Conjugated Polymer Solutions Research Articles

Synergetic effect of microfluidic flow and ultrasonication on chains pre-ordering in conjugated polymer solution

Multi-physical fields solution processing strategy provides a universal and facile way to prepare various conjugated polymer (CP) films and high-performance devices, whereas the hierarchical structures evolution and crystallization of the polymer chains are elusive particularly under the far-from-equilibrium state in solution. In this work, we employed a combined microfluidic flow and ultrasonication strategy (FU) for CP solution processing and found a pronounced synergetic effect of these fields in promoting the pre-ordering of chains in solution. This conformation order and anisotropy of the solution were revealed by using UV–Vis absorption, polarized optical microscopy (POM) and cryogenic transmission electron microscopy (Cryo-TEM) characterizations. A non-classical nucleation model for the conjugated polymer crystallization in the procedure of non-equilibrium solution processing was confirmed. The roles of microfluidic flow and ultrasonication on the chain aggregation and crystallization were addressed with the aim of a multi-physical simulation based on pressure acoustics streaming, fluid heat transfer and thermoviscous boundary layer impedance. Compared to pristine solutions, the FU strategy showed improved solution anisotropy and crystallization kinetics, substantially giving rise to a larger crystallinity in films and much increased mobilities for the organic field-effect transistor (OFET) devices by more than an order of magnitude. With an appropriate balance between the solvation and interchain interactions, the FU processing strategy is universal for regulation of chains conformation and aggregation in conjugated polymer solution.

Study of the Dynamic Process of Enhancing the Stability of Conjugated Polymer Solutions and Films Induced by an External Electric Field

Study of the Dynamic Process of Enhancing the Stability of Conjugated Polymer Solutions and Films Induced by an External Electric Field

Solvation-Shell-Induced Entropic Repulsion and Insights into Solvent Quality of Crystalline Conjugated Polymer Solutions

Solvation-Shell-Induced Entropic Repulsion and Insights into Solvent Quality of Crystalline Conjugated Polymer Solutions

The relationship between the concentration of conjugated polymer of an aggregation status and absorbance of UV–Vis absorption spectra during the aggregation process of conjugated polymer solutions

The relationship between the concentration of conjugated polymer of an aggregation status and absorbance of UV–Vis absorption spectra during the aggregation process of conjugated polymer solutions

Cellulose-Templated Stable Foldable Oriented Films with Polarized RGB Luminescence

Solution processing in a vacuum-free system is highly advantageous because printing, coating, and roll-to-roll processes can be used for large-area and scalable manufacturing. However, producing a flat surface with high orientation is challenging. In addition, high folding stability is essential for building a basis for foldable devices. Herein, we present a valuable method to obtain oriented films of π-conjugated polymers, which we describe as a “Simple way of Orienting Films prepared by Templating cellulose,” abbreviated as SOFT. In this method, a glass or flexible substrate was uniaxially coated by a single-sweep process using a wet cloth containing a cellulose solution. A conjugated polymer solution, an OLED material, was deposited onto the cellulose film by spin coating, followed by thermal annealing. A uniaxially oriented film was obtained with orientation factors up to 0.9, and its polarized fluorescence was verified for red/green/blue colors. The oriented films were stable at various positions and showed no degradation of orientation factors after folding 100–500 times at a folding angle of 320°. The homogeneous area and surface roughness of the films were approximately 2 × 3 cm2 and 50 nm, respectively, with an orientation reproducibility of ∼96%. A high tensile strength of 30 MPa was measured on the oriented films. The orientation mechanism was attributed to the alignment of the backbone structure of the conjugated polymers along the surface anisotropy of a uniaxially coated cellulose film.

