Taming Charge Transport and Mechanical Properties of Conjugated Polymers with Linear Siloxane Side Chains

Abstract

A series of conjugated polymers on the basis of diketopyrrolopyrrole and thienothiophene with different lengths of linear hybrid siloxane-terminal side chains were designed and synthesized. The number of silicon atoms in the side chains was 3, 5, and 7 (PTDPPTT-Si-3, PTDPPTT-Si-5, and PTDPPTT-Si-7, respectively, with two accompanying reference polymers, PTDPPTT-Ref-1 and PTDPPTT-Ref-2). Compared with PTDPPTT-Si-3, PTDPPTT-Si-5 and PTDPPTT-Si-7 had longer siloxane-terminal groups, which allowed them to maintain higher solution processability and excellent mobilities of 2.44 and 2.18 cm −2 V −1 s −1 , respectively. In addition, the extended siloxane segment has high flexibility, which provides a good opportunity to improve the mechanical properties of rigid conjugated polymers. PTDPPTT-Si-7 exhibited excellent ductility and a low tensile modulus of 108 ± 21 MPa and retained 80% of its initial electrical properties under 100% stretching, indicating that long linear siloxane side chainmodified semiconductor polymers have great potential for wearable electronics. Our research provides an important guiding principle concerning the molecular engineering of semiconductor polymers with siloxane side chains.

Aggregation Behavior and Electrical Performance Control of Isoindigo-Based Conjugated Polymers via Carbosilane Side Chain Engineering

“…Conjugated polymers (CPs) have great potential as organic semiconductors for applications in the next-generation electronics because of their flexibility, light weight, and solution processability. − The rigid backbones of CPs are generally substituted with flexible side chains, not only to solubilize but also to optimize the conformation and aggregation behavior of the main chain to achieve improved semiconducting performance. − For example, hydrophobic fluorinated side chains have demonstrated the ability of isolating atmospheric water/oxygen , and promoting close packing of naphthalene diimide-based CPs for enhanced charge transport property and air stability . The bulky siloxane side chains, even placed farther away from the conjugated backbone, imparted good solubility to the polymers while allowing for tight molecular packing. ,− In our previous work, by moving the branch point of alkyl side chains away from the diketopyrrolopyrrole backbone, CPs that formed well-aligned films under shear force for organic thin-film transistors (OTFTs) were obtained . Comparative studies confirmed that a favorable branch point position determined the formation of the alignable anisotropic precursor in solution and was critical for improved electrical performance.…”

Role of Molecular Weight in the Mechanical Properties and Charge Transport of Conjugated Polymers Containing Siloxane Side Chains

“…[19] Recently, our group has synthesized long, linear siloxane side chains and found that they were effective in improving the solubility of conjugated polymers. [20][21][22][23] The introduction of siloxane side chains also improves the flexibility of the polymer chains and reduces the film crystallinity and elastic modulus, thus significantly enhancing the stretchability of conjugated polymers. [22] However, the effect of the molecular weight on the structure and properties of conjugated polymers with siloxane side chain modifications has not been investigated.…”

“…[20][21][22][23] The introduction of siloxane side chains also improves the flexibility of the polymer chains and reduces the film crystallinity and elastic modulus, thus significantly enhancing the stretchability of conjugated polymers. [22] However, the effect of the molecular weight on the structure and properties of conjugated polymers with siloxane side chain modifications has not been investigated. Therefore, it is important to explore the effect of the molecular weight on the structure and properties of conjugated polymers modified with siloxane side chains.…”

Small-Molecule Electron Transport Layer with Siloxane-Functionalized Side Chains for Nonfullerene Organic Solar Cells

“…In methanol solution and thin films (Figures d and S3), PDI-N and PDI-OSi exhibit identical absorption bands in the 400–600 nm range because they have the same conjugated backbone structure. Compared to PDI-N, PDI-OSi displays a diminished vibration intensity of the absorption peak near 300 nm, which signals that the PDI backbone conformation is more bent because siloxane side chains aggrandize the spatial repulsion between the molecular side chains . Compared with the solution state, the absorption wavelengths of the thin-film states of PDI-N and PDI-OSi exhibit a significant red shift (∼83 nm for the former and ∼29 nm for the latter), as shown in Figure d, which is primarily on account of the stacking of the PDI backbone by intermolecular interactions.…”