Nanosphere Templated Continuous PEDOT:PSS Films with Low Percolation Threshold for Application in Efficient Polymer Solar Cells

Nanometer-sized monodisperse polystyrene nanospheres (PS NS) were designed as an opal template for the formation of three-dimensionally continuous poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films. The resultant films were successfully applied as the anode buffer layer (ABL) to produce highly efficient polymer solar cells (PSCs) with enhanced stability. The conductivity of the PS NS-PEDOT:PSS films was maintained up to ϕ_PS = 0.75–0.80, indicating that the formation of continuous PEDOT:PSS films using PS NS templates was successful. To demonstrate the applicability of the PS NS-PEDOT:PSS film for organic electronics, the PS NS-PEDOT:PSS films were used as ABLs in two different PSCs: P3HT:PCBM and P3HT:OXCBA. The photovoltaic performances of both PSCs were maintained up to ϕ_PS = 0.8. In particular, the power conversion efficiency of the P3HT:OXCBA PSC with a PS NS-PEDOT:PSS ABL (ϕ_PS = 0.8) was greater than 5% and the air stability of the device was significantly enhanced

Nanoparticle Surfactants as a Route to Bicontinuous Block Copolymer Morphologies

The surface chemistry of nanoparticles can be modified so that these particles behave like surfactants and localize at interfaces between two fluids. We demonstrate that small volume fractions φP of such surfactant nanoparticles added to lamellar diblock copolymers lead initially to a decrease in lamellar thickness with φP, a consequence of decreasing interfacial tension, up to a critical value of φP, beyond which the block copolymer adopts a bicontinuous morphology. These bicontinuous morphologies have stable domain spacings below 100 nm that further decrease with increasing φP and offer new routes to nanoscopically engineered polymer films with potential photovoltaic, fuel cell, and battery applications

Effect of Molecular Structure of Photoswitchable Surfactant on Light-Responsive Shape Transition of Block Copolymer Particles

Photoactive shape-changing particles offer a promising platform for smart materials with tunable properties at high spatiotemporal resolutions. Herein, a series of spiropyran-based surfactants with different alkyl spacer lengths are developed to achieve photoactive, shape-changing particles through confined self-assembly of polystyrene-block-poly­(4-vinylpyridine) (PS-b-P4VP) within an evaporative emulsion. The length of the alkyl chain spacer between the spiropyran headgroup and ionic chain-end is modulated from hexyl to ethyl decanoate to provide surfactants with tunable amphiphilicity. Under UV light, the hydrophilic ring-opened merocyanine surfactants produce onion-like microspheres with a P4VP surface. Conversely, by exposure to visible light, the ring-closure reaction of the spiropyran moieties shifts their hydrophobicity and yields striped ellipsoids with axially stacked PS and P4VP blocks. This sphere-to-ellipsoid transition is observed only for surfactants that contain spacers longer than or equal to octyl. The effects of photoswitchable surfactants on their interfacial properties and corresponding morphological evolution of the particles are investigated to elucidate the mechanism of the shape transition of the photoactive particles

Bicontinuous Block Copolymer Morphologies Produced by Interfacially Active, Thermally Stable Nanoparticles

Polymeric bicontinuous morphologies were created by thermal annealing mixtures of poly(styrene-<i>b</i>-2-vinylpyridine) (PS-<i>b</i>-P2VP) block copolymers and stabilized Au-core/Pt-shell (Au–Pt) nanoparticles. These Au–Pt nanoparticles have a cross-linked polymeric shell to promote thermal stability and are designed to adsorb strongly to the interface of the PS-<i>b</i>-P2VP block copolymer due to the favorable interaction between P2VP block and the exterior of the cross-linked shell of the nanoparticle. The interfacial activity of these Au–Pt nanoparticles under thermal annealing conditions leads to decrease in domain size of the lamellar diblock copolymer. As nanoparticle volume fraction ϕ_p was increased, a transition from a lamellar to a bicontinuous morphology was observed. Significantly, the effect of these shell-cross-linked Au–Pt nanoparticles under thermal annealing conditions was similar to those of traditional polymer grafted Au nanoparticles under solvent annealing conditions reported previously. These results suggest a general strategy for producing bicontinuous block copolymer structures by thermal processing through judicious selection of polymeric ligands, nanoparticle core, and block copolymer

Architectural Effects on Solution Self-Assembly of Poly(3-hexylthiophene)-Based Graft Copolymers

While solution assembly of conjugated block copolymers has been widely used to produce long 1-D nanowires (NWs), it remains a great challenge to provide a higher level of control over structure and function of the NWs. Herein, for the first time, we report the solution assembly of graft copolymers containing a conjugated polymer backbone in a selective solvent and demonstrate that their self-assembly behaviors can be manipulated by the molecular structures of the graft copolymers. A series of poly­(3-hexylthiophene)-<i>graft</i>-poly­(2-vinylpyridine) (P3HT-<i>g</i>-P2VP) copolymers was designed with two different architectural parameters: grafting fraction (<i>f</i>_g) and molecular weight of P2VP chains (<i>M</i>_n,P2VP) on the P3HT backbone. Interestingly, crystallization of the P3HT-<i>g</i>-P2VP copolymers was systematically modulated by changes in <i>f</i>_g and <i>M</i>_n,P2VP, thus allowing for control of the growth kinetics and curvatures of solution-assembled NWs. When <i>M</i>_n,P2VP (4.4 to 15.1 kg/mol) or <i>f</i>_g (2.8 to 9.2%) of the P3HT-<i>g</i>-P2VP polymers was increased, the crystallinity of the copolymers was reduced significantly. Steric hindrance from the grafted P2VP chains apparently modified the growth of NWs, leading to shorter NWs with a greater degree of curvature for graft copolymers with more hindrance. Therefore, we envision that such conjugated chain-based graft copolymers can be versatile building blocks for producing NWs with controlled length and shape, which can be important for tailoring the optical and electrical properties of NW-based devices

