Grazing Incidence Wide-angle X-ray Scattering Research Articles

Solutions Are the Problem: Ordered Two-Dimensional Covalent Organic Framework Films by Chemical Vapor Deposition.

Covalent organic frameworks (COFs) are a promising class of crystalline polymer networks that are useful due to their high porosity, versatile functionality, and tunable architecture. Conventional solution-based methods of producing COFs are marred by slow reactions that produce powders that are difficult to process into adaptable form factors for functional applications, and there is a need for facile and fast synthesis techniques for making crystalline and ordered covalent organic framework (COF) thin films. In this work, we report a chemical vapor deposition (CVD) approach utilizing co-evaporation of two monomers onto a heated substrate to produce highly crystalline, defect-free COF films and coatings with hydrazone, imine, and ketoenamine COF linkages. This all-in-one synthesis technique produces highly crystalline, 40 nm-1 μm-thick COF films on Si/SiO2 substrates in less than 30 min. Crystallinity and alignment were proven by using a combination of grazing-incidence wide-angle X-ray scattering (GIWAXS) and transmission electron microscopy (TEM), and successful conversion of the monomers to produce the target COF was supported by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV-vis measurements. Additionally, we used atomic force microscopy (AFM) to investigate the growth mechanisms of these films, showing the coalescence of triangular crystallites into a smooth film. To show the wide applicability and scope of the CVD process, we also prepared crystalline ordered COF films with imine and ketoenamine linkages. These films show potential as high-quality size exclusion membranes, catalytic platforms, and organic transistors.

Evolution of the characterization of horizontally aligned organic light‐emitting molecules and their recent progress of molecular design

AbstractThis review article surveys the organic small molecular materials, light‐emitting for most of them, being studied for the molecular alignment or orientation in thin films. Following a chronicle order, three practical characterization techniques, variable angle spectroscopic ellipsometry (VASE), angle‐dependent photoluminescence (ADPL), and grazing incidence wide‐angle x‐ray scattering (GIWAXS) have been used to probe phosphorescence, thermally activated delayed fluorescence (TADF) materials, as well as those of non‐phosphorescence and non‐TADF materials.

Intermediate Phase Free α-FAPbI3 Perovskite via Green Solvent Assisted Perovskite Single Crystal Redissolution Strategy.

Perovskite single-crystal redissolution (PSCR) strategy is highly desired for efficient formamidinium lead triiodide (FAPbI3 ) perovskite photovoltaics with enhanced phase purity, improved film quality, low trap-state density, and good stability. However, the phase transition and crystallization dynamics of FAPbI3 remain unclear in the PSCR process compared to the conventional fabrication from the mixing of precursor materials. In this work, a green-solvent-assisted (GSA) method is employed to synthesize centimeter-sized α-FAPbI3 single crystals, which serve as the high-purity precursor to fabricate perovskite films. The α-FAPbI3 PSCR strategy facilitates direct α-phase formation and inhibits the complex intermediate phases monitored by in situ grazing-incidence wide-angle X-ray scattering. Moreover, the α-phase stability is prolonged due to the relaxation of the residual lattice strain through the isotropic orientation phase growth. Consequently, the GSA-assisted PSCR strategy effectively promotes crystallization and suppresses non-radiative recombination in perovskite solar cells, which boosts the device efficiency from 22.08% to 23.92% with significantly enhanced open circuit voltage. These findings provide deeper insight into the PSCR process in terms of its efficacy in phase formation and lattice strain release. The green low-cost solvent may also offer a new and ideal solvent candidate for large-scale production of perovskite photovoltaics.

