Breaking Fundamental Limitation of Flow-Induced Anisotropic Growth for Large-Scale and Fast Printing of Organic Single-Crystal Films

Advanced organic electronic technologies have put forward a pressing demand for cost-effective and high-throughput fabrication of organic single-crystal films (OSCFs). However, solution-printed OSCFs are typically plagued by the existence of abundant structural defects, which pose a formidable challenge to achieving large-scale and high-performance organic electronics. Here, it is elucidated that these structural defects are mainly originated from printing flow-induced anisotropic growth, an important factor that is overlooked for too long. In light of this, a surfactant-additive printing method is proposed to effectively overcome the anisotropic growth, enabling the deposition of uniform OSCFs over the wafer scale at a high speed of 1.2 mm s-1 at room temperature. The resulting OSCF exhibits appealing performance with a high average mobility up to 10.7 cm2 V-1 s-1, which is one of the highest values for flexible organic field-effect transistor arrays. Moreover, large-scale OSCF-based flexible logic circuits, which can be bent without degradation to a radius as small as 4.0 mm and over 1000 cycles are realized. The work provides profound insights into breaking the limitation of flow-induced anisotropic growth and opens new avenues for printing large-scale organic single-crystal electronics.

Topology-Mediated Molecule Nucleation Anchoring Enables Inkjet Printing of Organic Semiconducting Single Crystals for High-Performance Printed Electronics

Printable organic semiconducting single crystals (OSSCs) offer tantalizing opportunities for next-generation wearable electronics, but their development has been plagued by a long-standing yet inherent problem─spatially uncontrolled and stochastic nucleation events─which usually causes the formation of polycrystalline films and hence limited performance. Here, we report a convenient approach to precisely manipulate the elusive molecule nucleation process for high-throughput inkjet printing of OSSCs with record-high mobility. By engineering curvature of the contact line with a teardrop-shaped micropattern, molecule nucleation is elegantly anchored at the vertex of the topological structure, enabling formation of a single nucleus for the subsequent growth of OSSCs. Using this approach, we achieve patterned growth of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene single crystals, yielding a breakthrough for an organic field-effect transistor array with a high average mobility of 12.5 cm2 V-1 s-1. These findings not only provide keen insights into controlling molecule nucleation kinetics but also offer opportunities for high-performance printed electronics.

Thiol functionalised gold nanoparticles loaded with methotrexate for cancer treatment: From synthesis to in vitro studies on neuroblastoma cell lines

HYPOTHESIS

Colloidal gold nanoparticles (AuNPs) functionalised with hydrophilic thiols can be used as drug delivery probes, thanks to their small size and hydrophilic character. AuNPs possess unique properties for their use in nanomedicine, especially in cancer treatment, as diagnostics and therapeutic tools.

EXPERIMENTS

Thiol functionalised AuNPs were synthesised and loaded with methotrexate (MTX). Spectroscopic and morphostructural characterisations evidenced the stability of the colloids upon interaction with MTX. Solid state (GISAXS, GIWAXS, FESEM, TEM, FTIR-ATR, XPS) and dispersed phase (UV-Vis, DLS, ζ-potential, NMR, SAXS) experiments allowed to understand structure-properties correlations. The nanoconjugate was tested in vitro (MTT assays) against two neuroblastoma cell lines: SNJKP and IMR5 with overexpressed n-Myc.

FINDINGS

Molar drug encapsulation efficiency was optimised to be >70%. A non-covalent interaction between the π system and the carboxylate moiety belonging to MTX and the charged aminic group of one of the thiols was found. The MTX loading slightly decreased the structural order of the system and increased the distance between the AuNPs. Free AuNPs showed no cytotoxicity whereas the AuNPs-MTX nanoconjugate had a more potent effect when compared to free MTX. The active role of AuNPs was evidenced by permeation studies: an improvement on penetration of the drug inside cells was evidenced.

Scalable Growth of Organic Single-Crystal Films via an Orientation Filter Funnel for High-Performance Transistors with Excellent Uniformity

Organic single-crystal films (OSCFs) provide an unprecedented opportunity for the development of new-generation organic single-crystal electronics. However, crystallization of organic films is normally governed by stochastic nucleation and incoherent growth, posing a formidable challenge to grow large-sized OSCFs. Here, an "orientation filter funnel" concept is presented for the scalable growth of OSCFs with well-aligned, singly orientated crystals. By rationally designing solvent wetting/dewetting patterns on the substrate, this approach can produce seed crystals with the same crystallographic orientation and then maintain epitaxial growth of these crystals, enabling the formation of large-area OSCFs. As a result, this unique concept for crystal growth not only enhances the average mobility of organic film by 4.5-fold but also improves its uniformity of electrical properties, with a low mobility variable coefficient of 9.8%, the new lowest record among organic devices. The method offers a general and scalable route to produce OSCFs toward real-word electronic applications.

