The pursuit of intelligent optoelectronics could have profound implications on our future daily life. Simultaneous enhancement of the electrical performance, mechanical stretchability, and optical transparency of semiconducting polymers may significantly broaden the spectrum of realizable applications for these materials in future intelligent optoelectronics, i.e., wearable devices, electronic skin, stretchable displays, and a vast array of biomedical sensors. Here, semiconducting films with significantly improved mechanical elasticity and optical transparency, without affecting the film’s electronic conductivity even under 100% strain, were prepared by blending only a small amount (below 1 wt %) of either p-type or n-type commercial semiconductor polymers. We demonstrate that a self-organized versatile conjugated polymer film displaying an interpenetrating polymer network is formed in the semiconducting films and is crucial for the observed enhancement of elasticity, optical transparency, and charge-carrier mobility. On the basis of this versatile semiconducting film, we explored a new practical approach to directly integrate all the stretchable components for a large area transistor array through solution processing and a final single, mechanical peel-off step. We demonstrate robust transistor arrays exhibiting charge carrier mobilities above 1.0 cm2/V s with excellent durability, even under 100% strain. We believe our achievements will have great impact on stretchable optoelectronic devices for practical applications and represent promising directions for industry-scale production of stretchable displays and wearable electronic devices.

Long-range ordering emerges in poly­(3-hexylthiophene) (P3HT) solutions during time-dependent aggregation. Here, aggregation of P3HT in chloroform solution was induced by ultrasonication, aging, and combinations thereof. UV–vis spectroscopy and polarized optical microscopy demonstrated that long-range ordering in the solution and subsequently the solid state depends on assembled P3HT fiber length, as determined by film atomic force microscopy. Ultrasonication induced the formation of fibers that were relatively short compared to those obtained through aging. As a result, ultrasonication afforded isotropic solutions and films, whereas aging afforded anisotropic solutions and films. The impact of fiber length and anisotropy on macroscopic charge transport performance was evaluated using an organic field-effect transistor (OFET) architecture. Both aged and sonicated solutions exhibited charge carrier mobilities that were an order of magnitude higher than that obtained for pristine samples. Aging of sonicated solutions enabled semiconducting thin films with significantly higher mobilities (1.5 × 10–1 cm2 V–1 s–1) than those of either solution processing technique. Furthermore, the results indicate that grain boundary morphology has a significant impact on macroscopic charge carrier mobility. Grazing incidence wide-angle X-ray scattering demonstrated that the combined sonication/aging method affords a solidified film where the semiconductor exhibits a highly edge-on orientation. The results suggest that the nucleation and growth of aggregates can be controlled via solution processing methods and thus may allow the manipulation of active layer orientation, crystal packing density, and crystallite size. The investigation provides insight into the conjugated polymer solution process parameters that impact polymer ordering and aggregation in solution and resultant thin films for high-performance organic electronic devices.

The electron deficiency and trans-planar conformation of bithiazole is potentially beneficial for the electrontransport performance of organic semiconductors. However, the incorporation of bithiazole into polymers through a facile synthetic strategy remains a challenge. Herein, 2,2′-bithiazole was synthesized in one step and copolymerized with dithienyldiketopyrrolopyrrole to afford poly(dithienyldiketopyrrolopyrrole-bithiazole), PDBTz. PDBTz exhibited electron mobility reaching 0.3 cm 2 V −1 s −1 in organic field-effect transistor (OFET) configuration; this contrasts with a recently discussed isoelectronic conjugated polymer comprising an electron-rich bithiophene and dithienyldiketopyrrolopyrrole, which displays merely hole-transport characteristics. This inversion of charge-carrier transport characteristics confirms the significant potential for bithiazole in the development of electron-transport semiconducting materials. Branched 5-decylheptacyl side chains were incorporated into PDBTz to enhance polymer solubility, particularly in nonhalogenated, more environmentally compatible solvents. PDBTz cast from a range of nonhalogenated solvents exhibited film morphologies and field-effect electron mobility similar to those cast from halogenated solvents.

Experimental details, synthesis and analysis of the monomers and polymers, additional figures, and additional characterization data (PDF).

