidic conditions. The FT-IR and solid state 13C NMR spectra showed that the addition of acid compounds acted catalytically and increased the generation of 5-HMF in uncured adhesives. The dimethylene-ether bridges and methylene bridge were formed during the heat treatment. The water resistance of the particleboards manufactured by TSC and TSH adhesives were notably enhanced when the hot-pressing temperature was 180 °C. However, an increased hot pressing temperature did not improve the mechanical properties of the particleboard bonded by TSH, which was due to cellulose and hemicellulose decomposition under strong acidity conditions.

Intrinsic structural anisotropy in methylammonium (MA) and formamidinium (FA) lead halide perovskites were examined and by various laboratory X-ray diffraction techniques including both out-of-plane and in-plane geometries. Our quantitative analysis revealed the presence of anisotropic strain in the cubic perovskites. Comparative studies on FAPbBr 3 and MAPbBr 3 showed that the FAPbBr 3 lattice was more strained and the anisotropic features were rationalized using ab initio molecular dynamics simulations (AIMD). Our results shed light on future perovskite film design to minimize strain induced decomposition.

Mixed-cation lead mixed-halide perovskite thinfilms are a promising alternative to methylammonium lead iodide due to higher long-term stability, photostability and bandgap tenability. However, the crystallinity of the absorber layer plays an important role for charge carrier collection as well as for an efficient transport between the different device layers. In this contribution, we investigate the influence of grain size by changing the molar concentration of the perovskite precursor containing Rb, Cs, MA, FA, Pb, I and Br on the charge carrier dynamics. We find that with increasing molar precursor concentration, the grain sizes increase and the perovskite grains become more oriented with an improved charge carrier lifetime. In particular, films with small grains show mostly random grain orientation angles, whereas films with larger grains are oriented with {100} planes around an angle of 20° relative to the surface normal. These findings may be the crucial factor in engineering high-quality films leading to high power conversion efficiencies.

The development of biomaterials-based adhesives is one of the main research directions for the wood-based material industry. In previous research, tannin and sucrose were used as adhesive to manufacture particleboard. However, the reaction conditions need to be optimized. In this study, sulfuric acid was added to the tannin&ndash, sucrose adhesive as a catalyst to improve the curing process. Thermal analysis, insoluble mass proportion, FT-IR, and solid state 13C NMR were used to investigate the effects of sulfuric acid on the curing behavior of tannin and sucrose. Thermal analysis showed weight loss and endotherm temperature reduced from 205 and 215 to 136 and 138 &deg, C, respectively, by adding sulfuric acid. In case of the adhesive with pH = 1.0, the insoluble mass proportion achieved 81% at 160 &deg, C, which was higher than the reference at 220 &deg, C. FT-IR analysis of the uncured adhesives showed that adding sulfuric acid leads to hydrolysis of sucrose, then, glucose and fructose converted to 5-hydroxymehthylfurfural (HMF) and levulinic acid. Dimethylene ether bridges were observed by FT-IR analysis of the cured adhesives. The results of solid state 13C NMR spectrum indicated that 5-HMF participated in the curing process and formed methylene bridges with the C8 position of the resorcinol A-rings of tannin, whereas dimethylene ether bridges were detected as a major chemical chain of the polymer. Lab particleboards were produced using 20 wt % resin content at 180 &deg, C and 10 min press time, the tannin&ndash, sucrose adhesive modified with sulfuric acid to pH = 1.0 exhibited better performance than the unmodified tannin&ndash, sucrose adhesive, the properties of the boards fulfilled the requirement of Japanese Industrial Standard (JIS) A5908 type 15.

© 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim There is current interest in finding nontoxic alternatives to lead-halide perovskites for optoelectronic applications. Silver–bismuth double perovskites have recently gained attention, but evaluating their carrier lifetime and recombination mechanisms from photoluminescence measurements is challenging due to their indirect bandgap. In this work, transient absorption spectroscopy is used to directly track the photocarrier population in Cs2AgBiBr6 by measuring the ground state bleach dynamics. A small initial drop is resolved in the ground state bleach on a picosecond timescale, after which the remaining photocarriers decay monoexponentially with a lifetime of 1.4 µs. The majority of the early-time decay is attributed to hot-carrier thermalization from the direct transition to the indirect bandgap, and the 1.4 µs lifetime represents the recombination of most photocarriers. From this lifetime, a steady-state excess carrier density of 2.2 × 1016 cm−3 under 1 sun is calculated, which is an order of magnitude larger than that for methylammonium lead iodide, suggesting that charge transport and extraction can be efficient in Cs2AgBiBr6 solar cells.

