Experimental and Theoretical Investigations of Different Diketopyrrolopyrrole-Based Polymers

Diketopyrrolopyrrole (DPP)-based polymers are often considered las the most promising donor moiety in traditional bulk heterojunction solar cell devices. In this paper, we report the synthesis, characterization of various DPP-based copolymers with different molecular weights, l and polydisper sity where other aromatic repeating units (phenyl or thiophene based) are connected by alternate double bonds or triple bonds. Some of the copolymers were used for device fabrication and the crucial parameters such as fill factor (FF) and open circuit voltage (V-oc) were calculated. The density functional theory was used to optimize the geometries and deduce highest occupied molecular orbital lowest unoccupied molecular orbital gaps of all the polymers and'theoretically predict their optical and electronic properties. Optical properties of all the polymers, electrochemical properties and band gaps were also obtained experimentally and compared with the theoretically predicted values

Flexible Microsupercapacitors Using Silk and Cotton Substrates

Flexible microsupercapacitors (MSCs) are needed to power ultrasmall wearable electronic devices. Silk cocoons comprise microfibers of silk, which is an attractive natural resource to fabricate MSCs. These fibers are insulators; hence, they must be converted to conducting surfaces. Polyphenols from green tea have been used as a protective layer that also acted as a reducing agent for silver ions. The reduction of silver ions resulted in the formation of silver nanoparticles that subsequently reduced gold ions to gold. The gold film imparts conductivity to the silk fiber without affecting the mechanical strength of the silk fiber. The mechanical strength of uncoated silk fiber and gold coated silk fiber were found to be 5.2 and 5 GPa, respectively. A pseudocapacitive polymer, poly­(3,4-ethylenedioxythiophene), was used as the active material to fabricate MSCs. The MSCs showed an impressive gravimetric capacitance of 500 F/g and areal capacitance of 62 mF/cm². The power and energy densities were calculated to be 2458 W/kg and 44 Wh/kg, respectively. The device was coiled on a cylinder, and the performance of the device was found to be same as that of the uncoiled device. To demonstrate that the approach is not specific to silk, we also coated gold on cotton fibers using the protocol used to coat gold on silk. Coiled and uncoiled supercapacitors were fabricated using PEDOT coated cotton fibers. The gravimetric capacitance was found to be 250 F/g with energy and power densities of 5.5 Wh/kg and 1118 W/kg, respectively. We have also demonstrated that the devices can be connected in parallel and series to improve the performance of the miniaturized devices

Chemically Reduced Organic Small-Molecule-Based Lithium Battery with Improved Efficiency

Organic lithium batteries are attractive because of the possibility of fabricating lightweight and flexible devices. However, the organic lithium batteries have a few drawbacks. The specific capacity is usually lower than the theoretical capacity, which further decreases upon cycling. Often, the specific capacity is very low compared to theoretical capacity while discharging the battery at moderate and high <i>C</i> rates. To circumvent this issue, we chemically reduced carboxylic acid functionality substituted perylene diimide (benzoic-PDI) with hydrazine. Indeed, we found that the rate of redox reaction as well as the conductivity of the benzoic-PDI increased upon chemical reduction. The battery comprising reduced benzoic-PDI exhibits 100% Coulombic efficiency and specific capacity while discharging at 20<i>C</i>. The battery also exhibits very high specific energy (213 Wh/kg) and specific power (8548 W/kg). The control experiments confirm our hypothesis of using chemical reduction to improve the performance of organic lithium battery

Self-Assembled Spheres, Flowers, and Fibers from the Same Backbone and Similar Side Chains

Rylene imides (RIs) self-assemble into various nanostructures. Often, the synthesis of unsymmetrical RIs (URIs) is required to achieve nanostructures. However, the synthesis of URIs is nontrivial. Thus, a structurally similar alternative is desirable. iso-Indigo (<i>i</i>-indigo) has a π core and lactam rings that are structurally similar to the RIs. Unsymmetrical iso-indigo (<i>i</i>-indigo) can be easily synthesized by condensing oxindole and isatin. We have synthesized a series of unsymmetrical <i>i</i>-indigo molecules. In these molecules, the π–π interaction, hydrogen bonding, and van der Waals interactions are in operation. Because of these, the molecules self-assemble into spheres, fibers, and dahlia flower morphologies. If the hydrogen bonding interaction is disrupted, then all of them form fibers. Control experiments indicate that the complete absence of hydrogen bonding is deleterious to self-assembly. We also show that the lower analogs of <i>i</i>-indigo are not sufficient to form self-assembled nanostructures

Copolymers Comprising Monomers with Various Dipoles and Quadrupole as Active Material in Organic Field Effect Transistors

Copolymers of 4,4-difluoro-4-borata-3a-azonia-4a-aza-s-indacene (BODIPY) and diketopyrrolopyrrole (DPP) were synthesized. The BODIPY has a permanent dipole and the DPP has a quadrupole. The dipole and the quadrupole in the monomers are expected to bring the polymers closer and to improve the charge-transport properties. By judicious choice of these monomers, the electron wave function is evenly distributed through the molecules. However, we notice that the torsional angle at the connecting point of BODIPY and DPP is a function of the methyl moieties at the β, β′ position of the BODIPY. We found that the polymer comprising DPP and BODIPY without methyl moiety at β, β′ position showed a torsional angle of 27°, the lowest among the three polymers studied in this work. The absorption spectrum of the polymer showed transitions because of vibronic coupling indicating linearity along the polymer backbone. The band gap of the polymer was found to be 1.2 eV. The thermally stable polymer showed an ambipolar charge transport of 0.01 cm²/(V s)

