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The bicontinuous microemulsion (BμE) phase is an equilibrium morphology characterized by cocontinuous domains, high interfacial areas, and nanoscale domain dimensions. These characteristics make the BμE potentially suitable for use in organic photovoltaic applications. Here, we use a combination of simulations and experiments to investigate the equilibrium morphologies formed by a ternary blend of conjugated polymer, all-conjugated diblock copolymer, and fullerene derivative PCBM. Using coarse-grained simulations, we identify the blend compositions that are most likely to result in donor/acceptor morphologies resembling the BμE. Experimentally, we probe these compositions through transmission electron microscopy and grazing-incidence X-ray scattering measurements. We demonstrate that all-conjugated block copolymer additives can be used to produce thermally stable, cocontinuous donor/acceptor morphologies at higher additive contents and longer annealing times than previously reported. These results demonstrate that conjugated BCP compatibilizers can be used as a means to achieve equilibrium, cocontinuous morphologies in donor/acceptor blends.

Sequential infiltration synthesis (SIS) is a route to the precision deposition of inorganic solids in analogy to atomic layer deposition but occurs within (vs upon) a soft material template. SIS has enabled exquisite nanoscale morphological complexity in various oxides through selective nucleation in block copolymers templates. However, the earliest stages of SIS growth remain unresolved, including the atomic structure of nuclei and the evolution of local coordination environments, before and after polymer template removal. We employed In K-edge extended X-ray absorption fine structure and atomic pair distribution function analysis of high-energy X-ray scattering to unravel (1) the structural evolution of InOxHy clusters inside a poly(methyl methacrylate) (PMMA) host matrix and (2) the formation of porous In2O3 solids (obtained after annealing) as a function of SIS cycle number. Early SIS cycles result in InOxHy cluster growth with high aspect ratio, followed by the formation of a three-dimensional network with additional SIS cycles. That the atomic structures of the InOxHy clusters can be modeled as multinuclear clusters with bonding patterns related to those in In2O3 and In(OH)3 crystal structures suggests that SIS may be an efficient route to 3D arrays of discrete-atom-number clusters. Annealing the mixed inorganic/polymer films in air removes the PMMA template and consolidates the as-grown clusters into cubic In2O3 nanocrystals with structural details that also depend on SIS cycle number.

Infiltration of inorganic oxides inside polymers using sequential infiltration synthesis (SIS) is an effective method for creating materials for a broad range of applications. The reactions between...

Organic–inorganic composite membranes are of great interest in modern water treatment processes because they offer potentially superior separation efficiency and advanced functionality by integrating the properties of polymers and inorganics. The biggest challenge in the fabrication and applications of organic–inorganic composite membranes is the incompatibility of organic–inorganic interfaces. In this minireview, we summarize the most recent advances in molecular engineering to tailor the properties of interfaces in composite membranes. Three typical models (i.e. mixed matrix models, interface composite models, and dual-layer composite models) are presented to demonstrate how to regulate these interfaces via molecular engineering and how the interfacial properties ultimately affect the membrane performance.

The sequential infiltration synthesis (SIS) of group 13 indium and gallium oxides (In2O3 and Ga2O3) into poly(methyl methacrylate) (PMMA) thin films is demonstrated using trimethylindium (TMIn) and trimethylgallium (TMGa), respectively, with water. In situ Fourier transform infrared (FTIR) spectroscopy reveals that these metal alkyl precursors reversibly associate with the carbonyl groups of PMMA in analogy to trimethylaluminum (TMAl), however, with significantly lower affinity. This is demonstrated to have important kinetic consequences that dramatically alter the synthetic parameters required to achieve material growth. Ab initio density functional theory simulations of the methyl methacrylate monomer with group 13 metal alkyls corroborate association energy that is 3× greater for TMAl than for either TMIn or TMGa. As a consequence, the kinetics of activated diffusion within the film is observed to be far more rapid for TMIn and TMGa than for TMAl. Spectroscopic ellipsometry and scanning electron micros...

The dewetting dynamics of a supported bilayer polymer thin film on a solid substrate is investigated using grazing incidence x-ray photon correlation spectroscopy. We find that the top layer dewets via the spinodal mechanism. The kinetics of the dewetting is studied by monitoring the time evolution of the surface diffuse x-ray scattering intensity. We study the time evolution of fluctuations about the average surface structure by measuring the two-time x-ray intensity fluctuation correlation functions. Using these two-time correlation functions we quantify the crossover from early-time diffusive dynamics to hydrodynamics. The early diffusive regime satisfies dynamic universality. The two-time correlation functions also quantify the onset of hydrodynamic effects. The hydrodynamic regime is observed during the spinodal dewetting process as these interactions are not screened.