Enhanced Optical Contrast and Switching in Near‐Infrared Electrochromic Devices by Optimizing Conjugated Polymer Oligo(Ethylene Glycol) Sidechain Content and Gel Electrolyte Composition

AbstractA detailed investigation addressing the effects of functionalizing conjugated polymers with oligo(ethylene glycol) (EGn) sidechains on the performance and polymer‐electrolyte compatibility of electrochromic devices (ECDs) is reported. The electrochemistry for a series of donor‐acceptor copolymers having near‐infrared (NIR)‐optical absorption, where the donor fragment is 3,4‐ethylenedioxythiophene (EDOT) or an EGn functionalized bithiophene (g2T) and the acceptor fragment is diketopyrrolopyrrole (DPP) functionalized with branched alkyl or EGn sidechains, is extensively probed. ECDs are next fabricated and it is found that EGn sidechain incorporation must be finely balanced to promote polymer‐electrolyte compatibility and provide efficient ion exchange. Proper electrolyte‐cation pairing and polymer structural tuning affords a 2x increase in optical contrast (from 12% to 24%) and >60x reduction in switching time (from 20 to 0.3 s). Atomic force microscopy (AFM)/grazing incidence wide‐angle X‐ray scattering (GIWAXS) characterization of the polymer film morphology/microstructure reveals that an over‐abundance of EGn sidechains generates large polymer crystallites, which can suppress ion exchange. Lastly, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) indicates sidechain/electrolyte identity does not influence the electrolyte penetration depth into the films, and EGn sidechain inclusion increases electrolyte cation uptake. The material structural design insight and guidelines regarding the polymer‐electrolyte ion insertion/expulsion dynamics reported here should be of significant utility for developing next‐generation mixed ionic‐electronic conducting materials.

Green Colloidal Synthesis of MoS2 Nanoflakes.

Currently, two approaches dominate the large-scale production of MoS2: liquid-phase exfoliation, referred to as the top-down approach, and bottom-up colloidal synthesis from molecular precursors. Known colloidal synthesis approaches utilize toxic precursors. Here, an alternative green route for the bottom-up synthesis of MoS2 nanoflakes (NFs) is described. The NFs were synthesized by colloidal synthesis using [Mo(CH3COO)2]2 and a series of sulfur (S)-precursors including thioacetamide (TAA), 3-mercaptopropionic acid (3-MPA), l-cysteine (L-CYS), mercaptosuccinic acid (MSA), 11-mercaptoundecanoic acid (MUA), 1-dodecanethiol (DDTH), and di-tert-butyl disulfide (DTBD). While TAA, an S-precursor most commonly used for MoS2 NF preparation, is a known carcinogen, the other investigated S-precursors have low or no known toxicity. High-resolution scanning transmission electron microscopy (HR-STEM) and grazing incidence wide-angle X-ray scattering (GIWAXS) confirmed that in all cases, the syntheses yielded single-layer MoS2 NFs with lateral sizes smaller than 15 nm and a well-defined crystal structure. Electronic absorption and Raman spectra showed characteristic features associated with the MoS2 monolayers. The evolution of the absorption spectra of the growth solution during the syntheses reveals how the kinetics of the NF formation is affected by the S-precursor as well as the nature of the coordinating ligands.

Tailoring the electronic properties of the SnO2 nanoparticle layer for n-i-p perovskite solar cells by Ti3C2TX MXene

The effect of the Ti3C2Tx MXene modification of the SnO2 electron transport layer (ETL) was studied for the concentration range 0–7.4 wt% MXene. The electronic properties of the MXene-modified ETL were studied by the electrical conductivity measurements, density of states mapping by the energy-resolved electrochemical impedance spectroscopy, ultraviolet photoelectron spectroscopy, and photoluminescence. The structure and morphology of the MXene-modified ETL and the top perovskite layer were analyzed by the scanning electron microscopy (SEM), scanning transmission electron microscopy, grazing-incidence X-ray diffraction and in situ grazing-incidence wide-angle X-ray scattering (GIWAXS). The increased electrical conductivity and electron selectivity for the MXene-modified SnO2 ETL was confirmed up to 1 wt% MXene. For 7.4 wt% MXene, significant suppression of the hole blocking property of the ETL was found. The in situ GIWAXS was performed during the post-deposition annealing of the perovskite layer. The increased perovskite grain size on the SnO2 ETL modified by MXene compared to the pure SnO2 ETL visible by SEM was confirmed. The uniaxial texture of the perovskite crystals was revealed in both cases with an increased misorientation angle for the MXene-modified ETL. The grain size and misorientation angle do not exhibit any systematic temporal changes during the post-deposition annealing. The increasing number of the grains during the annealing was observed. These results are explained using the nucleation and growth model. The increased power conversion efficiency from 17.4% to 18.3% of the archetypal methylammonium-lead-iodide perovskite solar cell after the modification of the SnO2 ETL with 0.1 wt% MXene is the effect of two contributions - increased electrical conductivity of the ETL and improved crystallinity and larger grain size compared to the pure SnO2 ETL, which lowers the total boundary area and charge recombination at trap states typically formed at grain boundaries.

