Grazing Incidence Wide-angle X-ray Scattering Research Articles

In Situ Grazing-Incidence Wide-Angle Scattering Reveals Mechanisms for Phase Distribution and Disorientation in 2D Halide Perovskite Films.

2D hybrid halide perovskites with the formula (A')2 (A)n -1 Pbn I3 n +1 have remarkable stability and promising efficiency in photovoltaic and optoelectronic devices, yet fundamental understanding of film formation, key to optimizing these devices, is lacking. Here, in situ grazing-incidence wide-angle X-ray scattering (GIWAXS) is used to monitor film formation during spin-coating. This elucidates the general film formation mechanism of 2D halide perovskites during one-step spin-coating. There are three stages of film formation: sol-gel, oriented 3D, and 2D. Three precursor phases form during the sol-gel stage and transform to perovskite, first giving a highly oriented 3D-like phase at the air/liquid interface followed by subsequent nucleations forming slightly less oriented 2D perovskite. Furthermore, heating before crystallization leads to fewer nucleations and faster removal of the precursors, improving orientation. This outlines the primary causes of phase distribution and perpendicular orientation in 2D perovskite films and paves the way for rationally designed film fabrication techniques.

GIWAXS-SIIRkit: scattering intensity, indexing and refraction calculation toolkit for grazing-incidence wide-angle X-ray scattering of organic materials

Grazing-incidence wide-angle X-ray scattering (GIWAXS) has become an increasingly popular technique for quantitative structural characterization and comparison of thin films. For this purpose, accurate intensity normalization and peak position determination are crucial. At present, few tools exist to estimate the uncertainties of these measurements. Here, a simulation package is introduced called GIWAXS-SIIRkit, where SIIR stands for scattering intensity, indexing and refraction. The package contains several tools that are freely available for download and can be executed in MATLAB. The package includes three functionalities: estimation of the relative scattering intensity and the corresponding uncertainty based on experimental setup and sample dimensions; extraction and indexing of peak positions to approximate the crystal structure of organic materials starting from calibrated GIWAXS patterns; and analysis of the effects of refraction on peak positions. Each tool is based on a graphical user interface and designed to have a short learning curve. A user guide is provided with detailed usage instruction, tips for adding functionality and customization, and exemplary files.

Constructing highly efficient all-inorganic perovskite solar cells with efficiency exceeding 17% by using dopant-free polymeric electron-donor materials

Abstract Development of all-inorganic perovskite solar cells (PSCs) is highly desirable due to its excellent thermal stability and great potential for tandem solar cells. One main bottleneck that restricts its further development is the absence of the ideal hole-transporting materials which is critical to device performance and stability. Herein, we construct a brand-new architecture of all-inorganic PSCs via employing a series of doping-free polymeric organic photovoltaic donor materials as hole transport materials including J71, PBDB-T, PM6 with suitable energy level and carrier transport ability. The mechanism in terms of film molecular microscopic structure, electrical transport dynamics, electrical potential distribution were systematically investigated by grazing incidence wide-angle X-ray scattering (GIWAXS), conductive atomic force microscope (C-AFM) and kelvin probe force microscopy (KPFM) measurements. This work not only proposes a series of new dopant-free polymeric hole transporting materials for all-inorganic PSCs, but also demonstrates the fabrication of high efficiency devices with power conversion efficiencies over 17%, a record of all-inorganic PSCs based on dopant-free polymeric materials to our knowledge.

Quantitative Determination of the Vertical Segregation and Molecular Ordering of PBDB-T/ITIC Blend Films with Solvent Additives