We report the sequential infiltration synthesis (SIS) of aluminum oxide (Al2O3) into polyethersulfone (PES) ultrafiltration (UF) membranes to form hybrid nanocomposites. SIS relies on chemical interactions between precursor vapors and polymer functional groups, and enables nucleation and growth of inorganic materials to controlled depth. Using in situ Fourier-transform infrared spectroscopy and ellipsometry measurements, we demonstrate that trimethylaluminum associates with the sulfonyl groups in PES, extending the library of SIS-modified polymer nanocomposites to a previously undescribed polymer system and new application space: PES UF membranes. Depth-profiled x-ray photoelectron spectroscopy showed that the trimethylaluminum purge time dictates the extent of Al2O3 infiltration. Energy dispersive spectroscopy revealed the differences between SIS and atomic layer deposition in the membranes. This work demonstrates the viability of SIS to access the entire macroporous volume of PES UF membranes.

Crude oil fouling on membrane surfaces is a persistent, crippling challenge in oil spill remediation and oilfield wastewater treatment. In this research, we present how a nanosized oxide coating can profoundly affect the anti-crude-oil property of membrane materials. Select oxide coatings with a thickness of ∼10 nm are deposited conformally on common polymer membrane surfaces by atomic layer deposition to significantly mitigate fouling during filtration processes. TiO2- and SnO2-coated membranes exhibited far greater anti-crude-oil performance than ZnO- and Al2O3-coated ones. Tightly bound hydration layers play a crucial role in protecting the surface from crude oil adhesion, as revealed by molecular dynamics simulations. This work provides a facile strategy to fabricate crude-oil-resistant membranes with negligible impact on membrane structure, and also demonstrates that, contrary to common belief, excellent crude oil resistance can be achieved easily without implementation of sophisticated, hierarchical structures.

Sequential infiltration synthesis (SIS) is an emerging materials growth method by which inorganic metal oxides are nucleated and grown within the free volume of polymers in association with chemical functional groups in the polymer. SIS enables the growth of novel polymer-inorganic hybrid materials, porous inorganic materials, and spatially templated nanoscale devices of relevance to a host of technological applications. Although SIS borrows from the precursors and equipment of atomic layer deposition (ALD), the chemistry and physics of SIS differ in important ways. These differences arise from the permeable three-dimensional distribution of functional groups in polymers in SIS, which contrast to the typically impermeable two-dimensional distribution of active sites on solid surfaces in ALD. In SIS, metal-organic vapor-phase precursors dissolve and diffuse into polymers and interact with these functional groups through reversible complex formation and/or irreversible chemical reactions. In this perspective, we describe the thermodynamics and kinetics of SIS and attempt to disentangle the tightly coupled physical and chemical processes that underlie this method. We discuss the various experimental, computational, and theoretical efforts that provide insight into SIS mechanisms and identify approaches that may fill out current gaps in knowledge and expand the utilization of SIS.

High-density arrays of gold nanodots and nanoholes on indium tin oxide (ITO)-coated glass surfaces are fabricated using a nanoporous template fabricated by the self-assembly of diblock copolymers of poly (styrene-block-methyl methacrylate) (PS-b-PMMA) structures. By balancing the interfacial interactions between the polymer blocks and the substrate using random copolymer, cylindrical block copolymer microdomains oriented perpendicular to the plane of the substrate have been obtained. Nanoporous PS films are created by selectively etching PMMA cylinders, a straightforward route to form highly ordered nanoscale porous films. Deposition of gold on the template followed by lift off and sonication leaves a highly dense array of gold nanodots. These materials can serve as templates for the vapor-liquid-solid (VLS) growth of semiconductor nanorod arrays for next generation hybrid optoelectronic applications.

Large-scale fabrication of nanofilms directly on macro-porous substrates remains a major challenge in preparing advanced separation membranes. In this work, polyphenol/polyamine nanofilms with a minimum thickness around 13 nm were formed at the gas/liquid interface and simultaneously composited onto hydrophobic macro-porous substrates with the pore size of several hundreds of nanometers, a process driven by high oxygen concentration and interfacial energy at the interface. The as-prepared nanofilms show nearly complete rejection to a wide spectrum of dye molecules, and above 90% rejection to divalent cations such as Mg2+ and Ca2+ with a relative high permeate flux above 15 L m−2 h−1 bar−1, demonstrating great potential in ionic and molecular sieving processes.