Chemical Behavior and Local Structure of the Ruddlesden-Popper and Dion-Jacobson Alloyed Pb/Sn Bromide 2D Perovskites.

The alloyed lead/tin (Pb/Sn) halide perovskites have gained significant attention in the development of tandem solar cells and other optoelectronic devices due to their widely tunable absorption edge. To gain a better understanding of the intriguing properties of Pb/Sn perovskites, such as their anomalous bandgap's dependence on stoichiometry, it is important to deepen the understanding of their chemical behavior and local structure. Herein, we investigate a series of two-dimensional Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phase alloyed Pb/Sn bromide perovskites using butylammonium (BA) and 3-(aminomethyl)pyridinium (3AMPY) as the spacer cations: (BA)2(MA)n-1PbxSnn-xBr3n+1 (n = 1-3) and (3AMPY)(MA)n-1PbxSnn-xBr3n+1 (n = 1-3) through a solution-based approach. Our results show that the ratio and site preference of Pb/Sn atoms are influenced by the layer thickness (n) and spacer cations (A'), as determined by single-crystal X-ray diffraction. Solid-state 1H, 119Sn, and 207Pb NMR spectroscopy analysis shows that the Pb atoms prefer the outer layers in n = 3 members: (BA)2(MA)PbxSnn-xBr10 and (3AMPY)(MA)PbxSnn-xBr10. Layered 2D DJ alloyed Pb/Sn bromide perovskites (3AMPY)(MA)n-1PbxSnn-xBr3n+1 (n = 1-3) demonstrate much narrower optical band gaps, lower energy PL emission peaks, and longer carrier lifetimes compared to those of RP analogs. Density functional theory calculations suggest that Pb-rich alloys (Pb:Sn ∼4:1) for n = 1 compounds are thermodynamically favored over 50:50 (Pb:Sn ∼1:1) compositions. From grazing-incidence wide-angle X-ray scattering (GIWAXS), we see that films in the RP phase orient parallel to the substrate, whereas for DJ cases, random orientations are observed relative to the substrate.

High‐Resolution and Stable Ruddlesden–Popper Quasi‐2D Perovskite Flexible Photodetectors Arrays for Potential Applications as Optical Image Sensor

AbstractThe development of an efficient fabrication route to achieve high‐resolution perovskite pixel array is key for large‐scale flexible image sensor devices. Herein, a high‐resolution and stable 10 × 10 flexible PDs array based on formamidinium(FA+) and phenylmethylammonium (PMA+) quasi‐2D (PMA)2FAPb2I7 (n = 2) perovskite is demonstrated by developing SiO2‐assisted hydrophobic and hydrophilic treatment process on polyethylene terephthalate substrate. By introducing Au nanoparticles (Au NPs), the perovskite film quality is improved and grain boundaries are reduced. The mechanism by which Au NPs upgrade the photoelectric quality of perovskite is mainly revealed by glow discharge‐optical emission spectroscopy (GD‐OES) and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS). To further improve the photoelectric performance of the devices, a post‐treatment strategy with formamidinium chloride (FACl) is used . The optimized flexible PDs arrays show excellent optoelectronic properties with a high responsivity of 4.7 A W−1, a detectivity of 6.3 × 1012 Jones, and a broad spectral sensitivity. The device also exhibits excellent electrical stability even under severe bending and excellent flexural strength, as well as excellent environmental stability. Finally, the integrated flexible PDs arrays are used as sensor pixels in an imaging system to obtain high‐resolution imaging patterns, demonstrating the imaging capability of the PDs arrays.

