Crystal Films Research Articles

CaF2 Nanoparticle-Induced γ-CsPbI2.81Br0.19 Heterogeneous Crystallization for High-Efficiency Flexible All-Inorganic Perovskite Solar Cells.

All-inorganic CsPbI3 films necessitate higher annealing temperatures for high-quality crystallization. Consequently, the conventional low-temperature solution approach often results in poor crystallization in flexible CsPbI3 films, significantly degrading the optoelectronic performance and stability of flexible perovskite solar cells (f-PSCs). Herein, a heterogeneous CaF2 nanocrystal seed-induced strategy has been successfully utilized to achieve enhanced crystallization of a flexible CsPbI2.81Br0.19 film. Due to their good lattice match with the perovskite material, CaF2 nanoparticles can decrease the critical Gibbs free energy of CsPbI2.81Br0.19 perovskite nucleation, thereby accelerating γ-phase CsPbI2.81Br0.19 crystallization at low temperatures. This leads to an improved crystalline quality of the flexible perovskite film at low temperatures, which minimizes defects and enhances the stability of f-PSCs. The CsPbI2.81Br0.19 f-PSCs achieved a champion power conversion efficiency of 15.03% and demonstrated mechanical stability, retaining 98.1% of their initial efficiency even after 60 000 bending cycles with a curvature radius of 5 mm.

Mechanochromic 3D Soft Photonic Crystals Enabled Anticounterfeiting and Encryption Information Storage

AbstractInspired by the color‐changing abilities of natural organisms, this research focuses on the design and fabrication of mechanochromic liquid crystal photonic crystal thin films with periodic self‐assembly structures. Benefiting from its unique 3D self‐assembled structure with a body‐centered cubic lattice, BP I film exhibits excellent mechanical properties, characterized by superior elasticity and toughness due to the presence of rigid and flexible microdomains and suitable dislocation line volumes. As the strain increases, the structural color of the BP I film demonstrates a repeatable and rapid shift from red to blue, covering the entire visible light spectrum with high reflectivity. The incorporation of fluorescent molecules further enhances the mechanical properties and endowing the film with circularly polarized luminescence under UV light irradiation. Utilizing different fluorescent dyes as inks, arbitrary patterned writing can be performed on the BPI film, enabling specific information hiding and encryption. The prepared label exhibits excellent environmental stability, presenting promising applications in information storage, anti‐counterfeiting, and flexible 3D displays. The study may contribute to a deeper understanding of the relationship between microstructure, mechanical deformation, and optical properties, potentially advancing the development of innovative responsive materials and multifunctional devices.

The role of SiO2 buffer layer in the molecular beam epitaxy growth of CsPbBr3 perovskite on Si(111)

Here we present the growth of molecular beam epitaxy (MBE) CsPbBr3 perovskite films in the orthorhombic crystal structure, with unique structural and morphological properties. CsPbBr3 MBE perovskite films, with thickness ranging from a few nm to 300 nm, were grown in ultra-high vacuum on a Si(111)7 × 7 reconstructed surface, and after the formation of about 2 nm of SiO2, obtained exposing the clean reconstructed Si surface to molecular oxygen that serves to decouple the film from substrate. X-ray diffraction, and electron microscopies, such as scanning electron microscopy and high-angle annular dark-field scanning transmission electron microscopy measurements showed remarkable structural, as well as morphological features, indicating extremely high crystallinity over a large area and across the bulk of the perovskite film. Through the X-ray diffraction patterns we found very narrow (002) and (110) reflections of CsPbBr3 in pure orthorhombic phase, exhibiting a full width at half maximum of only 0.035°, value similar to a bulk Si single crystals, and a surface morphology composed of flat areas up to micrometres in lateral size. Our results shed new light both on preparation of high crystal quality perovskite films, and on the intrinsic properties of this striking fully-inorganic materials, which are exploitable for potential applications in electronic/optoelectronic devices and next generation photovoltaic solar cells.