All-conjugated block copolymers bring together hole- and electron-conductive polymers and can be used as the active layer of solution-processed photovoltaic devices, but it remains unclear how molecular structure, morphology, and electronic properties influence performance. Here, the role of the chemical linker is investigated through analysis of two donor–linker–acceptor block copolymers that differ in the chemistry of the linking group. Device studies show that power conversion efficiencies differ by a factor of 40 between the two polymers, and ultrafast transient absorption measurements reveal charge separation only in block copolymers that contain a wide bandgap monomer at the donor–acceptor interface. Optical measurements reveal the formation of a low-energy excited state when donor and acceptor blocks are directly linked without this wide bandgap monomer. For both samples studied, it is found that the rate of charge recombination in these systems is faster than in poly­mer–polymer and polymer–fullerene blends. This work demonstrates that the linking group chemistry influences charge separation in all-conjugated block copolymer systems, and further improvement of photovoltaic performance may be possible through optimization of the linking group. These results also suggest that all-conjugated block copolymers can be used as model systems for the donor–acceptor interface in bulk heterojunction blends.

A facile approach is reported to process rod-coil block copolymers (BCPs) into highly ordered nanostructures in a rapid, low-energy process. By introducing a selective plasticizer into the rod-coil BCPs during annealing, both the annealing temperature and time to achieve thermodynamic equilibrium and highly ordered structures can be decreased. This process improvement is attributed to enhanced chain mobility, reduced rod-rod interaction, and decreased rod-coil interaction from the additive. The novel method is based on kinetically facilitating thermodynamic equilibrium. The process requires no modification of polymer structure, indicating that a wide variety of desired polymer functionalities can be designed into BCPs for specific applications.

Sequential infiltration synthesis (SIS) is a method for growing inorganic materials within polymers in an atomically controlled fashion. This technique can increase the etch resistance of optical, electron-beam, and block copolymer (BCP) lithography resists and is also a flexible strategy for nanomaterials synthesis. Despite this broad utility, the kinetics of SIS remain poorly understood, and this knowledge gap must be bridged in order to gain firm control over the growth of inorganic materials inside polymer films at a large scale. In this paper, we explore the reaction kinetics for Al2O3 SIS in PMMA using in situ Fourier transform infrared spectroscopy. First, we establish the kinetics for saturation adsorption and desorption of trimethyl aluminum (TMA) in PMMA over a range of PMMA film thicknesses deposited on silicon substrates. These observations guide the selection of TMA dose and purge times during SIS lithography to achieve robust organic/inorganic structures. Next, we examine the effects of TMA ...

We have measured in situ the progression of dewetting from a large number of holes in immiscible polymer bilayer films. Using x-ray photon correlation spectroscopy (XPCS) in grazing incidence we probe independently the evolving dewetting process both at the top surface and the buried interface of the bilayer. At an early stage, differences in the evolution of the velocities measured by XPCS between the surface and buried interface indicate that the holes do not penetrate the bottom layer. The rim velocity at late stages decays according to a wave-vector-dependent power law, which indicates inhomogeneous flows in the film. The changes in the static scattering show that observed slow-down of the dewetting velocity is correlated with the changing roughness at the buried interface of the polymer bilayer.

Control over refractive index and thickness of surface coatings is central to the design of low refraction films used in applications ranging from optical computing to antireflective coatings. Here, we introduce gas-phase sequential infiltration synthesis (SIS) as a robust, powerful, and efficient approach to deposit conformal coatings with very low refractive indices. We demonstrate that the refractive indices of inorganic coatings can be efficiently tuned by the number of cycles used in the SIS process, composition, and selective swelling of the of the polymer template. We show that the refractive index of Al2O3 can be lowered from 1.76 down to 1.1 using this method. The thickness of the Al2O3 coating can be efficiently controlled by the swelling of the block copolymer template in ethanol at elevated temperature, thereby enabling deposition of both single-layer and graded-index broadband antireflective coatings. Using this technique, Fresnel reflections of glass can be reduced to as low as 0.1% under no...