The Role of Device Mobility on the Charge Generation Process in Polymerized Small-Molecule Acceptor Based Organic Solar Cells

We investigate the role of backbone tuning of contemporary polymerized small-molecule acceptors (PSMAs), namely PJ2, PJTVT, and PJTET, on the charge generation process when blended with JD40 polymers to explain the difference between their device short circuit current, JSC. We utilize transient absorption (TA) spectroscopy and grazing incidence wide-angle X-ray scattering (GIWAXS) measurements to demonstrate the face-on π–π and lamellar stackings impact on the diffusion of excitons in pristine films. Comparing the charge generation process to data obtained from space-charge-limited current (SCLC) measurements, we show that the generation of free charge carriers, although limited by geminate recombination of charge transfer (CT) pairs, is improved with a higher charge-carrier device mobility. A higher mobility is found to also drive charge generation limited by the same recombination more efficiently than blend systems where the charges recombine nongeminately. We show that an increment of ∼0.1 eV corresponds to an ∼5% increase in the device EQE for the same mobility. Based on the data compiled from the literature and the study herein, a mobility of at least 10–3 cm2 V–1 s–1 is postulated for an EQE of at least 90%. Finally, we observe an apparent logarithmic relationship between the charge-carrier mobility and the generation of photocurrent, in lieu of a linear relationship introduced by the Braun–Onsager model. The same trend remains for surveyed literature data of contemporary Y-series acceptor-based OPV devices. This work highlights that to improve the JSC of current state-of-art OPV devices, the mobility of a device can be improved through material designs and device engineering for a higher charge generation efficiency.

How to GIWAXS: Grazing Incidence Wide Angle X‐Ray Scattering Applied to Metal Halide Perovskite Thin Films

AbstractThe frequency of reports utilizing synchrotron‐based grazing incident wide angle X‐ray scattering (GIWAXS) to study metal halide perovskite thin films has exploded recently, as this technique has proven invaluable for understanding several structure‐property relationships that fundamentally limit optoelectronic performance. The GIWAXS geometry and temporal resolution are also inherently compatible with in situ and operando setups (including ISOS protocols), and a relatively large halide perovskite research community has deployed GIWAXS to unravel important kinetic and dynamic features in these materials. Considering its rising popularity, the aim here is to accelerate the required learning curve for new experimentalists by clearly detailing the underlying analytical concepts which can be leveraged to maximize GIWAXS studies of polycrystalline thin films and devices. Motivated by the vast range of measurement conditions offered, together with the wide variety of compositions and structural motifs available (i.e., from single‐crystal and polycrystalline systems, to quantum dots and layered superlatices), a comprehensive framework for conducting effective GIWAXS experiments is outlined for different purposes. It is anticipated that providing a clear perspective for this topic will help elevate the quality of future GIWAXS studies—which have become routine—and provide the impetus required to develop novel GIWAXS approaches to resolve unsettled scientific questions.

A Novel Multi‐Functional Thiophene‐Based Organic Cation as Passivation, Crystalline Orientation, and Organic Spacer Agent for Low‐Dimensional 3D/1D Perovskite Solar Cells

AbstractRecently, the mixed‐dimensional (3D/2D or 3D/1D) perovskite solar cells using small organic spacers have attracted interest due to their outstanding long‐term stability. Here, a new type of thiophene‐based organic cation 2‐(thiophene‐2yl‐)pyridine‐1‐ium iodide (ThPyI), which is used to fabricate mixed‐dimensional 3D/1D perovskite solar cells, is presented. The ThPyI‐based 1D perovskitoid is applied as a passivator on top of a 3D methyl ammonium lead iodide (MAPI) to fabricate surface‐passivated 3D/1D perovskite films or added alone into the 3D perovskite precursor to generate bulk‐passivated 3D MAPI. The 1D perovskitoid acts as a passivating agent at the grain boundaries of surface‐passivated 3D/1D, which improves the power conversion efficiency (PCE) of the solar cells. Grazing incidence wide‐angle X‐ray scattering (GIWAXS) studies confirm that ThPyI triggers the preferential orientation of the bulk MAPI slabs, which is essential to enhance charge transport. Champion bulk‐passivated 3D and surface‐passivated 3D/1D devices yield 14.10% and 19.60% PCE, respectively. The bulk‐passivated 3D offers favorable stability, with 84% PCE retained after 2000 h without encapsulation. This study brings a new perspective to the design of organic spacers having a different binding motif and a passivation strategy to mitigate the impact of defects in hybrid 3D/1D perovskite solar cells.

