Elastomeric Polydimethylsiloxane Endcaps to Achieve Solubility and Melt-Processability in DPP-based Polymer Semiconductors

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Polymer semiconductors (PSCs) combining high charge carrier mobility with superior mechanical properties and solution-processability are ideal candidates to achieve large-area electronic applications on flexible substrates, e.g. displays, sensors or photovoltaics. The electronic performance of PSCs improved considerably in the recent years, and state-of-the-art donor-acceptor (D-A) polymers now routinely achieve charge carrier mobilities exceeding 1 cm2 V-1s-1, the classic benchmark of amorphous silicon. Yet the control over the physical properties of the materials did not progress at the same rate, and current high performance PSCs suffer from a range of shortcomings closely related to the conjugated molecular structure and well-stacked morphology which bestow record-setting charge carrier mobilities: They are strongly aggregated, leading to brittle films and limiting flexible applications, and are furthermore poorly soluble, causing batch-to-batch variations in polymer synthesis and poor reproducibility of device fabrication. Solution-deposition of these materials usually requires elevated temperatures, dilute solutions, and halogenated solvents, conditions which are hampering cost-efficient printing processes. An even more interesting fabrication approach would be the solvent-free processing from polymer melt, which would eliminate toxic solvents from the process and grant higher reproducibility and morphology control. Yet while melt-processing is a standard technique in many fields of polymer research and processing, only few melt-processable D-A PSCs were obtained and investigated so far. So far, the tuning of the physical properties of PSCs, such as solubility, melting point and tensile modulus, is explored by either modifying the backbone or the side chains. Endcap engineering could be a new strategic pathway to improve physical properties, e.g. solubility, tune mechanical characteristics, e.g. stretchability, and enable the melt-processing of PSCs. In this project, we will endcap state-of-the-art diketopyrrolopyrrole (DPP) based PSCs with elastomeric polydimethylsiloxane (PDMS) chains, and investigate the resulting second order block co-polymers physico-chemically, electrically and with regards to their morphology and phase separation. The elastomer-endcapped PSCs are expected to exhibit enhanced solubility and, for higher PDMS-to-PSC ratios, melt-processability.