Poly((2‐alkylbenzo[1,2,3]triazole‐4,7‐diyl)vinylene)s for organic solar cells

Poly((2‐Alkylbenzo[1,2,3]triazole‐4,7‐diyl)vinylene)s (pBTzVs) synthesized by Stille coupling show different absorption spectra, solid‐state morphology, and photovoltaic performance, depending on straight‐chain versus branched‐chain (pBTzV12 and pBTzV20) pendant substitution. Periodic boundary condition density functional computations show limited alkyl pendant effects on isolated chain electronic properties; however, pendants could influence polymer backbone conjugative planarity and polymer solid film packing. The polymers are electronically ambipolar, with best performance by pBTzV12 with hole and electron transport mobilities of 4.86 × 10^?6 and 1.96 × 10^?6 cm² V^?1 s^?1, respectively. pBTzV12 gives a smooth film morphology, whereas pBTzV20 gives a very different fibrillar morphology. For ITO/PEDOT:PSS/(1:1 w/w polymer:PC₇₁BM)/LiF/Al devices, pBTzV12 gives power conversion efficiency (PCE) up to 2.87%, and pBTzV20 gives up to PCE = 1.40%; both have open‐circuit voltages of V_OC = 0.6–0.7 V. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1539–1545     

Synthesis and properties of the [2.2]paracyclophane‐containing conjugated polymer with benzothiadiazole as an electron acceptor

A novel donor–acceptor type conjugated polymer based on PPE with [2.2]paracyclophane and benzothiadiazole units in the main chain was synthesized by the Sonogashira coupling reaction. The obtained polymer was quite soluble in common organic solvents, and the transparent and uniform thin film of the polymer was obtained easily by casting or spin‐coating from a toluene solution. The polymer showed an extension of π‐delocalization via the through‐space with π‐π stacking according to the UV–visible (UV–vis) absorption spectra in comparison with that of the model compound. The polymer exhibited orange photoluminescence in solution (fluorescence quantum efficiency = 0.13) and in the solid state. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5891–5899, 2004     

Structure of P3HT in the solid state

Poly(3‐hexylthiophene) (P3HT) is a polymer widely used in organic photovoltaic devices. Discrepancies in information exist in the literature about its morphological structure in solution and in the solid state. This work is a theoretical study, in which the structure of P3HT in the solid state is deduced from its structure in solution and comparisons with optical absorption data. The results indicate that P3HT is not planar, either in solution or in the solid state. However, the effective conjugation length in the solid state is similar to that of a planar chain. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1350–1354     

Nanoscale degradation of polypyrrole films under oxidative stress: An atomic force microscopy study and review

Atomic force microscopy (AFM) is employed to monitor the surface morphology of polypyrrole (PPy) films grown on vitreous carbon substrates during the catalytic reduction of Cr(VI) to Cr(III). The morphology of freshly-prepared films depends on substrate characteristics. Upon reaction, uniform nodules of aggregated PPy clusters appear. No significant differences in surface morphology are found between its oxidized and reduced forms. Loss of catalytic activity after 8-9 oxidation/reduction cycles of exposure to the chromate solution (oxidation) and electrochemical recharging of the film at negative potentials (reduction) correlates well with the observed polymer film dissolution/detachment from the carbon substrate. Formation of well-defined circular features (PPy rings) at different stages leads to a model for the film degradation process that includes formation of Cl₂ gas inside the polymer matrix. In the final stages, the bulk of the film typically fractures and detaches from the electrode. A catalytically inactive, ultrathin PPy layer remains on the substrate even after prolonged exposure to the target solution. A review of techniques for the study of PPy aging/degradation is given.     