High-efficiency organic solar cells (OSCs) can be produced through optimization of component molecular design, coupled with interfacial engineering and control of active layer morphology. However, vertical stratification of the bulk-heterojunction (BHJ), a spontaneous activity that occurs during the drying process, remains an intricate problem yet to be solved. Routes toward regulating the vertical separation profile and evaluating the effects on the final device should be explored to further enhance the performance of OSCs. Herein, we establish a connection between the material surface energy, absorption, and vertical stratification, which can then be linked to photovoltaic conversion characteristics. Through assessing the performance of temporary, artificial vertically stratified layers created by the sequential casting of the individual components to form a multilayered structure, optimal vertical stratification can be achieved. Adjusting the surface energy offset between the substrate results in donor and acceptor stabilization of that stratified layer. Further, a trade-off between the photocurrent generated in the visible region and the amount of donor or acceptor in close proximity to the electrode was observed. Modification of the substrate surface energy was achieved using self-assembled small molecules (SASM), which, in turn, directly impacted the polymer donor to acceptor ratio at the interface. Using three different donor polymers in conjunction with two alternative acceptors in an inverted organic solar cell architecture, the concentration of polymer donor molecules at the ITO (indium tin oxide)/BHJ interface could be increased relative to the acceptor. Appropriate selection of SASM facilitated a synchronized enhancement in external quantum efficiency and power conversion efficiencies over 10.5%.

Although stretchable polymer-based devices with promising electrical performance have been produced through the polymer blend strategy, the interplay between the blend film microstructure and macroscopic device performance under deformation has yet to be unambiguously articulated. Here, we discuss the formation of robust semiconducting networks in blended films through a thermodynamic perspective. Thermodynamic behavior along with the linear absorption and photoluminescence measurements predict the competition between polymer phase separation and semiconductor crystallization processes during film formation. Semiconducting films comprised of different pi-conjugated semiconductors were prepared and shown to have mechanical and electronic properties similar to those of films comprised of a model P3HT and PDMS blend. These results suggest that a film’s microstructure and therefore robustness can be refined by controlling the phase separation and crystallization behavior during film solidification. Fine-tuning a film’s electrical, mechanical, and optical properties during fabrication will allow for advanced next-generation of optoelectronic devices.

The ability to process conjugated polymers via aqueous solution is highly advantageous for reducing the costs and environmental hazards of large scale roll-to-roll processing of organic electronics. However, maintaining competitive electronic properties while achieving aqueous solubility is difficult for several reasons: (1) Materials with polar functional groups that provide aqueous solubility can be difficult to purify and characterize, (2) many traditional coupling and polymerization reactions cannot be performed in aqueous solution, and (3) ionic groups, though useful for obtaining aqueous solubility, can lead to a loss of solid-state order, as well as a screening of any applied bias. As an alternative, we report a multistage cleavable side chain method that combines desirable aqueous processing attributes without sacrificing semiconducting capabilities. Through the attachment of cleavable side chains, conjugated polymers have for the first time been synthesized, characterized, and purified in organic solvents, converted to a water-soluble form for aqueous processing, and brought through a final treatment to cleave the polymer side chains and leave behind the desired electronic material as a solvent-resistant film. Specifically, we demonstrate an organic soluble polythiophene that is converted to an aqueous soluble polyelectrolyte via hydrolysis. After blade coating from an aqueous solution, UV irradiation is used to cleave the polymer’s side chains, resulting in a solvent-resistant, electroactive polymer thin film. In application, this process results in aqueous printed materials with utility for solid-state charge transport in organic field effect transistors (OFETs), along with red to colorless electrochromism in ionic media for color changing displays, demonstrating its potential as a universal method for aqueous printing in organic electronics.

Solution shearing has attracted great interest for the fabrication of robust and reliable, high performance organic electronic devices, owing to applicability of the method to large area and continuous fabrication, as well as its propensity to enhance semiconductor charge transport characteristics. To date, effects of the design of the blade shear features (especially the microfluidic shear design) and the prospect of synergistically combining the shear approach with an alternate process strategy have not been investigated. Here, a generic thin film fabrication concept that enhanced conjugated polymer intermolecular alignment and aggregation, improved orientation (both nanoscale and long-range), and narrowed the π-π stacking distance is demonstrated for the first time. The impact of the design of shearing blade microfluidic channels and synergistic effects of fluid shearing design with concomitant irradiation strategies were demonstrated, enabling fabrication of polymer-based devices with requisite morphologies for a range of applications.