Incidence Wide-angle X-ray Diffraction Research Articles

Improving Photovoltaic Performance of All-Polymer Solar Cells by Adding An Amorphous B←N Embedded Polymer as the Third Component.

Currently, most of the disclosed ternary strategies to improve photovoltaic performance of all-polymer solar cells commonly focus on the guest polymers having similar structures with the host polymer donors or acceptors. Herein, we develop a distinctive ternary method that adding an amorphous B←N embedded polymer named BN-Cl-2fT to a crystallized host polymer blend of PM6 and PY-TT (a copolymer of Y6 and thieno[3,2-b]thiophene). Although the structures between BN-Cl-2fT and PM6 and PY-TT are completely different, excellent miscibility is found between BN-Cl-2fT and both of the host PM6 and PY-TT, which can be interpreted by the crowded phenyl groups anchoring along the backbone of BN-Cl-2fT, leading to weak self-aggregation. GIWAXS measurements explicitly confirm the crystallization of PM6 and PY-TT and amorphous feature of BN-Cl-2fT. Furthermore, adding 10 wt% BN-Cl-2fT to PM6:PY-TT could significantly enhance the crystallization of the host polymers. Thus the ternary devices based on PM6:PY-TT:BN-Cl-2fT afford promoted JSC (23.29versus 21.80mA/cm2 ), FF (62.4%versus 60.0%), and PCE (13.70%versus 12.23%) in contrast to these parameters of binary devices based on PM6:PY-TT. We provide a unique and enlightening avenue to design high performance all-PSCs by adding amorphous B←N embedded polymers as guest component to enhance host-crystallization. This article is protected by copyright. All rights reserved.

Polymer-Gated Transistors with Only One Solution-Processed, Single Crystalline Organic Microwire for Light and Oxygen Detection.

Organic semiconductors employed in single crystalline form have several advantages over polycrystalline films, such as higher charge carrier mobility and better environmental stability. Herein, we report the fabrication and characterization of a solution-processed microsized single-crystalline organic wire of n-type N,N'-dipentyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C5). The crystal was applied as an active layer in polymer-gated organic field-effect transistors (OFETs) and organic complementary inverter circuits. The single crystaiiline nature of PTCDI-C5 wires were characterized using two-dimensional grazing incidence wide-angle X-ray diffraction (2D-GIXD) and polarized optical microscopy. OFETs with the PTCDI-C5 crystals exhibited high n-type performance and air stability under ambient conditions. To investigate the electrical properties of the single-crystalline PTCDI-C5 wire more precisely, OFETs with only one PTCDI-C5 microwire in the channel were fabricated, and clear n-type characteristics with satisfactory saturation behavior were observed. The device with only one crystal wire exhibited characteristics with significantly lower variation compared to the multicrystal devices, which shows that the density of crystal wires is a critical factor in precisely investigating device performance. The devices exhibited a reversible threshold voltage shift under vacuum and oxygen conditions, without changing the charge carrier mobility. Light-sensitive characteristics were also observed. Additionally, this solution-processed, highly crystalline organic semiconductor can be used in high-performance organic electronic circuits as well as in gas or light sensors.

Efficient Hole Transfer from a Twisted Perylenediimide Acceptor to a Conjugated Polymer in Organic Bulk-Heterojunction Solar Cells.

Non-fullerene acceptors have recently attracted tremendous interest due to their potential as alternatives to fullerene derivatives in bulk-heterojunction solar cells. Nevertheless, physical understanding of charge carrier generation and transfer mechanism that occurred at the interface between the non-fullerene molecule and donor polymer is still behind their enhanced photovoltaic performance. Here we report examples of a non-planar perylene dimer (TP) as an electron acceptor and achieve a power conversion efficiency of 6.29% in a fullerene-free solar cell. Photoluminescence (PL) measurements show high quenching efficiency driven by the excitons of both conjugated polymer and TP molecule, respectively, indicating efficient electron and hole transfer, which can support a highly intermixed phase of blends measured by atomic force microscopy (AFM) and grazing incident wide-angle X-ray diffraction (GIWAXS). Femtosecond transient absorption spectroscopy (fs-TAS) reveals that the fast exciton dissociation process from TP molecule to donor polymer contributes to additionally increasing current density, leading to stronger incident photon to current efficiency in the visible region.

