Semiconducting Polymer Blends Research Articles

Leveraging Insulator's Tacticity in Semiconducting Polymer Blends.

Blending conjugated polymers with insulating matrices is often utilized for engineering extrinsic properties in organic electronics. Semiconductor/insulator blends are typically processed to form a uniformly distributed network of conductive domains within the insulating matrix, marrying electronic and physical properties from individual components. Understanding of polymer-polymer interactions in such systems is thus crucial for property co-optimization. One of the commonly overlooked parameters is the structural configuration of the insulator on the resulting properties, especially the electronic properties. This study investigated how the tacticity of the matrix polymer, among other relevant parameters in play, impacts solid state crystallization in semiconductor/matrix blends and hence the resulting charge transport properties. We found an intricate dependence of the film morphology, aggregation behavior, electronic charge transport, and mixed ionic-electronic coupling properties on the insulator's tacticity. Our experimentally iterative approach shows that for a given application, when selecting semiconductor/insulator combinations, the tacticity of the matrix can be leveraged to optimize performance and vary solid-state structure.

Enhanced Electrical Conductivity and Mechanical Properties of Stretchable Thermoelectric Generators Formed by Doped Semiconducting Polymer/Elastomer Blends.

Recent research efforts have concentrated on the development of flexible and stretchable thermoelectric (TE) materials. However, significant challenges have emerged, including increased resistance and reduced electrical conductivity when subjected to strain. To address these issues, rigid semiconducting polymers and elastic insulating polymers have been incorporated and nanoconfinement effects have been exploited to enhance the charge mobility. Herein, a feasible approach is presented for fabricating stretchable TE materials by using a doped semiconducting polymer blend consisting of either poly(3-hexylthiophene) (P3HT) or poly(3,6-dithiophen-2-yl-2,5-di(2-decyltetradecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-alt-thienylenevinylene-2,5-yl) (PDVT-10) as the rigid polymer with styrene-ethylene-butylene-styrene (SEBS) as the elastic polymer. In particular, the blend composition is optimized to achieve a continuous network structure with SEBS, thereby improving the stretchability. The optimized polymer films exhibit well-ordered microstructural aggregates, indicative of good miscibility with FeCl3 and enhanced doping efficiency. Notably, a lower activation energy and higher charge-carrier concentration contribute to an improved electrical conductivity under high tensile strain, with a maximum output power of 1.39 nW at a ΔT of 22.4 K. These findings offer valuable insights and serve as guidelines for the development of stretchable p-n junction thermoelectric generators based on doped semiconducting polymer blends with potential applications in wearable electronics and energy harvesting.

Polyethylene and Semiconducting Polymer Blends for the Fabrication of Organic Field-Effect Transistors: Balancing Charge Transport and Stretchability

Polyethylene is amongst the most used polymers, finding a plethora of applications in our lives owing to its high impact resistance, non-corrosive nature, light weight, cost effectiveness, and easy processing into various shapes from different sizes. Despite these outstanding features, the commodity polymer has been underexplored in the field of organic electronics. This work focuses on the development of new polymer blends based on a low molecular weight linear polyethylene (LPE) derivative with a high-performance diketopyrrolopyrrole-based semiconducting polymer. Physical blending of the polyethylene with semiconducting polymers was performed at ratios varying from 0 to 75 wt.%, and the resulting blends were carefully characterized to reveal their electronic and solid-state properties. The new polymer blends were also characterized to reveal the influence of polyethylene on the mechanical robustness and stretchability of the semiconducting polymer. Overall, the introduction of LPE was shown to have little to no effect on the solid-state properties of the materials, despite some influence on solid-state morphology through phase separation. Organic field-effect transistors prepared from the new blends showed good device characteristics, even at higher ratios of polyethylene, with an average mobility of 0.151 cm2 V−1 s−1 at a 25 wt.% blend ratio. The addition of polyethylene was shown to have a plasticizing effect on the semiconducting polymers, helping to reduce crack width upon strain and contributing to devices accommodating more strain without suffering from decreased performance. The new blends presented in this work provide a novel platform from which to access more mechanically robust organic electronics and show promising features for the utilization of polyethylene for the solution processing of advanced semiconducting materials toward novel soft electronics and sensors.

