Fast Crystallization Process Research Articles

Multiscale simulations of amorphous and crystalline AgSnSe2 alloy for reconfigurable nanophotonic applications

AbstractChalcogenide phase‐change materials (PCM) have been explored in novel nonvolatile memory and neuromorphic computing technologies. Upon fast crystallization process, the conventional PCM undergo a semiconductor–to–semiconductor transition. However, some PCM change from a semiconducting amorphous phase to a metallic crystalline phase with low conductivity (“bad metal”). In this work, we focus on new “bad metal” PCM, namely, AgSnSe2, and carry out multiscale simulations to evaluate its potential for reconfigurable nanophotonic devices. We study the structural features and optical properties of both crystalline and amorphous AgSnSe2 via density functional theory (DFT) calculations and DFT‐based ab initio molecular dynamic (AIMD) simulations. Then we use the calculated optical profiles as input parameters for finite difference time domain (FDTD) modeling of waveguide and metasurface devices. Our multiscale simulations predict AgSnSe2 to be a promising candidate for phase‐change photonic applications.

Cross‐Linkable Fullerene Enables Elastic and Conductive Grain Boundaries for Efficient and Wearable Tin‐Based Perovskite Solar Cells

AbstractTin‐based perovskite solar cells (TPSCs) have received increasing attention due to their low toxicity, high theoretical efficiency, and potential applications as wearable devices. However, the inherent fast and uncontrollable crystallization process of tin‐based perovskites results in high defect density in the film. Meanwhile, when fabricated into flexible devices, the prepared perovskite film exhibits inevitable brittleness and high Young's modulus, seriously weakening the mechanical stability. In this work, we design and synthesize a cross‐linkable fullerene, thioctic acid functionalized C60 fulleropyrrolidinium iodide (FTAI), which has multiple interactions with perovskite components and can finely regulate the crystallization quality of perovskite film. The obtained perovskite film shows an increased grain size and a more matched energy level with the electron transport material, effectively improving the carrier extraction efficiency. The FTAI‐based rigid device achieves a champion efficiency of 14.91 % with enhanced stability. More importantly, the FTAI located at the perovskite grain boundaries could spontaneously cross‐link during the perovskite annealing process, which effectively improves the conductivity and elasticity of grain boundaries, thereby giving the film excellent bending resistance. Finally, the FTAI‐based wearable device yields a record efficiency of 12.35 % and displays robust bending durability, retaining about 90 % of the initial efficiency after 10,000 bending times.

Cross-Linkable Fullerene Enables Elastic and Conductive Grain Boundaries for Efficient and Wearable Tin-Based Perovskite Solar Cells.

Tin-based perovskite solar cells (TPSCs) have received increasing attention due to their low toxicity, high theoretical efficiency, and potential applications as wearable devices. However, the inherent fast and uncontrollable crystallization process of tin-based perovskites results in high defect density in the film. Meanwhile, when fabricated into flexible devices, the prepared perovskite film exhibits inevitable brittleness and high Young's modulus, seriously weakening the mechanical stability. In this work, we design and synthesize a cross-linkable fullerene, thioctic acid functionalized C60 fulleropyrrolidinium iodide (FTAI), which has multiple interactions with perovskite components and can finely regulate the crystallization quality of perovskite film. The obtained perovskite film shows an increased grain size and a more matched energy level with the electron transport material, effectively improving the carrier extraction efficiency. The FTAI-based rigid device achieves a champion efficiency of 14.91 % with enhanced stability. More importantly, the FTAI located at the perovskite grain boundaries could spontaneously cross-link during the perovskite annealing process, which effectively improves the conductivity and elasticity of grain boundaries, thereby giving the film excellent bending resistance. Finally, the FTAI-based wearable device yields a record efficiency of 12.35 % and displays robust bending durability, retaining about 90 % of the initial efficiency after 10,000 bending times.

Oriented nucleation in formamidinium perovskite for photovoltaics.

The black phase of formamidinium lead iodide (FAPbI3) perovskite shows huge promise as an efficient photovoltaic, but it is not favoured energetically at room temperature, meaning that the undesirable yellow phases are always present alongside it during crystallization1-4. This problem has made it difficult to formulate the fast crystallization process of perovskite and develop guidelines governing the formation of black-phase FAPbI3 (refs. 5,6). Here we use in situ monitoring of the perovskite crystallization process to report an oriented nucleation mechanism that can help to avoid the presence of undesirable phases and improve the performance of photovoltaic devices in different film-processing scenarios. The resulting device has a demonstrated power-conversion efficiency of 25.4% (certified 25.0%) and the module, which has an area of 27.83 cm2, has achieved an impressivecertified aperture efficiency of 21.4%.