Fluorinated Benzothiadiazole-based polymers with chalcogenophenes for organic field-effect transistors

The effect of incorporating chalcogenophene comonomers, namely, furan, thiophene, and selenophene, on the optoelectrical properties of cyclopentadithiophene-based polymers (P1, P2, and P3, respectively) for organic field-effect transistors is reported. The optical, electrical, and morphological properties of the P1, P2, and P3 are investigated. Compared to the other polymers, the P2 showed the highest crystallinity with the shortest π–π stacking distance ( d π–π ≈ 3.58 Å) and the longest crystalline length ( L c ≈ 40 Å), as confirmed by two-dimensional grazing incidence wide-angle X-ray diffraction. However, P3 had the highest hole mobility ( μ = 0.25 cm 2 /V-s), which is higher than P1 ( μ = 0.06 cm 2 /V-s) and P2 ( μ = 0.20 cm 2 /V-s). The relatively lower mobility of the P2 than of the P3 is attributed to its island-like crystalline domains, confirmed by atomic force microscopy results and the edge-on dominant orientation. Our findings suggest a new design guideline for developing high-mobility π-conjugated polymers. • We first address the importance of size of substituted atoms in determining optoelectronic properties and thin film crystallinity of the FBT-based polymers. • The influence of chalcogenophene atom substitution on optoelectrical properties of the FBT-based polymers was thorough investigated. • Combining a highly-crystallized molecular packing with effective morphologies led to the best hole mobilities of 0.25 cm 2 V −1 s −1 for P3.

Surface crystalline structure of thin poly(l-lactide) films determined by the long-range substrate effect

Due to the stepwise crystallization behavior of polymorphous poly(l-lactide) (PLLA) films, the surface crystalline structures of thin PLLA films supported on Si/SiOx substrates with various thicknesses of both the film and adsorbed layer were investigated separately by grazing incidence wide-angle X-ray diffraction (GIWAXD). An unusual highly packed α-form crystal was observed at the surface at a crystallization temperature of 346 K, which transformed to a loosely packed δ-form (or called α′-form) crystal with decreasing film thickness or increasing adsorbed layer thickness. The mobility of the surface chains of PLLA films was scaled by the surface crystallization rate to elucidate the substrate effect on the corresponding surface crystalline structure. It was found that if the surface mobility is suppressed by the long-range substrate effect from much faster to slower than that in the bulk, then the surface crystalline structure changes from α-crystal to δ-crystal. A phase diagram was ultimately constructed to predict the surface crystalline structure at 346 K in thin PLLA films with various thicknesses of both the film and adsorbed layer.

Morphological study of isotactic polypropylene thin films on different substrates using grazing incidence wide-angle X-ray diffraction

Isotactic polypropylene (iPP) is one of the most commonly used polymers owing to its excellent mechanical properties and well-balanced physical properties. These properties can be achieved and controlled through a better understanding of its hierarchical structures. The crystal structures of iPP thin films of ∼120 nm thickness formed on graphite and silicon substrates were investigated via grazing incidence wide-angle X-ray diffraction (GIWAXD) with hard and tender X-rays along with grazing incidence small-angle X-ray scattering, atomic force microscopy, and transmission electron microscopy. The lamellae were found to be edge-on-oriented on the graphite substrate due to epitaxial iPP crystal growth and flat-on-oriented on the silicon substrate due to iPP crystal growth along the thermodynamically dominant orientation. GIWAXD results obtained with tender X-rays revealed that the orientation of the crystal lamellae did not change along the thickness direction and that the degree of crystallinity at the surface was lower than that in the interior of the iPP thin films for each substrate. These results indicate that crystallization at the substrate-film interface played a significant role in the formation of the crystal structure of the iPP thin film, that is, the crystals grew throughout the thin films along the substrate-induced orientation even in the case of edge-on orientation, where the growth axes of the crosshatched lamellae were not parallel to the thickness direction. The relationship between the growth axes of lamella and the growth of surface-induced orientation along the normal direction of the substrates was successfully clarified for the first time using the thin film systems. The obtained results can be extended to interface-induced crystallization inside bulk composite materials.

