In the past two decades, significant progress has been made in the fabrication of polymer-based devices, such as organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) or organic photovoltaics (OPVs), predominantly due to important improvements of existing materials and the creation of a wealth of novel compounds. Many challenges, however, still exist: from achieving reliable device fabrication, increasing the device stability and, more fundamentally, gaining a complete understanding how structural features over all length scales affect important optoelectronic and photophysical processes in such polymers, including charge transport, charge generation, and general photovoltaic processes. Here we demonstrate how classical polymer science tools can be used to elucidate the structure development of semiconducting polymers from the liquid phase, how such knowledge can be exploited to manipulate their phase transformations and solid-state order and, in turn, their electronic features and device performances. To exemplify our approach, we discuss bulk heterojunction solar cells, which are comprised of active layers that are generally comprised of a complex phase morphology where intermixed and neat phases of the donor and acceptor material co-exist. We show that the fate of photogenerated electron/hole pairs –whether they will dissociate to free charges or geminately recombine– is determined at ultrafast times, despite the fact that their actual spatial separation can be much slower. The local arrangement of the donor and acceptor plays a critical role in this phenomena as we demonstrate on a series of donor polymer:fullerenes binaries by combining 2D-NMR data with time-resolved ultra-fast spectroscopy results as well as detailed structural data. We discuss that similar considerations apply also to other functional blends, such as semiconducting polymer:dopant systems that can lead to highly conductive systems. The spatial arrangement of the polymer with the dopant, which is dictated by the blends phase behavior, strongly affects charge transport in analogy to the photovoltaic donor:acceptor systems. We will conclude with providing a tentative picture of the complex correlation of structure and electronic landscape for the understanding of organic photovoltaic cells as well as doped, conducting “plastics” of metallic-type transport – and beyond.

Polymers for optoelectronic devices: Opportunities and challenges

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.