The vertical component distribution of bulk heterojunction (BHJ) active film shows a significant impact on determining the device performance in polymer solar cells (PSCs). Processing solvent additives are well known for regulating the BHJ active layer morphology; however, there are few reports regarding the quantitative evaluation of the effect. Herein, a study of the quantitative determination of the vertical segregation in combination of molecular ordering of PBDB-T/ITIC blend films with various 1,8-diiodooctane (DIO) contents is provided. A 0.5% (volume ratio) DIO-added blend film achieves the highest power conversion efficiency of 10.75%. The reduced performance of the PSCs resulted from the excessive vertical component segregation and overcrystallization investigated by various techniques. X-ray photoelectron spectroscopy indicates that DIO aggravates the PBDB-T enrichment region at the air side. Neutron reflectivity further quantitatively figures out the phase separation effect. Although increased crystallinity of ITIC and a higher face-on ratio of PBDB-T in active layer were obtained with increased DIO content approved by grazing-incidence wide-angle X-ray scattering (GIWAXS), the enhanced vertical distribution along with the enhanced crystal size of ITIC leads to the reduced performance of the PSCs due to the reduced carrier transportation paths between donor and acceptor.

In situ observation of δ phase suppression by lattice strain in all-inorganic perovskite solar cells

Abstract The phase control and ordered crystal growth play a crucial role in the efficiency and stability of all-inorganic perovskite solar cells (PSCs). However, the innate dynamics of crystal growth driving the stable phase and high performance are unknown. Here, we for the first time unraveled that the degree of lattice strain is responsible for the suppression of the δ phase growth by in situ Grazing-Incidence Wide-Angle X-ray Scattering (GIWAXS) technique. We shadow the internal crystal structural changes in real time and successfully decoupled crystal growth dynamics under different substrate temperatures. The symmetrical crystal lattice and vertical substrate growth were finally achieved. This finding provides insights on the inorganic perovskite crystal growth and has significant benefit for high performing all-inorganic PSCs.

Crystallization of poly(ε-caprolactone) at the air-water interface studied by IRRAS and GI-WAXS

Poly (ε-caprolactone) (PCL) dissolved in chloroform was spread on the water surface of a Langmuir trough and after solvent evaporation, the surface pressure vs area (π-A) Langmuir isotherm was recorded. An extended plateau region indicates a 1st order phase transition related to PCL crystallization as also confirmed by Brewster angle microscopy (BAM). Infrared reflection absorption spectroscopy (IRRAS) and grazing incidence wide angle X-ray scattering (GI-WAXS) reveal details of the PCL crystallization process on a molecular level. The IRRAS and GI-WAXS experiments confirm that crystallization occurs at the plateau region of the π-A Langmuir isotherm. GI-WAXS also confirms that the polymer chains in the crystals are tilted by ≈ 21° with respect to the water surface normal direction. This value is consistent with IRRAS data at a maximum compression state of ≈ 2 Å2.

Synthesis of Dinaphtho[2,3-d:2',3'-d']anthra[1,2-b:5,6-b']dithiophene (DNADT) Derivatives: Effect of Alkyl Chains on Transistor Properties.

To investigate organic field-effect transistor (OFET) properties, a new thienoacene-type molecule, 4,14-dihexyldinaphtho[2,3-d:2’,3’-d’]anthra[1,2-b:5,6-b’]dithiophene (C6-DNADT), consisting of π-conjugated nine aromatic rings and two hexyl chains along the longitudinal molecular axis has been successfully synthesized by sequential reactions, including Negishi coupling, epoxidation, and cycloaromatization. The fabricated OFET using thin films of C6-DNADT exhibited p-channel FET properties with field-effect mobilities (µ) of up to 2.6 × 10−2 cm2 V−1 s−1, which is ca. three times lower than that of the parent DNADT molecule (8.5 × 10−2 cm2 V−1 s−1). Although this result implies that the installation of relatively short alkyl chains into the DNADT core is not suitable for transistor application, the origins for the FET performance obtained in this work is fully discussed, based on theoretical calculations and solid-state structure of C6-DNADT by grazing incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) analyses. The results obtained in this study disclose the effect of alkyl chains introduced onto the molecule on transistor characteristics.

Multi-Stimuli-Responsive Field-Effect Transistor with Conjugated Polymer Entailing Spiropyran in the Side Chains

Multi-stimuli-responsive field-effect transistors (FETs) with organic/polymeric semiconductors have received increasing attention. Herein, we report a novel strategy for fabricating multi-stimuli-r...

A Reversible Structural Phase Transition by Electrochemically-Driven Ion Injection into a Conjugated Polymer.

