Inducing Elasticity through Oligo‐Siloxane Crosslinks for Intrinsically Stretchable Semiconducting Polymers

Abstract

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 ε = 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.

Plastic Deformation of Polymer Blends as a Means to Achieve Stretchable Organic Transistors

“…While there was a drop in charge mobility with strain cycle when the film is held at its lower strain limit, the change is relatively small, particularly compared with changes observed in previous approaches such as semiconductor fibril - elastomer composites. [15, 17] The OTFT results reported here are compared to recent demonstrations in the literature of stretchable organic semiconductors using a similar testing method in Table 1. The comparison includes demonstrations based on block co-polymers, [13] cross-linked polymer semiconductor, [15] crack network films, [37] and fibril-elastomer composite approaches.…”

“…[15, 17] The OTFT results reported here are compared to recent demonstrations in the literature of stretchable organic semiconductors using a similar testing method in Table 1. The comparison includes demonstrations based on block co-polymers, [13] cross-linked polymer semiconductor, [15] crack network films, [37] and fibril-elastomer composite approaches. [16, 18] As shown in Table 1, the findings reported here represent the highest combination of charge mobility and strain-range reported to date.…”

“…More recently, a cross-linked diketopyrrolopyrrole (DPP) polymer was synthesized with a consistent field effect mobility above 0.4 cm 2 V -1 s -1 over a strain range of 20%. [15] Another approach has been to form a fibril network of polymer semiconductor material embedded into an elastomer host. [16-18] However, this approach consists of a sparse network of semiconductor material that may limit performance, and can still result in fibril fracture at large strain.…”

The Effects of Side Chains on the Charge Mobilities and Functionalities of Semiconducting Conjugated Polymers beyond Solubilities

“…a) Reproduced with permission . Copyright 2015, American Chemical Society; b) Reproduced with permission . Copyright 2016, Wiley‐VCH.…”

The Critical Role of Electron‐Donating Thiophene Groups on the Mechanical and Thermal Properties of Donor–Acceptor Semiconducting Polymers

“…[41] Furthermore, carefully designed nonconjugated linkers can also improve the solution processability of DPP polymers, which can be dissolved in benign solvents. [45] Noncovalent crosslinking like hydrogen bonding was also shown to be useful by introducing self-healable electrical and mechanical properties to the polymer system. Wang et al showed that covalent cross-linking between side chains using oligosiloxane can improve the elasticity and the ductility of the system, while maintaining the electrical performance even after 500 cycles of stretching at 20% strain.…”