Evolution Of Film Morphology Research Articles

Enhanced Performance and Stability of Perovskite Solar Cells Through Surface Modification with Benzocaine Hydrochloride.

Current development of inverted p-i-n perovskite solar cells (PSCs), with nickel oxide as the hole transport layer, is progressing toward lower net costs, higher efficiencies, and superior stabilities. Unfortunately, the high density of defect-based traps on the surface of perovskite films significantly limits the photoelectric conversion efficiency and operational stability of perovskite solar cells. Finding cost-effective interface modifiers is crucial for the further commercial development of p-i-n PSCs. In the present work, we report a passivation strategy using a multifunctional molecule, benzocaine hydrochloride (BHC), which is shown to reduce defect density and enhance the photovoltaic performance and stability of the resultant p-i-n PSCs. It has been revealed that BHC strongly interacts with perovskite precursor components and triggers the evolution of the perovskite absorber film morphology and enables improved surface energy level alignment, thus promoting charge carrier transport and extraction. These properties are beneficial for improving open-circuit voltage (VOC) and fill factor (FF). Our results show that the photoelectric conversion efficiency (PCE) of p-i-n PSCs with nickel oxide as the hole transport layer increased from an initial 20.0% to 22.1% after being passivated with BHC, and these passivated devices also exhibited improved stability. DFT calculations reveal the unusual ability of the BHC passivant to improve band alignment while also preventing the accumulation of holes at the interface. In this work, the advantages of BHC passivation are demonstrated by linking theoretical calculations with optical and electrical characterizations.

Research on the epitaxial direction control and mechanism of polycrystalline diamond grains

The control of diamond film growth is crucial for the application of diamond films. In this article, different diamond film samples were prepared by adding nitrogen and oxygen in different proportions during the growth process. The key conditions for controlling the growth of diamond film with preferred orientation were obtained using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy characterizations. During the growth process, the growth of the diamond film with (100) preferred orientation could be achieved by adjusting nitrogen content. It was necessary to introduce nitrogen and oxygen in the growth process, and precisely regulate the ratio of the two to obtain the (111) preferred orientation of the diamond film. When only oxygen was introduced during growth, the preferred orientation of the diamond could not be achieved, leading to a smaller grain size and poorer crystal quality. From the perspective of grain morphology to film morphology evolution, this study obtained the crystal orientation control conditions during the diamond film growth, which has important guiding significance for the application of the diamond film. This study seeks to drive progress in the large-scale growth of readily machinable diamond and the evolution of diamond-grain optical fiber sensing through comprehensive investigations into the correlation between the preferred orientation in polycrystalline diamonds and reaction conditions.

Preparation of graphitic foil with high thermal conductivity using Vitamin C as reductant and binder

In the face of increased heat dissipation requirements of high-power electronic devices, the fabrication of graphitic foil with high thermal conductivity is urgently needed. In this work, graphitic foil with the thickness ranging from 424 to 900 μm is innovatively prepared by blade coating, hot-pressing, and graphitization process through solution-derived graphene oxide (GO), employing Vitamin C (VC) as reductant and binder. VC amount is optimized, the acting mechanism of VC is clarified, and the morphology and structure evolution of GO film are extensively investigated. The results indicate that VC can mildly reduce the oxygen-containing function group of GO, and the cross-linked derivatives of VC can effectively fuse the multilayer reduced graphene oxide (rGO) films and regulate the microstructure of graphitic foil. When the VC/GO mass ratio is 1, the prepared graphitic foil with a thickness of 680 µm has the best thermal diffusion ability and mechanical strength. It has a high thermal conductivity of 1042 W m−1 K−1 and tensile strength of 42.05 MPa. The thermal diffusion ability, expressed as h × K value, reaches as high as 0.708 W K−1. This study provides a pioneering strategy for constructing advanced thermal conductive materials.

On the O2 "Surfactant" Effect during Ag/SiO2 Magnetron Sputtering Deposition: The Point of View of In Situ and Real-Time Measurements.