Lead‐Free Tin‐Based Perovskite Solar Cells with over 1600 Hours Stability in N2 Achieved by Multifunctional Additive

Lead‐free tin‐based perovskite solar cells have received great attention due to their promising photovoltaic performance and ecofriendly properties. However, the fast crystallization process and easy oxidation of Sn2+ limit the device performance. Herein, a multifunctional zinc ethylphenyl dithiocarbamate (Ze) additive is introduced to tune the crystallization process of tin‐based perovskite and suppress the oxidation of Sn2+. Meantime, the interaction between Ze and Sn2+ can effectively passivate defects and reduce nonradiative recombination. As a result, the Ze‐modified solar cells show an efficiency of 4.64% along with excellent long‐term stability.

Efficient Environment‐friendly Lead‐free Tin Perovskite Solar Cells Enabled by Incorporating 4‐Fluorobenzylammonium Iodide Additives

Development of tin (Sn)‐based perovskite solar cells (PSCs) largely lags behind that of lead counterparts due to fast crystallization process of Sn perovskite and numerous defects in both bulk and surface of Sn perovskite films. Herein, this work reports a facile strategy of introducing 4‐fluorobenzylammonium iodide (FBZAI) as additives into Sn perovskite precursor to synergistically modulate the roles of benzylamine and fluorine in Sn‐based PSCs. Incorporation of FBZAI can increase crystallinity, passivate defects, and inhibit the oxidation of Sn2+, leading to suppression of nonradiative recombination and enhancement of charge transport and collection in devices. As a result, the best‐performing Sn‐based PSC with the FBZAI additive achieves the maximum PCE of 13.85% with the enhanced fill factor of 77.8% and open‐circuit voltage of 0.778 V. Our unencapsulated device exhibits good stability by maintaining 95% of its initial PCE after 160 days of storage.

Investigation of the possibility of controlling the formation of physical and mechanical properties of aluminum alloys under pressure crystallization

The study of scientific and technical materials showed that the existing control systems for technological processes of casting with crystallization under pressure are not effective enough. The paper presents a control system capable of real-time measurement, control and correction of the main technological parameters of the process, such as the time and nature of the temperature distribution in the tooling and casting, the rate of pressure imposition on the crystallizing metal, the magnitude of the applied pressure. These parameters have a direct impact on the formation of the properties of the final product. The paper defines the parameters of the response of the control system to fast crystallization processes for the timely prediction of the properties of the final product. The paper proposes a technology for metal processing by pressure prior to the onset of crystallization. In the process of conducting experimental studies in castings, it was possible to achieve the same uniform distribution of components, gas and non-metallic inclusions, as in a superheated liquid metal, bypassing the development of diffusion. As a result of ultrafast application of pressure to a level of 500 MPa on the liquid metal, it was possible to realize the process of compression of the crystal lattice to such limits at which it was possible to exclude the diffusion of components along structural defects. Due to the programmed application of pressure on the liquid and crystallizing one, the idea of controlling the processes of distribution of intermetallic compounds, non-metallic and gaseous inclusions has been realized.

Thiourea with sulfur-donor as an effective additive for enhanced performance of lead-free double perovskite photovoltaic cells

Lead-free inorganic Cs2AgBiBr6 double perovskites have emerged as promising materials in perovskite solar cells (PSCs) to tackle the inferior stability and toxicity issues of organic–inorganic hybrid PSCs. However, the power conversion efficiencies (PCEs) of Cs2AgBiBr6 solar cells are remarkably restricted by the intrinsic and extrinsic defects of Cs2AgBiBr6 films. More specifically, the fast crystallization process in the formation of Cs2AgBiBr6 films strongly prevents the homogeneous growth of perovskite crystals, leading to inferior Cs2AgBiBr6 film quality. This work introduces a facile strategy to retard the crystallization of Cs2AgBiBr6 perovskites by introducing Lewis base additives into the precursor solution. The incorporation of a strongly coordinated thiourea additive with a sulfur donor leads to the generation of a Lewis acid base adduct, which retards the crystallization process for Cs2AgBiBr6 crystals, improves the quality of the Cs2AgBiBr6 film, decreases the defect density and inhibits charge carrier recombination. After optimization, the cell delivers a superior PCE of 3.07%, surpassing that reported for most Cs2AgBiBr6-based solar cells in the literature, and exhibits outstanding stability with a PCE retention rate of 95% after 20 days of storage in air. This work provides an effective strategy for further improvements in the performance of inorganic lead-free Cs2AgBiBr6-based photovoltaic cells.