Intrinsically Viscoelastic Supramolecular Conjugated Polymer toward Suppressing Coffee-Ring Effect

Intrinsically Viscoelastic Supramolecular Conjugated Polymer toward Suppressing Coffee-Ring Effect

Data Science Guided Experiments Identify Conjugated Polymer Solution Concentration as a Key Parameter in Device Performance

Data Science Guided Experiments Identify Conjugated Polymer Solution Concentration as a Key Parameter in Device Performance

The study of aggregation dynamics of conjugated polymer solutions in UV-vis absorbance spectra by considering the changing rate of average photon energy

The changing rate of average photon energy ('Eave) can describe the UV-vis absorbance spectra over a wavelength range. During the aggregation process of poly (3-hexylselenophene) (P3HS) and poly (3-hexylthiophene) (P3HT) solutions that form J-aggregates, 'Eave always decrease and the relationship between 'Eave and time is an exponential model. 'Eave can predict the time when the aggregation process is completed or how far the aggregation process is from the completion. Hansen Solubility Parameter (HSP) of the solvent can be used to predict 'Eave of some conjugated polymer solutions without doing experiments. ''E0ave (changing rate of 'Eave at the beginning of the aggregation process) has been calculated to reflect the overall changing trend of 'Eave and reflects the compatibility between solvent and solute. Therefore, 'Eave is suitable to describe the aggregation dynamics of conjugated polymer solutions by evaluating the aggregation process in UV-vis absorbance spectra.

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 solution behavior, i.e., single chain conformation, chain shape, size and chains aggregated density were studied by means of static/dynamic laser light scattering (DLS/SLS) and exponential law etc. Effect of solvent properties on condensed state structure of the semi-rigid conjugated polymer film was studied by UV absorption spectroscopy, PL spectroscopy and electron microscopy etc. The essential reasons for the influence were discovered and the mechanism was revealed. It was found that solution behavior with different solvent properties had an essential physical relationship with chains condensed state structure of the semi-rigid conjugated polymers. More importantly, there was a quantitative structure-activity relationship between solution and film. The key to this relationship depended on the interaction between solvent molecules and the semi-rigid conjugated polymer chains. This interaction could also affect optoelectronic devices performance. This study is of great significance to effectively control the condensed state structure of the semirigid conjugated polymers in the process of dynamic evolution from solutions to films. It not only enriches the knowledge and understanding of both semi-rigid conjugated polymer solution behaviors and film condensed state physics based on polymer physics, but also is meaningful to practical application for conjugated polymer and other traditional polymer systems.

Phase Diagrams of Ternary π-Conjugated Polymer Solutions for Organic Photovoltaics.

Phase diagrams of ternary conjugated polymer solutions were constructed based on Flory-Huggins lattice theory with a constant interaction parameter. For this purpose, the poly(3-hexylthiophene-2,5-diyl) (P3HT) solution as a model system was investigated as a function of temperature, molecular weight (or chain length), solvent species, processing additives, and electron-accepting small molecules. Then, other high-performance conjugated polymers such as PTB7 and PffBT4T-2OD were also studied in the same vein of demixing processes. Herein, the liquid-liquid phase transition is processed through the nucleation and growth of the metastable phase or the spontaneous spinodal decomposition of the unstable phase. Resultantly, the versatile binodal, spinodal, tie line, and critical point were calculated depending on the Flory-Huggins interaction parameter as well as the relative molar volume of each component. These findings may pave the way to rationally understand the phase behavior of solvent-polymer-fullerene (or nonfullerene) systems at the interface of organic photovoltaics and molecular thermodynamics.

Tunable WGM Laser Based on the Polymer Thermo-Optic Effect.

In this work, the thermo-optic effect in polymers was used to realize a temperature-tunable whispering-gallery-mode laser. The laser was fabricated using a capillary tube filled with a light-emitting conjugated polymer solution via the capillary effect. In the whispering-gallery-mode laser emission wavelength can be continuously tuned to about 19.5 nm using thermo-optic effect of polymer. The influence of different organic solvents on the tuning rate was studied. For a typical lasing mode with a bandwidth of 0.08 nm, a temperature-resolved tuning rate of ~1.55 nm/°C was obtained. The two-ring coupling effect is responsible for the suppression of the WGM in the micro-cavity laser. The proposed laser exhibited good reversibility and repeatability as well as a sensitive response to temperature, which could be applied to the design of photothermic and sensing devices.

Enhanced Electrospinning of Active Organic Fibers by Plasma Treatment on Conjugated Polymer Solutions.