Thermomechanical enhancement of DPP‐4T through purposeful π‐conjugation disruption

AbstractThe design of polymer‐based organic semiconductors that offer mechanical deformability while maintaining efficient semiconducting characteristics remains a significant challenge. Recent synthetic efforts have incorporated small alkyl segments directly into otherwise π‐conjugated polymer backbones to enhance processability, mechanical deformability, and other properties. The resulting polymers can be used as stand‐alone materials or as matrix polymers in complementary semiconducting polymer blends offering reasonable charge‐carrier transport properties, thermal healing, and deformability. Here, a family of diketopyrrolopyrrole‐tetrathiophene variants is explored via large‐scale atomistic molecular dynamics simulations to examine the effect of alkyl segments incorporated into the polymer backbone on the polymer structure, dynamics, and thermal properties. Longer alkyl segments lead to polymer chains that are more flexible, compact, and mobile, with lower glass transition temperatures for the condensed phase.

Alignment of linear polymeric grains for highly stable N-type thin-film transistors

Summary Temperature-insensitive properties are attractive for most electronics, including polymeric semiconducting devices. Especially, polymeric field-effect transistors (FETs) with high mobility have been important research targets due to their broad applications. However, polymeric FETs with stable charge transport operating at extremely cold or hot zones are faced with enormous challenges. In this study, the polyacrylonitrile was found to significantly tune the sizes of pre-aggregates of polymers in solutions and the crystallinity of the polymeric films. The orientation of 5–25 μm linear grains in the films were prepared through the bar-coating process with polyacrylonitrile as an additive, which stabilized the electron mobility over a wide range of temperatures. The linear-grain morphology of the film contributed to reducing the holes and grain boundaries in the transport paths of carriers. Typically, the top-gate FETs based on P(NDI2OD-T2) displayed a stable electron transporting behavior from 200 to 460 K, with mobility greater than 3.5 cm2V−1s−1.

Non-destructive depth-dependent morphological characterization of ferroelectric:semiconducting polymer blend films

Herein, we investigate the technologically relevant blend of the ferroelectric polymer poly(vinylidene fluoride-co-trifluoroethylene), P(VDF-co-TrFE), with the semiconducting polymer poly(3-hexylthiophene), P3HT, by means of a combination of scanning probe microscopy techniques, namely atomic force microscopy, conductive force microscopy, kelvin probe force microscopy, and piezoresponse force microscopy. This combination proves to be a powerful tool for the non-destructive morphological reconstruction of multi-functional nano-structured thin films, as those under study. Each modality allows discerning the two blend constituents based on their functionality, and, additionally, probes layers of different thickness with respect to the film surface. The depth-dependent information that is collected allows a qualitative reconstruction of the blend’s composition and morphology both in-plane and out-of-plane of the film. We demonstrate that P3HT exhibits the tendency to reside the film surface at an almost constant composition of 15%, independent of blend’s composition. Increasing the P3HT content in the blend results in the segregation of P3HT at the upper layers of the films, partially buried below a P(VDF-co-TrFE) superficial layer. The depletion of P3HT from the substrate/film interface is reflected by the poor existence of conducting pathways that connect the top and bottom planes of the film. The three-dimensional morphology of this polymer blend that is revealed thanks to the employed techniques deviates substantially from the ideal morphology proposed for the efficient performance of the targeted memory devices.

N-Type Complementary Semiconducting Polymer Blends

Complementary semiconducting polymer blends (c-SPBs) have been demonstrated as an effective approach to balance performance and processing of semiconducting polymers for organic field-effect transi...

Semiconducting Polymer Blends: Spontaneous Phase Separation of Poly(3‐hexylthiophene)s with Different Regioregularity for a Stretchable Semiconducting Film (Adv. Funct. Mater. 35/2019)

Semiconducting Polymer Blends: Spontaneous Phase Separation of Poly(3‐hexylthiophene)s with Different Regioregularity for a Stretchable Semiconducting Film (Adv. Funct. Mater. 35/2019)

Semiconducting polymer blends that exhibit stable charge transport at high temperatures.

Although high-temperature operation (i.e., beyond 150°C) is of great interest for many electronics applications, achieving stable carrier mobilities for organic semiconductors at elevated temperatures is fundamentally challenging. We report a general strategy to make thermally stable high-temperature semiconducting polymer blends, composed of interpenetrating semicrystalline conjugated polymers and high glass-transition temperature insulating matrices. When properly engineered, such polymer blends display a temperature-insensitive charge transport behavior with hole mobility exceeding 2.0 cm2/V·s across a wide temperature range from room temperature up to 220°C in thin-film transistors.

