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Recent work in structure–processing relationships of polymer semiconductors have demonstrated the versatility and control of thin-film microstructure offered by meniscusguided coating (MGC) techniques. Here, we analyze the qualitative and quantitative aspects of solution shearing, a model MGC method, using coating blades augmented with arrays of pillars. The pillars induce local regions of high strain rates—both shear and extensional—not otherwise possible with unmodified blades, and we use fluid mechanical simulations to model and study a variety of pillar spacings and densities. We then perform a statistical analysis of 130 simulation variables to find correlations with three dependent variables of interest: thin-film degree of crystallinity and transistor field-effect mobilities for charge-transport parallel (Μpara) and perpendicular (Μperp) to the coating direction. Our study suggests that simple fluid mechanical models can reproduce substantive correlations between the induced fluid flow and important performance metrics, providing a methodology for optimizing blade design. Polymer semiconductors have opened up a new frontier of electronics that can be flexible, stretchable, implantable, or biodegradable. While the chemical and electronic properties of these materials are important for their function as the active material in organic electronic devices, the manner by which these organic semiconductors are deposited onto a substrate can significantly influence its charge-transport properties. While a variety of techniques have been investigated to enhance charge-transport behavior, there are few reports approaching the issue in terms of the fluid dynamical considerations relevant during deposition from the solution phase. In this article, we analyze the fluid flow that occurs during thin-film deposition by solution shearing, a representative meniscusguided coating method amenable to high-throughput processing. We investigate a variety of variables related to fluid flow that can be estimated from fluid mechanical simulations of solution shearing with a coating blade patterned with a regular array of pillars used to induce higher fluid strain rates. We find correlations suggestive of underlying relationships between strain rates associated with certain directions and polymer charge-transport properties in the final deposited film. This article establishes a statistical approach using simulation data that can guide patterned blade design to enhance polymer deposition and realize high-performance devices.

One major advantage of organic electronics is their superior processability relative to traditional silicon-based materials. However, most high-performing polymer semiconductors exhibit poor solubility and require toxic chlorinated solvents coupled with inefficient coating methods such as spin-coating for device fabrication. Therefore, developing polymer semiconductors that are processable in environmentally benign solvents and compatible with effective printing techniques while maintaining good charge transport properties is crucial for the industrialization of low-cost and lightweight plastic electronics. In this study, alkyl flexible linkers with branched tertiary carbon atoms are inserted to a high-mobility diketopyrrolopyrrole-based polymer backbone to suppress polymer aggregation in solution, decrease crystallinity, and increase free volume. The polymer readily dissolves in industrial solvents and shows a 70-fold increase in solubility compared to its fully conjugated counterpart. Furthermore, due t...

Crucial to the development and refinement of organic electronics is a fundamental understanding of how deposition processes affect the active material’s resulting microstructure in the thin film. Meniscus-guided coating (MGC) methods are attractive because of their amenability to high-throughput, industrially relevant continuous processes like roll-to-roll deposition, but the mechanism of solid film formation has not been elucidated and is valuable for the precise control of thin-film morphology and thus ultimate device performance. In this work, we investigate the microstructural evolution of thin films of a diketopyrrolopyrrole–terthiophene donor–acceptor polymer semiconductor using both in situ and ex situ X-ray diffraction methods. On the basis of a comparison of disorder between the film bulk and the top surface and a depth profiling of the out-of-plane orientation of crystallites, we find that faster coating speeds introduce more disorder into the resulting films because the stochastic nucleation of...

