Asymmetric side-chain engineering in semiconducting polymers: a platform for greener processing and post-functionalization of organic electronics

Abstract

Organic semiconducting polymers are a powerful platform for the design of next-generation technologies due to their excellent optoelectronic properties and solution processability, allowing access to low-cost and scalable manufacturing techniques...

Unravelling the influence of side-chain symmetry on device performance: insights from isoindigo-based polymers in thin-film transistors

“…27 Recently, our group reported the development of an amphiphilic-designed asymmetric isoindigo-bithiophene (iI-BT) polymer with one solubilizing branched alkyl chain and one terminal dodecanol side chain, towards understanding the influence of an asymmetric polar head group on the electronic and processing capabilities of conjugated polymers. 19 In our findings, we discovered that through the incorporation of a simple terminal hydroxyl group per monomer residue, the solubility of the material was able to be altered, becoming processable in greener, non-chlorinated solvents, and achieving higher hole charge carrier mobility when used in OFETs. Notably, when investigated using cryogenic electron microscopy (Cryo-EM), it was found that the polymer exhibited long-range, fiber-like aggregation, suggesting that in addition to the asymmetric nature, the amphiphilic design could promote ordered self-assembly.…”

“…Three different isoindigo-bithiophene (iI-BT) polymers were synthesized by slightly modified procedures from previous literature, as detailed in ESI (Schemes S1-S4 †). 19,26,[32][33][34][35] The synthesis of the three different monomers was performed via alkylation of isoindigo with the selected side-chain halides or tosylates under basic conditions. The symmetric monomers, M1 and M2, only required the addition of one side chain each: hydrophobic compound 1 for M1 and hydrophilic compound 2 for M2.…”

“…As summarized in Table 1, all three polymers demonstrated similar HOMO and LUMO energy levels characteristic of organic semiconducting polymers. 14,19,32 The decomposition temperatures of the polymers were measured by thermogravimetric analysis (Fig. S4 †).…”

“…As discussed in previous reports, this phenomenon may be the result of charge injection from the gold source electrode into the polymer channel, thus building up some contact resistance at low V D and leading to initially reversed current. 19,40 To better contrast the performances of the three different polymers, Fig. S5 † illustrates the output curves of the three polymers along the same scale range of I D (from −3.0 × 10 −7 to 5.0 × 10 −8 A).…”

“…[14][15][16] Among the various strategies that have been developed for tuning the solid-state structure and packing of conjugated polymers for electronic performance, asymmetric side-chain engineering, defined as functionalizing the semiconducting polymer with two different side-chain motifs, has become an emerging approach to modulate the thermomechanical, optoelectronic, and solid-state properties of these materials in organic electronics. 14,[17][18][19][20][21][22][23][24] Particularly, the combination of solubilizing branched alkyl chains in combination with carbosilane chains has been shown to improve the charge carrier mobility, power conversion efficiency (PCE), and stability of materials in thin-film transistors and photovoltaic devices. 14,21,24 Notably, Lin et al reported a systematic study of a library of asymmetric side chain isoindigo-based polymers using different types of carbosilane groups.…”