Confined Crystallization in the Self-Assembled Nanostructures of Cellulose Nanocrystals and Polyethylene Glycol

Thin layers of semicrystallized polymers covered on nanoparticles significantly influence the multiple properties of their nanocomposites because of the confined crystallization of polymers. Cellulose nanocrystal (CNC) nanorods have a hydroxy-rich surface that favors the hydrogen-bonding interaction with polymers and a twisted nanostructure, which can construct a chiral nematic liquid-crystal phase scaffold for the filling of polymers. All these make CNCs’ self-assembled nanostructure a unique confined condition for polymers. Understanding the crystallization of polymers in the coassembled CNC/polymer composites presents a challenge in this regard. In this study, we focus on the confinement crystallization in the coassembled composites of CNCs and poly(ethylene glycol)(PEG). The composition-dependent changes in composite morphology and crystallization have been extensively characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, synchrotronic powder X-ray diffraction, synchrotronic grazing incidence wide-angle X-ray diffraction, and differential scanning calorimetry. At low PEG content (10 wt.%), strong confinement has been identified, showing an extremely low crystallinity with tiny PEG crystallites. As the PEG reached 30 wt.%, the PEG (120) plane with the flat-on orientation of the crystal lamella appeared. As the PEG content increased continuously (40 wt.% to 50 wt.%), the intensity of the (120) plane of the PEG crystal became larger, accompanied by an increasing flat-on orientation degree. When the PEG weight percentage was up to 60 wt.%, the crystals grew randomly, losing their preferential orientation. The free growth of PEG crystals also induced a significantly decreased orientation degree of CNCs. The CNC/PEG system presents a mutual influence from two components, which enriches our understanding of the coassembly and confined crystallization of polymer composites. It will benefit the further modulation of CNC-based nanocomposites, both in their structures and properties.

Evaluation of Preferential Orientation in the Film Depth Direction by Two-Dimensional Grazing Incident Wide-Angle X-ray Diffraction of CeO2 Film on Sapphire Single Crystal Substrate with Different Film Formation Conditions

Evaluation of Preferential Orientation in the Film Depth Direction by Two-Dimensional Grazing Incident Wide-Angle X-ray Diffraction of CeO₂ Film on Sapphire Single Crystal Substrate with Different Film Formation Conditions

An effect of crystallographic distortion on carrier mobility in poly(3-hexylthiophene) thin films

The aggregation states and physical properties of polymers in thin films deviate from those found in the bulk. Although an effect of the thickness on the carrier mobility for thin films of poly(3-hexylthiophene) (P3HT) has been widely studied, there is a lack of discussion in terms of crystallographic distortion. Here, we demonstrate how the out-of-plane hole mobility in P3HT, which is a typical semiconducting polymer, changes with decreasing film thickness. Time-of-flight measurements with an analysis using the Gaussian disorder model revealed that the zero-field out-of-plane hole mobility decreased with decreasing thickness because of an increase in the energetical and spatial distribution of hopping sites. Grazing incidence wide-angle x-ray diffraction measurements revealed that such distributions of charge carriers were induced by the crystallographic distortion of P3HT in the thin films.

Molecular aggregation structure and water repellency of Poly(perfluorohexyl acrylate) with a carbamate linkage