Dielectric behavior and defects of nitrogen-containing single crystal diamond films

Single crystal diamond (SCD) film, as a new substrate material, has attracted growing attention because of its low dielectric loss. The nitrogen was usually introduced into microwave plasma chemical vapor deposition (MPCVD) process in order to enhance the growth rate of SCD films. So SCD films with nitrogen were prepared by MPCVD compared with the undoped film. The impurities and defects of diamond films were characterized by Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and photoluminescence spectroscopy (PL). The dielectric behavior of SCD films was measured using the LCR measurement in the frequency range of 1 kHz to 110 MHz. The results indicate that the primary dielectric loss in SCD films is conductivity loss and space charge polarization below 1 MHz, while the main dielectric loss is dipole orientation polarization and electronic relaxation polarization in the frequency range of 1 MHz to 110 MHz. Point defects like substitutional N+, NV− and SiV− exert a significant influence on polarization loss. This is essential to improve the growth of SCD with excellent dielectric properties.

LiNbO3-based ferroelectric tunnel junctions with changeable electroresistance for data storage

Ferroelectric tunnel junctions (FTJs) have attracted considerable attention for potential applications in the next-generation data storage technologies. In this work, we have grown high-quality LiNbO3 single crystal films on STO (111) substrates by rotational epitaxy. The certain ferroelectricity was achieved in nanoscale epitaxial LiNbO3 films. Then, the Au/LiNbO3/Nb: SrTiO3 FTJ was fabricated, and the nonvolatile resistive switching controlled by the nonvolatile polarization switching was observed. The Au/LiNbO3/Nb: SrTiO3 FTJs regulate the quantum tunneling effect through ferroelectric polarization reversal to obtain multi-level resistive states, thereby achieving data storage functionality. At room temperature, the ON/OFF current ratio can exceed 103. Furthermore, the FTJs also exhibit excellent retention for more than 103 s and good switching endurance for 2000 cycles. The results suggest the application potential of this LiNbO3-based FTJ for next generation nonvolatile ferroelectric memories.

Organic-Inorganic Hybrid Silica Film with a TGBA* Structure.

Twisted grain boundary (TGB) phases exhibit highly frustrated and complex liquid crystal structures, and have attracted enormous interest because of their unique internal structure, textures and properties. However, among the few real concerns related to these interesting structures, applying them to prepare polymer-stabilized colored liquid crystal films has been challenging. Herein, the organic-inorganic hybrid silica (OIHS) films with a TGBA* structure were prepared using two organosilanes and one chiral additive under an acidic condition. The structural color of the films can be adjusted by varying the polycondensation temperature and the concentration of the chiral additive. A structurally colored pattern was prepared by the inject printing, which was suitably applied for decoration and anti-counterfeiting.

Study on the enhancement of device performance by the action of carbonohydrazide at the buried bottom interface of inverted mesoporous perovskite solar cells

The interface of perovskite solar cells (PSCs) significantly influences their efficiency and stability. Researchers tend to pay more attention to the upper surface of the perovskite absorber layer and conduct relatively less research on the bottom buried interface, mainly because the bottom of the perovskite film is challenging to peel off, which increases the difficulty of the characterization of the observation and analysis. Defects at the bottom interface make it more challenging to optimize the treatment than the upper surface. For inverted PSCs, the interface located in direct contact between the light absorption layer of perovskite and the hole transport layer is the buried interface. The buried interface is the direct interface for transporting charge carriers of PSCs and is also the center of non-radiative compound enrichment. The defect density is higher than the defect density of perovskite film crystal. Due to the DMSO initially left in the commonly used perovskite precursor solution during the film formation process, evaporation during the annealing and crystallization process creates vacancy holes at the bottom of the perovskite layer film. These holes and crystal boundaries tend to produce many non-radiative recombinations. These holes are also the sites of photodecomposition, leading to reduced efficiency and stability in PSCs, ultimately impacting the overall performance of PSCs. The work adds an Al2O3 mesoporous layer on top of the hole transport layer (HTL), which reduces the direct contact area between PTAA and perovskite film. In the perovskite precursor solution, we incorporate a solid additive called Carbonohydrazide (CBH), this substance replaces some of the DMSO and fills in the voids at the bottom of the perovskite film that is left when the DMSO evaporates. This process helps to reduce non-radiative recombination and photodegradation caused by the voids at the bottom of the perovskite, leading to an improvement in the efficiency and stability of the cell. The optimization of the buried bottom interface has improved the cell’s average efficiency from 17.6 % to 19.7 %, an 11.9 % increase. The aperture area of the devices in this work is 0.048 cm2, and the photoelectric conversion efficiency of our device still reaches 80.64 % of the initial efficiency after 600 h of continuous heating in a glove box with a nitrogen atmosphere, maintaining a test temperature of 60 °C.