Ordered Solid‐State Microstructures of Conjugated Polymers Arising from Solution‐State Aggregation

Controlling the solution‐state aggregation of conjugated polymers for producing specific microstructures remains challenging. Herein, a practical approach is developed to finely tune the solid‐state microstructures through temperature‐controlled solution‐state aggregation and polymer crystallization. High temperature generates significant conformation fluctuation of conjugated backbones in solution, which facilitates the polymer crystallization from solvated aggregates to orderly packed structures. The polymer films deposited at high temperatures exhibit less structural disorders and higher electron mobilities (up to two orders of magnitude) in field‐effect transistors, compared to those deposited at low temperatures. This work provides an effective strategy to tune the solution‐state aggregation to reveal the relationship between solution‐state aggregation and solid‐state microstructures of conjugated polymers.     

Fabrication of polymer Langmuir-Blodgett films containing regioregular poly(3-hexylthiophene) for application to field-effect transistor

Semiconducting thin films consisting of regioregular poly(3-hexylthiophene) (RR-PHT) and poly(N-dodecylacrylamide) (pDDA) were constructed by the Langmuir-Blodgett (LB) technique. A mixture of RR-PHT and pDDA spread from a chloroform solution on a water surface forms a stable monolayer, which can be transferred onto solid substrates by the LB method, yielding a well-defined polymer LB film. Surface morphology studies of the LB film indicate that the RR-PHT is dispersed uniformly throughout the surface. The polymer thin film was chemically doped by contacting with FeCl3 acetonitrile solution, and a conductivity of 5.6 S/cm was achieved. Further, the LB film was utilized as the semiconducting film in the field-effect transistor (FET), and mobilities of 2.2 x 10(-4) and 4.4 x 10(-4) cm2 V(-1) s(-1) were obtained by analyzing the saturated and linear regions of the current-voltage characteristic, respectively.     

Ion‐Specific Self‐Assembly of Low‐Dimension Aggregate Structures of Conjugated Polymer at Two‐Phase Interface

A novel and facile approach to manipulate the morphology of Cu²⁺‐ion‐specific assembly of conjugated polymer by coordinative interaction at an oil–water two‐phase interface is present. The application of increasing importance is the use of π‐conjugated polymers as receptors, exploiting their ability to selectively form complexes, which can obviously change the optical properties in solution and induce the formation of varied solid nano/microstructures. By this method, microtubes are formed through self‐rolling of a strained ionic bilayer film at the oil/water interface.     

芴酮对聚醚侧链聚芴体系的影响:合成,表征及光物理性质的研究

利用Yamamoto聚合反应, 通过调节单体2,7-二溴9,9'-二-(三乙氧基甲基)芴和2,7-二溴芴酮的比例, 合成了侧链为极性聚醚链, 芴酮含量逐渐增加的聚芴系列. 通过聚合物溶液及固态薄膜的紫外荧光谱图, 深入研究芴酮作为能量受体的能量转移过程及其对聚合物光物理性质的影响. 结果表明: 稀溶液中体系呈现聚芴本征态的荧光发射, 能量转移对溶液浓度具有依赖性; 固态薄膜中能量转移效率随芴酮含量的增加而快速增长, 退火后这种现象更加明显.     

O2 Binding and Dissociation and Ligand Exchange Reaction of O2 with CO in Polymer Composite Films of Hemoglobin

A polymer composite film of hemoglobin (Hb–polymer film) was prepared by the casting of an Hb–polymer mixed solution (weight ratio of Hb to polymer is 1 to 1). The percentages of O₂ and CO saturation of the Hb–dextran film were 46% and 70%, respectively. In the Hb solution, 100% saturation was observed for both ligands, and a humidified Hb–dextran film also showed 100% saturation. Water molecules would provide flexibility to the matrix polymer and promote a structural change in the Hb from a tense state (T) to a relaxed state (R). Thus the ligand binding to the Hb in the polymer films was strongly affected by the degree of interaction of Hb with the matrix polymers and the physical properties of the polymers. Inositol hexaphosphate (IHP) worked as an allosteric effector even in the solid polymer film and lowered the oxygen affinity of Hb. The O₂ transport through an Hb–polyethyleneimine (PEI) film with IHP showed the facilitated O₂ transport in comparison with the film without IHP because of the high dissociation rate of O₂ from Hb with IHP. © 1997 John Wiley & Sons, Ltd.     