Effect of Addition of a Diblock Copolymer on Blend Morphology and Performance of Poly(3-hexylthiophene):Perylene Diimide Solar Cells

Effect of Addition of a Diblock Copolymer on Blend Morphology and Performance of Poly(3-hexylthiophene):Perylene Diimide Solar Cell

Novel Templating Route Using Pt Infiltrated Block Copolymer Microparticles for Catalytic Pt Functionalized Macroporous WO₃ Nanofibers and Its Application in Breath Pattern Recognition

We propose a new route for transferring catalysts onto macroporous metal oxide nanofibers (NFs) using metallic nanoparticles (NPs) infiltrated block copolymer microparticles as sacrificial templates. Pt decorated polystyrene-<i>b</i>-poly­(4-vinylpyridine) (PS-<i>b</i>-P4VP) copolymer microparticles (Pt-BCP MPs), produced from oil-in-water emulsions, were uniformly dispersed within electrospun PVP/W precursor composite NFs. The macropore-loaded WO₃ NFs (macroporous Pt-WO₃ NFs), which are additionally functionalized by Pt NPs (10 nm), were achieved by decomposition of polymeric components and oxidization of W precursor after high-temperature calcination. In particular, macropores with the similar size distribution (50–300 nm) with BCP MPs were also formed on interior and exterior of WO₃ NFs. Chemical sensing performance of macroporous Pt-WO₃ NFs was investigated for pattern recognition of simulated breath gas components at highly humid ambient (95% RH). The result revealed that superior hydrogen sulfide sensitivity (<i>R</i>_air/<i>R</i>_gas = 834.2 ± 20.1 at 5 ppm) and noticeable selectivity were achieved. In addition, H₂S pattern recognition against other chemical components (acetone, toluene, and methyl mercaptan) was clearly identified without any overlapping of each pattern. This work demonstrates the potential application of BCP-templated maroporous Pt-WO₃ NFs in exhaled breath analysis for noninvasive monitoring of physical conditions

Morphological Evolution of Block Copolymer Particles: Effect of Solvent Evaporation Rate on Particle Shape and Morphology

Shape and morphology of polymeric particles are of great importance in controlling their optical properties or self-assembly into unusual superstructures. Confinement of block copolymers (BCPs) in evaporative emulsions affords particles with diverse structures, including prolate ellipsoids, onion-like spheres, oblate ellipsoids, and others. Herein, we report that the evaporation rate of solvent from emulsions encapsulating symmetric polystyrene-<i>b</i>-polybutadiene (PS-<i>b</i>-PB) determines the shape and internal nanostructure of micron-sized BCP particles. A distinct morphological transition from the ellipsoids with striped lamellae to the onion-like spheres was observed with decreasing evaporation rate. Experiments and dissipative particle dynamics (DPD) simulations showed that the evaporation rate affected the organization of BCPs at the particle surface, which determined the final shape and internal nanostructure of the particles. Differences in the solvent diffusion rates in PS and PB at rapid evaporation rates induced alignment of both domains perpendicular to the particle surface, resulting in ellipsoids with axial lamellar stripes. Slower evaporation rates provided sufficient time for BCP organization into onion-like structures with PB as the outermost layer, owing to the preferential interaction of PB with the surroundings. BCP molecular weight was found to influence the critical evaporation rate corresponding to the morphological transition from ellipsoid to onion-like particles, as well as the ellipsoid aspect ratio. DPD simulations produced morphologies similar to those obtained from experiments and thus elucidated the mechanism and driving forces responsible for the evaporation-induced assembly of BCPs into particles with well-defined shapes and morphologies

Thermomechanical Behavior of Poly(3-hexylthiophene) Thin Films on the Water Surface

The thermomechanical behavior of a conjugated polymer (CP) in a thin film state has rarely been studied despite the importance of understanding the polymer morphologies and optimizing the thermal processes of organic semiconductors. Moreover, the seamless integration of multilayers without mechanical failures in CP-based electronic devices is crucial for determining their operational stability. Large differences in the coefficients of thermal expansion (CTEs) between the multilayers can cause serious degradation of devices under thermal stress. In this study, we measure the intrinsic thermomechanical properties of poly­(3-hexylthiophene) (P3HT) thin films in a pseudo-freestanding state on the water surface. The as-cast P3HT thin films exhibited a large thermal shrinkage (−1001 ppm K–1) during heating on the water surface. Morphological analyses revealed that the thermal shrinkage of the polymer films was caused by the rearrangement of the polymer chain networks accompanied by crystallization, thus indicating that preheating the polymer films is essential for estimating their intrinsic CTE values. Moreover, the rigidity of the substrate significantly influences the thermomechanical behavior of the polymer films. The polymer films that were preheated on the glass substrate showed nonlinear thermal expansion due to the substrate constraint inhibiting sufficient relaxation of the polymer chains. In comparison, a linear expansion behavior is observed after preheating the films on the water surface, exhibiting a consistent CTE value (185 ppm K–1) regardless of the number of thermal strain measurements. Thus, this work provides a direct method for measuring in-plane CTE values and an in-depth understanding of the thermomechanical behaviors of CP thin films to design thermomechanically reliable organic semiconductors