We find that conjugated polymers can undergo reversible structural phase transitions during electrochemical oxidation and ion injection. We study poly[2,5-bis(thiophenyl)-1,4-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)benzene] (PB2T-TEG), a conjugated polymer with glycolated side chains. Using grazing incidence wide-angle X-ray scattering (GIWAXS), we show that, in contrast to previously known polymers, this polymer switches between two structurally distinct crystalline phases associated with electrochemical oxidation/reduction in an aqueous electrolyte. Importantly, we show that this unique phase change behavior has important physical consequences for ion-polaron pair transport. Notably, using moving front experiments visualized by both optical microscopy and super-resolution photoinduced force microscopy (PiFM), we show that a laterally propagating ion-polaron pair front in PB2T-TEG exhibits non-Fickian transport, retaining a sharp step-edge profile, in stark contrast to the Fickian diffusion more commonly observed in polymers like P3MEEMT. This structural phase transition is reminiscent of those accompanying ion uptake in inorganic materials like LiFePO4. We propose that the engineering of similar properties in future conjugated polymers may enable the realization of new materials with superior performance in electrochemical energy storage or neuromorphic memory applications.

Introducing Trifluoromethyl to Strengthen Hydrogen Bond for High Efficiency Organic Solar Cells.

Nowadays, the ternary strategy has become a common way to improve the power conversion efficiency (PCE) of organic solar cells (OSCs). The intermolecular interaction between the third component and donor or acceptor plays a key role in achieving a high performance. However, hydrogen bond as a strong intermolecular interaction is rarely considered in ternary OSCs. In this work, we introduce trifluoromethyl on a newly synthesized small molecular DTBO to strength hydrogen bonds between DTBO and IEICO-4F. Due to the existence of hydrogen bonds has a strong impact on electrostatic potential (ESP) and benefits π-π stacking in the active layer, the ternary OSCs show superior charge extraction and low charge recombination. In DTBO, PTB7-Th and IEICO-4F based ternary devices, the PCE increases from 11.02 to 12.48%, and short-circuit current density (JSC) increases from 24.94 to 26.43 mA/cm2 compared with typical binary devices. Moreover, the addition of DTBO can realize an energy transfer from DTBO to PTB7-Th and broaden the absorption spectrum of blend films. Grazing-incidence wide-angle X-ray scattering (GIWAXS) patterns show that the π-π stacking distance of IEICO-4F decreased after adding 10 wt% DTBO. The effect of the hydrogen bond is also achieved in the PM6: Y6 system, showing 16.64% efficiency by comparison to the 15.49% efficiency of binary system. This work demonstrates that introduce trifluoromethyl to enhance hydrogen bond which improve π-π stacking can achieve higher performance in OSCs.

Morphology Changes in Perfluorosulfonated Ionomer from Thickness and Thermal Treatment Conditions.

The morphological changes of Nafion thin films with thicknesses from 10 to 200 nm on Pt substrate with various annealing histories (unannealed to 240 °C) were systematically investigated using grazing incidence small-angle X-ray scattering (GISAXS) and grazing incidence wide-angle X-ray scattering (GIWAXS). The results revealed that the hydrophilic ionic domain and hydrophobic backbone in Nafion thin films changed significantly when the annealing treatment exceeded the cluster transition temperature, which decreased proton conductivity, due to the constrained hydrophilic/hydrophobic phase separation, and increased the crystalline-rich domain. This research contributed to the understanding of ionomer thermal stability in the catalyst layer, which is subjected to thermal annealing during the hot-pressing process.

The Key Role of Side Chain Linkage in Structure Formation and Mixed Conduction of Ethylene Glycol Substituted Polythiophenes.