Active SnO2 Crystal Planes Enable Efficient and Ultra‐Bendable n‐i‐p Perovskite Solar Cells with Record Certificated Power Conversion Efficiency

AbstractThe tin (IV) oxide (SnO2) electron transport layer (ETL) has been widely employed to fabricate high‐performance perovskite solar cells (PSCs). It has been reported that carbon quantum dots (CQDs) can be used to enhance electron mobility of SnO2. However, an in‐depth understanding of the driving force in this process is still lacking. Here, a high‐angle annular dark‐field scanning transmission electron microscope (HAADF‐STEM) is employed, for the first time, to reveal the SnO2 crystal face changes with one new type of CQD doping. Synchrotron‐based grazing incidence wide‐angle X‐ray scattering (GIWAXS) can penetrate the flexible substrate to detect the buried region of the perovskite layer, showing the crystallinity and phase purity of the perovskite are significantly improved with CQD‐modified SnO2. The flexible n‐i‐p PSCs delivers a power conversion efficiency (PCE) up to 23.57% (22.75%, certificated), which is one of the highest values for single‐junction n‐i‐p flexible PSCs. The corresponding n‐i‐p flexible modules achieve a PCE of 17.79% with aperture area ~ 24 cm2. Furthermore, the flexible PSCs show excellent stability, preserving ≈95% of their initial efficiency after 1200 h under 40% relative humidity and 1‐sun light irradiation at 25 °C, and maintained > 90% of initial efficiency after 2500 bending cycles at a bending radius of 6 mm.

Residual Strain Evolution Induced by Crystallization Kinetics During Anti-Solvent Spin Coating in Organic-Inorganic Hybrid Perovskite.

Organic-inorganic hybrid perovskite (OIHP) polycrystalline thin films are attractive due to their outstanding photoelectronic properties. The anti-solvent spin coating method is the most widely used to synthesize these thin films, and the residual strain is inevitably originates and evolves during the process. However, this residual strain evolution induced by crystallization kinetics is still poorly understood. In this work, the in situ and ex situ synchrotron grazing-incidence wide-angle X-ray scattering (GIWAXS) are utilized to characterize the evolution and distribution of the residual strain in the OIHP polycrystalline thin film during the anti-solvent spin coating process. A mechanical model is established and the mechanism of the crystallization kinetics-induced residual strain evolution process is discussed. This work reveals a comprehensive understanding of the residual strain evolution during the anti-solvent spin coating process in the OIHP polycrystalline thin films and provides important guidelines for the residual strain-related strain engineering, morphology control, and performance enhancement.

Grazing-incidence diffraction reveals cellulose and pectin organization in hydrated plant primary cell wall

The primary cell wall is highly hydrated in its native state, yet many structural studies have been conducted on dried samples. Here, we use grazing-incidence wide-angle X-ray scattering (GIWAXS) with a humidity chamber, which enhances scattering and the signal-to-noise ratio while keeping outer onion epidermal peels hydrated, to examine cell wall properties. GIWAXS of hydrated and dried onion reveals that the cellulose (110/1overline{1}0) lattice spacing decreases slightly upon drying, while the (200) lattice parameters are unchanged. Additionally, the (110/1overline{1}0) diffraction intensity increases relative to (200). Density functional theory models of hydrated and dry cellulose microfibrils corroborate changes in crystalline properties upon drying. GIWAXS also reveals a peak that we attribute to pectin chain aggregation. We speculate that dehydration perturbs the hydrogen bonding network within cellulose crystals and collapses the pectin network without affecting the lateral distribution of pectin chain aggregates.

