Conjugated Polymer Composites Research Articles

Electrically Switchable Film Structure of Conjugated Polymer Composites

Domains rich in different blend components phase-separate during deposition, creating a film morphology that determines the performance of active layers in organic electronics. However, morphological control either relies on additional fabrication steps or is limited to a small region where an external interaction is applied. Here, we show that different semiconductor-insulator polymer composites can be rapidly dip-coated with the film structure electrically switched between distinct morphologies during deposition guided by the meniscus formed between the stationary barrier and horizontally drawn solid substrate. Reversible and repeatable changes between the morphologies used in devices, e.g., lateral morphologies and stratified layers of semiconductors and insulators, or between phase-inverted droplet-like structures are manifested only for one polarity of the voltage applied across the meniscus as a rectangular pulse. This phenomenon points to a novel mechanism, related to voltage-induced doping and the doping-dependent solubility of the conjugated polymer, equivalent to an increased semiconductor content that controls the composite morphologies. This is effective only for the positively polarized substrate rather than the barrier, as the former entrains the nearby lower part of the coating solution that forms the final composite film. The mechanism, applied to the pristine semiconductor solution, results in an increased semiconductor deposition and 40-times higher film conductance.

Enhanced miscibility and strain resistance of blended elastomer/π‐conjugated polymer composites through side chain functionalization towards stretchable electronics

AbstractThis work presents improved compatibility in an elastomer/π‐conjugated polymer blend through side chain functionalization of the electronic polymer. Poly[(3‐(6‐bromohexyl)thiophene)‐ran‐(3‐hexylthiophene)] (P3BrxHT, x = 0%–100%) was synthesized (i) to improve miscibility with polybutadiene (PB) elastomer through altered π–π interactions and (ii) to covalently bond across phase‐segregated interfaces. Functionalization led to morphology with reduced domain sizes to improve crack onset strain from 7% to 40%. Furthermore, UV‐activated crosslinking reinforced mechanically weak interfaces and yielded at least an additional 40% increase in crack onset strain. Charge mobility in PB/P3BrxHT organic field‐effect transistors showed minimal dependence on bromide concentration and no negative effects from crosslinking. Functionalization was an effective method to reduce brittleness in PB/P3BrxHT blends through morphology modification and crosslinking to improve stability towards strain for potential stretchable electronic applications. © 2019 Society of Chemical Industry

Contributions to composite conductivity and Seebeck coefficient in commercial Bi2Te3—Conjugated polymer composites

We demonstrated the use of as-received conjugated polymer P3HT [poly (3-hexylthiophene-2,5 diyl)] doped with F4TCNQ (2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane) as a matrix for forming a composite with as-received, commercially available p-type Bi2Te3 powder. The optimized formulation exhibits a power factor of up to 5.3μWK−2m−1, about nine times higher than the highest power factor that we achieved from mixtures of only P3HT and F4TCNQ. Bi2Te3 was responsible for increases in both the Seebeck coefficient and the electrical conductivity. P3HT, with a higher hole mobility, was superior to PQT-12 [poly(bisdodecylquaterthiophene)], and F4TCNQ was at least as good as FeCl3, for matrix and dopant, respectively, for this purpose. The power factor obtained is about 40% of that reportedly obtained from synthesized Bi2Te3 nanowires in FeCl3-doped P3HT. We calculated the expected contributions of the bulk Bi2Te3 to the composite conductivity and then examined the resistance caused by interfaces on four different size distributions of Bi2Te3 particles, as well as a solid macroscopic ingot. A nonlinear I–V relationship was found for the doped P3HT-ingot bilayer. While our doped conjugated polymer system made only from commercial-grade components was shown to support the extraction of thermoelectric performance by a commonly used inorganic semiconductor, our results also suggest that an advantage of the smallest Bi2Te3 domains, including nanowires, may arise from their having less interfacial resistance than larger Bi2Te3 particles and pieces.

Organic thin film transistor with conjugated polymers for highly sensitive gas sensors

The ease in structural modification, redesign and development of multi-functional polymer semiconductors have led to significant advances in organic electronic device applications such as organic light emitting diodes (OLED), organic photovoltaics (OPV), organic thin film transistors (OTFT), and organic sensors. In this article, we reviewed recent techniques and strategies employed toward the optimization of conjugated polymer films for high sensing performance in OTFT-based gas sensors. Significant enhancements, particularly in gas selectivity, sensitivity, detection limit, response/recovery time of OTFT-based gas sensors by polymer film morphology and thickness control, functionalization of conjugated polymers with chemical groups and the use of doped/blended inorganic or dielectric materials and conjugated polymer composites as active layers are discussed here.

