Film Formation Process Research Articles

Role of solution concentration in formation kinetics of bromide perovskite thin films during spin-coating monitored by optical in situ metrology.

Optoelectronic devices based on metal halide perovskites continue to show a improved performance, and solution-based coating techniques pave the way for large-area applications. However, not all parameters influencing the thin film formation process of metal halide perovskites are identified and entirely rationalised over their full compositional range, thus hampering optimised thin film fabrication. Furthermore, while the perovskite deposition via spin-coating and annealing is an easily accessible technique, more profound insights into the chemical formation process are still lacking. Varying the precursor solution concentration is commonly used to vary the resulting thin film thickness. This study shows that varying the precursor solution concentration also affects the thin film morphology and optoelectronic quality. Hence, we herein investigate the influence of the precursor solution concentration on the formation process of a pure bromide-based triple cation perovskite (Cs0.05MA0.10FA0.85PbBr3) by fiber-based optical in situ measurement. During the spin-coating process, in situ UV-vis and PL measurements reveal formation kinetics are strongly dependent on the concentration. Furthermore, we identify delayed nucleation and retarded growth kinetics for more concentrated precursor solutions. In addition, we quantify the shifting chemical equilibrium of colloidal pre-coordination in the precursor solution depending on concentration. Namely, colloids are pre-organised to a higher degree and higher-coordination lead-bromide complexes tend to form in more concentrated precursor solutions. Thus, the modified solution chemistry rationalises retarded perovskite formation kinetics and highlights the precursor concentration as an influential and optimisable parameter for solution-based thin film deposition.

Analysis of fuel film formation process at low temperature by wall impingement direct injection gasoline spray

Analysis of fuel film formation process at low temperature by wall impingement direct injection gasoline spray

Development of advanced electrolytes in Na-ion batteries: application of the Red Moon method for molecular structure design of the SEI layer.

This review aims to overview state-of-the-art progress in the collaborative work between theoretical and experimental scientists to develop advanced electrolytes for Na-ion batteries (NIBs). Recent investigations were summarized on NaPF6 salt and fluoroethylene carbonate (FEC) additives in propylene carbonate (PC)-based electrolyte solution, as one of the best electrolytes to effectively passivate the hard-carbon electrode with higher cycling performance for next-generation NIBs. The FEC additive showed high efficiency to significantly enhance the capacity and cyclability of NIBs, with an optimal performance that is sensitive at low concentration. Computationally, both microscopic effects, positive and negative, were revealed at low and high concentrations of FEC, respectively. In addition to the role of FEC decomposition to form a NaF-rich solid electrolyte interphase (SEI) film, intact FECs play a role in suppressing the dissolution to form a compact and stable SEI film. However, the increase in FEC concentration suppressed the organic dimer formation by reducing the collision frequency between the monomer products during the SEI film formation processes. In addition, this review introduces the Red Moon (RM) methodology, recent computational battery technology, which has shown a high efficiency to bridge the gap between the conventional theoretical results and experimental ones through a number of successful applications in NIBs.

The Study of Graphene Oxide on the Regulations and Controls of the Sol-Gel Film Structure and Its Performance

A facile strategy to boost anticorrosion potency of graphene oxide/silica hybrid sol-gel coating is developed through fully exploiting the capabilities of graphene oxide (GO). Together with a barrier to corrosives and crack inhibitor, GO was further explored herein as a regulator to regulate the gelation process and provide robust coating films with stratified microstructures and ultimately extended diffusion paths. The sol-gel coating with stratified microstructure achieved on AA5052 aluminum alloy surface afforded greatly enhanced corrosion protection capability as assessed by electrochemical measurements and immersion tests. The corrosion current density of the sample of a hybrid GO sol-gel film was about 30 times less than that of sample of pure sol-gel film sample. The regulation mechanism of GO during the film formation process and the anticorrosive protection properties of the film were discussed.