GIWAXS Characterization of Metal–Organic Framework Thin Films and Heterostructures: Quantifying Structure and Orientation

AbstractFor optoelectronic applications of metal–organic framework (MOF) thin films, it is important to be able to fabricate films and heterostructures that are highly oriented relative to the substrate's surface normal. However, process optimization to achieve this is difficult without sufficiently detailed structural characterization of the deposited films. It is demonstrated that 2D grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) data from a laboratory system go a long way to providing such characterization and can 1) better test structural models than 1D scans, 2) provide a quantitative estimate—useful for process optimization—of the fraction of the deposited film that has the desired surface‐oriented texture (2D powder), and 3) deliver such information as a function of depth into the film—useful for heterostructure characterization. Herein, GIWAXS data collection and analysis are introduced in the context of understanding MOF thin films, then it is shown how the desired oriented fraction (2D powder fraction) of UiO‐66 fabricated by vapor‐assisted conversion can be increased from 4% to over 95% by minimizing nucleation in solution. Finally, it is demonstrated that heterostructures of UiO‐66 and UiO‐67 can be grown wherein both layers are highly ordered (UiO‐66 83%, UiO‐67 >94%) once synthetic protocols are optimized.

Not Just Surface Energy: The Role of Bis(pentafluorophenoxy) Silicon Phthalocyanine Axial Functionalization and Molecular Orientation on Organic Thin-Film Transistor Performance.

Understanding the effect of surface chemistry on the dielectric-semiconductor interface, thin-film morphology, and molecular alignment enables the optimization of organic thin-film transistors (OTFTs). We explored the properties of thin films of bis(pentafluorophenoxy) silicon phthalocyanine (F10-SiPc) evaporated onto silicon dioxide (SiO2) surfaces modified by self-assembled monolayers (SAMs) of varying surface energies and by weak epitaxy growth (WEG). The total surface energy (γtot), dispersive component of the total surface energy (γd), and polar component of the total surface energy (γp) were calculated using the Owens-Wendt method and related to electron field-effect mobility of devices (μe), and it was determined that minimizing γp and matching γtot yielded films with the largest relative domain sizes and highest resulting μe. Subsequent analyses were completed using atomic force microscopy (AFM) and grazing-incidence wide-angle X-ray scattering (GIWAXS) to relate surface chemistry to thin-film morphology and molecular order at the surface and semiconductor-dielectric interface, respectively. Films evaporated on n-octyltrichlorosilane (OTS) yielded devices with the highest average μe of 7.2 × 10-2 cm2·V-1·s-1 that we attributed to it having both the largest domain length, which were extracted from power spectral density function (PSDF) analysis, and a subset of molecules with a pseudo edge-on orientation relative to the substrate. Films of F10-SiPc with the mean molecular orientation of the π-stacking direction being more edge-on relative to the substrate also generally resulted in OTFTs with a lower average VT. Unlike conventional MPcs, F10-SiPc films fabricated by WEG experienced no macrocycle in an edge-on configuration. These results demonstrate the critical role of the F10-SiPc axial groups on WEG, molecular orientation, and film morphology as a function of surface chemistry and the choice of SAMs.

The Multiplicity of π-π Interactions of Fused-Ring Electron Acceptor Polymorphs on the Exciton Migration and Charge Transport.

Efficient long-range exciton migration and charge transport are the key parameters for organic photovoltaic materials, which strongly depend on the molecular stacking modes. Herein, we extracted the stacked structures of the archetype fused-ring electron acceptor molecule, ITIC, based on the information on four polymorphic crystals and investigated the relationship between molecular stacking modes and exciton migration/charge transport properties through the intermolecular Coulomb coupling and charge transfer integral calculation. Experimentally, the thin film texture is crystallized through a post-annealing treatment through grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements, which lead to the enhanced exciton migration through exciton-exciton annihilation in the femtosecond transient absorption (fs-TA) measurements. This work demonstrates the relationship between the molecular arrangement and the exciton migration and electron transport and highlights the significance of optimizing molecular stacking for the development of high-performance electron acceptor materials.