Elastomeric Conducting Polyaniline Formed Through Topological Control of Molecular Templates.

A strategy for creating elastomeric conducting polyaniline networks is described. Simultaneous elastomeric mechanical properties (E < 10 MPa) and electronic conductivities (σ > 10 S cm(-1)) are achieved via molecular templating of conjugated polymer networks. Diblock copolymers with star topologies processed into self-assembled elastomeric thin films reduce the percolation threshold of polyaniline synthesized via in situ polymerization. Block copolymer templates with star topologies produce elastomeric conjugated polymer composites with Young's moduli ranging from 4 to 12 MPa, maximum elongations up to 90 ± 10%, and electrical conductivities of 30 ± 10 S cm(-1). Templated polyaniline films exhibit Young's moduli up to 3 orders of magnitude smaller compared to bulk polyaniline films while preserving comparable bulk electronic conductivity. Flexible conducting polymers have prospective applications in devices for energy storage and conversion, consumer electronics, and bioelectronics.

Device and morphological engineering of organic solar cells for enhanced charge transport and photovoltaic performance

Conjugated polymers are potential materials for photovoltaic applications due to their high absorption coefficient, mechanical flexibility, and solution-based processing for low-cost solar cells. A bulk heterojunction (BHJ) structure made of donor–acceptor composite can lead to high charge transfer and power conversion efficiency. Active layer morphology is a key factor for device performance. Film formation processes (e.g., spray-coating, spin-coating, and dip-coating), post-treatment (e.g., annealing and UV ozone treatment), and use of additives are typically used to engineer the morphology, which optimizes physical properties, such as molecular configuration, miscibility, lateral and vertical phase separation. We will review electronic donor–acceptor interactions in conjugated polymer composites, the effect of processing parameters and morphology on solar cell performance, and charge carrier transport in polymer solar cells. This review provides the basis for selection of different processing conditions for optimized nanomorphology of active layers and reduced bimolecular recombination to enhance open-circuit voltage, short-circuit current density, and fill factor of BHJ solar cells.

Low‐Cost Solar Cell Based on a Composite of Silicon Nanowires and a Highly Conductive Nonphotoactive Polymer

Hybrid bulk heterojunction solar cells based on inorganic-nanowire (NW)/conjugated-polymer composites have been shown to achieve a power conversion efficiency (PCE) of 1–3 %, which is much lower than theoretically expected. This work addresses the short exciton diffusion lengths in common photoactive polymers with a new solar-cell design that has a PCE of 4.68 % (see scheme; ITO=indium tin oxide, G-PEDOT:PSS=glycerol-doped poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate); E=electropolymerized; a=amorphous).

The Optical and Electrical Properties of Graphene Oxide with Water-Soluble Conjugated Polymer Composites by Radiation

In order to overcome the difficulty of dispersion and low conductivity in composite containing graphene, graphene oxide (GO) has been used instead of neat graphene. And the GO treated by radiation, could give improved conductivity of the GO-containing polymer composite. In this study, fluorene based water-soluble conjugated polymer (WPF-6-oxy-F) was introduced in GO solution to investigate the change of optical and electrical properties through radiation process. UV-Vis absorption of irradiated WPF-6-oxy-F-GO composite was red shifted and I(D)/I(G) ratio of Raman spectra decreased. XPS analysis showed that C-N bonds was formed after the irradiation and confirmed the increased bonds between the GO and the water-soluble conjugated polymer matrix. From the AFM and XPS analysis, it was found that the water-soluble conjugated polymer matrix was stacked between the modified GO in the morphology of irradiated WPF-6-oxy-F-GO composite was increased after gamma ray irradiation up to 10(-2) S/cm.

Field enhanced charge carrier reconfiguration in electronic and ionic coupled dynamicpolymer resistive memory

Dynamic resistive memory devices based on a conjugated polymer composite (PPy0DBS − Li + (PPy:polypyrrole; DBS − : dodecylbenzenesulfonate)), with field-driven ion migration, have been demonstrated. Inthis work the dynamics of these systems has been investigated and it has been concludedthat increasing the applied field can dramatically increase the rate at which informationcan be ‘written’ into these devices. A conductance model using space charge limited currentcoupled with an electric field induced ion reconfiguration has been successfully utilized tointerpret the experimentally observed transient conducting behaviors. The memory devicesuse the rising and falling transient current states for the storage of digital states.The magnitude of these transient currents is controlled by the magnitude andwidth of the write/read pulse. For the 500 nm length devices used in this work anincrease in ‘write’ potential from 2.5 to 5.5 V decreased the time required to createa transient conductance state that can be converted into the digital signal by50 times. This work suggests that the scaling of these devices will be favorableand that ‘write’ times for the conjugated polymer composite memory deviceswill decrease rapidly as ion driving fields increase with decreasing device size.