Anions Tuned Solid Electrolyte Interphase in Lithium‐Ion Batteries

AbstractIt is a key and challenging problem to study how the lithium salt anion affects the solid electrolyte interphase (SEI) film formation process. However, the current research focuses on the solvation structure of electrolytes with a general considered conclusion of the preferential reduction effect of anions, while the action mechanism of anions on the solvation structure is rarely studied. Herein, the specific role of anions in the SEI film formation process is illustrated by comparing the influence of anions on the solvation structure with two kinds of boron containing lithium salts. It is found that lithium salt anions can affect the coordination capability of lithium ions and solvents, and then affect the energy consumption in the desolvation process of lithium ions and the composition of SEI film. This work provides a method to study the film formation process, which have certain reference and guide significance for the research of electrolyte field.

Design and preparation of nanocomposite acrylate coating agents for binder-free dry coating of 100 µm-sized drug-containing particles and their coating performance

For binder-free dry particulate coating to prepare controlled-release micron-sized particles, we designed nanocomposite coating agents with the intention to form a core-shell structure composed of two types of acrylic polymers with different glass transition temperatures (Tg) and evaluated their coating performance. A series of nanocomposite acrylic latexes synthesized by emulsion polymerization was freeze-dried after salting-out to create the powder form. An ion-exchange resin loaded with diclofenac sodium (DS, a model drug) (IER-DS) with a median diameter of approximately 100 µm was used as the core particle. Dry coating of the IER-DS with nanocomposite coating agents was carried out using a laboratory-made coating apparatus assisted with mild-intensity vibration and zirconia bead impaction. The coated particles were cured by heating at a temperature 20 °C higher than the Tg for 12 h to complete the film-forming process. It was found that the highest coating efficiency (more than 70%) and a remarkably prolonged release period of the drug (the time required for 50% release reached approximately 12 h) could be achieved when nanocomposite coating agents with a soft polymeric core (Tg = 30 °C) and a hard polymeric shell (Tg = 80 °C) were applied. In contrast, nanocomposite coating agents with a combination of a hard polymeric core and a soft polymeric shell resulted in lower coating efficiency. These results demonstrate that nanocomposite polymeric coating agents composed of a soft core and a hard shell are effective for the production of drug-loaded microparticles with a prolonged release function by a binder-free dry-coating process.

One-step electrochemical modification of pencil graphite electrode with reduced graphene oxide/phosphotungstic acid/sol–gel, and its application to the trace analysis of lead(II)

To determine lead ions, the reduced graphene oxide/phosphotungstic acid (rGO/PWA) composite was used to modify the pencil graphite electrode (PGE). To enhance the efficiency of the sensor, sol–gel was used for the modification, which had a favorable effect of stabilizing, dispersing and increasing the effective sites produced by rGO/PWA. Instead of the traditional sol–gel film preparation method, the modifier composite (rGO/PWA/Sol-Gel) was deposited on the electrode surface electrochemically in a single step in a suitable solution by applying a constant potential. During the sol–gel film formation process, film mesoporous channels were used as a model for the growth of rGO/PWA conductor modifier arrays. The whole process of electrodeposition on the electrode surface took place in a short time (120 s). The modifier was evaluated by SEM and EIS. The effective surface of the modified electrode was calculated, and it was shown that the conductivity of the electrode was increased after using the sol–gel substrate. The modified electrode was used to measure Pb(II) using the differential pulse anodic stripping voltammetry (DPASV) method. Several influential factors were optimized in the designing sensor and measurement of Pb(II). A linear range of 5.0 × 10-10–5.0 × 10-7 M and a detection limit of 2.2 × 10-11 can be accessed by the modified electrode. The measurement of Pb(II) was performed successfully in real samples of drinking water and urine.

Optimization of preparation process of egg white protein/ κ ‐carrageenan composite film