Tubular or subsurface morphology of octabutoxyphthalocyanine upon self-assembly in polymer matrices: effect of the casting solvent

Spontaneous phase-separated, controlled aggregate structures of photo- and electroactive molecules in polymer matrices are of interest for device fabrication. We show that the self-assembly of octabutoxyphthalocyanine (Pc) in polymer matrices leads to tubular morphology of Pc when the film is prepared with tetrachloroethane (TCE) and subsurface droplet morphology with chloroform. The same morphology is seen with both bisphenol A polycarbonate (BPAPC) and poly(methyl methacrylate) (PMMA) as the matrix. The subsurface morphology results from the rapid association of Pc in the polymer matrix, as the film forms. With the tubular morphology in the films prepared with TCE, percolation threshold is reached with a concentration of Pc as low as 3% (wt) in the polymer. Such phase-separated self-assembly occurs, without any annealing of the films. Even in the absence of the polymer, Pc crystallized from TCE also shows tubular morphology, whereas it exhibits a columnar morphology with chloroform. X-ray diffraction of Pc crystallized from either solvent shows the columnar stacking of the Pc molecules. However, the morphology is tubular when TCE is used. We attribute the difference in the morphology to the higher viscosity of TCE and the diffusion-limited growth, which causes the tubular morphology, whereas the instantaneous self-assembly in less-viscous chloroform leads to droplets. The solvent effect observed here could be used to tailor the morphology of such photoconductive molecules in polymer matrices.     

Relaxation phenomena in dense,glassy membranes prepared from a polymer solution,monitored by changes in dielectric properties

The drying of a solvent-cast polymer film is monitored in a non-invasive way, by measuring the changes in time of dielectric properties, using interdigitated or comb electrodes. Experimentally, the vitrification of the polymer solution is observed at a distinct time, followed by the slow evaporation of solvent from the glassy state. As the solvent diffusion coefficient is a strong function of the concentration in the polymer film, removal of residual solvent proceeds at a self-decreasing rate. With a simple model, solvent mass transfer coefficients in the glassy state are determined from the experiments. It is shown that volume relaxation may be slow compared to the drying process, when preparing thin solvent-cast membranes and using solvents that diffuse relatively fast through the glassy polymer film.     

Macromolecular dynamics of conjugated polymer in donor-acceptor blends with charge transfer complex

Donor-acceptor blends based on conjugated polymers are the heart of state-of-the-art polymer solar cells, and the control of the blend morphology is crucial for their efficiency. As the film morphology can inherit the polymer conformational state from solution, the approaches for probing and controlling the polymer conformational state in the blends are of high importance. In this study, we show that the macromolecular dynamics in solutions of the archetypical conjugated polymer, MEH-PPV, is essentially changed upon addition of an acceptor 2,4,7-trinitrofluorenone (TNF) by using dynamic light scattering (DLS). We have observed four new types of the macromolecular dynamics absent in the parent polymer determined by the polymer and acceptor content. The MEH-PPV?:?TNF ground-state charge-transfer complex (CTC) is suggested to result in these dynamics. In the dilute polymer solution, the CTC formation leads to slower dynamics as compared with the pristine polymer. This is evidence of aggregates formed by intercoil links that are the CTCs involving two conjugated segments of different coils with acceptor molecules being sandwiched between them. At low acceptor content, the aggregates are not stable but at high acceptor content, they are. In the semidilute solution at low acceptor content, the dynamics becomes faster as compared with the pristine polymer that is explained by confinement of the coupled motions of entangled polymer chains. At high acceptor content, the dynamics is far much slower with a characteristic long-range correlation at the scale 3-5 μm that is explained by aggregation of polymer chains in clusters. One can expect that the DLS technique could become a useful tool to study the nano- and microstructure of donor-acceptor conjugated polymer blends to achieve controllable morphology in the corresponding blend films.     