Sequential infiltration synthesis (SIS) has been recently demonstrated to increase the etch resistance of optical, e-beam, and block copolymer lithography resists for sub-50 nm pattern transfer. Although SIS can dramatically enhance pattern transfer relevant to device applications, the complex processes involved in SIS are not clearly understood. Fundamental knowledge of the chemistry underlying SIS is necessary to ensure a high degree of perfection in large-scale lithography. To this end, we performed in situ Fourier transform infrared (FTIR) spectroscopic measurements during the SIS of Al2O3 using trimethylaluminum (TMA) and H2O into poly(methyl methacrylate) (PMMA). The FTIR results revealed that TMA reacts quickly with PMMA to form an unstable complex. The subsequent conversion of this intermediate complex into stable Al—O linkages is slow and must compete with rapid TMA desorption. We support this interpretation of the FTIR data using density functional theory to calculate plausible structures for th...

A series of isoindigo-based low-band-gap copolymers (PnTI) containing an extended thiophene unit in the donor segment of the polymer were synthesized. The results show that the extended thiophene unit with centrosymmetric conformation simultaneously broadens the polymer absorption and enhances the crystallinity and, thus, hole mobility. Consequently, with additional improved solubility, the polymer P6TI exhibits the highest PCE of 7.25% (and a high Jsc of 16.24 mA cm−2) among isoindigo-based low-band-gap copolymers. This work demonstrates that by simply adjusting the donor segment and with relatively simple synthetic schemes, a material for high-performance and scalable PSCs will become available.

We found that synthetic polymers containing metals and metal centers have experienced rapid growth in the last two decades. Metal-containing polymers and these have an unprecedented role to play in modern high-tech applications including nanomanufacturing, sensing, separation and catalysis. Advancement in synthetic strategies for macromolecules has enabled the synthesis of novel, exotic and use-inspired metallopolymers. Using state-of-the-art design strategies, it is now possible to perform targeted synthesis of macromolecules with varied complexity that contain a range of metal centers either in the backbone or in the side chains of the organic moiety. Moreover, the presence of an inorganic element (metals and metal centers) in organic moieties has led to a number of new physicochemical properties while implementing novel functionality to the polymer matrix. This review covers nanotechnology influenced by distinctive features of metal-containing macromolecular systems, particularly in developing flexible, functional materials.

Conjugated block copolymers represent a class of materials with potential applications in electronics and optoelectronics. Three block copolymer model compounds were made by first synthesizing 5-ethynyl-2,2′:5′,2″-terthiophene, 5-(2-propynyl)-2,2′:5′,2″-terthiophene and 5-(3-butynyl)-2,2′:5′,2″-terthiophene and then performing hydroboration polymerization from the alkyne of the terthiophene. The impact of the connectivity between the polymer blocks of these compounds was investigated. Theoretical and experimental studies indicated that charge transfer was occurring within the all-conjugated copolymer model compound, and that electronic coupling decreased with increasing length of the linking bridge between the n-type and p-type materials. Preliminary efforts to synthesize the related regioregular poly(3-hexylthiophene) all-conjugated diblock copolymer and use this material as the active layer in photovoltaic cells are discussed.

Conjugated block copolymers have the potential to improve solution processed optoelectronic devices such as organic photovoltaics (OPVs), but significant synthetic challenges exist and systematic studies investigating structure–property relationships are lacking. We demonstrate a new route to conjugated block copolymers via copper-catalyzed click coupling and apply this method to synthesize a series of poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene) (P3HT-b-PF) conjugated block copolymers with varying block weight fractions. The resulting block copolymers are comprised of two conjugated polymers joined by a flexible, nonconjugated linker. The series of conjugated block copolymers prepared enables an investigation into the role of polymer block lengths and composition on crystallization and self-assembly behavior. Grazing incidence wide-angle X-ray scattering measurements indicate the formation of highly oriented P3HT and/or PF crystallites in thermally annealed block copolymer films. Crystallizatio...

While the performance of polymer–polymer bulk heterojunction organic photovoltaics (OPVs) is poor compared with polymer–fullerene OPVs, reducing or eliminating micrometer-scale phase separation in all-polymer OPVs may dramatically improve performance. Herein, we demonstrate that 2-ureido-4[1H]-pyrimidinone (UPy) quadruple hydrogen bonding interactions can be used to prevent micrometer-scale phase separation at temperatures and processing conditions typically used to prepare bulk heterojunction OPVs. UPy-terminated polymers are synthesized by coupling hydroxyl or primary amine terminated polymers to a reactive isocyanate–UPy group in a one-step reaction. Polymer blend films are subsequently prepared by solution blending, casting onto a surface, and thermal and/or solvent annealing. Film microstructure including the presence of phase-separated domains and polymer crystallinity is analyzed by optical microscopy, atomic force microscopy (AFM), and grazing-incidence wide-angle X-ray scattering (GIWAXS). In con...