Solvent-Dependent Functional Aggregates of Unsymmetrical Squaraine Dyes on TiO2Surface for Dye-Sensitized Solar Cells

Alkyl group wrapped donor-acceptor-donor (D-A-D) based unsymmetrical squaraine dyes SQ1, SQ5, and SQS4 were used to evaluate the effect of sensitizing solvents on dye-sensitized solar cell (DSSC) efficiency. A drastic change in DSSC efficiency was observed when the photo-anodes were sensitized in acetonitrile (bad solvent when considering dye solubility) and chloroform (good solvent) with an Iodolyte (I-/I3-) electrolyte. The DSSC device sensitized with squaraine dyes in acetonitrile showed better photovoltaic performance with enhanced photocurrent generation and photovoltage compared to the device sensitized in chloroform. In a good sensitizing solvent, dyes with long hydrophobic alkyl chains are deleterious forming aggregates on the TiO2surface, which results in an incident photon-to-current conversion efficiency (IPCE) response mostly from monomeric and dimeric structures. Meanwhile, a bad sensitizing solvent facilitates the formation of well-packed self-assembled structures on the TiO2surface, which are responsible for a broad IPCE response and high device efficiencies. The photoanode sensitized in the bad sensitizing solvent showed enhanced VOCvalues of 642, 675, and 699 mV; JSCvalues of 6.38, 11.1, and 11.69 mA/cm2and DSSC device efficiencies of 3.0, 5.63, and 6.13% for the SQ1, SQ5, and SQS4 dyes in the absence of a coadsorbent (chenodeoxycholic acid (CDCA)), respectively, which were further enhanced by CDCA addition. Meanwhile, the photoanode sensitized in the good sensitizing solvent showed relatively low photovoltaic VOCvalues of 640, 652, and 650 mV; JSCvalues of 5.78, 6.79, and 6.24 mA/cm2and device efficiencies of 2.73, 3.35, and 3.20% for SQ1, SQ5, and SQS4 in the absence of CDCA, respectively, which were further varied with equivalents of CDCA. The best DSSC device efficiencies of 6.13 and 3.20% were obtained for SQS4 without CDCA, where the dye was sensitized in acetonitrile (bad) and chloroform (good) sensitizing solvents, respectively

Elastic Compressible Energy Storage Devices from Ice Templated Polymer Gels treated with Polyphenols

Design and fabrication of rechargeable energy storage devices that are robust to mechanical deformation is essential for wearable electronics. We report the preparation of compressible supercapacitors that retain their specific capacitance after large compression and that recover elastically after at least a hundred compression–expansion cycles. Compressible supercapacitors are prepared using a facile, scalable method that readily yields centimeter-scale macroporous objects. We ice template a solution of polyethylenimine in green tea extract to prepare a macroporous cross-linked polymer gel (PG) whose walls are impregnated with green tea derived polyphenols. As the PG is insulating, we impart conductivity by deposition of gold on it. Gold deposition is done in two steps: first, silver nanoparticles are formed on the PG walls by in situ reduction by polyphenols and then gold films are deposited on these walls. Gold coated PGs (GPGs) were used as electrodes to deposit poly­(3,4-ethylenedioxythiophene) as a pseudocapacitive material. The specific capacitance of PEDOT coated GPGs (PGPG) was found to be 253 F/g at 1 A/g. PGPG could be compressed and expanded over a hundred cycles without any suffering mechanical failure or loss of capacitative performance. The capacitance was found to be 243 F/g upon compressing the device to 25% of its original size (viz. compressive strain = 75%). Thus, even large compression does not affect the device performance. This device shows power and energy densities of 2715 W/kg and 22 Wh/kg, respectively, in the uncompressed state. The macroporous nature of PGPG makes it possible to fill the PGPG pores with gel electrolyte. We report that the gel electrolyte filled supercapacitor exhibited a specific capacitance of 200 F/g, which increased by 4% upon 75% compression

Reversible Assembly and Disassembly of Micelles by a Polymer That Switches between Hydrophilic and Hydrophobic Wettings

Supramolecular complexes involving nanoscopic amphiphilic assemblies (AAs) and polyelectrolytes have been used to prepare a variety of materials, wherein the dynamic AAs retain the structural features, but the polyelectrolytes undergo conformational changes. Here we show that a charge bearing rigid conjugated polymer can alter the structural features and disassemble AAs. We also demonstrate reversible assembly and disassembly of AAs by controlling the number of charges on the rigid polymer. During the disassembly, the guest molecules sequestered in the AAs are released. The rate of release has been modulated by changing the morphology of the charge bearing polymer. Concomitant to the AAs disassembly, the polymer surface becomes hydrophobic due to the binding of the amphiphiles on the charges of the polymer backbone. By controlling the charges on the polymer, the surface wettability was varied gradually from hydrophilic to hydrophobic

Experimental and Theoretical Investigations of Different Diketopyrrolopyrrole-Based Polymers

Diketopyrrolopyrrole (DPP)-based polymers are often considered as the most promising donor moiety in traditional bulk heterojunction solar cell devices. In this paper, we report the synthesis, characterization of various DPP-based copolymers with different molecular weights, and polydispersity where other aromatic repeating units (phenyl or thiophene based) are connected by alternate double bonds or triple bonds. Some of the copolymers were used for device fabrication and the crucial parameters such as fill factor (FF) and open circuit voltage (Voc) were calculated. The density functional theory was used to optimize the geometries and deduce highest occupied molecular orbital–lowest unoccupied molecular orbital gaps of all the polymers and theoretically predict their optical and electronic properties. Optical properties of all the polymers, electrochemical properties, and band gaps were also obtained experimentally and compared with the theoretically predicted values