Attaining Melt Processing of Complementary Semiconducting Polymer Blends at 130 °C via Side-Chain Engineering

Complementary semiconducting polymer blends (c-SPBs) have been proposed and tested to achieve melt-processed high-performance organic field-effect transistors (OFETs). Prior to this study, melt processing requires temperatures as high as 180 °C. To implement this technique into low-cost and large-area thin-film manufacturing for flexible organic electronics, semiconducting materials meltable at temperatures tolerable by ubiquitous plastic substrates are still needed. We report here the design and melt processing of a c-SPB consisting of a matrix polymer (DPP-C5) and its fully conjugated analogue. By utilizing a siloxane-terminated alkyl chain and a branched alkyl chain as solubilizing groups, the matrix polymer DPP-C5 presents a melting temperature of 115 °C. The resulting c-SPB containing as low as 5% of the fully conjugated polymer could be melt-processed at 130 °C. The obtained OFET devices exhibit hole mobility approaching 1.0 cm2/(V s), threshold voltages below 5 V, and ION/IOFF around 105. This combination of efficient charge-carrier transport and considerably low processing temperatures bode well for melt processing of semiconducting polymer-based organic electronics.

Zone‐Annealing‐Assisted Solvent‐Free Processing of Complementary Semiconducting Polymer Blends for Organic Field‐Effect Transistors

AbstractSemiconducting polymer thin films, which are usually formed by solution‐casting from their organic solutions, are critical in the development of flexible and printed electronics. To seek out a method that can further improve the electrical properties of semiconducting polymers and also be industrially applicable is of vital significance. In this study, the impact of zone annealing on the charge‐transport properties of diketopyrrolopyrrole‐based complementary semiconducting polymer blends in field‐effect transistor devices is investigated. An average mobility increased from 0.66 to 0.87 cm2 V−1 s−1, with a highest of 1.6 cm2 V−1 s−1, is observed. It is also demonstrated that zone annealing can be integrated with melt processing to realize a solvent‐free process for polymer thin films for organic field‐effect transistors (OFETs) and achieve improved charge transport characteristics with a record mobility of 0.54 cm2 V−1 s−1 among melt‐processed OFETs. This work provides an alternative, green, and sustainable processing method to advance polymer‐based organic electronics.

Complementary Semiconducting Polymer Blends: Influence of Side Chains of Matrix Polymers

The concept of complementary semiconducting polymer blends (c-SPBs) has been recently proposed to achieve enhanced solution processability and/or melt-processing capability for organic electronics. In the previous study, we demonstrated the impact of conjugation-break spacers of matrix polymers. In the current work, we explore the influence of the side chains of the matrix polymer on the physical properties of the pure polymers and their corresponding c-SPBs, including electrical properties and phase transition behaviors. Six diketopyrrolopyrrole (DPP)-based polymers with pentamethylene conjugation-break spacers (CBSs) and various side chains, including branched-alkyl, triethylene glycol (TEG), and siloxane-terminated side chains, were synthesized and characterized. The UV–vis spectra show that the side chains have a noticeable impact on the intermolecular interactions in the solid states. In addition, side chains also have a significant influence on the thermal behaviors of the polymers. Polymers with as...

Melt-Processing of Complementary Semiconducting Polymer Blends for High Performance Organic Transistors.

Melt-processing of complementary semiconducting polymer blends provides an average charge carrier mobility of 0.4 cm2 V-1 s-1 and current on/off ratios higher than 105 , a record performance for melt-processed organic field-effect transistors.

Quantifying the efficiency of förster-assisted optical gain in semiconducting polymer blends by excitation wavelength selective amplified spontaneous emission

We study the correlation between Förster resonance energy transfer (FRET) and optical gain properties in conjugated polymer blends based on regioregular poly(3-hexylthiophene) (P3HT) and poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT). First, FRET dynamics are investigated with femtosecond transient absorption spectroscopy observing a sub-picosecond energy transfer from F8BT to P3HT (550 fs) at medium doping levels (40% wt P3HT in F8BT). Amplified spontaneous emission (ASE) is then characterized in blends upon exciting predominantly the host and guest polymers, respectively. The corresponding density of absorbed photons at threshold conditions is compared upon host or guest photoexcitation as a method to quantitatively determine the FRET-assisted ASE efficiencies. We observe a reduction in ASE efficiency upon host photoexcitation of 20%, in the best case, respect to guest photoexcitation. Our results confirm that even in strongly coupled host:guest mixtures delayed exciton population by energy transfer is subtle to losses ascribed to exciton–exciton annihilation. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 2311–2317.