Liquid repellency of comb-shaped polyacrylates with perfluoroalkyl side-chains associates with the ordered structure of the side-chains at the surface. The molecular aggregation structure and surface properties of poly{2-[(perfluorohexylethyl)carbamate]ethyl}acrylate (PFAUr-C6) were studied using differential scanning calorimetry (DSC), polarized optical microscopy (POM), powder wide-angle X-ray diffraction (WAXD), grazing incidence wide-angle X-ray diffraction (GI-WAXD), temperature-controlled Fourier transform infrared spectroscopy (FTIR), contact angle measurements, and X-ray photoelectron spectroscopy (XPS). Poly[2-(perfluorohexyl)ethyl]acrylate (PFA-C6) was compared with PFAUr-C6 to verify the effect of carbamate linkage on the aggregation structure and surface properties. The perfluorohexyl groups in PFAUr-C6 produced a double-layered smectic structure, whereas the perfluorohexyl groups in PFA-C6 showed no ordered structure. The double-layered smectic structure in PFAUr-C6 was induced by the hydrogen bonding interaction in the carbamate linkers. PFAUr-C6 showed poor water repellency similar to PFA-C6 because of the rapid surface rearrangement. Although the perfluorohexyl groups produced smectic order structure at the film surface, the lack of positional order in the smectic layers and the low ordered structure content allowed the surface rearrangement.

Molecular orientation and stability of poly(3-hexylthiophene) nanogratings affected by the fabricated solvent vapor.

During the nanoimprinting lithography (NIL) process, the role of solvent vapor in fabricating the pattern structure and inducing the molecular alignment of nanoimprinted polymer film has been attracting significant attention. We demonstrate here that the molecular orientation and thermal stability of poly(3-hexylthiophene) (P3HT) nanograting film can be affected obviously by the fabricated solvent vapor. A solvent-vapor nanoimprinting lithography (SV-NIL) technique based on a polydimethylsiloxane (PDMS) template is employed to fabricate a P3HT nanograting structure film successfully and solvent vapor is offered by chlorobenzene, chloroform and carbon disulphide, respectively. The molecular orientation of the polymer film is carefully characterized by grazing incidence wide angle X-ray diffraction (GIWAXD) measurements to investigate the effect of various solvent vapors on the molecular orientation of the P3HT nanograting film. For the P3HT nanograting film fabricated by chloroform and chlorobenzene solvent, the edge-on molecular orientation of the typical form II crystallographic structure is induced. However, this indicates that there are both the face-on molecular orientations of the form II and form I crystallographic conformation present for the P3HT nanograting film fabricated by carbon disulphide solvent. Therefore, the fabricated solvent vapor plays a significant role in determining the formation of the molecular orientation of the polymer nanostructure. Then, the role of thermal annealing in the stability of the molecular orientation was investigated for the P3HT nanograting film after a fixed temperature. As for the annealed nanograting film fabricated by chlorobenzene and chloroform solvent vapor, a single edge-on molecular orientation mode of the form I crystallographic structure has been obtained. However, for the annealed nanograting film fabricated by the carbon disulphide solvent, the edge-on and face-on molecular orientations of the form I crystallographic structure are still retained. This indicates that the stability of the form II crystallographic conformation is mainly dependent on the thermal annealing process. Therefore, after the annealing process, the final determining of the molecular alignment and crystallographic conformation depends significantly on the orientation type of the nanograting film before the annealing history, and it can be further inferred that the molecular orientation of the annealed polymer film is still affected by the fabricated solvent vapor significantly. Thus this will provide new understanding and guidance for the research of the topographical structure and molecular alignment of conjugated polymers.

A Nanoconfinement Effect Imposed by the Limited End-to-End Distance of the Grafted Chains on a Molecular Aggregation of Polymer Brushes with Crystalline Side Groups

We demonstrated, using grazing incidence wide-angle X-ray diffraction (GI-WAXD), sum frequency generational spectroscopy (SFG), and atomic force microscopy (AFM), that the aggregation state and mol...

Lamellar orientation in isotactic polypropylene thin films: a complement study via grazing incidence X-ray diffraction and surface/cross-sectional imaging

The crystalline structures of isotactic polypropylene (iPP) thin films were investigated using grazing incident wide-angle X-ray diffraction (GIWAXD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The out-of-plane (110) reflection split with 99° inclination in the GIWAXD pattern. The film surface was covered with flat-on mother lamellae with orthogonal daughter lamellae. The cross-sectional TEM image and the fast Fourier transform-processed image showed vertically aligned daughter lamellae and cross-hatched lateral mother lamellae. Flat-on lamellae may be preferentially produced at the substrate interface, after which the mother lamellae may yield daughter lamellae from the ac plane to give vertically aligned lamellae. The daughter lamellae yield in-plane lamellae with flat-on alignment from the ac plane, resulting in the global growth of a cross-hatched lamellar structure.