The use of gaseous species has been proposed in the literature to counteract the three-dimensional growth tendency of noble metals on dielectric substrates and favor an earlier percolation without compromising electrical properties. This "surfactant" effect is rationalized herein in the case of O2 presence during magnetron sputtering deposition of Ag films on SiO2. In situ and real-time techniques (X-ray photoemission, film resistivity, UV-visible optical spectroscopy) and ex situ characterizations (X-ray diffraction and transmission electron microscopy) were combined to scrutinize the impact of O2 addition in the gas flow (%O2), revealing three regimes of evolution of film resistivity, morphology, structure, and chemical composition. At low oxygen flow conditions (%O2 < 4), the observed drastic decrease of the percolation threshold is assigned to a combination of (i) a change in nanoparticle density, wetting, and crystallographic texture and (ii) a delayed coalescence effect. The driving force is ascribed to the presence of specific adsorbed oxygen moieties, the nature of which starts evolving at intermediate oxygen flow conditions (10 ≤ %O2 < 20). At high oxygen flow (20 ≤ %O2 < 40), the found detrimental impact on film resistivity is assigned to an actual oxidation in the form of a Ag2O-like poorly crystallized compound. For all %O2, a composition gradient is observed across the film thickness, with a more metallic Ag at the substrate interface. A correlation between percolation and the nature of the detected O moieties is observed. In parallel to an oxygen spillover mechanism, this gradient can be explained by the competition between different surface processes occurring before percolation, namely, aggregation, metal oxidation, and substrate reactivity. Such findings pave the way to a rational use of O2 as a modifier for Ag growth.

TiO2 nanotube arrays grown in ethylene glycol-based media containing fluoride: Understanding the effect of early anodization stages on the morphology

In this work, we develop a phenomenological model describing the growth of TiO2 nanotube arrays (NTA-TiO2) by titanium anodization in ethylene glycol-based electrolytes containing fluoride. NTA-TiO2 formation is described in terms of the well-known High-Field mechanism (HFM) considering film thinning by dissolution, and the electronic current contribution according to the Oxygen Bubble Mold (OBM) model, as it has been previously reported. For the first time, the inclusion of the nucleation of oxygen bubbles as the rate determining step at early anodization times is considered. By simultaneous fitting of the potentiostatic j/t profiles and the time evolution of morphological features such as pore radius, layer thickness and density of pores, the behavior observed for several experimental conditions is accurately described, in contrast to previously reported Field Assisted Dissolution (FAD) and OBM models. Proposed model allows obtaining physical and phenomenological information concerning the formation and growth of nanoporous oxide films as well as their morphological properties. Results also indicate that fluoride species play a key role at the early anodization stages, determining the subsequent film morphology evolution. Also, conclusive evidence for a chemical-type instead of field-assisted film dissolution process is obtained.

Fabrication of PtIrPd Noble Metal Medium Entropy Alloy Thin Film by Atomic Layer Deposition

Noble metal medium entropy alloy (MEA) thin films have recently attracted enormous research interests recently because of their great potential in the catalytic application. However, conventional bottom‐up fabrication methods for MEA thin film such as magnetron sputtering face enormous challenges including precise control over film thickness and consumption of costly high‐purity noble metal targets. Herein, a facile and tunable approach is developed coupling sequential atomic layer deposition (ALD) of noble metal layers with electric Joule heating (EJH) alloying process to grow platinum‐iridium‐palladium (PtIrPd) MEA thin films. The PtIrPd MEA thin film with a thickness of ≈20 nm and an atomic ratio of 35:35:30 is successfully fabricated. The effect of EJH processing temperature on the film morphology and structure evolution is investigated. ALD provides flexibility in the metal deposition sequence with meticulous thickness control and atomic composition precision, while the ultrafast EJH ramping/cooling rates promote homogeneous alloying of MEA combinations inhibiting phase separation. Furthermore, the integrated method circumvents a major obstacle of finding a common ALD temperature window for different noble metal precursors as well as opens new pathways for the controllable synthesis of multicomponent metal alloy thin films with potential catalytic, magnetic, and optical properties.

Vectorial feature and evolution of run-in attractors for the AgCu-MoS2/AgCu10 tribo-pair

Run-in process is a very critical stage before the solid self-lubricating friction pair reaches a steady state. For the identification and prediction of run-in states for AgCu-MoS2/AgCu10 tribo-pair, it is important to understand its evolution law. The run-in tests were carried out under different conditions with a pin-on-disc tribometer, and its friction coefficient signal was collected. Reconstructing phase trajectories using phase space reconstruction and principal component analysis is presented. As an alternative to traditional parameters, we propose vectorial feature parameters with minimum cosine similarity (S_cos_min) and maximum distance between adjacent phase points (Dist_max). S_cos_min and Dist_max identify changes in state and characteristics of the run-in attractor, as well as describe its evolution. The evolution of transfer film morphology on the counter surface demonstrated that the vectorial feature parameters could be used as run-in criteria.