Classic Fluorophores With a Horizontal Alignment for Enhancing Light Outcoupling Efficiency (≈30%) and External Quantum Efficiency (≈7%) of Near Ultraviolet (λmax < 400 nm) Organic Light‐Emitting Diodes

AbstractBased on the classic 1,1′:4′,1″‐terphenyl fluorophore, a novel near‐ultraviolet (NUV) fluorescent BB4Ph (4,4″′‐bis(2,3,4,5‐tetraphenylphen‐1‐yl)(1,1′:4′,1″‐terphenyl) is designed, synthesized, and characterized. BB4Ph exhibits a NUV fluorescence with a λmax of 373 and 380 nm in solution and as a thin film, respectively. The grazing incidence wide‐angle X‐ray scattering (GIWAXS) reveals BB4Ph having a high value of order parameter (SGIWAXS) of 0.59 for a molecular layer array normal to the substrate; the angle‐dependent photoluminescence (ADPL) measurement shows Θ (horizontal–dipole ratios) as high as 95% with the neat film. The non‐doped BB4Ph organic light‐emitting diodes (OLEDs) show external quantum efficiency (EQE) up to 5.24% with 1931 Commission Internationale de l’ Eclairage coordinates (CIEx,y) of (0.16, 0.04), a NUV electroluminescence. With 4P‐Cz (9,9′‐(1,1′:4′,1″:4″,1′″‐quaterphenyl‐4,4′″‐diyl)dicarbazole) as a dopant emitter, doped BB4Ph OLEDs show the highest EQE of 6.99% and a NUV 1931 CIEx,y (0.16, 0.04). The photoluminescence quantum yield is measured for the thin film of BB4Ph and 4P‐Cz:BB4Ph as 68% and 96%, respectively. Hence, the low limits of light outcoupling efficiency (ηout) of the two individual OLEDs are estimated as 31% and 29%, respectively.

Hyperaging-induced H2-selective thin-film composite membranes with enhanced submicroporosity toward green hydrogen supply

Repurposing the existing natural gas infrastructure by blending hydrogen with methane (i.e., Hythane) is one feasible option to develop a low-carbon hydrogen supply chain, although this process requires extraction of the hydrogen from Hythane after distribution. Membrane technology is a potential solution to tackle this application given its many advantages over other separation methods. However, industrial use of developed membrane materials has been challenging due to several practical concerns; for example, insufficient separation abilities and accelerated physical aging of thin membranes in high-free-volume glassy polymers. Herein, we propose an integrated strategy to develop highly H2-selective thin-film composite (TFC) membranes by tuning the aging behavior of polymers of intrinsic microporosity (PIM) thin films. Detailed gas permeation and two-dimensional (2D) grazing incidence wide-angle x-ray scattering (GIWAXS) studies reveal that triptycene-based PIM TFC membranes can exploit beneficial aging effects resulting from aging-induced enhancement in submicroporosity. To directly deploy TFC membranes, a simple post-treatment step was introduced to increase the aging rate, termed “hyperaging.” The hyperaged TFC membranes exhibited high H2/CH4 mixed-gas selectivity (>100), moderate H2 permeance (∼100 GPU), and good long-term stability when tested using a binary mixture with dilute H2 concentration (20 mol%), demonstrating promise for downstream hydrogen extraction toward green hydrogen supply.

Influence of Tacticity on the Structure Formation of Poly(methacrylic acid) in Langmuir/Langmuir–Blodgett and Thin Films

AbstractA perfect isotactic poly(methacrylic acid) (it‐PMAA) is synthesized and characterized by NMR spectroscopy. Surface pressure versus mean area per repeat unit (π−A) isotherms are recorded and compared with atactic poly(methacrylic acid) (at‐PMAA). it‐PMAA exhibits a π−A isotherm, indicating the formation of a stable Langmuir film. The isotherm has a characteristic pseudo‐plateau at π of ≈11–14 mN m−1 attributed to the creation of worm‐like entities confirmed by atomic force microscopy (AFM) in Langmuir–Blodgett (LB) films. These structures transform into spherical nanoparticles of ≈40 to 80 nm seen in LB films transferred at the end of the pseudo‐plateau of the isotherm. Grazing incidence wide‐angle X‐ray scattering (GI‐WAXS) shows a broad scattering signal (halo‐like) at a q position of ≈11.12 nm−1, revealing the amorphous nature of the nanoparticles. An ordered morphology, however, is observed in thin films prepared by precipitating it‐PMAA from dimethylformamide (DMF) solution under vigorous stirring and coating them on a solid support. Optical microscopy (OM), AFM, and GI‐WAXS reveal more details about the structure. Finally, various structural modifications of PMAAs are explained based on their tacticity and the subsequent hydrogen bonding effects between the carboxylic acid groups.