Solvent Annealing Research Articles

Conformal 3D Nanopatterning by Block Copolymer Lithography with Vapor-Phase Deposited Neutral Adlayer.

Block copolymer (BCP) lithography is an effective nanopatterning methodology exploiting nanoscale self-assembled periodic patterns in BCP thin films. This approach has a critical limitation for nonplanar substrate geometry arising from the reflow and modification of BCP films upon the thermal or solvent annealing process, which is inevitable to induce the mobility of BCP chains for the self-assembly process. Herein, reflow-free, 3D BCP nanopatterning is demonstrated by introducing a conformally grown adlayer by the initiated chemical vapor deposition (iCVD) process. A highly cross-linked poly(divinylbenzene) layer was deposited directly onto the BCP thin film surface by iCVD, which effectively prevented the reflow of BCP thin film during an annealing process. BCP nanopatterns could be stabilized on various substrate geometry, including a nonplanar deformed polymer substrate, a pyramid shape substrate, and a graphene fiber surface. A fiber-type hydrogen evolution reaction (HER) catalyst is suggested by stabilizing lamellar Pt nanopatterns on severely rough graphene fiber surfaces.

Controlling the ordered transition of PS-b-P4VP block copolymer ultrathin films by solvent annealing

A change in morphology of ultrathin films of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblock copolymer was induced by annealing under chloroform and toluene vapor and was investigated by atomic force microscopy (AFM). The microphase separation morphology with spherical structures were formed when PS-b-P4VP was dissolved in toluene, which is a selective solvent for polystyrene (PS) segments. After chloroform annealing, a series of surface morphologies of PS-b-P4VP were observed, including spherical and network structures such as gyroid structures. During the continuous annealing treatment for the films with network structures by toluene, a reversible structure conversion from network to sea-island was observed. In addition, we have demonstrated that Au-NPs can be easily adhered to the PS-b-P4VP films with network structure on surface.

Catalytic Biosensors from Complex Coacervate Core Micelle (C3M) Thin Films.

Enzymes have been applied to a variety of industrially and medically relevant chemistries as both catalysts and sensors. Incorporation of proteins and enzymes into complex coacervates has been demonstrated to improve the thermal, chemical, and temporal stability of enzymes in solution. In this work, a neutral-cationic block copolymer and an enzyme, alkaline phosphatase, are incorporated into complex coacervate core micelles (C3Ms) and coated onto a solid substrate to create a biocatalytic film from aqueous solution. The incorporation of photo-cross-linkable groups into the neutral block of the polymer allows the film to be cross-linked under ultraviolet light, rendering it insoluble. The morphology of the film is shown to depend most strongly on the protein loading within the film, while solvent annealing is shown to have a minimal effect. These films are then demonstrated as specific sensors for Zn2+ in solution in the presence of other metals, a model reaction for ion-selective heavy metal biosensing useful in environmental monitoring. They are shown to have low leaching and maintain sufficient activity and response for sensing for 1 month after aging under ambient conditions and at 40 °C and 50% relative humidity. The C3M immobilization method demonstrated can be applied to a wide variety of proteins with minimal chemical or genetic modification and could be used for immobilization of charged macromolecules in general to produce a wide variety of thin-film devices.

Shape-Persistent π-Conjugated Macrocycles with Aggregation-Induced Emission Property: Synthesis, Mechanofluorochromism, and Mercury(II) Detection.

Shape-persistent conjugated macrocycles are fundamentally important because of their unique structure and properties. Herein, a series of π-conjugated macrocycles with a shape-persistent architecture, an adaptive backbone, and aggregation-induced emission (AIE) properties are synthesized via oxidative coupling of acetylene-terminated tetraphenylethylene precursor with a half-ring topology and following transformation from butadiynylene linkers into thienylene ones. Characterization by NMR spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry provided unambiguous proofs for the macrocyclic structures. In particular, the free rotation of aromatic rings in the rigid macrocyclic backbone was validated by two-dimensional NMR spectroscopy, variable-temperature NMR measurements, and theoretical calculations. Moreover, these shape-persistent macrocyclic chromophores all exhibited obvious AIE phenomena and remarkable mechanofluorochromism behaviors with a red-shifted luminescence upon grinding and blue-shifted emission after solvent annealing. Also, the introduction of S atoms into the macrocyclic frameworks endowed the macrocyclic luminogen the capability to selectively detect mecury(II) ions in aqueous media among other metal ions.

