Exploiting π–π Stacking for Stretchable Semiconducting Polymers

Abstract

Although intermolecular charge transport is known to occur via π–π stacking, the influence of π–π stacking on the mechanical properties of polymers has received little attention compared with other dynamic noncovalent interactions. Herein, we demonstrate a method to enhance stretchability via lowering crystallinity and increasing π–π stacking of thiophene-based random copolymer chains, which causes π–π stacking-induced polymer networks to form within the fully conjugated semiconducting polymer matrix. The polymer networks contain coiled amorphous chains that aid energy dissipation when the polymer film is subjected to strain; furthermore, the π–π stacking prevents the chains from irreversible sliding out of place due to the applied strain and provides interchain charge transport. Consequently, we are able to improve the polymer’s mechanical properties such as elongation at break, tensile strength, and toughness along with charge mobility. Additionally, our polymer shows great tolerance to a 40% strain without a decrease in mobility while maintaining a stable electrical performance even after 5000 stretching cycles at 30% strain.

Enhanced miscibility and strain resistance of blended elastomer/π‐conjugated polymer composites through side chain functionalization towards stretchable electronics

“…). This further corresponds with previous work where brittleness in polythiophenes was reduced by irregular side chains . These results demonstrate that increased crack onset strain was achieved in PB/P3Br x HT through improved compatibility by side chain functionalization.…”

Spontaneous Phase Separation of Poly(3‐hexylthiophene)s with Different Regioregularity for a Stretchable Semiconducting Film

“…Similarly, ultrasonicated RR PHT/PS (1:7) blend solutions, as a control system, showed absorption peaks at λ 2 = 566 and λ 3 = 615 nm, which tended to be slightly blueshifted with an increase in t sonic , as reported in literature (Figure a,b) . For the ultrasound‐assisted neat RR PHT and RR PHT/PS films, the intensities of the absorption peaks at λ 2 and λ 3 increased significantly in comparison to those of the pristine spun‐cast films (Figure d,e) …”

“…Note that all the UV–vis spectra of rr PHT‐loaded RR PHT blends were plotted after normalizing, i.e., subtracting the broad absorption spectra of rr PHT ranging from 300 to 800 nm from the original spectra (Figure S4a,b, Supporting Information). As shown in Figure a,b, the UV–vis absorption spectra of pristine (i.e., not ultrasonicated) neat RR PHT and RR PHT/PS blend solutions showed a broad peak (marked as 1) at wavelength (λ 1 ) = 452 nm, corresponding to the intrachain π–π* transition of RR PHT . On the other hand, the absorption peak of rr PHT was indicated at 430 nm and blue‐shifted, originating from a decrease in the conjugation length on the twisted rr PHT backbones .…”

“…Peng et al have reported a stretchable OTFT based on a PHT–poly(methyl acrylate)–PHT triblock copolymer film with a good Young's modulus of 6 MPa even at strain of 140%, yielding a low µ value of below 10 −3 cm 2 V −1 s −1 . Son and co‐workers have reported that RR PHT copolymer derivatives chemically modified with thiophene segments generated better π‐conjugated and deformable film structures; an OTFT with 40% stretched semiconducting film had a µ value of ≈0.04 cm 2 V −1 s −1 , equal to ≈50% of the unstretched device . As another simple approach, the physical blending of semiconducting polymers with elastomers or amorphous polymers is also practicable for the fabrication of stretchable semiconducting films.…”

Effect of Nonconjugated Spacers on Mechanical Properties of Semiconducting Polymers for Stretchable Transistors

“…Along with the DMA measurement, X‐ray diffraction analysis again confirms that C12‐DPP exhibited lowest degree of ordering. In amorphous domains, coiled polymer chains can be stretched more easily than in crystalline domains, and stretching polymer chains can dissipate energy under stress . Therefore, low crystallinity of C12‐DPP induced by the flexible dodecyl spacer is the primary reason for its high stretchability.…”