Biopolymer with good biocompatibility and biodegradability can replace petroleum-based plastics materials, which can improve the safety of food and is the development direction of modern food green packaging materials. Based on this, egg white protein (EWP) and κ-carrageenan (κ-C) were used as raw materials to prepare an EWP/κ-C composite film in this paper. First, the pH environment and mechanism of the film-forming dispersion (FFD) were explored. On this basis, the single factor and response surface optimization experiments were carried out, and the optimal film-forming process was obtained. The results of the rheological study were consistent with those of turbidity, zeta-potential, and particle size analysis, indicating that the stability of alkaline film-forming environment was improved and film-forming ability was stronger than that of acidic and neutral. The optimal technological parameters of composite film were as follows: 1.8% of EWP, 1.6% of κ-C, 0.50 g/ml of glycerol, and pH 10.5. Under these conditions, the elongation at break (EAB) of the composite film was 12.24%. It is concluded that the optimized composite film has good mechanical properties and can be used as food packaging materials in food industry. This study provides theoretical basis and reference for the production and application of new edible composite film. Novelty impact statement ● pH environment and mechanism of the film-forming dispersion were explored. ● The optimized composite film of protein and κ-carrageenan was determined by response surface methodology. ● It provides a reference for application of edible packaging materials and improving food safety.

Column bio-oxidation of low-grade refractory gold ore containing high-arsenic and high-sulfur: Insight on change in microbial community structure and sulfide surface corrosion

Currently, there is a lack of research on column bio-oxidation for low-grade refractory gold ore with high arsenic and sulfur content. Therefore, it is essential and significative to investigate column bio-oxidation for this type of gold ore. The column bio-oxidation process of refractory gold ore was characterized by a variety of analytical methods, including X-ray diffraction, 16S rRNA gene analysis, scanning electron microscope coupled with energy-dispersive X-ray spectroscopy and 3D confocal laser scanning microscopy. The evolution of the microbial community structure was analyzed. Simultaneously, the process of passive film formation and the behavior of the dynamic corrosion on the sulfide surfaces were described in detail. The results showed that the cyanidation of gold yielded 81 ± 2% after column bio-oxidation. The oxidation extent for As, Fe and S were 57 ± 1%, 38 ± 1% and 44 ± 1%, respectively. The community structure of attached and planktonic microorganisms was different and changed with the oxidation time. Importantly, the Sulfur film was observed on the arsenopyrite surface under scanning electron microscope, yet it was not found on the pyrite surface. This finding revealed that the inhibitory effect generated by the passive film of arsenopyrite was significantly higher than that of pyrite. Furthermore, the average corrosion pit volume per unit area of pyrite and arsenopyrite were 161 ± 6 μm3/μm2 and 65 ± 3 μm3/μm2. This indicated that arsenopyrite was more easily oxidized during the column bio-oxidation.

Comparison of the Efficiency of Three Primary Driers during the Auto-Oxidation of Alkyd and Boiled Linseed Oil

When using binders in coatings, whose film formation process relays on the oxygen uptake to start the cross-linking reaction, the use of special metal salts, so called driers, can catalyze the process, accelerating the curing of the film and reducing the waiting time between the applications of the next layers of paint. In this work, three primary driers, based on cobalt, iron and manganese are compared, to determine which one is more efficient in drying of alkyd and boiled linseed oil based coating. The study has been done using FTIR spectroscopy to investigate the rate of drying for each drier. The obtained results confirm that using the cobalt drier, the film formation is faster than with the other two alternative driers.

Optimizing the Crystallization Behavior and Film Morphology of Donor–Acceptor Conjugated Semiconducting Polymers by Side-Chain–Solvent Interaction in Nonpolar Solvents

The solution state of a conjugated polymer plays a critical role in the film morphology and charge carrier mobility of the solution process organic field-effect transistors (OFETs). However, it remains challenging to establish the relationship between solution-state and solid-state morphologies. Herein, we report an effective strategy to control the film formation process and film morphology by regulating the solution state, specifically, through the interaction between the branched side chain of poly[4-(4,4-bis(2-octyldodecyl)-4H-cyclopenta[1,2-b:5,4-b′]dithiophen-2-yl)-alt-[1,2,5]-thiadiazolo[3,4-c]pyridine] (PCDTPT-ODD) and the nonpolar solvent. A precise adjustment of the solution state using the Hansen solubility parameter distance (Ra) has been achieved. Compared to the polar solvent, ordered aggregates were formed in the solution formed by nonpolar solvents. Interestingly, a highly ordered chain arrangement was observed in solutions with suitable Ra’s (8.2 and 9.4 MPa1/2 for hexane and isooctane, respectively). Importantly, solution-state aggregation was maintained in the drop-casting film due to the memory effect; the as-prepared films were composed of different fiber sizes and crystal regions. The fiber consisted of a face-on region, with the polymer chains in the fiber aligned perpendicular to the long axis of the fibers. The crystallization process of the edge-on region was independent of the face-on region. The face-on and edge-on regions were produced through the aggregated and disordered parts, respectively. As the Ra increased, the fiber size and the face-on region content increased. Finally, the OFET device mobility was optimized with a significant increase in μ (from 9.7 × 10–5 to 1.3 × 10–3 cm2 V–1 s–1). These results showed that the precise regulations of the solution state by the side-chain–solvent interaction play an important role in the film formation process, film morphology, crystallization behavior, and device properties.