In Situ Coupling Applied Voltage and Synchrotron Radiation: Operando Characterization of Transistors

A compact voltage application setup has been developed for in situ electrical testing of organic field effect transistors in combination with X-ray scattering studies at a synchrotron beamlines. Challenges faced during real condition in-operando test of newly developed OFETs originated an idea of creation of a new setup which excludes number of factors that make experiments complicated. The application of the setup is demonstrated on a prototype of an organic transistors based on α,ω-dihexyl-α-quaterthiophene molecules. The new setup allows to monitor material structural changes by X-ray scattering under applied voltage conditions and their direct correlations. The versatile setup eliminates possible shadowing effects and short circuits due to misalignment of the contacts. The electrical stability of the prototypes was characterized by the application of different voltage values. Corresponding structural changes were monitored by grazing X-ray scattering technique before, during and after the voltage was applied. The selected oligothiophene material with proved transistor properties shows high stability and directional anisotropy under applied voltage conditions. Thanks to a compact and flexible design of the setup, different type of small dimension devices could be studied under external voltage conditions at various synchrotron beamlines.

Raw and processed data used in the simultaneous analysis of electrical characteristics and microstructure of crystallised PEDOT:PSS based OECTs under strain

Here is presented raw and analysed data collected during study of the evolution, with uniaxial stretching, of the electrical and microcrystalline characteristics of polystyrene sulfonate doped poly(3,4-ethylenedioxythiophene) (PEDOT:PSS) organic electrochemical transistors (OECTs). X-ray diffraction data from GIWAXS measurements of the PEDOT:PSS material, performed at the SOLEIL light source are presented in raw and partially analysed forms. Current-voltage data, collected concurrently with the GIWAXS data, are also presented, and the evolution of the transconductance of the OECT devices with stretching is shown. GIWAXS data are only examined along the qz specular reflection ridge, and scans along this ridge are extracted and presented. However, the off-specular data may also be of interest to readers and is therefore made available here in its entirety.

Direct Observations of the Structural Properties of Semiconducting Polymer: Fullerene Blends under Tensile Stretching

We describe the impact of tensile strains on the structural properties of thin films composed of PffBT4T-2OD π-conjugated polymer and PC₇₁BM fullerenes coated on a stretchable substrate, based on a novel approach using in situ studies of flexible organic thin films. In situ grazing incidence X-ray diffraction (GIXD) measurements were carried out to probe the ordering of polymers and to measure the strain of the polymer chains under uniaxial tensile tests. A maximum 10% tensile stretching was applied (i.e., beyond the relaxation threshold). Interestingly we found different behaviors upon stretching the polymer: fullerene blends with the modified polymer; fullerene blends with the 1,8-Diiodooctane (DIO) additive. Overall, the strain in the system was almost twice as low in the presence of additive. The inclusion of additive was found to help in stabilizing the system and, in particular, the π-π packing of the donor polymer chains.

Local scale structural changes of working OFET devices

We present an in situ nanobeam grazing-incidence X-ray diffraction (nanoGIXD) study of real-sized organic field effect transistors (OFET) under applied voltage. The nano-sized beam allows for spatially resolved monitoring of the structural behavior across the poly(3-hexylthiophene) (P3HT) polymer channel and the interfacial regions of the source and drain gold electrodes before and after the operation cycle. We observe major alterations of the gold contacts, in particular diffusion of Au atoms into the polymer channel and a local reorientation of the recrystallized Au nanocrystallites quantified by Hermans' orientation factors. Therefore, the initially sharp electrode-polymer interfaces are significantly modified as a result of device operation. Our findings demonstrate that nanoGIXD has a high potential to probe functionality and reliability of working organic devices.