Towards an all-polymer cathode for dye sensitized photovoltaic cells

Highly conducting conjugated polymer composite was deposited by vapour phase polymerization. Poly[3,4-ethylenedioxythiophene: para-toluenesulfonate] (PEDOT:PTS) itself was used as the counter electrode in a dye sensitized solar cell. The maximum photocurrent of 9.7 mA/cm 2, open circuit voltage of 759 mV, fill factor of 0.71 with a power conversion efficiency of 5.25% were observed for glass based wet type dye sensitized solar cell, under illumination of 100 mW/cm 2. It was observed that the resistance, during operation of the dye sensitized solar cells, due to the I 3 − conversion was less with PEDOT:PTS coated cathodes than with standard platinum coated fluorine doped tin oxide and was confirmed by steady state electrochemical measurements.

Dynamic resistive crossbar memory based on conjugated polymer composite

A semiconducting polypyrrole composite was designed to exhibit electric field dependent charge carrier distributions. Junctions were grown electrochemically on gold crossbars. Application of fields results in the drift of mobile cations, creating regions with higher conductivity and increased current. The field induced carrier redistribution results in field- and time-dependent current with good junction-to-junction repeatability. The electrical transport dominated by space charge limited current will have better scaling behavior than surface dominated and Ohmic devices as the dimensions are reduced to the nanometer scale.

Photovoltaic Cells with TiO2 Nanocrystals and Conjugated Polymer Composites

Various compositional photovoltaic cells based on the blend of poly(3-hexylthiophene) (P3HT) as donors and TiO2 nanocrystals as acceptors are fabricated and investigated. It is demonstrated that the blend ratio of P3HT and TiO2 nanocrystals could greatly influence the performance of the photovoltaic cells. The maximum of 0.411% in power conversion efficiency under AM 1.5, 100mW/cm2, and 44.4% of fill factor are obtained in the solar cell with the blend weight ratio 1:1 of P3HT and TiO2 nanocrystals. The function of nanocrystal composition is discussed in terms of the results of photoluminescence spectroscopy, atomic force microscopy, transmission electron microscopy, and charge transport I–V curve.

Fluorescence resonance energy transfer in conjugated polymer composites for radiation detection

Fluorescence resonance energy transfer in conjugated polymer composite materials was exploited for the detection of gamma ray dosage with high sensitivity and response linearity.

Poly(3-hexythiophene)/multi-walled carbon nanotube composites: electrochemical and optical characterization

ABSTRACTCarbon nanotubes (CNT) / conjugated polymer composites have been used for the preparation of thin film-modified electrodes. Thin, short, multi-walled CNT (MWNT) (purity higher than 95%) was completely coated by regioregular poly(3-hexylthiophene) (P3HT) through precipitation of a mixture of both in the non-solvent methanol. This work reports the electrochemical and optical characterization of P3HT and composites after dissolution in xylene and spin casting of films with thickness &lt;1 micrometer. Cyclic voltammetry showed that all samples were characterized by a semi-reversible behavior. The samples with 0% and 2% of MWNT, for instance, present anodic peak potential at +0.67 and +0.68V respectively when cycling at 100 mV/s. Optical properties, such as optical absorption and photoluminescence (PL), have been investigated. The samples showed maximum of absorption at ˜530 nm and intense PL in the orange. PL spectra of nanocomposites exhibited a new band at lower energy characteristic of a structure with higher conjugation length when compared to P3HT.

Photovoltaic devices from CdSe nanocrystals and conjugated polymer composites

The preparation of CdSe nanospheres (ns-CdSe) and their application as electron acceptor in conjugated polymer photovoltaic devices are reported. ns-CdSe with diameters of 5 nm were prepared through an organometallic method. The transmission electron microscopy (TEM), ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectra indicate that the CdSe nanocrystals (NCs) are monodispersed nanospheres with the first exciton absorption peak at around 625 nm and the emission peak at around 652 nm. The PL spectra of the ns-CdSe/polymer composite films show that the PL of the conjugated polymers is effectively quenched upon the addition of ns-CdSe. Photovoltaic devices were fabricated from the composites of ns-CdSe and poly[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) or poly(3-hexylthiophene) (P3HT). Under AM1.5 illumination (100 mW/cm2), the short circuit current (I SC), open circuit voltage (V OC), fill factor (FF) and energy conversion efficiency (η) reached 1.56 mA/cm2, 0.75 V, 34.5% and 0.40%, respectively for device from the ns-CdSe/MEH-PPV (15: 1 by weight) and 1.93 mA/cm2, 0.65 V, 38.4% and 0.48%, respectively for device from the ns-CdSe/P3HT (10: 1 by weight).