Insight into the fast crystallization process of SSZ-13 Zeolite by addition of K+ cation

Hydrothermal synthesis of SSZ-13 zeolite from precursors comprises many unanswered fundamental questions, in which understanding the effects of alkali metal cations on the structural rearrangement during the crystallizing period is an active and expanding area of research. Experimental results showed that the continuous crystallization process of SSZ-13 crystals can be easily hindered by the amorphous gel during the synthesis process. Accordingly, we carefully explored and repeated the crystallization period of SSZ-13 zeolite with different K+ mole ratios, which demonstrated significant effects on their crystallization behaviors with the easy breaking of amorphous gel state. The crystallization time was obviously shortened to 18 h. Theoretical calculation results also demonstrated that K+ cation in the precursor solution is more inclined to control the successive deprotonation process due to the higher activation energies for Si–O–Al bonds formation. Accordingly, the SSZ-13 zeolite sample tend to realize fast synthesis and transform into scattered crystals without aggregation by addition of K+ cation.

Controllable Introduction of Surface Defects on CH3NH3PbI3 Perovskite.

One of the unique characteristics of semiconductors is the strong dependence of their properties on crystal defects and doping. However, due to the species diversity and low density, it is very difficult to control the type and concentration of the defects. In perovskite materials, crystal defects are randomly formed during the fast crystallization process, causing large heterogeneity of the samples. Here, in this work, we report a controllable method to introduce surface defects on CH3NH3PbI3 perovskite materials via the interaction with 1,4-benzoquinone (BQ) molecules on the gas and solid interface. After the adsorption of BQ molecules on the perovskite surface, surface defects can be generated by photoinduced chemical reactions. The concentration of the defects can thus be controlled by precisely regulating the laser irradiation time. The concentration of the defects can be characterized by a gradually decreased PL intensity and lifetime and was found to influence the atmospheric response and the subsequent acetone-induced degradation of the materials. These results demonstrate that crystal defects in perovskite materials can be controllably introduced, which provides a possible way to fully understand the correlation between the nature and chemical structure of these defects.

Highly oriented MAPbI3 crystals for efficient hole-conductor-free printable mesoscopic perovskite solar cells

Highly crystalline perovskite films with large grains and few grain boundaries are conducive for efficient and stable perovskite solar cells. Current methods for preparing perovskite films are mostly based on a fast crystallization process, with rapid nucleation and insufficient growth. In this study, MAPbI3 perovskite with inhibited nucleation and promoted growth in the TiO2/ZrO2/carbon triple mesoscopic scaffold was crystallized by modulating the precursor and the crystallization process. N-methylformamide showed high solubility for both methylammonium iodide and PbI2 and hampered the formation of large colloids in the MAPbI3 precursor solution. Furthermore, methylammonium chloride was added to reduce large colloids, which are a possible source of nucleation sites. During the crystallization of MAPbI3, the solvent was removed at a slow controlled speed, to avoid rapid nucleation and provide sufficient time for crystal growth. As a result, highly oriented MAPbI3 crystals with suppressed non-radiative recombination and promoted charge transport were obtained in the triple mesoscopic layer with disordered pores. The corresponding hole-conductor-free, printable mesoscopic perovskite solar cells exhibited a highest power conversion efficiency of 18.82%. The device also exhibited promising long-term operational stability of 1000 h under continuous illumination at maximum power point at 55 ± 5 °C and damp-heat stability of 1340 h aging at 85 °C as well as 85% relative humidity.

Efficient application of intermediate phase for highly-oriented MAPbI3 perovskite solar cells in ambient air

Although the efficiency of inorganic-organic perovskite solar cells (PSCs) has increased significantly owing to intermediate phase induced slow crystallization using dimethyl sulfoxide (DMSO) as a co-solvent in N2-filled glovebox, PSCs are generally fabricated in ambient air via a fast crystallization process to protect the perovskite layer from H2O or O2. In this study, we suggest a possibility of slow crystallization process for MAPbI3 perovskite crystals via intermediate phase formation by adjusting the humidity of air at RH 20%–30%. We obtained high-quality perovskite grains by implementing the slow crystallization process using an antisolvent and the ratio of PbI2:MAI:DMSO in the precursor solution at RH 20%–30%. The amount and state of the intermediate phase inside the as-deposited film were analyzed by grazing incidence wide-angle X-ray scattering (GIWAXS) measurements. The deposited perovskite layer with the pure intermediate via extremely slow crystallization showed higher absorption, fewer grain boundaries, and suppressed defect recombination losses than the fast crystallized perovskite phase. Thus, we obtained higher stability and high power conversion efficiency of up to 18.56% in a p-i-n-structured MAPbI3-based perovskite solar cell under ambient air with RH 20%–30%.