In the midst of an exciting era of polymer nanoscience, where the development of materials and understanding of properties at the nanoscale remain a major R&D endeavor, there are several exciting phenomena that have been reported at the mesoscale (approximately an order of magnitude larger than the nanoscale). In this review article, we focus on mesoscale morphologies in polymer thin films from the viewpoint of origination of structure formation, structure development and the interaction forces that govern these morphologies. Mesoscale morphologies, including dendrites, holes, spherulites, fractals and honeycomb structures have been observed in thin films of homopolymer, copolymer, blends and composites. Following a largely phenomenological level of description, we review the kinetic and thermodynamic aspects of mesostructure formation outlining some of the key mechanisms at play. We also discuss various strategies to direct, limit, or inhibit the appearance of mesostructures in polymer thin films as well as an outlook toward potential areas of growth in this field of research.

Sequential infiltration synthesis (SIS), combining stepwise molecular assembly reactions with self-assembled block copolymer (BCP) substrates, provides a new strategy to pattern nanoscopic materials in a controllable way. The selective reaction of a metal precursor with one of the pristine BCP domains is the key step in the SIS process. Here we present a straightforward strategy to selectively modify self-assembled polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) BCP thin films to enable the SIS of a variety of materials including SiO(2), ZnO, and W. The selective and controlled interaction of trimethyl aluminum with carbonyl groups in the PMMA polymer domains generates Al-CH(3)/Al-OH sites inside the BCP scaffold which can seed the subsequent growth of a diverse range of materials without requiring complex block copolymer design and synthesis.

Thin-film poly(styrene- block -methyl methacrylate) diblock copolymer (PS- b -PMMA) is used to create chemically patterned surfaces via metal deposition combined with self-assembled monolayers (SAMs) and UV exposure. We use this method to produce surfaces that are chemically striped on the scale of a few tens of nanometers. Atomic force and transmission electron microscopies are used to verify the spatially localized organization of materials, and contact angle measurements confirm the chemical tunability of these scaffolds. These surfaces may be used for arraying nanoscale objects, such as nanoparticles or biological species, or for electronic, magnetic memory or photovoltaic applications.

Block copolymer self-assembly is a burgeoning subject in polymer and materials science driven by both fundamental and applied inspirations. Whereas the vast majority of block copolymer studies have focused on highly symmetric morphologies, here we report the first observation of an unusual asymmetric cylindrical phase in thick films of an organic/organometallic block copolymer, poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS). Microscopy and X-ray scattering data establish the lack of symmetry in this structure and reveal an unusual 3-D network organization. Following selective removal of the PS matrix, the remaining nanoporous film has characteristics of potential value in separation applications such as substantial interconnection (mechanical strength), uniform pore size, and chemical and physical stability.

It is commonly accepted that in order to develop high-performance organic and/or hybrid organic−inorganic solar energy devices, it is necessary to use, among other components, an active donor−acceptor layer with highly ordered nanoscale morphology. In an idealized morphology, the effectiveness of internal processes including exciton generation and separation and charge carrier migration is optimized, leading to an efficient conversion of photons to electricity. With this idea in mind, we have rationally designed and developed an ordered nanoscale morphology consisting of self-assembled poly(3-hexylthiophene) donor domains of molecular dimension, each of them separated by fullerene C60 hydroxide acceptor domains. A poly(3-hexylthiophene)-block-poly(l-lactide) block copolymer was used as a structure-directing agent to pattern active material into ordered nanostructures. Using this intimate morphological control, one can begin to probe structure−property relationships with unprecedented detail with the ultim...

Bottom-up patterning methodologies, predicated on chemical self-assembly, have the potential to transcend limitations associated with more traditional lithographies. By controlling the domain orientation of a cylinder-forming organic–inorganic block copolymer, poly(styrene-block-ferrocenyldimethylsilane), it is possible to straightforwardly fabricate massive arrays of either nanoscale dots or wires out of a film composed of a wide variety of materials. In the work reported here, orientational control is achieved by manipulating the polymer film thickness in concert with the annealing treatment. For films much thinner than the equilibrium periodicity of the microdomains, the cylinders spontaneously orient themselves perpendicular to the substrate. Films with thickness close to the equilibrium periodicity exhibit the more common in-plane orientation following thermal annealing. Solvent annealing leads to an in-plane orientation for the full range of film thicknesses studied. As a demonstration of the effectiveness of this method, semiconductor substrates were patterned with arrays of posts and wires, respectively, using the same starting polymeric material as the etch mask. Compatibility of this polymer with various substrate materials is also demonstrated.