Growth and Degradation Kinetics of Organic–Inorganic Hybrid Perovskite Films Determined by In Situ Grazing‐Incidence X‐Ray Scattering Techniques

Organic-inorganic halide perovskite (OIHP) solar cells hold a great promise for commercial breakthrough since their power conversion efficiency has been pushed beyond the mark of 25%, making them capable of competing with traditional crystalline silicon solar cells. The key to achieve efficient and stable perovskite solar cells is inherently related to the film morphology. The understanding of the kinetic processes of film formation and degradation opens up possibilities to tailor the film morphology via the regulation of precursor and processing parameters. In situ grazing-incidence X-ray scattering (GIXS) techniques allow for tracking the morphology evolution of thin films at different length scales and with high temporal resolution. In this review, the selected examples for application of in situ grazing-incidence wide-angle X-ray scattering and grazing-incidence small-angle X-ray scattering techniques to the growth and stability of OIHPs are summarized after a brief introduction to both techniques, highlighting particularly the morphological evolution of perovskite films over time. Then the correlated mathematical models are reviewed to give a toolbox for analyzing the mechanisms of film formation and degradation. Thus, an overview on the in situ GIXS methods is linked to the research of OIHP kinetics.

Constructing novel cross-linked polybenzimidazole network for high-performance high-temperature proton exchange membrane

Compared with linear polybenzimidazole (PBI) membranes, cross-linked phosphoric acid (PA)-PBI membranes with superior mechanical strength have greater potential for application in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). However, performances of conventional cross-linked membranes are usually limited by densely cross-linked network, and reduced concentration of proton-conductive imidazole units. Therefore, it still remains a big challenge to fabricate high-performance cross-linked PA-PBI membranes. Herein, we build covalently cross-linked PBI network using commercially available 2,6-bis(hydroxymethyl)-4-methylphenol (BHMP) as cross-linking agent through a well-established film-forming process. The optimized covalently cross-linked network can combine high mechanical properties, desired proton conductivity as well as excellent fuel cell performance, owing to a loose but tough cross-linked molecular structure and existence of favorable additional hydroxyl for proton transport. Especially, the covalently cross-linked membrane with BHMP content of 1% display a high proton conductivity of 168.4 mS cm−1 and a good power density of 597.5 mW cm−2 at 160 °C without humidification, outperforming the pristine OPBI membrane. Additionally, in long-term durability test, the voltage decay of cross-linked membrane is low (0.0212 mV h−1) at current density of 200 mA cm−2, suggesting an excellent membrane stability.

Intelligent colorimetric pH sensoring packaging films based on sugarcane wax/agar integrated with butterfly pea flower extract for optical tracking of shrimp freshness

A novel pH colorimetric film was prepared from various sugarcane wax (SW) concentrations (1, 1.5 and 2% w/v) on agar matrix (Agr) combined with butterfly pea flower (BF) extract for monitoring the shrimp freshness. A combination of BF anthocyanins with SW as lipid (hydrophobic) showed different changes in color under acidic conditions (pH 2–6) with slight changes under alkalinity (pH 7–12), which matched the visual color changes of two different ammonia vapors (50 and 100 mmol/l). FTIR, XRD spectra, and SEM micrographs revealed that SW was effectively fixed into the Agr-BF network during the film-forming process. The different homogenized SW films enhanced the physical and mechanical properties without significant differences in elongation and water vapor permeability. Remarkably, SW films displayed complete protection against UV–vis light (0%) and valuable reduction in visible light. This study presents SW colorimetric films as promising natural derivatives for smart packaging in tracking food freshness.