For miniaturized capacitive energy storage, volumetric and areal capacitances are more important metrics than gravimetric ones because of the constraints imposed by device volume and chip area. Typically used in commercial supercapacitors, porous carbons, although they provide a stable and reliable performance, lack volumetric performance because of their inherently low density and moderate capacitances. Here we report a high-performing electrode based on conductive hexaaminobenzene (HAB)-derived two-dimensional metal−organic frameworks (MOFs). In addition to possessing a high packing density and hierarchical porous structure, these MOFs also exhibit excellent chemical stability in both acidic and basic aqueous solutions, which is in sharp contrast to conventional MOFs. Submillimetre-thick pellets of HAB MOFs showed high volumetric capacitances up to 760 F cm−3 and high areal capacitances over 20 F cm−2. Furthermore, the HAB MOF electrodes exhibited highly reversible redox behaviours and good cycling stability with a capacitance retention of 90% after 12,000 cycles. These promising results demonstrate the potential of using redox-active conductive MOFs in energy-storage applications. Metal–organic frameworks (MOFs) are attractive electrodes for supercapacitors but generally suffer from low electric conductivity and chemical stability. Here the authors report stable conductive MOFs based on hexaminobenzene linker with volumetric and areal capacitances in excess of 700 F per cm3 and 15 F per cm2, respectively.

The promise of wearable and implantable devices has made stretchable organic semiconductors highly desirable. Though there are increasing attempts to design intrinsically stretchable conjugated polymers, their performance in terms of charge carrier mobility and maximum fracture strain is still lacking behind extrinsic approaches (i.e., buckling, Kirigami interconnects). Here, polymer crosslinking with flexible oligomers is applied as a strategy to reduce the tensile modulus and improve fracture strain, as well as fatigue resistance for a high mobility diketopyrrolopyrrole polymer. These polymers are crosslinked with siloxane oligomers to give stretchable films stable up to a strain e = 150% and 500 strain-and-release cycles of 100% strain without the formation of nanocracks. Organic field-effect transistors are prepared to assess the electrical properties of the crosslinked film under cyclic strain loading. An initial average mobility (μavg) of 0.66 cm2 V−1 s−1 is measured at 0% strain. A steady μavg above 0.40 cm2 V−1 s−1 is obtained in the direction perpendicular to the strain direction after 500 strain-and-release cycles of 20% strain. The μavg in the direction parallel to strain, however, is compromised due to the formation of wrinkles.

Increasing performance demands and shorter use lifetimes of consumer electronics have resulted in the rapid growth of electronic waste. Currently, consumer electronics are typically made with nondecomposable, nonbiocompatible, and sometimes even toxic materials, leading to serious ecological challenges worldwide. Here, we report an example of totally disintegrable and biocompatible semiconducting polymers for thin-film transistors. The polymer consists of reversible imine bonds and building blocks that can be easily decomposed under mild acidic conditions. In addition, an ultrathin (800-nm) biodegradable cellulose substrate with high chemical and thermal stability is developed. Coupled with iron electrodes, we have successfully fabricated fully disintegrable and biocompatible polymer transistors. Furthermore, disintegrable and biocompatible pseudo-complementary metal–oxide–semiconductor (CMOS) flexible circuits are demonstrated. These flexible circuits are ultrathin ( 2 ) with low operating voltage (4 V), yielding potential applications of these disintegrable semiconducting polymers in low-cost, biocompatible, and ultralightweight transient electronics.

Organic field-effect transistors have gained much attention for their potential use in low-cost, large-area, flexible electronics. High-performance organic transistors require a low density of grain boundaries in their organic films and a reduction of charge traps at the semiconductor-dielectric interface for efficient charge transport. In this respect, the role of the dielectric material is crucial because it primarily determines the growth of the film and the interfacial trap density. Here, we demonstrate the use of chemical-vapor-deposited hexagonal boron nitride (CVD h-BN) as a scalable growth template/dielectric for high-performance organic field-effect transistors. The field-effect transistors based on C60 films grown on single-layer CVD h-BN exhibit an average mobility of 1.7 cm^2V^-1s^-1 and a maximum mobility of 2.9 cm^2V^-1s^-1 with on/off ratios of 10^7. The structural and morphology analysis shows that the epitaxial, two-dimensional growth of C60 on CVD h-BN is mainly responsible for the superior charge transport behavior. We believe that CVD h-BN can serve as a growth template for various organic semiconductors, enabling large-area, high-performance flexible electronics.