Determination of Nanomaterial Energy Levels for Organic Photovoltaics by Cyclic Voltammetry

AbstractA wide variety of nanomaterials and associated nanomaterial/polymer composites are being developed in an effort to produce higher efficiency organic solar cells. This development requires a fundamental understanding of the energy levels for the individual materials, and their composites, to enable device designs which posess appropriate energy level matching. Cyclic voltammetry (CV) allows for the determination of the band gaps (Eg) and energy levels of these various nanomaterials and composites by measuring their oxidation and reduction potentials. These potentials correspond to a given material's ionization potential (IP) and electron affinity (EA), respectively. The results for the EA, IP, and Eg have been determined by CV for derivatized fullerenes and CdSe quantum dots (QD), measured in isolation, and in conjugated polymer composites with MEH-PPV. In addition, CV measurements conducted under dark and illuminated conditions were used to investigate the relationship between energy levels within the composites.

Electrical Bistability and Memory Phenomenon in Carbon Nanotube-Conjugated Polymer Matrixes

We have observed electrical bistability and large conductance switching in functionalized carbon nanotube (CNT)-conjugated polymer composites at room temperature. The concentration of the CNTs in the polymer matrix controlled the degree of bistability. Conduction mechanism applicable in each of the conducting states has been identified. The switching had an associated memory phenomenon and was reversible in nature. In the bistable devices, the active layer retained its high-conducting state until a reverse voltage erased it. We could "write" or "erase" a state and "read" it for many cycles for random-access memory applications.

Synthesis of size-controlled CdSe quantum dots and characterization of CdSe–conjugated polymer blends for hybrid solar cells

High-quality CdSe quantum dots (Qdots) were produced using the wet chemical synthetic method. These size-controlled CdSe Qdots were characterized by UV–vis absorption spectroscopy, photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD patterns and TEM images showed that the CdSe Qdots had a wurtzite crystalline structure. Bandgap-tuning CdSe Qdots were used to fabricate solar cells. We report the extensive experimental results of the CdSe Qdots–conjugated polymer composites used for the fabrication of the hybrid solar cells, by blending them between CdSe Qdots–poly (3-hexylthiophene) (P3HT) and CdSe Qdots/[poly(1-methoxy-4-(2-ethylhexyloxy-2,5-phenylenevinylene))] (MEH-PPV) polymer.

A New Approach to the Synthesis of Nanocrystal Conjugated Polymer Composites

A novel one pot process has been developed for the preparation of PbS nanocrystals in the conjugated polymer poly 2-methoxy, 5-(2 - ethyl-hexyloxy-p-phenylenevinylene) (MEH-PPV). Current techniques for making such composite materials rely upon synthesizing the nanocrystals and conducting polymer separately, and subsequently mixing them. This multi-step technique has two serious drawbacks: templating surfactant must be removed before mixing, and co-solvent incompatibility causes aggregation. In our method, we eliminate the need for an initial surfactant by using the conducting polymer to terminate and template nanocrystal growth. Additionally, the final product is soluble in a single solvent. We present materials analysis which shows PbS nanocrystals can be grown directly in a conducting polymer, the resulting composite is highly ordered and nanocrystal size can be controlled.

Photovoltaic Properties of Dye Functionalized Single-Wall Carbon Nanotube/Conjugated Polymer Devices

Photovoltaic properties of dye, N-(1-pyrenyl)maleimide (PM), functionalized single-walled carbon nanotubes (SWNT)−conjugated polymer, poly(3-octylthiophene) (P3OT), blend composites are reported. Devices were fabricated by drop or spin cast from the solution of composite onto ITO-coated glass. Improved performance was achieved by functionalizing the SWNT with dye molecules. Photovoltaic behavior with an open circuit voltage of 0.6−0.7 V was measured in diodes (Al/SWNT+PM−polymer/ITO). The short circuit current was found to increase by more than an order of magnitude compared to the SWNT−polymer diode without dye. Optical absorption spectra showed considerable ground-state interaction between SWNT+dye and the polymer. It is proposed that the main reason for the increase in short circuit current is due to efficient transfer of holes by dye molecules to P3OT at the dye/polymer interface and the rapid transfer of the generated electrons to the SWNTs at the dye/nanotube interface. It is shown that the dye functionalized SWNT−conjugated polymer composites represent an alternative class of organic semiconducting materials for dye-based organic photovoltaic cells.