Manipulating the sequences of block copolymer patterns on corrugated substrates

This paper describes manipulating the sequences of cylinder-forming block copolymer patterns on corrugated substrates. Upon thermal annealing, the topographic corrugation of the substrate generates a spontaneous flow-field of the block copolymer and induces thickness-dependent microdomains. The corrugation gradient has some range of surface roughness characterized by its topographic parameters. When the substrate topography matches the dimensions of the intrinsic surface relief structures of the block copolymer, the surface roughening is suppressed by inverted terrace formation, and sequenced patterns of in-plane cylinders and nonbulk lamella phases are generated. As soon as the surface roughening forms on the corrugated substrate with a roughness parameter lower than that of the surface relief structures, the reverse sequences of the alternative microphase separated structures are developed. However, enhanced mobility of the block copolymer induced by solvent annealing suppresses the pattern sequencing and the in-plane cylinders with a relatively high degree of ordering generated over the entire surface of the corrugated substrate. This observation may further enable new approaches for manipulating the sequences of spatially registered hierarchical surface patterns of block copolymers.

Complex core-shell morphologies of block copolymers revealed beneath the surface

This paper identifies and characterizes complex core-shell morphologies in thin films of a polybutadiene-block-poly(2-vinyl pyridine)-block-poly(tert-butyl methacrylate) (BVT) triblock terpolymer. The spin-coated BVT film develops into two distinct microphase separated structures with thickness variation during solvent annealing in a well-controlled atmosphere of THF vapor. Cylinders parallel to the film plane are found in thinner terraces and featureless areas that are characteristic of the lying lamella phase, or disordered structures are found in thicker terraces. Underneath the surface, we found that these microphase separated structures exhibit core-shell morphologies, i.e. surface ablation revealed core-shell cylinders and core-shell perforated lamellae under a cover layer in each terrace. Time-resolved study upon solvent annealing shows that the dynamics of microdomain evolution are affected by the extent of annealing time. The structural development in the BVT terpolymer films on corrugated supports demonstrates flow-field-induced sequenced ordering of the microdomains.

Surface modification-assisted solvent annealing to prepare high quality M-phase VO2 nanocrystals for flexible thermochromic films

Well-crystalline and stoichiometric M-phase vanadium dioxide (VO2 (M)) ultrafine nanoparticles are desired in fabricating high-efficient VO2-based flexible thermochromic films. In this study, a novel solvent annealing technique is developed to avoid growth and agglomeration of VO2 (M) nanoparticles in the post-annealing process. Oxygen-deficient VO2 (D) nanoparticles (~36 nm) are firstly prepared by a facial hydrothermal method. A double-layered reactor is designed to separate the surfactant-modified VO2 (D) nanoparticles physically from H2O2 which serves as the oxidant. The unique reactor enables the formation of a moderate oxygenation environment in the solvent annealing process, making the transformation of oxygen-deficient VO2 to VO2 (M) more controllable. The growth and agglomeration of VO2 nanoparticles are effectively suppressed due to the surface modification by polyvinyl pyrrolidone, liquid environment and low temperature. The obtained VO2 (M) nanoparticles have an average particle size of ~41 nm. The flexible film prepared with the VO2 (M) nanoparticles exhibit excellent thermochromic properties with ΔTsol reaching 18.03% and Tlum up to 58.33%. This amazing performance is attributed to the high quality of VO2 (M) nanoparticles and ultrafine particle size that makes the surface plasmon absorption take effect in the solar light region. This work demonstrates the proposed solvent annealing technique is an effective approach to prepare high-quality ultrafine VO2 (M) nanoparticles for achieving efficient thermochromic performance of the flexible smart windows.

Roll-to-Roll Scalable Production of Ordered Microdomains through Nonvolatile Additive Solvent Annealing of Block Copolymers

A new method, “nonvolatile solvent vapor annealing” (NVASA), has been developed to anneal block copolymers during film deposition by controlling the solvent drying process. Precise amounts of high ...

Post-treatment of Perovskite Films toward Efficient Solar Cells via Mixed Solvent Annealing

Post-treatment of perovskite films plays a crucial role in obtaining high-performance perovskite solar cells (PSCs). Solvent annealing (SA), as a universal post-treatment strategy, is profoundly be...

