Showing papers on "Crystallization published in 2021"

Unveiling the additive-assisted oriented growth of perovskite crystallite for high performance light-emitting diodes.

Abstract: Solution-processed metal halide perovskites have been recognized as one of the most promising semiconductors, with applications in light-emitting diodes (LEDs), solar cells and lasers. Various additives have been widely used in perovskite precursor solutions, aiming to improve the formed perovskite film quality through passivating defects and controlling the crystallinity. The additive’s role of defect passivation has been intensively investigated, while a deep understanding of how additives influence the crystallization process of perovskites is lacking. Here, we reveal a general additive-assisted crystal formation pathway for FAPbI3 perovskite with vertical orientation, by tracking the chemical interaction in the precursor solution and crystallographic evolution during the film formation process. The resulting understanding motivates us to use a new additive with multi-functional groups, 2-(2-(2-Aminoethoxy)ethoxy)acetic acid, which can facilitate the orientated growth of perovskite and passivate defects, leading to perovskite layer with high crystallinity and low defect density and thereby record-high performance NIR perovskite LEDs (~800 nm emission peak, a peak external quantum efficiency of 22.2% with enhanced stability). Additives have been widely used for passivating defects in perovskite semiconductors, yet the role of additive and their interaction is not clear. Here, the authors reveal an additive-assisted crystal formation in FAPbI3 perovskite by tracking the chemical interaction in the precursor solution and crystallographic evolution using multi-functional additives.

Crystallization of CsPbBr3 single crystals in water for X-ray detection.

Abstract: Metal halide perovskites have fascinated the research community over the past decade, and demonstrated unprecedented success in optoelectronics. In particular, perovskite single crystals have emerged as promising candidates for ionization radiation detection, due to the excellent opto-electronic properties. However, most of the reported crystals are grown in organic solvents and require high temperature. In this work, we develop a low-temperature crystallization strategy to grow CsPbBr3 perovskite single crystals in water. Then, we carefully investigate the structure and optoelectronic properties of the crystals obtained, and compare them with CsPbBr3 crystals grown in dimethyl sulfoxide. Interestingly, the water grown crystals exhibit a distinct crystal habit, superior charge transport properties and better stability in air. We also fabricate X-ray detectors based on the CsPbBr3 crystals, and systematically characterize their device performance. The crystals grown in water demonstrate great potential for X-ray imaging with enhanced performance metrics.

Modulation of perovskite crystallization processes towards highly efficient and stable perovskite solar cells with MXene quantum dot-modified SnO2

Abstract: Nanocrystalline tin (IV) oxide (SnO2) electron-transport layers (ETL) have shown great potential for achieving highly efficient, stable perovskite solar cells (PSCs), in particular low-temperature-processed flexible PSCs. Recently, studies have further shown that a modified SnO2 bottom layer facilitates the deposition of highly crystalline perovskite films, boosting the photovoltaic performance of the PSCs. The modulation of perovskite crystallization processes is a key to obtain highly crystalline and stable perovskite films; however, a fundamental understanding is still missing. Herein, we report an in situ synchrotron-based two-dimensional grazing-incidence X-ray diffraction technique to explore the SnO2 ETL-modulated perovskite crystallization kinetics for the first time. The titanium carbide (Ti3C2Tx)-MXene quantum dot-modified SnO2 (MQDs-SnO2) ETL was found to be able to rapidly induce perovskite nucleation from the precursor solution, forming an intermediate perovskite phase upon anti-solvent treatment. This substantially improves the crystal quality and phase stability of the as-fabricated perovskite film. Benefiting in addition from the superior charge extraction properties of the MQDs-SnO2 layer, a steady-state power conversion efficiency of up to 23.3%, as well as outstanding stability against humidity and light soaking was achieved for the corresponding PSCs.

Reversible disorder-order transitions in atomic crystal nucleation.