Functionalizing conjugated polymers with polar ethylene glycol side chains enables enhanced swelling and facilitates ion transport in addition to electronic transport in such systems. Here, we investigate three polythiophene homopolymers (P3MEET, P3MEEMT, and P3MEEET) having differently linked (without spacer and with methyl and ethyl spacer, respectively) diethylene glycol side chains. All the polymers were tested in organic electrochemical transistors (OECTs). They show drastic differences in the device performance. The highest μOECT C* product of 11.5 F/cm·V·s was obtained for ethyl-spaced P3MEEET. How the injection and transport of ions is influenced by the side-chain linkage was studied with electrochemical impedance spectroscopy, which shows a dramatic increase in volumetric capacitance from 80 ± 9 up to 242 ± 17 F/cm3 on going from P3MEET to P3MEEET. Thus, ethyl-spaced P3MEEET exhibits one of the highest reported volumetric capacitance values among p-type polymers. Moreover, P3MEEET exhibits in dry thin films an organic field-effect transistor (OFET) hole mobility of 0.005 cm2/V·s, highest among the three, which is one order of magnitude higher than that for P3MEEMT. The extracted hole mobility from OECT (oxidized swollen state) and the hole mobility in solid-state thin films (OFET) show contradictory trends for P3MEEMT and P3MEEET. In order to understand exactly the properties in the hydrated and dry states, the crystal structure of the polymers was investigated with wide-angle X-ray scattering (WAXS) and grazing incidence WAXS, and the water uptake under applied potential was monitored using electrochemical quartz crystal microbalance with dissipation monitoring (E-QCMD). These measurements reveal an amorphous state for P3MEET and a semicrystalline state for P3MEEMT and P3MEEEET. On the other hand, E-QCMD confirms that P3MEEET swells 10 times more than P3MEEMT in the oxidized state. Thus, the importance of the ethyl spacer toward crystallinity and mixed-conduction properties was clearly demonstrated, emphasizing the impact of side chain linkage of diethylene glycol. This detailed study offers a better understanding of how to design high-performance organic mixed conductors.

Thermally Durable Nonfullerene Acceptor with Nonplanar Conjugated Backbone for High‐Performance Organic Solar Cells

AbstractA nonfullerene acceptor (NFA) with acceptor–donor–acceptor (A–D–A) architecture, i‐IEICO‐2F, based on 4,9‐dihydro‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene as an electron‐donating core and 2‐(6‐fluoro‐2,3‐dihydro‐3‐oxo‐1H‐inden‐1‐ylidene)‐propanedinitrile as electron‐withdrawing end groups, is designed and synthesized. i‐IEICO‐2F has a twist structure in the main conjugated chain, which causes blueshifted absorption and leads to harmonious absorption with a high bandgap donor. The bandgap of i‐IEICO‐2F compliments the bandgap of suitable wide bandgap donor polymers such as J52, leading to complete light absorption throughout the visible spectrum. Devices based on i‐IEICO‐2F exhibit optimized photovoltaic performance including an open‐circuit voltage of 0.93 V, a short‐circuit current density of 16.61 mA cm−2, and a fill factor of 73%, and result in a power conversion efficiency (PCE) of 11.28%. The i‐IEICO‐2F‐based devices reach PCEs of >11% without using any additives or post‐treatments. Devices are found to be thermally stable and maintain 44% of their initial PCE after 184.5 h of continuous thermal annealing (TA) treatment at 150 °C. Based on UV, atomic force microscopy (AFM), and grazing incidence wide angle X‐ray scattering (GIWAXS) results, i‐IEICO‐2F devices show almost identical morphology and molecular orientation throughout the TA treatment and excellent stability compared to other IEICO derivatives.

Air‐Stable Highly Crystalline Formamidinium Perovskite 1D Structures for Ultrasensitive Photodetectors

AbstractState‐of‐the‐art optoelectronic devices based on metal‐halide perovskites demand solution‐processed structures with high crystallinity, controlled crystallographic orientation, and enhanced environmental stability. Formamidinium lead iodide (α‐FAPbI3) possesses a suitable bandgap of 1.48 eV and enhanced thermal stability, whereas perovskite‐type polymorph (α‐phase) is thermodynamically instable at ambient temperatures. Stable α‐FAPbI3 perovskite 1D structure arrays with high crystallinity and ordered crystallographic orientation are developed by controlled nucleation and growth in capillary bridges. By surface functionalization with phenylethylammonium ions (PEA+), FAPbI3 wires sustain a stable α‐phase after 28 day storage in the ambient environment with a relative humidity of 50%. Enhanced photoluminescence (PL) intensity and elongated PL lifetime demonstrate suppressed trap density and high crystallinity in these 1D structures, which is also reflected by the enhanced diffraction density and pure (001) crystallographic orientation in the grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) pattern. Based on these high‐quality 1D structures, sensitive photodetectors are achieved with average responsivities of 5282 A W−1, average specific detectivities of more than 1.45 × 1014 Jones, and a fast response speed with a 3 dB bandwidth of 15 kHz.

