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

Abstract

Nonconjugated segments in polymer semiconductors have been utilized to improve the processability of semiconducting polymers. Recently, several reports have described the improvement of stretchability of polymer semiconductors by incorporating nonconjugated spacers. However, the effect of relative flexibility of such conjugation breakers on mechanical and electrical properties has not yet been studied systematically. Here, conjugation breakers with different chain length and rigidity are incorporated into the backbone of diketopyrrolopyrrole-based semiconductors. Interestingly, it is observed that the longer and more flexible conjugation breakers result in greater ductility and lower elastic modulus without significantly affecting mobility. The enhancement of stretchability is attributed to the reduced modulus and the decrease in crystallinity, as confirmed by X-ray diffraction. With this newly established molecular design, transistors are prepared with a semiconducting polymer containing dodecyl segments as conjugation breakers. It is observed that this polymer retains a mobility of >0.36 cm 2 V −1 s −1 at 100% strain, and after 100 cycles at 50% strain. Finally, its high stability against strain is also observed with a fully stretchable transistor fabricated. Taken together, the above results indicate that molecular engineering of conjugated polymers, i.e., by incorporating suitable conjugation breakers, can effectively tune mechanical properties without significantly compromising their electrical properties.

Glass Transition Phenomenon for Conjugated Polymers

“…Recently, D‐A CPs with non‐conjugated spacers in the backbone have received considerable interest, owing to fact that these flexible spacers yield great improvement in the deformability while good charge transport mobility is not detrimentally affected . Meanwhile, as suggested by molecular dynamics simulation, the dynamics of polymer chains can be enhanced by the nonconjugated flexible spacers . On the contrary, with the insertion of a conjugated spacer like thiophene unit into the polymer backbone while maintaining the same sidechain length, PA4T‐BC2‐C10C12 shows a 25 °C increase in T g than that of PA3T‐BC2‐C10C12 (chemical structures shown in Table ).…”

F4‐TCNQ as an Additive to Impart Stretchable Semiconductors with High Mobility and Stability

“…Several strategies have been used to overcome this tradeoff. For example, researchers have reported the usage of chemically bound rubbery blocks, [ 30,31 ] soft crosslinkers, [ 32 ] energy dissipating moieties, [ 23 ] host elastomeric matrices, [ 25,27,33–35 ] nanoconfined semiconducting polymers, [ 7,22,36 ] conjugation breakers, [ 37–39 ] and molecular additives. [ 40 ] Such strategies have resulted in improved stretchability of semiconducting polymers, along with small decrease in mobility.…”

Material‐Based Approaches for the Fabrication of Stretchable Electronics

“…The stretchability of such polymers could be enhanced by modifying the chemical structure of the mono mer, including their backbone and side-chains, which greatly affect the chain dynamics and the internal morphology of the polymer. [208][209][210][211][212] Recently, Oh et al [116] introduced series of semiconducting co-polymers to manipulate the material properties of semiconducting polymers, also known as molecular structure engineering (Figure 5a). By inserting nonconjugated 2,6-pyridinedicarboxamide (PDCA) segments into the repeating segments of DPP-based original polymers, conjugation inside the polymeric network was disrupted and hydrogen bonds were newly formed between the adjacent polymer chains (P1 to P4).…”