The electronic devices that play a vital role in our daily life are primarily based on silicon and are thus rigid, opaque, and relatively heavy. However, new electronics relying on polymer semiconductors are opening up new application spaces like stretchable and self-healing sensors and devices, and these can facilitate the integration of such devices into our homes, our clothing, and even our bodies. While there has been tremendous interest in such technologies, the widespread adoption of these organic electronics requires low-cost manufacturing techniques. Fortunately, the realization of organic electronics can take inspiration from a technology developed since the beginning of the Common Era: printing. This review addresses the critical issues and considerations in the printing methods for organic electronics, outlines the fundamental fluid mechanics, polymer physics, and deposition parameters involved in the fabrication process, and provides future research directions for the next generation of printed polymer electronics., A primary advantage of polymer semiconductors compared to silicon-based semiconductors lies in its capability of being solution-processed for the large-scale fabrication of electronics that can be flexible, stretchable, implantable, biodegradable, and self-healing. Here, Gu and Shaw et al. review recent developments in meniscus-guided coating that can control thin-film morphology.

The alignment of organic semiconductors (OSCs) in the active layers of electronic devices can confer desirable properties, such as enhanced charge transport properties due to better ordering, charge transport anisotropy for reduced device cross-talk, and polarized light emission or absorption. The solution-based deposition of highly aligned small molecule OSCs has been widely demonstrated, but the alignment of polymeric OSCs in thin films deposited directly from solution has typically required surface templating or complex pre- or postdeposition processing. Therefore, single-step solution processing and the charge transport enhancement afforded by alignment continue to be attractive. We report here the use of solution shearing to tune the degree of alignment in poly(diketopyrrolopyrrole-terthiophene) thin films by controlling the coating speed. A maximum dichroic ratio of ∼7 was achieved on unpatterned substrates without any additional pre- or postdeposition processing. The degree of polymer alignment was found to be a competition between the shear alignment of polymer chains in solution and the complex thin film drying process. Contrary to previous reports, no charge transport anisotropy was observed because of the small crystallite size relative to the channel length, a meshlike morphology, and the likelihood of increased grain boundaries in the direction transverse to coating. In fact, the lack of aligned morphological structures, coupled with observed anisotropy in X-ray diffraction data, suggests the alignment of polymer molecules in both the crystalline and the amorphous regions of the films. The shear speed at which maximum dichroism is achieved can be controlled by altering deposition parameters such as temperature and substrate treatment. Modest changes in molecular weight showed negligible effects on alignment, while longer polymer alkyl side chains were found to reduce the degree of alignment. This work demonstrates that solution shearing can be used to tune polymer alignment in a one-step deposition process not requiring substrate patterning or any postdeposition treatment.

The solid-state packing and polymer orientation relative to the substrate are key properties to control in order to achieve high charge carrier mobilities in organic field effect transistors (OFET). Intuitively, shorter side chains are expected to yield higher charge carrier mobilities because of a denser solid state packing motif and a higher ratio of charge transport moieties. However our findings suggest that the polymer chain orientation plays a crucial role in high-performing diketopyrrolopyrrole-based polymers. By synthesizing a series of DPP-based polymers with different branched alkyl side chain lengths, it is shown that the polymer orientation depends on the branched alkyl chain lengths and that the highest carrier mobilities are obtained only if the polymer adopts a mixed face-on/edge-on orientation, which allows the formation of 3D carrier channels in an otherwise edge-on-oriented polymer chain network. Time-of-flight measurements performed on the various polymer films support this hypothesis by showing higher out-of-plane carrier mobilities for the partially face-on-oriented polymers. Additionally, a favorable morphology is mimicked by blending a face-on polymer into an exclusively edge-on oriented polymer, resulting in higher charge carrier mobilities and opening up a new avenue for the fabrication of high performing OFET devices.