Abstract: Nucleation in atomic crystallization remains poorly understood, despite advances in classical nucleation theory. The nucleation process has been described to involve a nonclassical mechanism that includes a spontaneous transition from disordered to crystalline states, but a detailed understanding of dynamics requires further investigation. In situ electron microscopy of heterogeneous nucleation of individual gold nanocrystals with millisecond temporal resolution shows that the early stage of atomic crystallization proceeds through dynamic structural fluctuations between disordered and crystalline states, rather than through a single irreversible transition. Our experimental and theoretical analyses support the idea that structural fluctuations originate from size-dependent thermodynamic stability of the two states in atomic clusters. These findings, based on dynamics in a real atomic system, reshape and improve our understanding of nucleation mechanisms in atomic crystallization.

Capturing the Moment of Emergence of Crystal Nucleus from Disorder.

Abstract: Crystallization is the process of atoms or molecules forming an organized solid via nucleation and growth. Being intrinsically stochastic, the research at an atomistic level has been a huge experim...

Stable Co-Continuous PLA/PBAT Blends Compatibilized by Interfacial Stereocomplex Crystallites: Toward Full Biodegradable Polymer Blends with Simultaneously Enhanced Mechanical Properties and Crystallization Rates

Abstract: Constructing stable co-continuous morphology of commercial immiscible polymer blends remains an ongoing challenge in terms of complex presynthetic routes, multiple parameter dependency, and intrinsic instability of phase morphology. Herein, we demonstrate a full biodegradable polymer blend, poly(lactic acid) (PLA) and poly(butylene adipate-co-terephthalate), where hitherto inaccessible co-continuous with asymmetric compositions (70/30) can be obtained with the assistance of interfacial stereocomplex crystallites (i-SCs) through reactive blending. By taking full advantages of this unprecedented compatibilizer, nanostructured co-continuous blends with synergistically enhanced comprehensive performance are achieved. First, due to the “rigid” i-SC, co-continuous morphology is induced through a simple melt blending procedure; second, considerable augmentation of the crystallization rate of the PLA matrix is accomplished on account of the in situ formed nucleation agent (i.e., i-SC); third, a super toughened material with simultaneously enhanced tensile strength, ductility, and impact strength can be acquired, resulting from the i-SC-induced co-continuous morphology; and fourth, i-SC can function as a “rigid” supporting layer between phases even above 200 °C, resulting in significantly enhanced morphology stability in melt. The versatile, facile, and practical strategy offers an industrially relevant technique to fabricate super-robust and fully biobased polymer materials.

Molten-Salt-Assisted CsPbI3 Perovskite Crystallization for Nearly 20%-Efficiency Solar Cells

Abstract: Dynamic manipulation of crystallization is pivotal to the quality of polycrystalline films. A molten-salt-assisted crystallization (MSAC) strategy is presented to improve grain growth of the all-inorganic perovskite films. Compared with the traditional solvent annealing, MSAC enables more intensive mass transfer by means of convection and diffusion, which is beneficial to the interaction among the precursor colloids and to inducing in-plane growth of perovskite grains, resulting in the formation of high-quality perovskite films with suppressed pinhole and crack formation. Additionally, the introduction of molten salt alters the intermediate phases, and thus changes the crystallization pathways by reducing the energy barrier to produce films with desired optical and electrical properties. As a result, the MSAC strategy endows the devices with champion steady-state output efficiency of 19.83% and open-circuit voltage (Voc ) as high as 1.2 V, among the highest for this type of solar cell, thanks to its effectively reduced Voc deficit.

Rapid hybrid perovskite film crystallization from solution

Abstract: The use of a solution process to grow perovskite thin films allows to extend the material processability. It is known that the physicochemical properties of the perovskite material can be tuned by altering the solution precursors as well as by controlling the crystal growth of the film. This advancement necessarily implies the need for an understanding of the kinetic phenomena for the thin-film formation. Therefore, in this work we review the state of the art of perovskite hybrid crystal growth, starting from a comprehensive theoretical description towards broad experimental investigations. One part of the study focuses on rapid thermal annealing as a tool to control nucleation and crystal growth. We deduce that controlling crystal growth with high-precision photonic sintering simplifies the experimental framework required to understand perovskite crystallization. These types of synthesis methods open a new empirical parameter space. All this knowledge serves to improve the perovskite synthesis and the thin films' quality, which will result in higher device performances.