A-site phase segregation in mixed cation perovskite

Mixed cation strategy greatly benefits the enhancement of device performance and chemical stability. However, adverse impact also accompanies the mixed cation system simultaneously. It brings the compositional instability, wherein the homogeneous film is likely to segregate into multi-phases during the fabrication and ageing process, thus resulting in the efficiency reduction of perovskite solar cells (PSCs) devices. This review focuses on the cation induced phase segregation, and elucidates the segregation mechanisms from the perspectives of film formation and ageing process, respectively. Furthermore, the influence of cation segregation on device performance and operational stability are discussed. And based on these understandings, viable strategies are proposed for the design of phase-stable mixed composition halide perovskites and for suppressing segregation to benefit its development towards commercial applications.

Multilevel Self-Healing Characteristics of Smart Polymeric Composite Coatings.

Smart polymeric composite coatings demonstrating multilevel self-healing characteristics were developed and characterized. The pH-responsive smart carriers were synthesized by loading halloysite nanotubes (HNTs) with the benzotriazole corrosion inhibitor (BTA) using the vacuum cycling method, referred to as (BTA-loaded HNTs). Similarly, mechanically triggered melamine urea-formaldehyde microcapsules encapsulated with the boiled linseed oil-self-healing agent (LO) denoted as (MUFMCs) having an average size of a ∼120 μm diameter with a wall thickness of ∼1.84 μm were synthesized by the in situ polymerization technique. The newly designed double-layered smart polymeric composite coatings (DLPCs) were developed by mixing 3 wt % BTA-loaded HNTs with epoxy and applying it on the clean steel substrate to form a primer layer. After its complete curing, a top layer of epoxy containing 5 wt % of MUFMCs was deposited on it. For an exact comparison, single-layer polymeric composite coatings (SLPCs) containing 3 wt % BTA-loaded HNTs were also developed. The Fourier transform infrared radiation spectra of MUFMCs and BTA-loaded HNTs indicate the existence of all desired functional groups, confirming the presence of loaded chemical species such as LO and BTA into the smart carriers. Thermogravimetric analysis (TGA) indicates that ∼18% BTA is successfully loaded into HNTs. Quantitative UV-spectroscopic analysis indicates a pH-responsive release of BTA from BTA-loaded HNTs, which is time-dependent, attaining its maximum value of ∼ 90% in an acidic medium after 30 h. Electrochemical impedance spectroscopy analysis conducted in 3.5 wt % NaCl solution at room temperature for different immersion times reveals that SLPC exhibits the maximum charge-transfer resistance (Rct) of 55.47 GΩ cm2 after the 7th day of immersion, and then, a declining trend is observed, reaching 26.6 GΩ cm2 after the 9th day. However, in the case of DLPC, the Rct values show a continuous increment, attaining a maximum value of 82.11 GΩ cm2 after the 9th day of immersion. The improved performance of DLPC can be ascribed to the efficient triggering of the individual carriers in the isolated matrices, resulting in the release of LO and BTA to form individual protective films at the damaged area due to the oxidative polymerization process and triazoles' ability of passive film formation on the substrate, respectively. The tempting self-healing properties of DLPCs justify their decent role for long-term corrosion protection in many industrial applications.

Synergistic passivation by alkali metal and halogenoid ions for high efficiency HTM-free carbon-based CsPbI2Br solar cells