Geometric defects in conjugated polymers play a critical role in determining electronic structure and properties such as charge carrier mobility and band gap. Because the relative roles of individual defects are experimentally difficult to discern, computational approaches provide valuable insight if appropriate molecular models are used. Poly(3-alkylthiophenes) are often modeled with very short backbones and without their side chains. We demonstrate the shortcomings of this approach for modeling torsional disorder in poly(3-hexylthiophene) (P3HT). Using a hybrid density functional model, we identify a minimal acceptable model to comprise approximately 10 monomers with explicitly treated alkane side chains. Potential applications of this work extend to polymer electronics and optoelectronics.

Conjugated polymers represent a promising class of organic semiconductors with potential applications in a variety of molecular devices. Poly(3-alkylthiophene)s, in particular, are garnering interest due to their large charge carrier mobility and band gap in the visible region of the spectrum. Defects play a pivotal role in determining the performance of polymer electronics, and yet the function of specific types of defects is still largely unknown. Density functional theory calculations of alkyl-substituted oligothiophenes are used to isolate the effect of static inter-ring torsion defects on key parameters such as electronic coupling between rings and band gap. Results have potential implications both for the fundamental understanding of intramolecular charge transport and for improving processing in organic devices.

Phase-segregated block copolymers have received significant attention in the last decade as enabling materials for future technologies. Their value to nanotechnology derives from the expedient tunability of the size, shape, and periodicity of the self-assembled domains by means of manipulating molecular characteristics. Recently, the potential opportunities for block copolymer applications have been bolstered by new methods, which give fine control over long-range ordering of the microdomain structures. Thin polymer films, by themselves, have limited device applications, but myriad functions can be addressed with hybrid hard/soft matter systems in which the organic layer is used as a scaffold for nanoscale organization of inorganic materials. Of specific interest is the interaction of surfactant-mediated colloidal nanoparticles and diblock copolymer films because the nanocrystal capping molecules can be tailored to exhibit preference for one of the polymer blocks. This hierarchical approach to create ordered nanostructures removes the linear correlation of size and patterning time associated with traditional lithographic techniques by self-assembling the entire surface in parallel. Also, the spatial limits of lithography can be transcended and the approach can potentially be adapted to industrial-scale processing. An alternative approach to the colloidal nanocrystal methodology is to use spherical- or cylindrical-phase diblock copolymers as etch masks to produce self-assembled arrays of nanoscale dots, pillars, or lines composed of various materials. The advantage of our approach is that the length-scale of the final functional material is an order of magnitude smaller than the original polymer domains.

We report a combined top-down/bottom-up hierarchical approach to fabricate massively parallel arrays of aligned nanoscale domains by means of the self-assembly of asymmetric polystyrene-block-poly(ethylene-alt-propylene) diblock copolymers. Silicon nitride grating substrates of various depths and periodicities are used to template the alignment of the high-aspect-ratio cylindrical polymer domains. Alignment is nucleated by polystyrene preferentially wetting the trough sidewalls and is thermally extended throughout the polymer film by defect annihilation. Topics discussed include a detailed analysis of the capacity of this system to accommodate lithographic defects and observations of alignment beyond the confined channel volumes. This graphoepitaxial methodology can be exploited in hybrid hard/soft condensed matter systems for a variety of applications.

Nanoscale diblock copolymer domains are aligned via top-down/bottom-up hierarchical assembly. Grating substrates template cylinder alignment with demonstrated 5000:1 aspect ratio for 100 μm domains extendable to arbitrary length scales. Depending on trough depth and amount of deposited polymer, aligned domains are (1) confined to the channels or (2) expanded across the grating frequently with (3) a complete absence of defects. This methodology can be exploited in hybrid hard/soft matter systems for electronics, catalysis, and sensors.