Pseudocapacitive porous amorphous vanadium pentoxide with enhanced multicolored electrochromism

Development of high-performance transparent multicolored electrochromic (EC) materials is crucial for promoting the EC technology for see-through displays and sunglasses. Here, we report a photochemical method for accessing macroporous amorphous vanadium pentoxide (a-V2O5) films with enhanced EC performance for multicolored transparent EC devices. By tracking the composition and morphology evolution of precursor film under UV irradiation, we propose a bubble-templating mechanism to elucidate the formation of macropores in the a-V2O5. The amorphous phase combined with the macroporosity endow the V2O5 films with significantly enhanced multicolored EC performance, which can be attributed to the surface pseudocapacitive mechanism. The pseudocapacitive EC process exhibits faster electrochemical kinetics, higher charge capacity, and less structural destruction to the films than the conventional diffusion-controlled ion insertion/extraction electrochromism, leading to enhanced response times, color palettes, and cycling stability. The high-performance a-V2O5 films enable the fabrication of multicolored see-through EC devices that demonstrate promising application for sun-glasses.

Additive-Induced Film Morphology Evolution for Inverted Dion–Jacobson Quasi-Two-Dimensional Perovskite Solar Cells with Enhanced Performance

In the past decade, three-dimensional (3D) perovskites have been under intense study. However, these devices always suffer from severe performance degradation. Recently, two-dimensional (2D) perovskites have attracted increasing attention due to their excellent environmental stability, but their low power conversion efficiency (PCE) limits their application. Therefore, many strategies have been applied to manipulate the crystallization and suppress the defects and low-n value phases. Additive engineering, as one of the most effective methods to achieve the above-mentioned goals, has been extensively studied. In this contribution, thiourea (TU) and methylammonium chloride (MACl) are successfully employed to contribute synergistically to optimize the crystallization process, leading to an enlarged grain size, smooth and dense surface morphology, and suppressed distribution of n values for improved phase purity. As a result, the optimized inverted Dion–Jacobson (DJ) 2D perovskite solar cell (PSC) device delivers an elevated PCE of 12.16% with a significantly improved short-circuit current density (JSC) of 18.78 mA cm–2 and fill factor (FF) of 62.70%. In addition, the optimized devices show good environmental stability when exposed to ambient air.

In-situ/operando characterization techniques for organic semiconductors and devices

Abstract The increasing demands of multifunctional organic electronics require advanced organic semiconducting materials to be developed and significant improvements to be made to device performance. Thus, it is necessary to gain an in-depth understanding of the film growth process, electronic states, and dynamic structure-property relationship under realistic operation conditions, which can be obtained by in-situ/operando characterization techniques for organic devices. Here, the up-to-date developments in the in-situ/operando optical, scanning probe microscopy, and spectroscopy techniques that are employed for studies of film morphological evolution, crystal structures, semiconductor-electrolyte interface properties, and charge carrier dynamics are described and summarized. These advanced technologies leverage the traditional static characterizations into an in-situ and interactive manipulation of organic semiconducting films and devices without sacrificing the resolution, which facilitates the exploration of the intrinsic structure-property relationship of organic materials and the optimization of organic devices for advanced applications.

Hierarchical formation of Ni sulfide single walled carbon nanotubes heterostructure on tin-sulfide scaffolds via mediated SILAR process: Application towards long cycle-life solid-state supercapacitors

For the enhancement of cyclic life in supercapacitors (SCs), hierarchically formed metallic single-walled carbon nanotubes (m-SWNTs) mediated nickel sulfides (c–NS–TS) heterostructures are synthesized on tin-sulfides (TS) scaffolds via successive ionic layer adsorption and reaction (SILAR) process. As compared with bare SnS2, c–NS–TS formation has effects to improve electrical conductivity and to reduce volume expansion in bare SnS2 scaffolds, leading to better specific capacitance and rate performance in SCs. The film structure, morphology evolution, and capacitive kinetics of c–NS–TS thin films are systematically investigated to understand the behind mechanism on the significantly improved electrochemical performance. Thus, the incorporation of highly conductive, nano-scale m-SWNTs (c–NS–TS) yields high capacitance (1120 Fg-1) with excellent cyclic stability (95%), possibly due to inter-linkage of pure m-SWNTs in the heterostructure. For the enhanced electro-kinetic activity, this is strongly affected by the preferable formation on 3-dimensional c–NS–TS heterostructures, along with highly conductive m-SWNTs, leading to the initiation of the electroactive sites for enhanced electro-kinetic activity. For practical validation on applicability, LED lighting is successfully demonstrated, anticipating that the synthesis concept and its electrochemical properties will contribute to next-generation high-performance SC devices.