Phase Transitions and Formation of a Monolayer-Type Structure in Thin Oligothiophene Films: Exploration with a Combined In Situ X-ray Diffraction and Electrical Measurements

A combination of in situ electrical and grazing-incidence X-ray diffraction (GIXD) is a powerful tool for studies of correlations between the microstructure and charge transport in thin organic films. The information provided by such experimental approach can help optimizing the performance of the films as active layers of organic electronic devices. In this work, such combination of techniques was used to investigate the phase transitions in vacuum-deposited thin films of a common organic semiconductor dihexyl-quarterthiophene (DH4T). A transition from the initial highly crystalline phase to a mesophase was detected upon heating, while only a partial backward transition was observed upon cooling to room temperature. In situ electrical conductivity measurements revealed the impact of both transitions on charge transport. This is partly accounted for by the fact that the initial crystalline phase is characterized by inclination of molecules in the plane perpendicular to the π-π stacking direction, whereas the mesophase is built of molecules tilted in the direction of π-π stacking. Importantly, in addition to the two phases of DH4T characteristic of the bulk, a third interfacial substrate-stabilized monolayer-type phase was observed. The existence of such interfacial structure can have important implications for the charge mobility, being especially favorable for lateral two-dimensional charge transport in the organic field-effect transistors geometry.

Large-Size Single-Crystal Oligothiophene-Based Monolayers for Field-Effect Transistors

High structural quality of crystalline organic semiconductors is the basis of their superior electrical performance. Recent progress in quasi two-dimensional (2D) organic semiconductor films challenges bulk single crystals because both demonstrate competing charge-carrier mobilities. As the thinnest molecular semiconductors, monolayers offer numerous advantages such as unmatched flexibility and light transparency as well  they are an excellent platform for sensing. Oligothiophene-based materials are among the most promising ones for light-emitting applications because of the combination of efficient luminescence and decent charge-carrier mobility. Here, we demonstrate single-crystal monolayers of unprecedented structural order grown from four alkyl-substituted thiophene and thiophene-phenylene oligomers. The monolayer crystals with lateral dimensions up to 3 mm were grown from the solution on substrates with various surface energies and roughness by drop or spin-casting with subsequent slow solvent evaporation. Our data indicate that 2D crystallization resulting in single-crystal monolayers occurs at the receding gas-solution-substrate contact line. The structural properties of the monolayers were studied by grazing-incidence X-ray diffraction/reflectivity, atomic force and differential interference contrast microscopies, and imaging spectroscopic ellipsometry. These highly ordered monolayers demonstrated an excellent performance in organic field-effect transistors approaching the best values reported for the thiophene or thiophene-phenylene oligomers. Our findings pave the way for efficient monolayer organic electronics highlighting the high potential of simple solution-processing techniques for the growth of large-size single-crystal monolayers with excellent structural order and electrical performance competing against bulk single crystals.

Impact of the solubility of organic semiconductors for solution-processable electronics on the structure formation: a real-time study of morphology and electrical properties

The control of structure formation in the active layers of organic solar cells allows for improvement in their processability and enhancement of the efficiency of the final devices. In the present work, in situ studies of film formation from binary toluene solutions of an electron donor, poly(3-hexylthiophene) (P3HT), and an electron acceptor such as [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) or indene-C60 bisadduct (ICBA) have been conducted. These experiments were carried out using GIWAXS with simultaneous electric current measurements. The comparative analysis of the intensity of the amorphous halo, and the 100 and 020 peaks of P3HT reveals the development of the semicrystalline morphology of the donor through a partly-ordered phase. The experiments show the impact of the chemical structure of the acceptor, as well as that of the donor : acceptor ratio on the kinetics of drying and crystallization. The optimal bulk heterojunction morphology was achieved for P3HT : ICBA 1 : 1, which exhibited the highest value of current. A more efficient phase separation in non-annealed P3HT:ICBA films as compared to P3HT:PCBM was accounted for by the differences in solubility of the components in toluene. The structure formation during solvent evaporation can be subdivided into three stages, including the ordering of the polymer in solution, phase separation during precipitation, and the perfectioning of P3HT crystals in the dry film.

High-Mobility, Ultrathin Organic Semiconducting Films Realized by Surface-Mediated Crystallization

The functionality of common organic semiconductor materials is determined by their chemical structure and crystal modification. While the former can be fine-tuned via synthesis, a priori control over the crystal structure has remained elusive. We show that the surface tension is the main driver for the plate-like crystallization of a novel small organic molecule n-type semiconductor at the liquid-air interface. This interface provides an ideal environment for the growth of millimeter-sized semiconductor platelets that are only few nanometers thick and thus highly attractive for application in transistors. On the basis of the novel high-performance perylene diimide, we show in as-grown, only 3 nm thin crystals electron mobilities of above 4 cm²/(V s) and excellent bias stress stability. We suggest that the established systematics on solvent parameters can provide the basis of a general framework for a more deterministic crystallization of other small molecules.