Influence of donor:acceptor ratio on charge transfer dynamics in non-fullerene organic bulk heterojunctions

The donor:acceptor (D:A) blend ratio plays a very important role in affecting the progress of charge transfer and energy transfer in bulk heterojunction (BHJ) organic solar cells (OSCs). The proper D:A blend ratio can provide maximized D/A interfacial area for exciton dissociation and appropriate domain size of the exciton diffusion length, which is beneficial to obtain high-performance OSCs. Here, we comprehensively investigated the relationship between various D:A blend ratios and the charge transfer and energy transfer mechanisms in OSCs based on PBDB-T and non-fullerene acceptor IT-M. Based on various D:A blend ratios, it was found that the ratio of components is a key factor to suppress the formation of triplet states and recombination energy losses. Rational D:A blend ratios can provide appropriate donor/accepter surface for charge transfer which has been powerfully verified by various detailed experimental results from the time-resolved fluorescence measurement and transient absorption (TA) spectroscopy. Optimized coherence length and crystallinity are verified by grazing incident wide-angle X-ray scattering (GIWAXS) measurements. The results are beneficial to comprehend the effects of various D:A blend ratios on charge transfer and energy transfer dynamics and provides constructive suggestions for rationally designing new materials and feedback for photovoltaic performance optimization in non-fullerene OSCs

Room‐Temperature Partial Conversion of α‐FAPbI3Perovskite Phase via PbI2Solvation Enables High‐Performance Solar Cells

AbstractThe two‐step conversion process consisting of metal halide deposition followed by conversion to hybrid perovskite has been successfully applied toward producing high‐quality solar cells of the archetypal MAPbI3hybrid perovskite, but the conversion of other halide perovskites, such as the lower bandgap FAPbI3, is more challenging and tends to be hampered by the formation of hexagonal nonperovskite polymorph of FAPbI3, requiring Cs addition and/or extensive thermal annealing. Here, an efficient room‐temperature conversion route of PbI2into the α‐FAPbI3perovskite phase without the use of cesium is demonstrated. Using in situ grazing incidence wide‐angle X‐ray scattering (GIWAXS) and quartz crystal microbalance with dissipation (QCM‐D), the conversion behaviors of the PbI2precursor from its different states are compared. α‐FAPbI3forms spontaneously and efficiently at room temperature from P2(ordered solvated polymorphs with DMF) without hexagonal phase formation and leads to complete conversion after thermal annealing. The average power conversion efficiency (PCE) of the fabricated solar cells is greatly improved from 16.0(±0.32)% (conversion from annealed PbI2) to 17.23(±0.28)% (from solvated PbI2) with a champion device PCE > 18% due to reduction of carrier recombination rate. This work provides new design rules toward the room‐temperature phase transformation and processing of hybrid perovskite films based on FA+cation without the need for Cs+or mixed halide formulation.

Crystal-structure of active layers of small molecule organic photovoltaics before and after solvent vapor annealing