Three-step nucleation of metal-organic framework nanocrystals.

Abstract: Metal-organic frameworks (MOFs) are crystalline nanoporous materials with great potential for a wide range of industrial applications. Understanding the nucleation and early growth stages of these materials from a solution is critical for their design and synthesis. Despite their importance, the pathways through which MOFs nucleate are largely unknown. Using a combination of in situ liquid-phase and cryogenic transmission electron microscopy, we show that zeolitic imidazolate framework-8 MOF nanocrystals nucleate from precursor solution via three distinct steps: 1) liquid-liquid phase separation into solute-rich and solute-poor regions, followed by 2) direct condensation of the solute-rich region into an amorphous aggregate and 3) crystallization of the aggregate into a MOF. The three-step pathway for MOF nucleation shown here cannot be accounted for by conventional nucleation models and provides direct evidence for the nonclassical nucleation pathways in open-framework materials, suggesting that a solute-rich phase is a common precursor for crystallization from a solution.

Reactive crystallization: a review

Abstract: Reactive crystallization is not new, but there has been recent growth in its use as a means of improving performance and sustainability of industrial processes. This review examines phenomena and processes in which reaction and crystallization are coupled in the production of a desired chemical species. Coverage includes fundamental phenomena, such as solubility, supersaturation, crystal nucleation and growth, and chemical kinetics. Systems examined are divided into two groups, those best described as undergoing ionic reactions (including neutralizations), which have near instantaneous rates and result in the formation of ionic bonds, and those undergoing covalent reactions in which the key step occurs at measurable rates and results in the formation of covalent bonds. Discussion of the latter category also includes the impact of catalysis. Examples of a variety of reactions and applications are enumerated, and special attention is given to the utility of reactive crystallization in chiral resolution. Integration of reactive crystallization into process design, including both batch and continuous operations, and the development and efficacy of modeling, monitoring and control are reviewed. Finally, a perspective addressing needs to advance the usefulness and applications of reactive crystallization is included.

Decimal Solvent-Based High-Entropy Electrolyte Enabling the Extended Survival Temperature of Lithium-Ion Batteries to −130 °C

Abstract: Freezing and crystallization of commercial ethylene carbonate-based binary electrolytes, leading to irreversible damage to lithium-ion batteries (LIBs), remain a significant challenge for the survi...

Balancing crystallization rate in a mixed Sn–Pb perovskite film for efficient and stable perovskite solar cells of more than 20% efficiency

Abstract: In the journey to obtain well-crystallized mixed tin (Sn)–lead (Pb) iodide perovskite films for solar cell application, great difficulties have been presented due to very different crystallization rates between Sn- and Pb-based perovskite components. Herein, we report a new strategy to grow highly crystallized Sn–Pb perovskite (FA0.7MA0.3Sn0.5Pb0.5I3) for perovskite solar cells (PSCs). An iso-pentylammonium tetrafluoroborate ([PNA]BF4) ionic salt layer is introduced on top of poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) to function as anchoring agent to bond Pb2+ to the surface of PEDOT:PSS, which can facilitate a quick crystallization of Pb-containing perovskite components and homogeneously distribute Sn/Pb elements inside the perovskite film in a vertical direction, uncovered by focused ion beam time-of-flight secondary ion mass spectrometry. Additionally, greatly reduced surface residual stress was also confirmed by X-ray diffraction. Lastly, these ionic salt molecules are able to encapsulate the acidic and hygroscopic surface of PEDOT:PSS to further ensure device stability. As a result, our strategies enabled a champion PCE of 20.11% for mixed Sn–Pb PSCs with improved thermal stability at 85 °C over 240 hours and shelf storage stability over 1200 hours. This work provides a new strategy to regulate the crystallization process of mixed Sn–Pb perovskites for both high performance and stability.