We investigate the variable temperature (100-450 K) and high-pressure (p = ambient - 0.74 GPa) crystal chemistry of the black perovskite formamidinium lead iodide, [(NH2)2CH]PbI3, using single crystal X-ray diffraction. In both cases we find a phase transition to a tetragonal phase. Our experimental results are combined with first principles calculations, providing information about the electronic properties of [(NH2)2CH]PbI3 as well as the most probable orientation of the [(NH2)2CH]+ cations.

The discovery of lead-free hybrid double perovskites\ud provides a viable approach in the search for stable and environmentally\ud benign photovoltaic materials as alternatives to lead-containing systems\ud such as MAPbX3 (X = Cl, Br, or I). Following our recent reports of\ud (MA)2KBiCl6 and (MA)2TlBiBr6, we have now synthesized a hybrid\ud double perovskite, (MA)2AgBiBr6, that has a low band gap of 2.02 eV\ud and is relatively stable and nontoxic. Its electronic structure and\ud mechanical and optical properties are investigated with a combination\ud of experimental studies and density functional theory calculations

The elastic properties and thermal expansion behavior of lead-free halide double perovskite, Cs2AgBiBr6, were studied first with the aid of first principles calculations, which were followed by experimental characterization. The calculated full elastic constants enable the complete mapping of Young's and shear moduli, and Poisson's ratios of Cs2AgBiBr6 along all crystallographic orientations. Results show that significant anisotropy in them despite the fact that Cs2AgBiBr6 possesses cubic symmetry. Detailed structural analysis and a spring model were utilized to rationalize the observed anisotropy. Further, the theoretical results were validated by recourse to nanoindentation and high-pressure synchrotron powder X-ray diffraction experiments. The superior mechanical behavior of Cs2AgBiBr6 over the hybrid bromide analogues, MAPbBr(3) (MA = CH3NH3+), were attributed to the higher framework stiffness of the former, which is a result of the presence of relatively stronger Ag-Br and Bi-Br bonds in it. Variable temperature single crystal X-ray diffraction reveal linear and volumetric thermal expansion coefficients to be about 20% lower than those of MAPbBr(3), again suggesting its higher framework rigidity. The superior stiffness, thermal expansion behavior, moisture stability, and nontoxicity of Cs2AgBiBr6 make it a strong candidate for potential applications in optoelectronics and photovoltaics. (C) 2017 Elsevier B.V. All rights reserved.

Density functional theory screening of the hybrid double perovskites (MA)2BIBiX6 (BI=K,Cu,Ag,Tl; X=Cl,Br,I) shows that systems with band gaps similar to those of the MAPbX3 lead compounds can be expected for BI=Cu,Ag,Tl. Motivated by these findings, (MA)2TlBiBr6, isoelectronic with MAPbBr3, was synthesised and found to have a band gap of ~2.0eV.

Organic-inorganic halide perovskites, especially methylammonium lead halide, have recently led to remarkable advances in photovoltaic devices. However, due to environmental and stability concerns around the use of lead, research into lead-free perovskite structures has been attracting increasing attention. In this study, a layered perovskite-like architecture, (NH4)3Bi2I9, is prepared from solution and the structure solved by single crystal X-ray diffraction. The band gap, which is estimated to be 2.04 eV using UV-visible spectroscopy, is lower than that of CH3NH3PbBr3. The energy-minimized structure obtained from first principles calculations is in excellent agreement with the X-ray results and establishes the locations of the hydrogen atoms. The calculations also point to a significant lone pair effect on the bismuth ion. Single crystal and powder conductivity measurements are performed to examine the potential application of (NH4)3Bi2I9 as an alternative to the lead containing perovskites.