Chemical Doping Effects in Multilayer MoS2 and Its Application in Complementary Inverter.

Multilayer MoS2 has been gaining interest as a new semiconducting material for flexible displays, memory devices, chemical/biosensors, and photodetectors. However, conventional multilayer MoS2 devices have exhibited limited performances due to the Schottky barrier and defects. Here, we demonstrate poly(diketopyrrolopyrrole-terthiophene) (PDPP3T) doping effects in multilayer MoS2, which results in improved electrical characteristics (∼4.6× higher on-current compared to the baseline and a high current on/off ratio of 106). Synchrotron-based study using X-ray photoelectron spectroscopy and grazing incidence wide-angle X-ray diffraction provides mechanisms that align the edge-on crystallites (97.5%) of the PDPP3T as well as a larger interaction with MoS2 that leads to dipole and charge transfer effects (at annealing temperature of 300 °C), which support the observed enhancement of the electrical characteristics. Furthermore, we demonstrate a complementary metal-oxide-semiconductor inverter that uses a p-type MoSe2 and a PDPP3T-doped MoS2 as charging and discharging channels, respectively.

Preparation of polymer brushes with well-controlled stereoregularity and evaluation of their functional properties

Polymer brushes in which one polymer chain end is tethered to a substrate show permanent properties related to the chemical structure of the polymer. However, they cannot accommodate functional molecules in the desired space because of the steric hindrance between neighboring polymer chains. To overcome this problem, the preparation of polymer brushes with ordered nanopores is strongly desired. High-density poly(methyl methacrylate) brushes with well-controlled stereoregularity were prepared using a surface-initiated living anionic polymerization method in the presence of a Lewis acid. A molecular weight range from 6 to 400 K with a narrow polydispersity index was obtained. Grazing incidence wide-angle X-ray diffraction measurements indicated that the polymer brushes formed a helical structure approximately 1 nm in diameter and consisting of encapsulated functional molecules or polymers, leading to the formation of inclusion complexes or stereocomplexes. Preparation of Polymer Brushes with Well-Controlled Stereoregularity and Evaluation of Their Functional Properties High-density poly(methyl methacrylate) (PMMA) brushes with well-controlled stereoregularity were prepared using a surface-initiated living anionic polymerization method in the presence of a Lewis acid. A molecular weight range from 6 K to 400 K with a narrow polydispersity index (PDI) was obtained. Grazing incidence wide-angle X-ray diffraction measurements indicated that the polymer brushes formed a helical structure approximately 1 nm in diameter and consisting of encapsulated functional molecules or polymers, leading to the formation of inclusion complexes or stereocomplexes.

Slight Structural Disorder in Bithiophene-based Random Terpolymers with Improved Power Conversion Efficiency for Polymer Solar Cells

A series of random terpolymers P2−P5 were designed and synthesized by randomly embedding 5 mol%, 10 mol%, 15 mol% and 25 mol% feed ratios of low cost 2,2-bithiophene as the third monomer to the famous donor-acceptor (D-A) type copolymer PTB7-Th (P1). All polymers showed similar molecular weight with number-average molecular weight (Mn) and weight-average molecular weight (Mw) in the range of (59−74) and (93−114) kg·mol−1, respectively, to ensure a fair comparison on the structure-property relationships. Compared with the control copolymer PTB7-Th, the random terpolymers exhibited enhanced absorption intensity in a wide range from 400 nm to 650 nm in both solution and film as well as in polymer/PC71BM blends. From grazing incident wide-angle X-ray diffraction (GIWAXS), compared with the regularly alternated copolymer PTB7-Th, the random terpolymers demonstrated mild structural disorder with reduced (100) lamellar stacking and slightly weakened (010) π-π stacking for the polymers as well as slightly reduced PC71BM aggregation in polymer/PC71BM blends. However, the measured hole mobility for terpolymers ((1.20−3.73) × 10−4 cm2·V−1·s−1) was evaluated to be comparable or even higher than 1.35 × 10−4 cm2·V−1·s−1 of the alternative copolymer. Enhanced average power conversion efficiency (PCE) from 7.35% to 8.11% and 7.79% to 8.37% was observed in both conventional and inverted device architectures from copolymer P1 to terpolymers P4, while further increasing the 2,2-bithiophene feed ratio decreased the PCE.