Assembly Control at a Low Péclet Number in Ultracentrifugation for Uniformly Sized Nanoparticles

The intrinsic high diffusion rate of colloids at low Péclet number results in an extremely fast crystallization process and instant formation of colloidal crystals, even at an ultracentrifugal field of extremely high intensity. By introducing a small number of clusters in sedimention, it should be possible to slow down the crystallization process, thus making the assembly order tunable in preparative ultracentrifugation experiments. Here, we used sodium dodecyl sulfate-stabilized polystyrene nanoparticles (with a size dispersity of 1.07) dispersed in a solution of high ionic strength. Sedimentation and assembly of these nanoparticles were done using preparative ultracentrifugation at various angular velocities. The sedimentation process was also analyzed in situ by analytical ultracentrifugation in real time. By creating as low as 3% of clusters into these nearly uniformly sized polystyrene nanoparticle dispersions during the sedimentation process, the superstructure order becomes easily tunable between glassy and crystalline. Theoretical calculations complemented the experiments to explain the mechanism of cluster formation in sedimentation. This work provides a novel methodology to produce superstructures with a tunable packing order for colloids at low Péclet number.

Lead-free tin perovskite solar cells

Summary The development of efficient and stable lead-free perovskite solar cells (PSCs) is crucial for addressing the concern of environmental pollution from the toxic element lead. In recent years, tin PSCs have emerged as a promising candidate for high-performance, eco-friendly photovoltaic technology with a high certified power conversion efficiency (PCE) of more than 11%, indicating a great potential for future applications. Here, we review the recent efficiency progress of tin PSCs based on the equivalent circuit model of solar cells. We then discuss approaches toward efficiency improvement from the device viewpoint, such as optimizing the band gap, increasing the light-harvesting efficiency and carrier diffusion length, surface passivation, and regulating the interface energy-level alignment. Finally, we point out the possibility of reaching 20% PCE for tin PSCs and issues regarding enlarging the cell size and realizing scalable production in the future. We expect that these perspectives will be helpful for accelerating the commercialization of tin PSCs.

Long PEO-based nanoribbons generated in a polystyrene matrix through reaction-induced microphase separation followed by a fast crystallization process.

A dispersion of elongated nanostructures with a high aspect ratio in polymer matrices has been reported to provide a material with valuable properties such as mechanical strength, barrier effect and shape memory, among others. In this study, we show the procedure to achieve a distribution of elongated crystalline nanodomains in a PS matrix employing the self-assembly of amphiphilic block copolymers (BCP). The selected BCP was polystyrene-block-polyethylene oxide (PS-b-PEO). It was dissolved at 10 wt% in a styrene (St) monomer and the blend was slowly photopolymerized over four days at room temperature, until the reaction was arrested by vitrification. This blend was initially homogeneous and nanostructuration took place in an early stage of the polymerization as a result of the microphase separation (MS) of PEO blocks. Due to its high tendency to crystallize, demixed PEO blocks crystallized almost concomitantly with MS triggering the growing of the nanostructures. Thus, the time window between the onset of crystallization and the vitrification of the matrix was almost four days, allowing all micelles to have the opportunity to couple to a growing nanostructure. As a result, a population of nanoribbons with average lengths surpassing 10 μm dispersed in a PS matrix was obtained. It was demonstrated that these ribbon-like nanostructures are preserved as long as the heating temperature is located below the Tg of the matrix. If the material is heated above this temperature, softening of the matrix allows the breakup of the molten PEO nanoribbons due to Plateau-Rayleigh instability.

Efficient all-inorganic perovskite light-emitting diodes enabled by manipulating the crystal orientation

center461554Crystal orientation manipulation improves the device performance of all-inorganic perovskite light-emitting diodes.