Two-Dimensional Film Growth of Zinc Tetraphenylporphyrin with the Aid of Solvent Coordination

Abstract Since the performance of an organic film device largely depends on the molecular arrangement in the film, control of the arrangement is crucial. Low molecular-weight organic semiconductor compounds, however, tend to have the edge-on orientation spontaneously due to crystallization on an inert surface. In fact, orientation control of a high-crystallinity compound is often difficult especially on an inert surface. In the present study, a face-on crystalline thin film of zinc tetraphenylporphyrin (ZnTPP) has readily been obtained on an inert surface by using solvent annealing (SA) with an appropriate solvent, formamide (FA). The prepared film is carefully analyzed by using the infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) and grazing incidence X-ray diffraction (GIXD) techniques. The measurements show that an FA molecule coordinated on a zinc atom blocks the stacking interaction sites of the porphyrin ring, and instead the side to side interaction between the C–H group of the porphyrin rings and π orbital of the phenyl rings forms a two-dimensional sheet-like structure realizing face-on orientation.

Hierarchically-organized C60 crystals obtained from a liquid/liquid interfacial precipitation method by using 1,2,3,4-tetrahydronaphthalene as a solvent

C60 crystals have potential applications in the optoelectronics, photoconducting devices and templated synthesis fields. However, their preparation is complex. A simple liquid-liquid interfacial precipitation method was used to fabricate hierarchically-organized C60 crystals with various topographic characteristics, using 1,2,3,4-tetrahydronaphthalene as a good solvent, and isopropanol, ethanol or methanol as a poor solvent. Results indicate that the morphology and shape of the as-prepared C60 crystals vary according to the solvent combination and the ratio of good to poor solvents. The SEM images of fractured surfaces and XRD patterns of the crystals reveal that the crystals are formed by the hierarchical organization of C60 molecules at the molecular level to nanocrystals that are assembled into micrometer crystals. The crystals are composed solely of C60 molecules, without polymerization and solvents, which are arranged in a face-centered cubic lattice. The surface roughness is increased by post washing with ethanol. The methodology described here is advantageous over the high-temperature conversion and solvent annealing methods reported previously.

Improving Performance and Stability of Planar Perovskite Solar Cells through Grain Boundary Passivation with Block Copolymers

Organic–inorganic metal halide perovskite solar cells (PSCs) exhibit excellent photovoltaic performance but have the drawbacks of instabilities against moisture and heat due to the inherent hydroscopic nature and volatility of their organic components. Herein, it is reported that using the block copolymer F127 as the passivation reagent in conjunction with the solvent annealing process can efficiently improve the performance and stability of corresponding organic–inorganic PSCs. It is anticipated that the hydrophilic poly(ethylene oxide) tails of F127 polymers connect with contiguous perovskite crystals and passivate defects at perovskite grain boundaries, whereas the dangling hydrophobic poly(phenyl oxide) centers suppress perovskite decomposition caused by moisture and heat. After the optimization of the F127 additive, planar PSCs with champion power conversion efficiencies of 21.01% and 18.71% are achieved on rigid and flexible substrates, respectively. The F127 passivation strategy provides an effective approach for fabricating high‐efficiency and stable PSCs.

Microphase segregation and selective chain scission of poly(2‐methyl‐2‐oxazoline)‐block‐polystyrene

ABSTRACTHerein, we report the design and synthesis of a block copolymer (BCP) with a high Flory–Huggins interaction parameter to access 10 nm feature sizes for potential lithographic applications. The investigated BCP is poly[(2‐methyl‐2‐oxazoline)‐block‐styrene] (PMeOx‐b‐PS), where the PMeOx segment functions as a hydrophilic segment. Two BCPs with different molecular weights were prepared using PMeOx as macroinitiator for copper(0) mediated controlled radical polymerization. The thin film self‐assembly of the obtained PMeOx‐b‐PS was performed by solvent annealing and investigated by atomic force microscopy. Both polymers formed PMeOx cylinders in a PS matrix with an average cylinder diameter of 10.5 nm. Additionally, the ability of the PMeOx domains to selectively degrade under ultraviolet irradiation was explored. It was shown that scission of the PMeOx block does occur selectively, and furthermore that the degraded domains can be removed while leaving the PS matrix intact. By combining synthetic accessibility, small feature sizes, and a selectively cleavable domain, this new BCP system holds significant promise as a lithographic mask for patterning surfaces with high precision. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1349–1357