Manipulating the film morphology evolution toward green solvent‐processed perovskite solar cells

AbstractHigh‐performance perovskite solar cells (PVSCs) with low energy consumption and green processing are highly desired, but constrained by the difficulty in morphology control and the poor understanding on morphology evolution mechanisms. To address this issue, here we studied the effect of antisolvents on the perovskite film formation. We found that both the antisolvents and the perovskite composition affect the perovskite film morphology greatly via influencing the intermediate phase, and different perovskite compositions require different antisolvents to reach the optimal morphology. This provides the opportunity to achieve high‐performance PVSCs with green antisolvent, that is, isopropanol (iPA) by changing the perovskite compositions, and leads to a power conversion efficiency (PCE) of 21.50% for PVSCs based on MA0.6FA0.4PbI3. Further, we fabricated “fully green” PVSCs with all layers prepared by green solvents, and the optimal PCE can reach 19%, which represents the highest among PVSCs with full‐green processing. This work provides insight into the perovskite morphology evolution and paves the way toward “green” processing PVSCs.

States of water in recast Nafion® films

The amount and states of water in a polymer electrolyte significantly affect the material's morphology as well as its mechanical and transport properties, and thus determine performance in many important applications such as fuel cells, electrolyzers, and other electrochemical energy conversion devices. In this study, recast H+-Nafion® films were characterized using attenuated total internal reflection FTIR (ATR-FTIR) spectroscopy before and after thermal annealing and subsequent rehydration. The states of water in the hydrated films were determined by analyzing the O–H stretching band of water using principle component analysis and multivariate curve resolution. It was found that annealing at a temperature above the glass transition temperature caused the water hydrogen-bonding networks in the water-ionic clusters to become restricted, suggesting that annealing forms a robust polymer matrix confining the water-ionic clusters. The evolution of film morphology with increasing thermal-annealing temperature was confirmed with small-angle X-ray scattering (SAXS) and CO2 diffusion measurements. Fuel cell performance tests using annealed and unannealed Nafion® in the cathode catalyst layer found improved stability when the cathode catalyst was annealed, indicating that thermal history is an important design parameter in electrochemical energy conversion device fabrication.

Metal-Insulator Transition of Ultrathin Sputtered Metals on Phenolic Resin Thin Films: Growth Morphology and Relations to Surface Free Energy and Reactivity.

Nanostructured metal assemblies on thin and ultrathin polymeric films enable state of the art technologies and have further potential in diverse fields. Rational design of the structure–function relationship is of critical importance but aggravated by the scarcity of systematic studies. Here, we studied the influence of the interplay between metal and polymer surface free energy and reactivity on the evolution of electric conductivity and the resulting morphologies. In situ resistance measurements during sputter deposition of Ag, Au, Cu and Ni films on ultrathin reticulated polymer films collectively reveal metal–insulator transitions characteristic for Volmer–Weber growth. The different onsets of percolation correlate with interfacial energy and energy of adhesion weakly but as expected from ordinary wetting theory. A more pronounced trend of lower percolation thickness for more reactive metals falls in line with reported correlations. Ex situ grazing incidence small angle X-ray scattering experiments were performed at various thicknesses to gain an insight into cluster and film morphology evolution. A novel approach to interpret the scattering data is used where simulated pair distance distributions of arbitrary shapes and arrangements can be fitted to experiments. Detailed approximations of cluster structures could be inferred and are discussed in view of the established parameters describing film growth behavior.

Lamellar orientation evolution of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) thin film with 3-hydroxyhexanoate comonomer content difference

The influence of 3-hydroxyhexanoate (HHx) comonomer molar fraction on the morphology and lamellar packing of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx) thin film under spatial confinement were carefully investigated by scanning probe microscope (SPM) and synchrotron radiation grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements. It was found that the HHx comonomer content plays an important role on the crystalline structure of PHBHx thin film on Si substrate. The morphology evolution of PHBHx thin film with increasing HHx content was evident. The crystalline lamellae are packed more loosely with the increase of HHx molar fraction, while the lamellar thickness is decreased.

Fast Organic Vapor Phase Deposition of Thin Films in Light-Emitting Diodes.

Fast deposition of thin films is essential for achieving low-cost, high-throughput phosphorescent organic light-emitting diode (PHOLED) production. In this work, we demonstrate rapid and uniform growth of semiconductor thin films by organic vapor phase deposition (OVPD). A green PHOLED comprising an emission layer (EML) grown at 50 Å/s with bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III) (Ir(ppy)2(acac)) doped into 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP) exhibits a maximum external quantum efficiency of 20 ± 1%. The morphology, charge transport properties, and radiative efficiency under optical and electrical excitation of the PHOLED EML are investigated as functions of the deposition rate via both experimental and theoretical approaches. The EML shows no evidence for gas phase nucleation of the organic molecules at deposition rates as high as 50 Å/s. However, the roll-off in quantum efficiency at high current progressively increases with deposition rate due to enhanced triplet-polaron annihilation. The roll-off results from accumulation of stress within the PHOLED EML that generates a high density of defect states. The defects, in turn, act as recombination sites for triplets and hole polarons, leading to enhanced triplet-polaron annihilation at high current. We introduce a void nucleation model to describe the film morphology evolution that is observed using electron microscopy.