Investigation on the Durability of PLA Bionanocomposite Fibers Under Hygrothermal Conditions

Hygrothermal ageing of neat poly(lactic acid) (PLA), PLA/microcrystalline cellulose (MCC) and PLA/cellulose nanowhiskers (CNW) fibers prepared by melt-spinning process was investigated at 95 % relative humidity (RH) and two temperatures, i.e., 45 and 60°C. PLA bionanocomposite fibers were melt compounded at filler content of 1 wt% in the presence of PLA-grafted-maleic anhydride (PLA-g-MA) (7 wt%) used as compatibilizer. The influence of the type of cellulosic filler and the temperature on the hydrolytic degradation kinetics was evaluated through changes in molecular structure and physico-mechanical properties of the samples. The study showed, that all exposed fibers to hygrothermal ageing, were subjected to chain scission mechanism responsible for the decrease in average molecular weight, thermal stability and tensile properties, however, more pronounced after 14 days at 60°C. Furthermore, an increase in crystallinity with a fast crystallization process was noticed for all exposed fibers. The study revealed that the hydrolysis rate increased by 5, 6 and 7 times after 14 days at 60°C compared to 25 days at 45°C for neat PLA, PLA/PLA-g-MA/MCC1 and PLA/PLA-g-MA/CNW1 fibers, respectively. This has been ascribed to the catalytic behavior of the cellulosic fillers which promotes water diffusion into the PLA matrix. Finally, the study concludes to the capacity of PLA fibers to better withdraw to hydrothermal ageing in comparison to PLA/cellulose bionanocomposites. The durability of PLA fibers to hygrothermal degradation is established in the following order: PLA>PLA/PLA-g-MA/MCC1>PLA/PLA-g-MA/CNW1.

Structure and physical properties evolution of ITO film during amorphous-crystalline transition using a highly effective annealing technique

Abstract Three kinds of amorphous ITO (a-ITO) films were deposited on chemically strengthened glass by DC magnetron sputtering at room temperature. A rapid infrared annealing (RIA) device was built, and an infrared fast crystallization process was developed. Not only the effects of RIA on the structural, optical, and electrical properties of ITO films, but also the effects of RIA on the mechanical properties of chemically strengthened glass substrates were investigated compared with those of conventional furnace annealing (CFA). The rules of the structural and physical properties during amorphous-crystalline transition are basically the same by RIA and CFA. However, the RIA time is only 10% of the CFA time, and the compressive stress reduction of chemically strengthened glass is only 4.2% at 500 °C, which is 38.5% by CFA. These results demonstrate that very effective RIA technology could replace the traditional annealing method (CFA), which can greatly reduce production costs and significantly improve production efficiency.

Solvent Directed Synthesis of Molecular Cage and Metal Organic Framework of Copper(II) Paddlewheel Cluster

AbstractA solvothermal reaction of a clip‐type dicarboxylic acid H2DCA [3,3′‐((5‐nitroisophthaloyl)bis(azanediyl))‐dibenzoic acid] and Cu(NO3)2 in equimolar ratio in dimethylformamide (DMF) yielded MOF(CuCG1) which was formed by interlinking [4+2] self‐assembled polyhedral cages via coordination between amide moiety present in the linker and the axial position of copper paddlewheel Cu2(CO2)4. Upon a change in the solvent from DMF to DMA [dimethylacetamide] the interlinking among the polyhedra was successfully terminated to get single crystals of a discrete coordination cage with DMA bound to axial position of Cu(II) (CuCG2). Similar termination of the interlinking was also achieved by a fast crystallization process to get discrete architecture CuCG1.

Electrical and crystallization properties of indium doped Ge-Sb-Se films

Rapid advances in information technology rely on large capacity, high speed, and thermally stable phase-change nonvolatile materials. This work is investigating the capacitance-voltage characteristics of multinary chalcogenides (Ge15Sb80Se5 and Ge15Sb70Se10In5) to study their electrical properties and their reliant on frequency, bias voltage, and temperature. The results show different capacitance behavior for the two films, Ge15Sb80Se5 and Ge15Sb70Se10In5. Adding indium to Ge-Sb-Se alloy improved its thermal stability by increasing the crystallization temperature by almost 20 K, and shows a fast crystallization process. The results illustrate that the capacitance of Ge15Sb70Se10In5 film has a nonlinear-temperature behavior and becomes negative at high temperatures. The negative capacitance could be attributed to a significant increase in the conductivity of the film due to temperature and applied bias voltage. Moreover, during the phase change, the amorphous-crystalline interfaces might behave as a junction with a potential barrier where charge carriers accumulate. The nonlinearity in the capacitance and conductance is attributed to the nucleation-growth mechanism when the temperature becomes close to the amorphous–crystalline transition temperature (Tc).