Preparation of porous crosslinked polymers with different surface morphologies via chemically induced phase separation

A novel and simple method for producing crosslinked polymers with controlled surface morphology is demonstrated in this study. The porous crosslinked polymers were made via stepwise polymerization of a mixture of epoxy resin, D.E.R. 331, and diethylene triamine in diisobutyl ketone (DIBK). Both the surface and bulk morphology of the cured polymers are dependent on the solvent fraction of the reactive solution. When the concentration of DIBK was more than about 30 vol %, chemically induced phase separation (CIPS) occurred during cure at 30 °C, and closed spherical pores, about 4 μm in diameter, appeared in the bulk of the crosslinked polymers, whose diameter increased to about 4.5 and 9 μm when the solvent was increased to 40% and 50%, respectively. The surface morphology of the epoxy networks is different from that of the bulk. Smaller pore size or dense skin was formed via the CIPS process, which can be tailored by covering the reactive solution with different contacting films during cure. The competition between the solvent‐rich and polymer‐rich phase absorbed onto the surface of contacting film could change the surface morphology. Therefore, the porous crosslinked polymers having similar bulk morphology could be prepared with a variety of surface structures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Effect and Mechanism of Solvent Properties on Solution Behavior and Films Condensed State Structure for the Semi-rigid Conjugated Polymers

Solvents have an essential association with polymer solution behavior. However, few researches have been deeply done on this respect. In recent years, our research group focus on the study on effect of solvent properties on solution behavior and film condensed state structure for semi-rigid conjugated polymer up till to apply for optoelectronic device. Herein, influence of solvent properties including solubility of solvent, aromaticity, polarity and hydrogen bonds on semi-rigid polymer chain sol...     

TOF-GISANS investigation of polymer infiltration in mesoporous TiO2 films for photovoltaic applications

The structure of porous TiO₂ films and TiO₂:poly(N-vinylcarbazole) (PVK) composite films is investigated with time-of-flight grazing incidence small-angle neutron scattering (TOF-GISANS). The TiO₂ films have been prepared by application of a sol–gel process with a diblock copolymer as structure directing agent, and the conductive polymer PVK is infiltrated in the porous network by spin coating and solution casting. The films show a hierarchical pore structure with mesopores 52 nm in size and additional large macropores with a diameter of about 180 nm. By matching the scattering contrast of the TiO₂ with the polymer information about the penetration of the polymer in the pores is determined. Whereas in the PVK film prepared by solution casting the pores are filled to a high degree; in the spin coated film, PVK wets only the TiO₂ pore walls and forms a solid overlying layer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1628–1635, 2010     

Synthesis and properties of poly(heteroaryleneethynylene)s consisting of electron‐accepting benzothiadiazole/quinoxaline units and electron‐donating alkyl thiophene units

Low‐band‐gap π‐conjugated polymers composed of π‐excessive thiophene and π‐deficient benzothiadiazole and quinoxaline units were prepared in high yields by a polycondensation method using palladium cross‐coupling reactions of alkylthiophene diacetylenes, 4,7‐dibromo‐2,1,3‐benzothiadiazole, and 5,8‐dibromo‐2,3‐dipyridine‐2‐ylquinoxaline. The copolymers were characterized by NMR, IR, UV, gel permeation chromatography, and elemental analysis. High‐molecular‐weight (weight‐average molecular weight up to 82,600 g/mol), thermostable, soluble, and film‐forming materials were obtained. The polymers were photoluminescent in chloroform and showed metallic luster in the solid state. The absorption and emission in solution and in the solid state of the polymers revealed that the polymers generated a π‐stacked structure in the solid state, and the polymer molecules in the film were ordered. Thin films of poly[3‐dodecylthiophen‐2,5‐diylethynylene‐(benzo[1,2,5]thiadiazole‐4,7‐diyl)ethynylene] ( P‐1 ), poly[3,4‐di dodecylthiophen‐2,5‐diylethynylene‐(benzo[1,2,5]thiadiazole‐4,7‐diyl)ethynylene] ( P‐2 ), poly[3‐dodecylthiophene‐2,5‐diylethynylene‐(2,3‐dipyridine‐2‐ylquinoxaline‐5,8‐diyl)ethynylene] ( P‐3 ), and poly[3,4‐didodecylthiophene‐2,5‐diylethynylene‐(2,3‐dipyridine‐2‐ylquinoxaline‐5,8‐diyl)‐ethynylene] ( P‐4 ) exhibited an optical band gap of ～1.85–2.08 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels of the polymers were determined from electrochemical measurements. In the absorption and emission spectra of these polymers in chloroform/methanol mixtures, all the polymers revealed solvatochromic effects, which were related to the formation of aggregates, as confirmed by temperature‐dependence absorption investigations. The absorption spectra of P‐2 and P‐4 at different temperatures also revealed significant effects of the structure on the molecular interactions. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6445–6454, 2005     