Hole transport material (HTM)-free carbon-based all-inorganic perovskite solar cells (C-PSCs) possess excellent thermal stability and low cost, which promise an alternative to replace the conventional organic–inorganic hybrid PSCs. The additive method is an effective approach to enhance the performance of PSCs by improving the quality of perovskite films. Herein, the synergistic passivation strategy of alkali metal and halogenoid ions in NaSCN additive is adopted to suppress nonradiative recombination in CsPbI2Br films. The Na+ is incorporated at the A-site of CsPbI2Br cell that enhances the I− diffusion barrier energy from 0.229 eV to 0.401 eV, suggesting suppressed iodide vacancy. Moreover, the SCN− plays a role in regulating the crystal growth dynamics during the CsPbI2Br film formation process, reducing defect density. This synergistic passivation strategy effectively improves the perovskite film quality, and increases the recombination resistance and the carrier extraction efficiency of CsPbI2Br films, therefore reducing nonradiative recombination loss in the final device. The assembled HTM-free carbon-based all-inorganic CsPbI2Br perovskite solar cells present a champion PCE of 14.63% (VOC = 1.267 V, JSC = 14.31 mA/cm2, fill factor (FF) = 0.807), which is among the best performances in the carbon-based all-inorganic perovskite solar cells.

First investigation of additive engineering for highly efficient Cs2AgBiBr6-based lead-free inorganic perovskite solar cells

Inorganic lead (Pb)-free Cs2AgBiBr6 double perovskite is one of the most promising light absorbers in perovskite solar cells (PSCs) to solve the instability and Pb toxicity problems of organic–inorganic perovskites. However, the intrinsic and extrinsic defects of Cs2AgBiBr6 films strongly limit the power conversion efficiencies (PCEs) of Cs2AgBiBr6-based PSCs. Herein, the first investigation of additive engineering in Cs2AgBiBr6-based PSCs is reported to achieve an outstanding efficiency. The introduction of guanidinium thiocyanate (GuaSCN) additive effectively controls the nucleation of Cs2AgBiBr6 crystals during the film formation process, improves the perovskite film quality, suppresses the charge carrier recombination, and accelerates the charge extraction simultaneously. Consequently, after optimizing the GuaSCN amount, the device shows a stable PCE of 3.02% under maximum power point tracking (MPPT) condition. Furthermore, the introduction of GuaSCN additive remarkably improves the ambient stability of the devices. This work provides insights on additive engineering for enhancing the efficiency and stability of inorganic Pb-free Cs2AgBiBr6-based PSCs toward future industrialization of this technology.

Formation of lithiated gold and its use for the preparation of reference electrodes \u2014 an EQCM study

Lithiated gold wires can be used to build reference electrodes with outstanding potential stabilities over several days and even over the course of one year. These electrodes are well suited for investigations in the context of lithium-ion batteries (LIBs). In this work, a detailed procedure for the preparation of such electrodes with tailored mechanical properties, which can be fitted gastight into electrochemical cells using commercially available fittings, is given. The electrochemical lithiation process is studied using the electrochemical quartz crystal microbalance (EQCM) technique, and the differences in lithiation of wire type and thin film type gold electrodes are discussed. All experiments were carried out with two different electrolytes, namely, a LiPF6 and a lithium bis(trifluoromethane sulfonyl) imide (LiTFSI)-based electrolyte, and we conclude that for a higher lithiation rate and long-term stability, the use of LiTFSI-based electrolyte in the preparation phase is beneficial. The EQCM data provides a better insight in the analysis of film formation processes, like the buildup of the solid electrolyte interphase (SEI) during the lithiation, the rate of deposition of metallic lithium, or additional information on the kinetics of Li-Au alloy formation.

A Systematic Review of Metal Halide Perovskite Crystallization and Film Formation Mechanism Unveiled by In Situ GIWAXS.

Metal halide perovskites are of fundamental interest in the research of modern thin-film optoelectronic devices, owing to their widely tunable optoelectronic properties and solution processability. To obtain high-quality perovskite films and ultimately high-performance perovskite devices, it is crucial to understand the film formation mechanisms, which, however, remains a great challenge, due to the complexity of perovskite composition, dimensionality, and processing conditions. Nevertheless, the state-of-the-art in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) technique enables one to bridge the complex information with device performance by revealing the crystallization pathways during the perovskite film formation process. In this review, the authors illustrate how to obtain and understand in situ GIWAXS data, summarize and assess recent results of in situ GIWAXS studies on versatile perovskite photovoltaic systems, aiming at elucidating the distinct features and common ground of film formation mechanisms, and shedding light on future opportunities of employing in situ GIWAXS to study the fundamental working mechanisms of highly efficient and stable perovskite solar cells toward mass production.