Influence of PECVD-TiO2 film morphology and topography on the spectroscopic ellipsometry data fitting process

TiO2 films of different thickness are deposited on silicon substrate at low temperature and pressure by a Helicon-PECVD reactor. The evolution of film morphology and topography is observed by scanning electron microscopy (SEM) and atomic force microscopy (AFM), meanwhile the spectroscopic ellipsometry (SE) measurements are performed to investigate the film growth mechanism and optical constants. The SEM and AFM observations show that all the films exhibit a columnar structure, moreover all the columns are vertical grown and well-organized when the thickness below [Formula: see text][Formula: see text]80 nm. As the thickness is increased to [Formula: see text][Formula: see text]150 nm, 250 nm and 450 nm, the column size is increased in the top layers, the whole film morphology becomes inhomogeneous, which leads to a decreased density and rougher surface. By fitting the SE measurements, a suitable gradient physical model is found to describe the film morphologies, the model consists of a native SiO2 layer on Si substrate, a mediate layer mixed TiO2 with void whose concentration gradient changed from bottom to top, and a top roughness layer. For thick films ([Formula: see text][Formula: see text]450 nm), the absorption and scattering on the rough surface is considered in order to keep the precision of SE fits. It is found that the optical index is decreased with film thickness, which is related to the evolution of structure in the top layers.

In situ tailoring the hierarchical microstructures in polyethylene films fabricated by thermally induced phase separation via temperature gradient fields

In this study, a series of polyethylene thin films were prepared by thermally induced phase separation (TIPS) method with di(2-ethylhexyl)phthalate as the diluent. Morphological observations showed that the microstructures at different locations were fairly distinct and could generally be divided into three layers. When the polymer concentration was lower than the monotectic point (Φm), both pore size and porosity in TIPS films were heavily determined by growth time and growth rate of the diluent droplets. At relatively higher polymer concentration, cooling rate heavily affected the pore size in the films primarily through its influence on polymers’ crystallization process. The relationship between the film microstructure and cooling rate was quantitatively investigated (especially the effect of quenching conditions on the evolution of film morphology) with the aid of an enthalpy transformation method, which established the three-dimensional temperature profiles and supplied an insight into the competition between phase separation kinetics and polymer crystallization. In addition, our findings showed that the pore size, porosity and thermal stability of films all increased with an increasing quenching temperature, which was significantly different from the trends of variation in water vapor transmission rate as well as the $$ E^{\prime}_{ \hbox{max} } $$ and $$ E^{\prime\prime}_{ \hbox{max} } $$ values of dynamic mechanical analysis as the quenching temperature increased. The present work presents a facile way of in situ tailoring hierarchical microstructures in TIPS films of crystalline polymers, which will be very useful to the design of polymer porous films with specific properties.

Atomistic kinetic Monte Carlo—Embedded atom method simulation on growth and morphology of Cu–Zn–Sn precursor of Cu2ZnSnS4 solar cells

Abstract

Development of residual stress and uniaxial magnetic anisotropy during growth of polycrystalline Co film

Growth of e-beam evaporated Co films on Si (001)/SiO2 substrate has been studied using real-time multi-beam optical stress sensor (MOSS), four probe resistivity (FPR) and in-situ magneto-optic Kerr effect (MOKE) measurements. While MOSS and FPR provide information about internal stress and film morphology, MOKE provides information about magnetic properties, thus making it possible to correlate the evolution of film stress and morphology with that of uniaxial magnetic anisotropy (UMA) in the film. Film grows via Volmer–Weber mechanism, where islands grow larger to impinge with other islands and eventually coalesce into a continuous film at around 10 nm thickness. Development of tensile stress in the film is found to be associated with the island coalescence process. The film exhibits a well-defined UMA, which varies synchronously with internal tensile stress developed during growth, suggesting that the observed UMA originates from minimization of magnetoelastic and morphological anisotropic energies in the presence of internal stress. Absence of UMA in Co film having Ag underlayer in the form of islands is understood in terms of random short-range stress in the film caused by arbitrary pinning by the Ag islands.