Aromatic carboxyl acid regulated nanoparticle deposition and passivation of tin oxide for high performance perovskite solar cells

The composition and nano particle agglomeration of hydrolyzed species in chemical bath deposition (CBD) plays a key role in obtaining efficient SnO2 film for high performance perovskite solar cells (PSCs). In this work, the aromatic acids with varied carboxyl groups were investigated to regulate the nano particle deposition and passivate the buried SnO2/perovskite interface. The quasi in-situ dynamic light scattering and Zeta potential results indicated that the nano particle agglomeration with trimesic acid (TMA) was significantly refined throughout the whole deposition process. The TMA-SnO2 achieved an ideal energy band alignment with perovskite and released the internal residual strain, promoting the growth and crystallization of the perovskite film due to the corrdination of carboxyl groups. As a result, the interface defects were effectively passivated with enhanced efficiency and stability. The small area device based on TMA-SnO2 obtained an efficiency of 25.07 %. The devices with an enlarged area of 1.4 cm2 and the 5x5 cm2 mini-module (active area 10.054 cm2) showed impressive PCEs of 23.93 % and 22.40 %, respectively. Furthermore, the unencapsulated devices exhibit enhanced long-term stability, maintaining 80 % and 90 % of the initial efficiencies under 80 ± 5°C thermal annealing in nitrogen for 1176 h and in air condition for 3224 h, respectively.

Inhibition oxidation of Sn(II) and regulation crystallization of Sn-Pb perovskite film through interaction engineering for high-performance photovoltaic

Inhibition oxidation of Sn(II) and regulation crystallization of Sn-Pb perovskite film through interaction engineering for high-performance photovoltaic

Infrequent trigonal crystal system CoNb thin films: investigation of growth behavior, microstructure and magnetic properties

Magnetic films with excellent initial permeability, high resonance frequency, suitable anisotropy fields, and well compatibility are highly desirable for on-chip inductors and transformers. Here, Co90Nb10 thin films with different thicknesses are grown on Si substrates of different orientations using an electron beam evaporation technique. A rare trigonal crystal structure of the CoNb films was observed and was virtually unaffected by substrate orientation. Films grown exhibit thickness-dependent magnetic behavior: coercivity initially decreases and then increases, while the in-plane anisotropy field progressively diminishes. Meanwhile, the initial permeability increases initially before decreasing, and the resonance frequency continuously decreases as the thickness increases. The resultant Co90Nb10/Si (111)-50 nm film displays a high μi of 496 and a great fr of 2.1GHz. The improved magnetic performance originates from the smaller crystallite size, smoother surface roughness, and suitable in-plane anisotropy field. Moreover, the in-plane anisotropy transition to the out-of-plane anisotropy in the Co90Nb10 films whose thickness exceeds 70nm, which is attributed to the growth of the coarse columnar grains once the critical thickness is exceeded. This study demonstrates the correlation between the growth behavior, microstructure, and magnetic properties of CoNb thin films, presenting a new potential for utilizing Co-based thin films in high-frequency applications.

Surface Alignment of Liquid Crystal Films on Nanometer-Thick 3D-Printed Line Patterns with Arbitrary Topologies: Implications for Polarization Gratings, Q-Plates, and Beam Steerers

Surface Alignment of Liquid Crystal Films on Nanometer-Thick 3D-Printed Line Patterns with Arbitrary Topologies: Implications for Polarization Gratings, Q-Plates, and Beam Steerers

In-situ passivating surface defects of ultra-thin MAPbBr3 perovskite single crystal films for high performance photodetectors

Ultra-thin single crystal film (SCF) without grain boundary, inherits low charge recombination probability as bulk single crystals. However, its low depth brings a high surface defects ratio and hinders carrier transport and extraction, which affects the performance and stability of optoelectronic devices such as photodetectors, and thus surface defect passivation is of great practical significance. In this paper, we used the space confined method to grow MAPbBr3 SCF and selected BA2PbI4 for surface defect passivation. The results reveal that BA cation passivates MA vacancy surface defects, reduces carrier recombination, and enhances carrier lifetime. The carrier mobility is as high as 33.6 cm2V−1s−1, and the surface defect density is reduced to 3.4 ​× ​1012 ​cm−3. Thus, the self-driven vertical MAPbBr3 SCF photodetector after surface passivation exhibits more excellent optoelectronic performance.