Realizing active, light-emitting fibers made of conjugated polymers by the electrospinning method is generally challenging. Electrospinning of plasma-treated conjugated polymer solutions is here developed for the production of light-emitting microfibers and nanofibers. Active fibers from conjugated polymer solutions rapidly processed by a cold atmospheric argon plasma are electrospun in an effective way, and they show a smoother surface and bead-less morphology, as well as preserved optical properties in terms of absorption, emission, and photoluminescence quantum yield. In addition, the polarization of emitted light and more notably photon waveguiding along the length of individual fibers are remarkably enhanced by electrospinning plasma-treated solutions. These properties come from a synergetic combination of favorable intermolecular coupling in the solutions, increased order of macromolecules on the nanoscale, and resulting fiber morphology. Such findings make the coupling of the electrospinning method and cold atmospheric plasma processing on conjugated polymer solutions a highly promising and possibly general route to generate light-emitting and conductive micro- and nanostructures for organic photonics and electronics.

A method to describe energy changes in UV–vis absorbance spectra during the aggregation process of conjugated polymer solutions

We have defined average photon energy (Eave) to describe energy changes in UV–vis absorbance spectra during the aggregation of conjugated polymer solutions quantitatively. During the aggregation process of P3HS (poly(3-hexylselenophene)), Eave always decreases and maximum aggregation absorbance (ABSmagg) always increases, and relationships between (Eave and ABSmagg) and time are single exponential models. The relationship between ABSmagg and Eave of P3HS is a single Gaussian model, so Eave can be used to predict the amount of aggregate. Eave and ABSmagg of P3HT (Poly(3-hexylthiophene)) follow similar rules of P3HS. This work describes energy changes and predicts the amount of aggregate in UV–vis spectra during the aggregation process.

A method to describe the shapes of UV–vis absorbance spectra during the aggregation process of conjugated polymer solutions quantitatively

We have defined a dimensionless parameter called shape quality factor to describe shapes of UV–vis absorbance spectra during aggregation process of conjugated polymer solutions quantitatively. Time-lapse UV–vis absorbance spectra of poly(3-hexylselenophene) (P3HS) solutions are obtained. Shape quality factors of UV–vis absorbance spectra during the aggregation process of P3HS solutions are calculated. Shape quality factors usually decrease during aggregation process when amount of aggregate is small, and increase when amount of aggregate is large. Relationship between shape quality factor and aggregation time can be fitted by double Gaussian functions. This work provides a simple way to describe shapes of UV–vis absorbance spectra of conjugated polymer solutions quantitatively.

Phase Diagrams of Binary Low Bandgap Conjugated Polymer Solutions and Blends

Liquid–liquid phase diagrams of binary polymer–solvent and fullerene–solvent mixtures were qualitatively predicted by using the Flory–Huggins (FH) lattice theory as a function of solvent, polymer, ...

Effect of solvent structural isomer on microstructural evolution in polythiophene film during solidification

Abstract Solvent solvation properties are one of the most important key parameters governing the characteristics of polymer film formation during solution processing. Here, we systematically investigated the effects of a solvent's structural isomer on the microstructure evolution of a semiconducting polymer film during solution deposition. We found that spin-casting a conjugated polymer solution over a short period of only a few seconds improved the molecular ordering and charge transport characteristics of the resulting polymer thin films, depending on the isomeric structure of the solvent. Here, we elucidated the effects of the solvent's isomeric structure on the drying kinetics during spin-coating and systematically investigated the film structural development during solidification of the conjugated polymers. We finally evaluated the performances of the resulting polymer field-effect transistors. We demonstrated that controlling the spinning time improved the molecular ordering and electrical characteristics of the polymer thin films in a trend that was strongly correlated with the crystallization, which depended on the isomeric structure (dipole moment) of the solvent.