Cation-Controlled Excimer Packing in Langmuir-Blodgett Films of Hemicyanine Amphiphilic Chromoionophores

Supramolecular structure of ultrathin films of hemicyanine dye bearing a crown ether group (CrHCR) was tuned by lateral pressure and investigated by means of compression isotherms, UV-vis and fluorescence spectroscopies, and X-ray reflectivity. Two different types of aggregation were revealed, depending on the absence or the presence of metal cations in the water subphase. While CrHCR forms at high surface pressures head-to-tail stacking aggregates on pure water, changing the subphase to a metal-cation-containing one leads to the appearance of well-defined excimers with head-to-head orientation. The structure of monolayers transferred onto solid supports by the Langmuir-Blodgett (LB) technique was examined by use of X-ray reflectivity measurements and molecular modeling. A model of cation-induced excimer formation in hemicyanine Langmuir monolayers is proposed. Finally, fluorescence emission properties of LB films of CrHCR can be managed by appropriate changes in the subphase composition, this last one determining the type of chromophore aggregation.

Impact of substrate temperature on the structure and electrical performance of vacuum-deposited α,α′-DH5T oligothiophene thin films

Remarkable structural changes are reported for α,α′-DH5T oligomer thin films evaporated at different substrate temperatures and directly correlated with the electrical performance where the order of π–π stacking plays a crucial role.

Influence of the molecular weight and size dispersion of the electroluminescent polymer on the performance of air-stable hybrid light-emitting diodes

The influence of the chain length and the molecular weight distribution of the electroluminescent polymer on the carrier transport properties and morphology of air stable hybrid light-emitting diodes is reported. It is found that variations between diverse as-received commercial batches play a major role in the performance of the devices, whose maximum luminance can differ up to 2 orders of magnitude. Through complementary optoelectronic, structural, and morphological characterization techniques, we provide insights into the relationship between charge dynamics and the structure of polymeric electroluminescent materials. The carrier dynamics are found to be dominated by both the polymeric chain length and the hole transport, which in turn is dependent on the concentration of trap states. Furthermore, the chain length is seen to affect the morphology of the active layer.

Local structure of semicrystalline P3HT films probed by nanofocused coherent X-rays

Spatially resolved x-ray study of semicrystalline P3HT films reveals nanoscale inhomogeneity of the conjugated network, as well as structural variations induced by Au nanoparticles.

Real time studies of thiophene-based conjugated oligomer solidification

Real time investigations of a solidification process of thiophene based oligomer system by simultaneous probing of the structure and the electrical response.

Easily processable highly ordered Langmuir-Blodgett films of quaterthiophene disiloxane dimer for monolayer organic field-effect transistors

Self-assembly of highly soluble water-stable tetramethyldisiloxane-based dimer of α,α'-dialkylquaterthiophene on the water-air interface was investigated by Langmuir, grazing incidence X-ray diffraction, and X-ray reflectivity techniques. The conditions for formation of very homogeneous crystalline monolayer Langmuir-Blodgett (LB) films of the oligomer were found. Monolayer organic field-effect transistors (OFETs) based on these LB films as a semiconducting layer showed hole mobilities up to 3 × 10(-3) cm(2)/(V s), on-off ratio of 10(5), small hysteresis, and high long-term stability. The electrical performance of the LB films studied is close to that for the same material in the bulk or in the monolayer OFETs prepared from water vapor sensitive chlorosilyl derivatives of quaterthiophene by self-assembling from solution. These findings show high potential of disiloxane-based LB films in monolayer OFETs for large-area organic electronics.

Local Orientational Structure of a P3HT π-π Conjugated Network Investigated by X-ray Nanodiffraction

We employed nanobeam X-ray diffraction using an X-ray spot size of 150 nm to investigate the local structure of P3HT thin films. We derived nanoscale real space maps of the X-ray diffraction properties at the π-π (020) diffraction peak. The X-ray data reveal a complex nanoscale structure of the polymer network with strong local variation where some areas of the film display a rather high degree of angular order. We quantify both the magnitude and direction of the angular order. Our results provide new insights into the local structural properties and connectivity of P3HT films.

Enhancement of field-effect mobility due to structural ordering in poly(3-hexylthiophene) films by the dip-coating technique

Organic field-effect transistors (OFETs) were fabricated by depositing a regioregular poly(3-hexylthiophene) (P3HT) active layer using a dip-coating method. The field-effect mobility in OFETs depends on chain orientation and crystallinity and is related to direction and withdrawal speed with respect to the source/drain orientation. In this paper, how to control the structural and transport properties of P3HT films by coating parallel and perpendicular to the dipping direction is demonstrated. X-ray diffraction curves taken in the perpendicular direction exhibit a higher degree of crystalline ordering and edge-on conformation compared with those in the parallel direction; this finding correlates with the directional anisotropy of the OFET mobility. Both structural anisotropy and transport properties are enhanced upon thermal treatment.