Methylammonium lead iodide (MAPbI3) perovskites are organic–inorganic semiconductors with long carrier diffusion lengths serving as the light-harvesting component in optoelectronics. Through a substitutional growth of MAPbI3 catalyzed by polar protic alcohols, evidence is shown for their substrate- and annealing-free production and use of toxic solvents and high temperature is prevented. The resulting variable-sized crystals (≈100 nm–10 µm) are found to be tetragonally single-phased in alcohols and precipitated as powders that are metallic-lead-free. A comparatively low MAPbI3 yield in toluene supports the role of alcohol polarity and the type of solvent (protic vs aprotic). The theoretical calculations suggest that overall Gibbs free energy in alcohols is lowered due to their catalytic impact. Based on this alcohol-catalyzed approach, MAPbI3 is obtained, which is chemically stable in air up to ≈1.5 months and thermally stable (≤300 °C). This method is amendable to large-scale manufacturing and ultimately can lead to energy-efficient, low-cost, and stable devices.

One approach for making inexpensive inorganic-organic hybrid photovoltaic (PV) cells is to fill highly ordered TiO(2) nanotube (NT) arrays with solid organic hole conductors such as conjugated polymers. Here, a new in situ UV polymerization method for growing polythiophene (UV-PT) inside TiO(2) NTs is presented and compared to the conventional approach of infiltrating NTs with pre-synthesized polymer. A nanotubular TiO(2) substrate is immersed in a 2,5-diiodothiophene (DIT) monomer precursor solution and then irradiated with UV light. The selective UV photodissociation of the C--I bond produces monomer radicals with intact pi-ring structure that further produce longer oligothiophene/PT molecules. Complete photoluminescence quenching upon UV irradiation suggests coupling between radicals created from DIT and at the TiO(2) surface via a charge transfer complex. Coupling with the TiO(2) surface improves UV-PT crystallinity and pi-pi stacking; flat photocurrent values show that charge recombination during hole transport through the polymer is negligible. A non-ideal, backside-illuminated setup under illumination of 620-nm light yields a photocurrent density of approximately 5 microA cm(2)-surprisingly much stronger than with comparable devices fabricated with polymer synthesized ex situ. Since in this backside architecture setup we illuminate the cell through the Ag top electrode, there is a possibility for Ag plasmon-enhanced solar energy conversion. By using this simple in situ UV polymerization method that couples the conjugated polymer to the TiO(2) surface, the absorption of sunlight can be improved and the charge carrier mobility of the photoactive layer can be enhanced.

Sequential infiltration synthesis (SIS) is a process derived from ALD in which a polymer is infused with inorganic material using sequential, self-limiting exposures to gaseous precursors. During the initial SIS cycles, the organometallic precursor (e.g. trimethyl aluminum, TMA) reacts preferentially with specific functional groups within the polymer, while in later cycles growth occurs in an ALD-like fashion on the inorganic “seeds” that have been planted inside the polymer. Consequently, it is possible to start with a blend of two polymers, such as a diblock coplymer, and selectively infuse just one of the two components. As a result of this selective, step-wise infusion, SIS can create novel composites with intermediate or even unique properties compared to those of the pure polymeric and inorganic constituents. Alternatively, the organic component can be removed through oxidation leaving a purely inorganic material, but with a mesostructure that mimics that of the starting polymer. One particularly attractive application for SIS is lithography: SIS can harden polymer resists rendering them more robust towards subsequent etching, and this permits deeper and higher-resolution patterning of substrates such as silicon. With this objective in mind, we have performed a series of investigations using in-situ Fourier transform infrared absorption spectroscopy (FTIR), in-situ synchrotron grazing incidence small angle X-ray scattering (GISAXS), and high resolution scanning transmission electron microscope (STEM) tomography of a model system: Al2O3 SIS using TMA and H2O within the diblock copolymer, poly(styrene-block-methyl methacrylate) (PS-b-PMMA). While the picture is far from complete, these studies reveal some important details: 1) TMA adsorption on PMMA occurs through a weakly-bound intermediate; 2) the SIS kinetics are diffusion-limited, but desorption is 10x slower than adsorption; 3) dynamic structural changes occur during the individual precursor exposures. All of findings impact the resulting composite, and hence will dictate the success of the lithography. Figure 1

Gradient sequence copolymers of 3-hexylthiophene (90 mol%) and 3-(6-bromohexyl)thiophene (10 mol%) were synthesized by catalyst transfer polycondensation. Post-polymerization conversion of the side-chain bromides into azides and subsequent Cu-catalyzed azide–alkyne cycloaddition installed C60-functional groups. Comparing blends of poly(3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) with and without the gradient copolymer additive revealed that, when the gradient copolymer was present, micron-scale phase separation was not observed even after prolonged thermal annealing times. In addition, the PCBM was still able to quench the P3HT emission after thermal annealing, indicating that the donor–acceptor interfacial area is maintained. Together, these data suggest that the gradient copolymers are an effective compatibilizer for P3HT/PCBM physical blends. This stabilized film morphology led to stable power conversion efficiencies (PCE) of the corresponding bulk heterojunction solar cells even upon extended thermal annealing. Nevertheless, the short circuit current and fill factor were reduced when the gradient copolymer was present, leading to a lower PCE. Overall, these gradient copolymer additives represent a promising tool for inhibiting micron-scale phase separation and producing robust polymer/fullerene-based solar cells.