Modelling nematic liquid crystal in fractal dimensions

In this paper we present a fractal Berreman's model which account for azimuthal surface anchoring of nematic liquid crystals which play a leading role nowadays in biomedical field and pharmaceutical controlled release dosage forms. The model is based on the concept of "product-like fractal measure" in anisotropic media which permits to describe liquid crystals formation in terms of fractal dimensions. It was observed that fractal dimensions affect both the polar azimuthal angle and the Franck excess elastic energy density of the distortion. For fractal dimensions close to unity, our analysis reveals the emergence of fluctuations and large deformations in the dynamical variables of the theory which suggest the presence of non-linear elastic instabilities or emergence of defect structures in liquid crystals. These fluctuations fade away for fractal dimensions much less than unity. We have evaluated the elastic energy per unit of area which is found to depend on the square of the fractal dimension. This leads to a decrease of the saturation voltage which is necessary to reduce the elastic energy of liquid crystals films in order to minimize the elastic energy. This reduction may describe nematic liquid crystals free from deformations, singularities or weak anchoring surfaces.

Synergetic effect of non-invasive posttreatment agents enables highly efficient and stable all-inorganic Sn-Pb perovskite solar cells

All-inorganic tin–lead perovskites present a promising avenue for achieving an ideal bandgap, approaching the Shockley-Queisser limit, while circumventing the use of volatile organic cations. However, challenges such as relatively low power conversion efficiency (PCE) and rapid degradation dynamics—stemming from complex film crystallization mechanisms and Sn oxidation—hinder their advancement. In this study, we employed sequential interface engineering on the CsPb0.6Sn0.4I3 system, utilizing non-invasive carbazole propylamine bromide and ethylenediamine diiodide as post-treatment agents. This approach significantly enhances both the bulk structure and surface morphology, thereby promoting charge transport, suppressing non-radiative recombination, and improving structural stability. The champion device achieved a PCE of 16.62 % and demonstrated over 2200 h of T80 stability in dry N2. Remarkably, stability in high-humidity environments was validated through device aging tests and in situ GIWAXS analysis. These results underscore the substantial potential of sub-1.4 eV bandgap all-inorganic Sn-Pb perovskite solar cells.

Epoxy resin-based polymer-wall stabilized liquid crystal films with low driving voltages and improved mechanical performance for smart window applications

Polymer stabilized liquid crystals (PSLCs) have wide applications in smart windows and light shutters. However, for most applications, it requires low driving voltages and high mechanical performance, which is arduous to achieve both. Herein, a novel epoxy resin-based PSLC device is prepared showing improved electro-optical and mechanical properties simultaneously. This is benefited from the construction of a period polymer wall structure in liquid crystal matrix through cationic polymerization of epoxy monomers and preparation of multi-functional surfaces through self-assembly of silane mixtures. The multi-functional surfaces could ensure homeotropic alignment of liquid crystals and photo-polymerize with the polymer networks. As a result, the polymer-wall stabilized liqduid crystal (PWSLC) film with multi-functional surfaces shows lower (24%) saturation voltage, higher (20%) contrast ratio and improved (2.4 times) peel strength than the PSLC film with only vertical alignment surfaces. This research provides important reference to experiment and manufacture of reverse-mode dimming films for smart windows applications.

Unveiling the role of Cs ion in perovskite phase formation during solid–vapor reactions

The preparation of perovskite solar cells (PSCs) using a solid–vapor reaction has shown great potential due to its scalability and lack of organic solvent. The phase formation process in the solid–vapor reaction is crucial for the crystallization of perovskite films. Previous studies mainly introduced Cs into the solid–vapor reaction, but insufficient attention was paid to the role of Cs in purifying the phase formation path during the crystallization process. In this study, we investigated the effect of Cs on the phase formation process in the solid–vapor reaction and found that Cs can decrease the crystallinity of lead halide films, induce a purified phase formation process to prevent the formation of δ-phase and other impurity phases, regulate the crystallization rate of perovskite, and produce high-quality, low-defect perovskite films. The result was achieving a champion power conversion efficiency (PCE) of 21.54 % for a small area (0.148 cm2) and 18.65 % for larger mini-modules (5 × 5 cm2). Furthermore, the devices maintained over 80 % of their initial efficiencies after 450 h of continuous operation under AM 1.5 G irradiation. This work underscores the importance of purified phase formation paths in solid–vapor reactions for outstanding crystal quality in high-performance perovskite solar cells.