Abstract It is demonstrated by a detailed structural analysis that the crystallinity and the efficiency of small molecule based organic photovoltaics can be tuned by solvent vapor annealing (SVA). Blends made of the small molecule donor 2,2′-[(3,3′″,3″″,4′-tetraoctyl[2,2′:5′,2″:5″,2′″:5′″,2″″-quinquethiophene]-5,5″″-diyl)bis[(Z)-methylidyne(3-ethyl-4-oxo-5,2-thiazolidinediylidene)]]bis-propanedinitrile (DRCN5T) and the acceptor [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) were annealed using solvent vapors with either a high solubility for the donor (tetrahydrofuran), the acceptor (carbon disulfide) or both (chloroform). The samples were analyzed by grazing-incidence wide-angle X-ray scattering (GIWAXS), electron diffraction, X-ray pole figures, and time-of-flight secondary ion mass spectrometry (ToF-SIMS). A phase separation of DRCN5T and PC71BM is induced by SVA leading to a crystallization of DRCN5T and the formation of a DRCN5T enriched layer. The DRCN5T crystallites possess the two dimensional oblique crystal system with the lattice parameters a = 19.2 Å, c = 27.1 Å, and β = 111.1° for the chloroform case. No major differences in the crystal structure for the other solvent vapors were observed. However, the solvent choice strongly influences the size of the DRCN5T enriched layer. Missing periodicity in the [010]-direction leads to the extinction of all Bragg reflections with k ≠ 0. The annealed samples are randomly orientated with respect to the normal of the substrate (fiber texture).

Laser nanostructuring of thin films of PEDOT:PSS on ITO: Morphology, molecular structure and electrical properties

Nanostructuring is one promising alternative to modify the functionalities of conducting polymers aiming at applications in technologies like organic solar cells, organic field-effect transistors and organic light-emitting diodes. Nowadays, there is an increasing interest in alternative ways of nanostructuring more economic, quicker and reproducible, avoiding the necessity of stringent environmental conditions like clean rooms, high vacuum or complex mask fabrication. Here we prove that Laser Induced Periodic Surface Structures (LIPSS) can be formed in films of Poly(3,4-ethylenedioxythiophene) complexed with Poly(styrenesulfonate) (PEDOT:PSS) prepared by spin-coating on planar Indium Tin Oxide. PEDOT:PSS has been irradiated with the 4th harmonic of a Nd:YAG laser resulting in LIPSS parallel to the laser polarization with a period close to the laser wavelength. LIPSS morphology has been characterized by Atomic Force Microscopy (AFM) and synchrotron Grazing Incidence Small Angle X-ray Scattering while the film structure was studied by Grazing-Incidence Wide-Angle X-ray Scattering and Raman spectroscopy. To analyze the impact of laser treatment on the electrical properties of PEDOT:PSS, conductive AFM was employed showing that LIPSS partially preserve the original electrical conductivity. These results can be of interest for achieving functional polymer nanostructures by a quick and reproducible approach with no need for clean room conditions.

Reorientation of π-conjugated molecules on few-layer MoS2 films.

Small π-conjugated organic molecules have attracted substantial attention in the past decade as they are considered as candidates for future organic-based (opto-)electronic applications. The molecular arrangement in the organic layer is one of the crucial parameters that determine the efficiency of a given device. The desired orientation of the molecules is achieved by a proper choice of the underlying substrate and growth conditions. Typically, one underlying material supports only one inherent molecular orientation at its interface. Here, we report on two different orientations of diindenoperylene (DIP) molecules on the same underlayer, i.e. on a few-layer MoS2 substrate. We show that DIP molecules adopt a lying-down orientation when deposited on few-layer MoS2 with horizontally oriented layers. In contrast, for vertically aligned MoS2 layers, DIP molecules are arranged in a standing-up manner. Employing in situ and real-time grazing-incidence wide-angle X-ray scattering (GIWAXS), we monitored the stress evolution within the thin DIP layer from the early stages of the growth, revealing different substrate-induced phases for the two molecular orientations. Our study opens up new possibilities for the next-generation of flexible electronics, which might benefit from the combination of MoS2 layers with unique optical and electronic properties and an extensive reservoir of small organic molecules.

Grazing-Incidence Small-Angle X-Ray Scattering (GISAXS) and Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS) Comparative Study on Malignant and Benign Human Cancer Cells and Tissues under Synchrotron Radiation

In the current study, we have experimentally and comparatively investigated and compared malignant human cancer cells and tissues before and after irradiating of synchrotron radiation using Grazing-Incidence Small-Angle X-Ray Scattering (GISAXS) and Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS). It is clear that malignant human cancer cells and tissues have gradually transformed to benign human cancer cells and tissues under synchrotron radiation with the passing of time.