Manipulating crystallization dynamics through chelating molecules for bright perovskite emitters

Abstract: Molecular additives are widely utilized to minimize non-radiative recombination in metal halide perovskite emitters due to their passivation effects from chemical bonds with ionic defects. However, a general and puzzling observation that can hardly be rationalized by passivation alone is that most of the molecular additives enabling high-efficiency perovskite light-emitting diodes (PeLEDs) are chelating (multidentate) molecules, while their respective monodentate counterparts receive limited attention. Here, we reveal the largely ignored yet critical role of the chelate effect on governing crystallization dynamics of perovskite emitters and mitigating trap-mediated non-radiative losses. Specifically, we discover that the chelate effect enhances lead-additive coordination affinity, enabling the formation of thermodynamically stable intermediate phases and inhibiting halide coordination-driven perovskite nucleation. The retarded perovskite nucleation and crystal growth are key to high crystal quality and thus efficient electroluminescence. Our work elucidates the full effects of molecular additives on PeLEDs by uncovering the chelate effect as an important feature within perovskite crystallization. As such, we open new prospects for the rationalized screening of highly effective molecular additives.

Effect of Crystallization Regulation on the Breakdown Strength of Metallized Polypropylene Film Capacitors

Abstract: In this work, polypropylene (PP) film samples doped with an organic phosphorus nucleating agent under three cooling processes are examined for the effects of regulating the crystallization The conductivity and DC breakdown strength of the film samples were tested at 25, 55 and 85 °C The average breakdown strength with 001 wt% nucleating agent increased by approximately 25% compared to un-nucleating samples and the DC conductivity decreased slightly For the three cooling methods in these tests, the slow process increased the crystallinity of the film samples and stabilized the electrical properties of the PP samples It is concluded that improving the insulation performance through crystallization control is feasible, and this method shows great potential for the modification of PP films

The origin of the high electrochemical activity of pseudo-amorphous iridium oxides

Abstract: Combining high activity and stability, iridium oxide remains the gold standard material for the oxygen evolution reaction in acidic medium for green hydrogen production. The reasons for the higher electroactivity of amorphous iridium oxides compared to their crystalline counterpart is still the matter of an intense debate in the literature and, a comprehensive understanding is needed to optimize its use and allow for the development of water electrolysis. By producing iridium-based mixed oxides using aerosol, we are able to decouple the electronic processes from the structural transformation, i.e. Ir oxidation from IrO2 crystallization, occurring upon calcination. Full characterization using in situ and ex situ X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and transmission electron microscopy allows to unambiguously attribute their high electrochemical activity to structural features and rules out the iridium oxidation state as a critical parameter. This study indicates that short-range ordering, corresponding to sub-2nm crystal size for our samples, drives the activity independently of the initial oxidation state and composition of the calcined iridium oxides.

Two-dimensional fractal nanocrystals templating for substantial performance enhancement of polyamide nanofiltration membrane.

Abstract: In this study, we report the emergence of two-dimensional (2D) branching fractal structures (BFS) in the nanoconfinement between the active and the support layer of a thin-film-composite polyamide (TFC-PA) nanofiltration membrane. These BFS are crystal dendrites of NaCl formed when salts are either added to the piperazine solution during the interfacial polymerization process or introduced to the nascently formed TFC-PA membrane before drying. The NaCl dosing concentration and the curing temperature have an impact on the size of the BFS but not on the fractal dimension (∼1.76). The BFS can be removed from the TFC-PA membranes by simply dissolving the crystal dendrites in deionized water, and the resulting TFC-PA membranes have substantially higher water fluxes (three- to fourfold) without compromised solute rejection. The flux enhancement is believed to be attributable to the distributed reduction in physical binding between the PA active layer and the support layer, caused by the exertion of crystallization pressure when the BFS formed. This reduced physical binding leads to an increase in the effective area for water transport, which, in turn, results in higher water flux. The BFS-templating method, which includes the interesting characteristics of 2D crystal dendrites, represents a facile, low-cost, and highly practical method of enhancing the performance of the TFC-PA nanofiltration membrane without having to alter the existing infrastructure of membrane fabrication.

Crystallization of Covalent Triazine Frameworks via a Heterogeneous Nucleation Approach for Efficient Photocatalytic Applications

Abstract: Crystalline covalent triazine frameworks (CTFs) have shown intriguing applications in photoelectric fields. So far, a number of synthetic strategies based on homogeneous nucleation have been report...