Benzyl viologen as an n-type dopant for organic semiconductors

Abstract This paper reports an n-type dopant, neutral benzyl viologen (BV0), for organic semiconductors and their application as active layers in organic field-effect transistors (OFETs). BV0 is blended in four commonly used n-type and ambipolar conjugated polymer solutions as charge transfer dopant. Electron mobility increased markedly to ∼10−1 cm2 V-1 s-1 from ∼10−3 cm2V−1s−1 for BV0 doped (6.7%v/v) ambipolar diketopyrrolopyrrole-thieno [3,2-b]thiophene (DPPT-TT) OFETs; whereas, only decreased off current was observed in BV0 doped (6.7%v/v) n-type OFETs based on strong electron transport polymers, including poly [[ N, N 9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)] (P(NDI2OD-T2)), poly{2,5-bis(2-dodecylhexadecyl)-3,6-di(thiophen-2-yl)pyrrolo-[3,4-c]pyrrole-1,4(2H, 5H)-dione-alt-(E)-1,2-bis(3-cyanothiophen-2-yl)ethene} (2DPP-2CNTVT) and poly{2,5-bis(7-dodecylhenicosyl)-3,6-di(thiophen-2-yl)pyrrolo-[3,4-c]pyrrole-1,4(2H, 5H)-dione-alt-(E)-1,2-bis(3-cyanothiophen-2-yl)ethene (7DPP-2CNTVT). This indicates that BV0 doping efficiency is strongly dependent on conjugated polymer structural differences and transport profiles as well as the interaction between their molecules and BV0 during the doping process.

Nanostructured Light-Emitting Polymer Thin Films and Devices Fabricated by the Environment-Friendly Push-Coating Technique.

Push-coating is a green and extremely low-cost process in which only few microliters of conjugated polymer solutions are used to produce thin films using capillary forces. Here, we adapt this fabrication technique to replicate self-assembled nanoporous structures on green and red light-emitting conjugated polymer thin films. These films display ring-like photoluminescence and are successfully integrated into polymer light-emitting devices as emitting layers. At low applied voltages, the green-emitting devices exhibit electroluminescence (EL) from hexagonally arranged nanopixel arrays resulting from a stronger electric field in the thinner areas inside the pores. By gradually increasing the voltage up to 10 V, the emission extends to the areas around the pores. At voltages higher than 10 V, a nonreversible nanopixel to nanoring-like switching of the EL can be observed. After filling the pores with a second blue-emitting conjugated polymer, voltage-dependent reversible color tuning of the EL is achieved in the nanostructured light-emitting bilayers.

High-Capacity Redox Polymer Electrodes: Applications in Molecular and Cellular Processing.

We present methods to fabricate high-capacity redox electrodes using thick membrane or fiber casting of conjugated polymer solutions. Unlike common solution casting or printing methods used in current organic electronics, the presented techniques enable production of PEDOT:PSS electrodes with high charge capacity and the capability to operate under applied voltages greater than 100 V without electrochemical overoxidation. The electrodes are shown integrated into several electrokinetic components commonly used in automated bioprocess or bioassay workflows, including electrophoretic DNA separation and extraction, cellular electroporation/lysis, and electroosmotic pumping. Unlike current metal electrodes used in these applications, the high-capacity polymer electrodes are shown to function without electrolysis of solvent (i.e., without production of excess H+, OH-, and H2O2 by-products). In addition, each component fabricated using the electrodes is shown to have superior capabilities compared with those fabricated with common metal electrodes. These innovations in electrokinetics include a low-voltage/high-pressure electroosmotic pump, and a "flow battery" (in which electrochemical discharge is used to generate electroosmotic flow in the absence of an applied potential). The novel electrodes (and electrokinetic demonstrations) enable new applications of organic electronics within the biology, health care, and pharmaceutical fields.

Effect of pre-aggregation in conjugated polymer solution on performance of diketopyrrolopyrrole-based organic field-effect transistors

In this work, we investigate the effect of pre-aggregated solutions of diketopyrrolopyrrole (DPP)-based conjugated polymers to achieve highly-aligned polymer films for high-performance organic field-effect transistors (OFETs). A suitable marginal solvent is selected for 5-octyl-pentadecyl branched DPP and selenophene-based semiconducting polymer (PDPP(SE)-ε-C8C15) by utilizing the Hansen solubility parameter calculation. The anisotropic one-dimensional aligned PDPP(SE)-ε-C8C15 film was off-center spin-coated from the pre-aggregated solution is studied by atomic force microscopy and polarized UV-Vis absorption spectroscopy. A significantly high hole mobility of 4.16 cm2V−1s−1 was achieved from the OFETs with a unidirectionally-aligned PDPP(SE)-ε-C8C15 film to the transistor channel direction.