Dual‐Characteristic Transistors Based on Semiconducting Polymer Blends

Dual‐Characteristic Transistors Based on Semiconducting Polymer Blends

Complementary Semiconducting Polymer Blends: The Influence of Conjugation-Break Spacer Length in Matrix Polymers

The concept of complementary semiconducting polymer blends (c-SPBs) for efficient charge transport was recently proposed and established by our group. In this study, we aim to reveal the influence of the length of conjugation-break spacers (CBSs) on charge transport properties of the matrix polymers and their corresponding complementary polymer blends. A series of 11 DPP-based semiconducting polymers DPP-Cm (m = 2–12) that incorporate CBSs of 2–12 methylene units along the polymer backbones were prepared and characterized. The UV–vis spectra and the ultraviolet photoelectron spectroscopy (UPS) measurements show that the CBS length has marginal influence on the polymer absorption spectra, energy levels, and band gaps. It also has little impact on polymer decomposition temperatures. However, the CBS length has a profound influence on polymer phase transition and the heat of fusion. As for the melt transitions, an odd–even effect is observed from DPP-C2 to DPP-C7, in which polymers with even-numbered CBSs sh...

High mobility transistors based on electrospray-printed small-molecule/polymer semiconducting blends

An electrospray-printing technique was employed for the fabrication of OFETs based on small-molecule:semiconducting polymer blends.

On/off-ratio dependence of bulk hetero junction photodiodes and its impact on electro-optical properties

Optical sensing from the near ultra-violet to the visible range of light is very important for industrial process monitoring, health care, and life science. Here, we present organic photodiodes (OPD), operating between 300 and 750nm wavelength fabricated in bottom absorption geometry with the semiconducting polymer blend PTB7:PC71BM. A maximal responsivity of ~100mA/W at 630nm with 54mW/cm2 light intensity has been achieved at room temperature. An approach to improve the on/off-ratio (light to dark) by modifying the absorption layer thickness has been investigated. The dark current decreases with the thickness of polymer blend PTB7:PC71BM. The transient response for OPD rise- and fall-time is in the μs regime, with an on/off-ratio of four orders of magnitude at −2V bias. The rise of responsivity is tunable by increasing the absorption layer thickness and shows a dependency in relation to dark current and transient response.

Complementary Semiconducting Polymer Blends for Efficient Charge Transport

Charge transport in polymeric thin films is a complicated process, which involves a multitude of coupled electronic events. Because of the growing appeal of semiconducting polymers in organic electronics, it makes the fundamental understanding of charge transport increasingly important. On the other hand, it urges the solution of the processability problem, frequently associated with high-performance polymers. In this study, we introduce complementary semiconducting polymer blends (c-SPBs), aiming to provide solutions for both the fundamental understanding of charge transport and the processability problem. The c-SPBs contain a highly crystalline matrix polymer with intentionally placed conjugation-break spacers (CBSs) along the polymer backbone, thus eliminating intrachain transport, and a tie chain polymer that is a fully conjugated polymer, restoring intrachain transport by connecting π-crystalline aggregates in the matrix polymer. The results show that the addition of as little as 1 wt % tie chain pol...

Liquid crystal alignment behavior and OTFT performance of poly(3-hexylthiophene) blends with comb-like poly(oxyethylene)

Alignment characteristics of nematic liquid crystal (LC) on the surface of conjugated semi-conducting polymer blends with a comb-like polymer were studied. Conoscopic polarized optical microscope images show vertical alignment of LC on the blend films regardless of blend ratio. The LC alignment behavior on the blended film surface can be explained by a preponderance of comb-like polymers at the film surface. The mobility values of organic thin film transistors (OTFT) prepared with the blend film as an active layer are found to be similar to those with a pure conjugated semi-conducting polymer film. This result suggests a novel route for effectively reducing the amount of active semi-conducting polymer without significant deterioration of charge carrier mobility in an OTFT device. Since the LC alignment can be controlled on the surface of channel layer of OTFT by employing the polymer blend as the semi-conducting layer, the LC alignment and OTFT performance with the blend composition can be investigated simultaneously.