Acceptor-Enhanced Local Order in Conjugated Polymer Films

Disorder in conjugated polymers is a general drawback that limits their use in organic electronics. We show that an archetypical conjugated polymer, MEH-PPV, enhances its local structural and electronic order upon addition of an electronic acceptor, trinitrofluorenone (TNF). First, acceptor addition in MEH-PPV results in a highly structured XRD pattern characteristic for semicrystalline conjugated polymers. Second, the surface roughness of the MEH-PPV films increases upon small acceptor addition, implying formation of crystalline nanodomains. Third, the low-frequency Raman features of the polymer are narrowed upon TNF addition and indicate decreased inhomogeneous broadening. Finally, the photoinduced absorption and surface photovoltage spectroscopy data show that photoexcited and dark polymer intragap electronic states assigned to deep defects disappear in the blend. We relate the enhanced order to formation of a charge-transfer complex between MEH-PPV and TNF in the electronic ground state. These findings may be of high importance to control structural properties as they demonstrate an approach to increasing the order of a conjugated polymer by using an acceptor additive.

Formation of self-assembled organosilicon-functionalized quinquethiophene monolayers by fast processing techniques

Different techniques for a relatively fast self-assembled monolayer film formation such as Langmuir-Blodgett (LB), spin-coating, and dip-coating methods have been compared using chloro[11-(5''''-ethyl-2,2':5',2″:5''',2''':5''',2''''-quinquethiophene-5-yl)undecyl]dimethylsilane as a reactive precursor. It was shown that both spin-coating and LB techniques are very promising methods for preparation of highly ordered monolayer films of organosilicon-functionalized quinquethiophene with vertical orientation of oligothiophene fragments, while dip-coating gives only partial coverage. Optimal conditions for complete filling out the substrate surface by the quinquethiophene-containing monolayer by spin-coating and LB methods have been found. Grazing incidence X-ray diffraction measurements confirmed formation of in-plane crystalline order within the monolayer film. Changes in the layer structure were established by X-ray reflectivity and grazing incidence X-ray diffraction methods.

Time-space transformation of femtosecond free-electron laser pulses by periodical multilayers

A scattering scheme to probe the time evolution of femtosecond pulses of a soft X-ray free-electron laser (FEL) in a multilayer structure is presented. The response of periodic multilayers (MLs) with low and high absorption and various numbers of bi-layers to a pulse train of Gaussian-shaped sub-pulses is calculated. During the passage of the incident pulse the interaction length increases and the scattering profile changes as a function of the spatial position of the pulse within the sample. Owing to stretching of the reflected pulse compared with the incident pulse, the time-dependent scattering evolution in the ML can be visualized along a spatial coordinate of a position-sensitive detector. Using a scattering geometry where the mean energy of the incident pulse train is slightly detuned from the energy of maximum reflectivity at the first-order peak, the response of the ML shows an oscillator behaviour along this spatial coordinate at the detector. For a FEL wavelength of 6.4 nm this effect is promising for MLs with low absorption, such as La/C for example. On the other hand, the oscillations will not be present for MLs with high absorption. Therefore a low-absorbing ML is a sensitive tool for studying the possible change of sample absorption caused by femtosecond-pulse interaction with matter.

Small-cell tumors of the liver: A cytological study of 91 cases and a review of the literature

This study was designed to consider the cytomorphological spectrum, differential diagnosis, and the role of ancillary studies in small-cell tumors of the liver. Three independent pathologists reviewed cytological slides from 91 cases of small-cell tumors of the liver. The results were compared with the findings of three recently published studies (Cytopathology 11 (2000) 262-267; Diagn Cytopathol 19 (1998) 29-32; and Acta Cytol 40 (1996) 937-947). The role of immunohistochemistry in reaching timely and specific diagnoses was also examined. The diagnostic categories included 44 cases of metastatic small-cell undifferentiated carcinoma, 15 cases of metastatic neuroendocrine carcinoma, 10 cases of metastatic adenocarcinoma, 7 cases of malignant lymphoma, 4 cases of hepatocellular carcinoma with small-cell features, 2 cases of cholangiocarcinoma, 1 case of poorly differentiated carcinoma, and 8 cases of rare tumors including granulosa cell tumor (2 cases), sarcoma (4 cases), malignant melanoma with small-cell features (1 case), and meningioma with small-cell features (1 case). Metastatic granulosa cell-tumor, metastatic melanoma, and metastatic meningioma should be included in the differential diagnoses of small-cell malignancies found in the liver.