Solution-Processed Bulk-Heterojunction Solar Cells containing Self-Organized Disk-Shaped Donors

Two molecular disks <b>1</b> and <b>2</b> composed of a central pyrene core, four oligothiopenes, and peripheral alkyl chains were synthesized and characterized with respect to optical and redox properties in solution and in solid films. It was found that the lowest unoccupied molecular orbital (LUMO) energy levels of <b>1</b> and <b>2</b> were ideal for achieving efficient electron transfer to fullerene derivatives PC₆₀BM and PC₇₀BM, and that <b>1</b> and <b>2</b> can function as electron donor components in solution-processed bulk-heterojunction (BHJ) solar cells. Disk-shaped molecules <b>1</b> and <b>2</b> organized ordered structures through intermolecular π–π interactions as monitored by temperature-controlled polarized optical microscope (TPOM), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). Solution-processed BHJ solar cells using <b>1</b> or <b>2</b> as electron donor materials and fullerene derivatives as acceptor materials were fabricated and investigated. The oligothiophene lengths were reflected in the performance characteristics of solar cell devices fabricated using disk-shaped donors <b>1</b> and <b>2</b>. Power conversion efficiency (PCE) of 2.6% was achieved for small-molecule BHJ solar cells containing self-organized crystals of <b>2</b> in the active layer under one sun condition

Flexible Tactile Sensor Using the Reversible Deformation of Poly(3-hexylthiophene) Nanofiber Assemblies

In this letter, we report a simple approach to fabricating scalable flexible tactile sensors using a nanofiber assembly of regioregular poly­(3-hexylthiophene) (P3HT). Uniform P3HT nanofibers are obtained through a continuous electrospinning process using a homogeneous solution of high-molecular-weight P3HT. The P3HT nanofibers are oriented by collecting them on a rotating drum collector. Small physical inputs into the self-standing P3HT nanofiber assemblies give rise to additional contact among neighboring nanofibers, which results in decreased contact resistance in directions orthogonal to the nanofiber orientation. The P3HT nanofiber assemblies could detect pressure changes and bending angles by monitoring the resistance changes, and the sensor responses were repeatable

Increased Light-Harvesting in Dye-Sensitized Solar Cells through Förster Resonance Energy Transfer within Supramolecular Dyad Systems

Novel pyridine-substituted subphthalocyanines were prepared for an additional harvesting of a green spectral region of the solar light spectrum for zinc phthalocyanine-based dye-sensitized solar cells. These compounds can bind with the central metal of zinc phthalocyanines to form the corresponding supramolecular complexes as monitored by the absorption and fluorescence spectral changes. The stability constants of these complexes were altered by the number and position of pyridine units in the pyridine-substituted subphthalocyanines. On the basis of fluorescence titration study, the complexes efficiently transfer energy from the subphthalocyanine to zinc phthalocyanine. The solar cells using TiO₂ electrodes stained with the supramolecular complexes, composed of zinc phthalocyanine sensitizer and pyridine-substituted subphthalocyanines, showed panchromatic responses, and the photocurrent generation in the range of 500–600 nm is attributed to the efficient Förster resonance energy transfer from subphthalocyanine to zinc phthalocyanine on the TiO₂ surface

Structural Effect of Donor in Organic Dye on Recombination in Dye-Sensitized Solar Cells with Cobalt Complex Electrolyte

The effect of the donor in an organic dye on the electron lifetime of dye-sensitized solar cells (DSSCs) employing a cobalt redox electrolyte was investigated. We synthesized organic dyes with donor moieties of carbazole, coumarin, triphenylamine, and <i>N</i>-phenyl-carbazole and measured the current–voltage characteristics and electron lifetimes of the DSSCs with these dyes. The cell with the triphenylamine donor dye produced the highest open circuit voltage and longest electron lifetime. On the other hand, the lowest open circuit voltage and shortest electron lifetime was obtained with coumarin donor dye, suggesting that the coumarin attracted the cobalt redox couples to the surface of the TiO₂ layer, thus increasing the concentration of cobalt complex. On the other hand, the longest electron lifetime with triphenylamine was attributed to the blocking effect by steric hindrance of the nonplanar structure of the donor

Low-Symmetrical Zinc(II) Benzonaphthoporphyrazine Sensitizers for Light-Harvesting in Near-IR Region of Dye-Sensitized Solar Cells

Two ring-expanded naphthalocyanine-based sensitizers <b>NcS1</b> and <b>NcS2</b> have been designed and synthesized to harvest near-IR light energy in dye-sensitized solar cells. Low-symmetrical “push-pull” structures of <b>NcS1</b> and <b>NcS2</b> enable the red-shift of absorption spectrum as well as the defined Q-band splitting. The zinc benzonaphthoporphyrazine sensitizer <b>NcS1</b> possessing one carboxylic acid and six 2,6-diisopropylphenoxy units showed a PCE value of 3.2% when used as a light-harvesting dye on a TiO₂ electrode under one sun condition. The <b>NcS1</b> cell showed a broad photoresponse at wavelengths from 600 to 850 nm

Aggregation Control of Robust Water-Soluble Zinc(II) Phthalocyanine-Based Photosensitizers