Integrated mechanism for the morphological structure development in HDPE melt‐blown and machine‐direction‐oriented films

The morphologies of a series of blown films and machine‐direction‐oriented (MDO) films, all produced from high density polyethylene, were characterized. In the blown film process, the crystalline morphology develops while the melt is under extensional stress. In the MDO process, drawing takes place in the solid state and deforms the crystalline morphology of the starting film. The films were characterized by wide‐angle X‐ray scattering (WAXS), small‐angle X‐ray scattering (SAXS) and atomic force microscopy to determine the lamellar morphology. The effect of the type of deformation on the lamellar morphology was studied and relationships were developed between the lamellar and polymer chain morphology using SAXS and WAXS. Blown and MDO films were found to have very different morphologies. However, an integrated mechanism was developed linking the sequential events in the deformation and morphology development in blown and MDO films. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1834–1844, 2007     

Theoretical and Experimental Studies on Photophysical Characteristics of Low Bandgap Polymers

The basic photophysical characteristics of low bandgap polymer poly{2,7＇-9,9-dioctylfluorene-alt-5- diethylhexyl-3,6-bis（5-bromothiophen-2-yl）pyrrolo[3,4-c]pyrrole-1,4-dione}（PDPP-F） have been systematically in- vestigated by means of theoretical and experimental methods. The quantum chemical calculations clarify the molecular structure and electronic transition properties of PDPP-F. The transient absorption data were used to compare the relaxation dynamics of PDPP-F in chlorobenzene and solid film. It is observed that the dynamics process of simulated emission relaxes much faster in comparison with that of excited state absorption in both the solution and solid film. Moreover, the excitation intensity-dependent dynamics of PDPP-F confirms that the interaction among intrachain excitons may occur under photoexcitation in the solution and solid film.     

Probing a conjugated polymer's transfer of organization-dependent properties from solutions to films

The dynamic transfer of a conjugated polymer's organization-dependent properties from the solution state to the solid film state was probed by circularly polarized luminescence (CPL) and circular dichroism (CD) spectroscopy. Different supramolecular organizations within films and aggregate solutions of a chiral poly(p-phenylenevinylene) derivative led to opposite CPL and CD spectra. These dramatic property differences were controlled by regulating the polymer's self-assembly through solvent selection and film annealing. Therefore, different processing conditions can greatly affect the functional properties of conjugated polymer films employed in various optoelectronic applications.     

Enhanced fluorescence of remote functionalized diaminodicyanoquinodimethanes in the solid state and fluorescence switching in a doped polymer by solvent vapors

Remote functionalized zwitterionic diaminodicyanoquinodimethanes are found to exhibit a dramatic enhancement of light emission in the solid state and when doped in polymer films, as compared to the solution state. Crystal structure analysis of prototypical molecules reveals the role of the remote functionality in the solid state molecular organization. Semiempirical quantum chemical computations provide a viable model to explain the interesting phenomenon of fluorescence enhancement as arising from the inhibition of geometry relaxation of the vertical excited state to a nonemitting state. The reversible switching of a doped polymer film fluorescence triggered by solvent vapors is demonstrated.