Self‐Assembled Biconvex Microlens Array Using Chiral Ferroelectric Nematic Liquid Crystals

AbstractRecently, it is shown (Popov et al, Sci. Rep, 2017, 7, 1603) that chiral nematic liquid crystal films adopt biconvex lens shapes underwater, which may explain the formation of insect eyes, but restrict their practical application. Here it is demonstrated that chiral ferroelectric nematic liquid crystals, where the ferroelectric polarization aligns parallel to the air interface, can spontaneously form biconvex lens arrays in air when suspended in submillimeter‐size grids. Using Digital Holographic Microscopy, it is shown that the lens has a paraboloid shape and the curvature radius at the center decreases with increasing chiral dopant concentration, i.e., with decreasing helical pitch. Simultaneous measurements of the imaging properties of the lenses show the focal length depends on the pitch, thus offering tunability. The physical mechanism of formation of the self‐assembled ferroelectric nematic microlenses is also discussed.

The Correlations between Microstructures and Color Properties of Nanocrystalline Cellulose: A Concise Review.

Cellulose nanocrystals (CNCs) are a green resource which can produce photonic crystal films with structural colors in evaporation-induced self-assembly; CNC photonic crystal films present unique structural colors that cannot be matched by other colored materials. Recently, the mechanisms of CNC photonic crystal films with a unique liquid crystal structure were investigated to obtain homogenous, stable, and even flexible films at a large scale. To clarify the mechanism of colorful CNC photonic crystal films, we briefly summarize the recent advances from the correlations among the preparation methods, microstructures, and color properties. We first discuss the preparation process of CNCs, aiming to realize the green application of resources. Then, the behavior of CNCs in the formation of liquid crystal phases is studied, considering the influence of the CNCs' size and shape, surface properties, and the types and concentrations of solvents. Finally, the film formation process of CNCs and the control of structural colors during the film formation are summarized, as well as the mechanisms of CNC photonic crystal films with full color. In summary, considering the above factors, obtaining reliable commercial CNC photonic crystal films requires a comprehensive consideration of the subsequent preparation processes starting from the preparation of CNCs.

Tailoring Crystallization Kinetics in Thin Sucrose Films during Convective Drying: Impact of Temperature and Humidity on Onset, Growth, and Nucleation Rate.

Drying experiments with varying air temperature and humidity were conducted to investigate the influence of the drying process on the crystallization of thin sucrose films. For the first time, the effects of the nucleation onset, nucleation rate, and growth rate were investigated in situ and their differentiated influence on product crystallinity could be assessed. The growth rate was not influenced by air humidity but showed a strong dependence on temperature. It increased with drying temperature; however, at high temperatures, growth was inhibited when the water content falls below a critical level. Noticeable differences in nucleation behavior could be observed with regard to air humidity. Dry air led to crystallization onsets at lower levels of supersaturation, while moderately humid air retarded it. At higher temperatures, nucleation onset commenced at lower water contents but at a constant supersaturation level. The nucleation rate doubled in experiments with moderately humid air (15% RH), while an elevated drying temperature showed generally lower nucleation rates. The observed differences in the nucleation onset and rate could be explained by the film-internal concentration profile, which is strongly influenced by drying parameters. The insights therefore provide a differentiated understanding of the formation of the physical state and how it can be influenced during convective drying.

Efficient perovskite light-emitting diodes on a flexible substrate.

The surface properties of target substrates are crucial for the in situ crystallization and growth of metal halide perovskite films fabricated by the anti-solvent method. In this work, a high-quality quasi-2D perovskite film with various-n phases is fabricated on the commonly used poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) by introducing a branched polyethylenimine (PEI) modifying layer. PEI suppresses the influence of acidic surface of the PEDOT:PSS and regulates the components of the perovskite film, increasing the proportion of large-n phases. Additionally, PEI reduces the formation of defects in perovskite films, leading to higher photoluminescence quantum efficiency and longer photoluminescence lifetime. Based on this high-quality perovskite film, a flexible light-emitting diode with an ultimate current efficiency of 63.2 cd/A is achieved, nearly twofold higher than that of the device (35.1 cd/A) without a PEI modifying layer.