Preparation of High-Density Polymer Brushes with a Multihelical Structure.

It is well-known that a mixture of isotactic and syndiotactic polymethyl methacrylate (PMMA) forms a stereocomplex consisting of a multihelical structure in which an isotactic chain is surrounded by a syndiotactic chain. Here, we report the basic structure of the stereocomplex formed when the syndiotactic PMMA chains are tethered to a silicon substrate and form a high-density polymer brush. The influence of geometric confinement was investigated by preparing the high-density polymer brushes on a flat and spherical substrate. In both cases, mixing the untethered isotactic PMMA with the grafted syndiotactic PMMA led to the formation of a stereocomplex with a multihelical structure. Static contact angle measurements showed a hindered surface mobility at the outermost surface of the polymer brush, indicating that the stereocomplex forms a crystalline structure. A syndiotactic polymer brush with substituted fluoroalkyl groups was prepared to increase the contrast for grazing incidence wide-angle X-ray diffraction (GIWAXD) measurements. The GIWAXD results verified that the stereocomplex forms a crystalline structure oriented perpendicular to the substrate with a relatively low degree of orientation.

Design of High-Density Helical Polymer Brush on Silica Nanoparticles for the Size Recognition of Fullerene Molecules.

High-density syndiotactic poly(methyl methacrylate) (st-PMMA) brushes form a helical structure and encapsulate fullerene molecules in their helical cavities, leading to a PMMA brush/fullerene inclusion complex. The brushes recognize the size of guest molecules and spontaneously adapt their helical diameter to the guest molecules. Both polymer brush/C60 and polymer brush/C70 inclusion complex on the flat substrate were characterized on the basis of grazing incidence wide-angle X-ray diffraction (GIWAXD) measurements, and it is revealed that the main chains oriented perpendicular to the substrate. Moreover, high-density st-PMMA brushes grafted onto nanoparticles efficiently separate C70 molecules from the mixture of C60 and C70 solution. Even after 5× repeating process, the selectivity for C70 molecules remains at 99%.

Orientation and crystallization of regioregular poly(3-dodecylthiophene) in alumina nanopores.

The orientation and crystallization of regioregular poly(3-dodecylthiophene) (P3DDT) in different diameter nanopores were investigated. P3DDT nanowires were prepared by a melt-wetting nonporous alumina template with P3DDT melts. The microstructure of the nanowires was analyzed by micro-Fourier transform infrared spectroscopy, grazing incidence wide angle X-ray diffraction, and differential scanning calorimetry. Although Form I modification prevails in all the nanowires, Form I crystals decrease and Form II crystals increase as the pore diameter decreases. The crystallites developed in the nanowires preferentially aligned with π-π stacking (b-axis) along the long axis of the wire and this orientation is marked as the wire diameter decreases. These results could provide guidance on designing polymeric nanomaterials for functional nanodevices in high performance organic photovoltaic cells, sensors, and electrodes.

Interphase crystal structure of polyamide 6 on carbon materials revealed by grazing incidence X-ray diffraction with synchrotron radiation

The orientation of polyamide6 (PA6) crystallites on the surface of carbon materials was investigated through grazing incidence wide-angle X-ray diffraction (GIWAXD) on the BL46XU beam line at SPring-8. PA6 films on graphite and amorphous carbon were implemented to model the interphase of the composite with PA6 and the carbon materials. Only the α crystal was observed in the in-plane GIWAXD profile of PA6 on a graphite plate. Further, it was found that the highly oriented graphite structure induced the α crystalline form of PA6 and made the methylene chains align/orient themselves epitaxially.