Trace impurities in organic solar cells, such as those from residual catalyst material in conjugated polymers, are often ignored but are known to deleteriously affect device performance. Batch-to-batch variations in the nature and quantity of such impurities leads to widespread issues with irreproducible optoelectronic function, yet to date no technique has emerged that is reliably capable of identifying the character of impurities or their concentration in organic photovoltaic active layer blends. Here we focus on state-of-the-art, high-performance bulk heterojunction blends and show that synchrotron-based X-ray fluorescence can detect and quantify trace concentrations of metal impurities in these systems. Adopting a strategy of artificially introducing known quantities of additional catalyst into polymer/fullerene blends, we identify both the threshold concentration at which performance degrades and the mechanism for the degradation. With the knowledge of a target impurity concentration and a technique in hand to accurately measure their presence, researchers can implement materials preparation processes to achieve consistent, high performance in organic solar cells.

The etch resistance of electron-beam lithography resists, poly(methyl methacrylate) (PMMA) and ZEP520A, is increased significantly by sequential infiltration synthesis (SIS). This process infiltrates the bulk of the resist film with alumina, rendering it resistant to plasma etching. The enhanced etch resistance eliminates the need for an intermediate hard mask and the associated process costs and pattern fidelity losses. Furthermore, the improvement is realized with no degradation to the line-edge roughness of lithographically defined patterns. The enhancement in etch resistance is especially strong at the edges of the printed lines, owing to diffusion of the SIS precursors from the resist sidewalls. These improvements enable the anisotropic transfer of sub-100 nm patterns deeply into silicon without the need for an intermediate hard mask.

Metals have a variety of behaviors when deposited onto diblock copolymer films, in particular, poly(styrene-b-methylmethacrylate). Silver is known to form nanowires, whereas gold forms ellipsoidal nanoparticles of different sizes on each of the blocks, and chromium creates a uniform film on PS-b-PMMA. We show that with UV light we can alter the separation between silver nanowires, by making each wire narrower. We also demonstrate the effects of UV light on PS-b-PMMA coated with thin layers of gold and chromium, as observed with atomic force microscopy and transmission electron microscopy. We have found that UV exposure increased corrugation of such metal–polymer hybrids by removing PMMA domains, but did not remove metal residing on top of those domains. The ability to manipulate the morphology of these nanomaterials has potential application in areas such as electronics and sensor technology.

In this paper we describe dewetting phenomena in organic (polystyrene, PS)/inorganic (polyferrocenyldimethylsilane, PFS) block copolymer thin films. Mesoscale dendritic structures are induced when the spin-cast thin film of this polymer is subjected to so-called hybrid annealing, which involves both thermal and solvent annealing. We show that the development and arrangement of these mesoscale dendritic structures depends on the initial film thickness in addition to the annealing time. Importantly, there are two criteria that must be fulfilled to achieve these mesoscale morphologies: (i) the film has to be subjected to hybrid annealing, i.e. either only thermal or only solvent annealing does not produce any notable mesostructures and (ii) both PS and PFS blocks must be present during the thermal and solvent annealing procedures; if one of the blocks, for instance PS, is removed before annealing then there is no mesostructure. Various possible mechanisms for the formation of these structures are discussed and results indicate that the PFS block dominates the structure formation. We also observe a ring- or worm-like nanostructure which develops only when the film is subjected to hybrid annealing at a particular film thickness. Apart from these results, here we demonstrate that mesoscale structures can be successfully transferred onto underlying substrates.

The authors have studied the effect of predeposition electron exposure on the diffusion behavior of silver evaporated on a diblock copolymer template. Unexposed regions display a highly selective adsorption of Ag clusters on the polystyrene domains. Exposure to the electron beam modifies the surface diffusion constants on each polymer block and produces a trend of smaller mean particle sizes with increased dose. While there is a loss of selectivity in this system upon exposure, alternative diblock chemistries or exposure procedures could enable one to engineer the selectivity of desired materials on polymer films.