A water-soluble zinc phthalocyanine (ZnPc) complex with four negatively charged electron-withdrawing sulfonic acid substituents at the nonperipheral positions (<b>α-ZnTSPc</b>) is found to have a high singlet oxygen (¹O₂) quantum yield and exhibits high photostability. The formation of aggregates is hindered and the highest occupied molecular orbital is significantly stabilized, making <b>α-ZnTSPc</b> potentially suitable for its use as a photosensitizer for photodynamic therapy and photoimmunotherapy. Atomic force microscopy (AFM) reveals that mixtures of the negatively charged <b>α-ZnTSPc</b> complex with a similar positively charged ZnPc were found to result in the self-assembly of one-dimensional accordion-like fibers. Supramolecular fibers can be formed in aqueous solutions through intermolecular electrostatic and donor–acceptor interactions between the two water-soluble ZnPcs

Deformation of Redox-Active Polymer Gel Based on Polysiloxane Backbone and Bis(benzodithiolyl)bithienyl Scaffold

Redox-active polymer gels consisting of polysiloxane backbone and bis­(benzodithiolyl)­bithienyl units have been designed and synthesized. The bis­(benzodithiolyl)­bithienyl units, which undergo interconversion between cyclic form and opened dicationic form, have been incorporated into polysiloxane backbone via hydrosilylation of vinyl-terminated bis­(benzodithiolyl)­bithienyl derivative and poly­(methylhydrosiloxane) (PMHS) or poly­(dimethylsiloxane-<i>co</i>-hydrogenmethylsiloxane) (PDMS-<i>co</i>-PMHS), resulting in polymer gels cross-linked with bis­(benzodithiolyl)­bithienyl units. After the incorporation of <b>M1</b> into polysiloxane backbone, these polymer gels (<b>P1</b> and <b>P2</b>) also exhibit redox responses associated with the electrochemical interconversion of the bis­(benzodithiolyl)­bithienyl moieties. The polymer gels show swelling behavior upon chemical oxidization, and bending behavior has been observed for the polymer gel immobilized poly­(vinylidene difluoride) (PVdF) film. These results provide a useful perspective for fabricating redox-triggered polymer gel actuators based on the conformational change of the functional molecular unit

Redox-Driven Molecular Switches Consisting of Bis(benzodithiolyl)bithienyl Scaffold and Mesogenic Moieties: Synthesis and Complexes with Liquid Crystalline Polymer

Molecular switches composed of a benzodithiolylbithienyl scaffold and biphenyl or terphenyl mesogenic substituents were designed and synthesized. The molecular switches could undergo redox-triggered interconversion between the cationic form and cyclized neutral form, and this was confirmed using cyclic voltammetry and UV–vis spectroscopy. Binary complexes consisting of the molecular switches and a liquid crystalline polymer (LCP) were prepared to investigate the function of these redox-active molecular switches as actuating dopants. X-ray diffraction measurements were performed to determine the differences between the layer spacings of the complexes in the liquid crystalline phase with the oxidized and reduced states of the molecular switches. The LCP that was doped with the oxidized cationic form of the molecular switch had layer spacings that were up to 4% larger than the layer spacings in the polymer that was doped with the reduced cyclized molecular switch. Our approach will allow stimulus-responsive deformable materials to be constructed and give an impetus for fabricating redox-driven soft actuators

Catalytic Oxidation of Thiols within Cavities of Phthalocyanine Network Polymers

Two three-dimensional (3D) network polymers (<b>1</b> and <b>2</b>), in which zinc­(II) or cobalt­(II) phthalocyanines were interconnected with twisted 9,9′-spirobifluorene linkers, were synthesized in order to investigate their performance as heterogeneous catalysts for thiol oxidations. From the spectroscopic analyses of two dimers (<b>3</b> and <b>4</b>) as component units of the network polymers, <b>3</b> connected with a short linker revealed electronic interaction between the two phthalocyanine units. Micrometer-sized polymer particles were formed due to the condensation of the twisted 9,9′-spirobifluorene linkers in the presence of zinc or cobalt ions. The dispersed solutions of <b>1</b> and <b>2</b> had sharp Q-bands, indicating the prevention of stacking among phthalocyanine moieties within the polymers. Powdered X-ray diffraction pattern and N₂ adsorption–desorption analyses suggested that <b>1</b> created small and rigid cavities as compared with <b>2</b> through the regular spatially arrangement of the phthalocyanine moieties in the 3D networks. The photocatalytic and catalytic activities of <b>1</b> and <b>2</b> for thiol oxidations using molecular oxygen were examined. We found that the catalytic activity of <b>1</b> was higher than that of <b>2</b> having larger cavities

Dye Aggregation Effect on Interfacial Electron-Transfer Dynamics in Zinc Phthalocyanine-Sensitized Solar Cells

Aggregation of adsorbed dye molecules on TiO₂ electrode typically decreases the yield of photoinduced charge separation at the dye/TiO₂ interface. The decreased yield could be caused by the alternations of energy levels and/or adsorption geometry of sensitizers by the aggregation. We investigated the origin of the decreased yield for the aggregated sensitizers by employing zinc phthalocyanine-sensitized TiO₂ electrode in redox-containing electrolytes. The degree of aggregation was controlled by the amount of coadsorbent, the addition of bulky molecular unit to phthalocyanine cores, and the alternation of the adsorption angle by changing the position of adsorption site. Femtosecond transient absorption measurements showed that injection yield was not significantly influenced by the aggregation but by dye adsorption angle and by the amount of dye. On the other hand, aggregation induced subnanosecond charge recombination, and the recombination seemed independent of the adsorption angle. These results appear to be not consistent with an interpretation where flat adsorption geometry enhances fast recombination. Here we interpreted the results with the dye-adsorption-density-dependent tunneling barrier height