Differentiation of Electric Response in Highly Oriented Regioregular Poly(3-hexylthiophene) under Anisotropic Strain

Microstructural Evolution of P(NDI2OD-T2) Films with Different Molecular Weight during Stretching Deformation

Conjugated polymers exhibit excellent electrical and mechanical properties when their molecular weight (Mw) is above the critical molecular weight (Mc). The microstructural changes of polymers under strain are crucial to establish a structure-performance relationship. Herein, the tensile deformation of P(NDI2OD-T2) is visualized, and cracks are revealed either along the (100) crystal plane of side chain packing or along the main chain direction which depends on the Mw is below or above the Mc. When Mw < Mc, the film cracks along the (100) plane under small strains. When Mw > Mc, the polymer chains first undergo stretch-induced orientation and then fracture along the main chain direction at large strains. This is attributed to the fact that the low Mw film exhibits large crystalline domains and the absence of interdomain connectivity, which are vulnerable to mechanical stress. In contrast, the high Mw film displays a nearly amorphous morphology with adequate entanglements, the molecular chains can endure stresses in the stretching direction to release substantial strain energy under greater mechanical deformation. Therefore, the film with Mw > Mc exhibits the optimal electrical and mechanical performances simultaneously, i.e., the electron mobility is retained under 100% strain and after 100 stretching-releasing cycles.

Alignment of organic conjugated molecules for high-performance device applications

High-performance organic semiconductor materials as the electroactive components of optoelectronic devices have attracted much attention and made them ideal candidates for solution-processable, large-area, and low-cost flexible electronics. Especially, organic field-effect transistors (OFETs) based on conjugated semiconductor materials have experienced stunning progress in device performance. To make these materials economically viable, comprehensive knowledge of charge transport mechanisms is required. The alignment of organic conjugated molecules in the active layer is vital to charge transport properties of devices. The present review highlights the recent progress of processing-structure-transport correlations that allow the precise and uniform alignment of organic conjugated molecules over large areas for multiple electronic applications, including OFETs, organic thermoelectric devices (OTEs), and organic phototransistors (OPTs). Different strategies for regulating crystallinity and macroscopic orientation of conjugated molecules are introduced to correlate the molecular packing, the device performance and charge transport anisotropy in multiple organic electronic devices. This article is protected by copyright. All rights reserved.

Controlling the organization and stretchability of poly(3-butylthiophene) spherulites

In this work, we report a simple strategy to readily prepare poly(3-butylthiophene) (P3BT) films with patterned spherulites by brushing the P3BT film surface and annealing the film with carbon disulfide (CS₂) vapor. The spherulites nucleated preferentially at the mechanically scratched areas over the unscratched region of the film. The ridge (formed at the side of the scratch) hinders the diffusion of the P3BT molecules, promoting the aggregation and nucleation of P3BT along the ridge to form spherulites upon the CS₂ vapor-annealing. The sizes of the ridge and the scratch have no effect on the nucleation and crystallization of the patterned spherulites. We evaluated the crack formation of the P3BT films with patterned spherulites in response to mechanical stretching along different directions. When the stretching direction was parallel to the scratching direction, cracks appeared preferentially at the boundary between the ordered spherulites. In contrast, cracks occurred first at the boundary of stochastic nucleated spherulites located away from the patterned spherulites, when the stretching direction was perpendicular to the scratching direction. The patterned spherulites with regulated mechanical properties may find applications in the design and fabrication of stretchable organic optoelectronic devices with enhanced stability and durability.