Design, Synthesis, and Postvapor Treatment of Neutral Fulleropyrrolidine Electron-Collecting Interlayers for High-Efficiency Inverted Polymer Solar Cells

A novel fullerene derivative (FBPNOH) grafted with bilateral polar pendants was explored as an efficient electron-collecting layer (ECL) for inverted polymer solar cells (i-PSCs). Using PTB7-Th:PC71BM as the photoactive material, the devices based on FBPNOH achieved power conversion efficiencies (PCEs) exceeding 8.85%, which are higher than those of the reference devices based on sol–gel ZnO. The impact of postsolvent treatment on the interfacial properties and charge transport ability of interlayers and the corresponding optoelectronic characteristics have been systematically investigated in comparison with those of its unilateral counterpart (FPNOH). The results show that the post-solvent annealing process is beneficial for enhancing the carrier transport and extraction characteristics of fullerene-based ECLs for PSCs. Meanwhile, according to ultraviolet photoelectron spectroscopy, dimethylformamide solvent annealing can further reduce the work function of indium tin oxide. The electron-selective device...

Sequential infiltration synthesis- and solvent annealing-induced morphological changes in positive-tone e-beam resist patterns evaluated by atomic force microscopy

Morphological changes in thin film patterns of a positive-tone electron beam resist induced by sequential infiltration synthesis and solvent annealing were revealed by atomic force microscopy for the fabrication of silica imprint molds with sub-15 nm trenches. In sequential infiltration synthesis, the wiggling of 40-nm-thick resist film patterns was attributed to decreasing the widths of the resist terraces and baking at 100 °C rather than exposure to a vapor of trimethylaluminum. Reducing the thickness of the resist film from 40 nm to 20 nm prevented the wiggling of resist film patterns after sequential infiltration synthesis. Solvent annealing with a toluene vapor at 20 °C increased mouse-bite defects appearing at the line edges of the resist film patterns, and significantly increased mouse-bite and line-break defects of silica imprint molds after dry etching. These results suggest that the polymer/substrate interface had a significant impact on the morphological fidelity of resist film patterns during electron beam lithography procedures.

Synthesis of amphiphilic triblock fullerene derivatives and their solvent induced self assembly in organic solar cells

Abstract Two A-B-C type amphiphilic triblock fullerene derivatives (C60-PEHBS and C60-2EHTPB) were synthesized and applied to modify zinc oxide (ZnO) layer in inverted organic solar cells (OSCs). These two fullerene derivatives are typical hydrophilic-amphiphilic-hydrophobic triblock macromolecules with hydrophobic fullerene block, amphiphilic fluorene block and hydrophilic fluorene block. The amphiphilic fluorene contains 1,2-diethoxyethane (-C6H14O2) on the side chains. And the hydrophilic fluorene blocks contain potassium butane-1-sulfonate (-C4H9SO3K) or N,N,N-trimethylpropan-1-aminium bromide (-C6H16BrN) side chains. When introducing as the cathode interface layers on ZnO, solvent annealing was applied on these two fullerene derivatives layers and then obvious self-assembly were observed, which were supported by X-ray diffraction (XRD) and water contact angle measurement. It was found that the fullerene derivatives could modify the nanoparticle of ZnO surface, passivate surface traps, suppress the recombination loss of carriers, reduce the series resistance and improve the electrical coupling of ZnO/active layer effectively. The power conversion efficiencies (PCEs) of the devices with structure of ITO/ZnO/fullerene derivatives/PTB7-Th: PC71BM/MoO3/Al are enhanced to 8.56% and 9.00% for C60-PEHBS and C60-2EHTPB respectively, compared to 8.13% of bare ZnO. The new amphiphilic triblock macromolecules and their solvent induced self-assembly opens an opportunity to study the morphologies in their super thin layers and develop their applications.

High-Quality Perovskite CH₃NH₃PbI₃ Thin Films for Solar Cells Prepared by Single-Source Thermal Evaporation Combined with Solvent Treatment.

In this work, solvent annealing process for CH3NH3PbI3 thin film prepared by single source evaporation was reported. Characterized by the scanning electron microscope (SEM), X-ray diffractometer (XRD), energy dispersive spectroscope (EDS), ultraviolet-visible (UV) spectrophotometer, and the photoluminescence (PL) spectrometer, our method ensured higher quality film with crystallinity, composition, well-defined grain structure, and reproducibility. The optimized solar cell device based on the structure of ITO/PEDOT:PSS/CH3NH3PbI3/PCBM/Ag achieved better performance in power conversion efficiency from 2.64% to 9.92%, providing an effective method to optimize the quality of perovskite film for solar cell application.

Ternary System with Intermolecular Hydrogen Bond: Efficient Strategy to High-Performance Nonfullerene Organic Solar Cells.

To boost organic solar cell (OSC) performance, numerous approaches have been developed, such as synthesizing new materials, using post-annealing (thermal or solvent annealing) or fabricating ternary devices. The ternary strategy is usually used as an uncomplicated and effective way, but how to choose the third component and the effect of interactions between materials on OSC performance still need to be clarified. Herein, we proposed a new finding that the carbonyl group of 3,9-bis(2-methylene-(3-(1,1-dicyanomethylene)-indanone))-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b'] dithiophene (ITIC) end groups can react with the dye molecule SR197 to form the N-H···O noncovalent interaction. The existence of intermolecular hydrogen bonds was confirmed using Fourier transform infrared spectra and two-dimensional proton nuclear magnetic resonance. The power conversion efficiency (PCE) was improved to 10.29% via doping SR197 into blends of PTB7-Th:ITIC, which exhibited a huge enhancement of approximately 30% compared with the binary OSCs (PCE = 7.92%). The ternary OSCs of PBDB-T:SR197:ITIC could also achieve high PCE (11.03%) without post-thermal or solvent annealing. Transmission electron microscopy and grazing-incidence wide-angle X-ray scattering showed the optimized morphology and enhanced crystallinity of ternary systems, which is facilitated to exciton dissociation and charge transmission. These conclusions mean that the H-bonding strategy is an effective way for selecting the third component and could achieve high-performance OSCs.

Nano Spray‐Dried Block Copolymer Nanoparticles and Their Transformation into Hybrid and Inorganic Nanoparticles

AbstractA novel combination of block copolymer (BCP) nano spray‐drying (NSD), solvent annealing, and selective metal oxide growth is utilized to create functional polymer nanoparticles, polymer‐metal‐oxide hybrid nanoparticles, and templated metal oxide nanoparticles with tunable composition, internal morphology, and porosity. NSD of BCPs from chloroform and toluene solutions results in porous and nonporous nanoparticles, respectively, with various degrees of phase separation. Further tuning of the nanoparticle internal morphology is performed by solvent annealing the spray‐dried particles with judicious choice of the nonsolvent dispersion medium and the surfactant, yielding assembly of both blocks at the surface of the nanoparticles. Finally, ZnO and Al2O3 are grown inside the polar blocks of phase‐ordered nanoparticles using a sequential infiltration synthesis method, in a post‐assembly process, resulting in hybrid BCP‐ZnO particles and BCP‐templated Al2O3 nanoparticles, as demonstrated by scanning transmission electron microscopy tomography. These structure engineering methods open new ways to direct and template functional nanoparticles.

Porous Polyimide and Carbon Nanotubes: Solvent Vapor–Induced Transformation in the Nanochannels of Anodic Aluminum Oxide Templates

AbstractPolyimides (PIs) have attracted wide attention because of their exceptional thermal stability and applications in areas such as printed circuit boards and multichip modules. It remains a great challenge, however, to control the morphologies and properties of PI‐based nanomaterials, especially porous PI‐based nanotubes. In this work, a versatile method to fabricate porous PI nanotubes via the template method is developed, with a solvent vapor–induced transformation process. First, polyamic acid (PAA) solutions are used as precursors and infiltrated into the nanochannels of anodic aluminum oxide templates, forming PAA nanotubes. After the samples are annealed in tetrahydrofuran or dimethylformamide vapors, depression of the PAA tubes occurs, causing the formation of pores. The porous PAA nanotubes can be further converted to porous PI and carbon nanotubes by imidization and carbonization processes, respectively. The pore sizes of the porous nanomaterials can be controlled by changing the type of the annealing solvent and the solvent annealing time.