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Abstract Organic semiconductors with high-spin ground states are fascinating because they could enable fundamental understanding on the spin-related phenomenon in light element and provide opportunities for organic magnetic and quantum materials. Although high-spin ground states have been observed in some quinoidal type small molecules or doped organic semiconductors, semiconducting polymers with high-spin at their neutral ground state are rarely reported. Here we report three high-mobility semiconducting polymers with different spin ground states. We show that polymer building blocks with small singlet-triplet energy gap (Δ E S-T ) could enable small Δ E S-T gap and increase the diradical character in copolymers. We demonstrate that the electronic structure, spin density, and solid-state interchain interactions in the high-spin polymers are crucial for their ground states. Polymers with a triplet ground state ( S = 1) could exhibit doublet ( S = 1/2) behavior due to different spin distributions and solid-state interchain spin-spin interactions. Besides, these polymers showed outstanding charge transport properties with high hole/electron mobilities and can be both n- and p-doped with superior conductivities. Our results demonstrate a rational approach to obtain high-mobility semiconducting polymers with different spin ground states.
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Nanoconfining solution-processed organic semiconductors for emerging optoelectronics
Solution-processable organic materials for emerging electronics can generally be divided into two classes of semiconductors, organic small molecules and polymers. The theoretical thermodynamic limits of device performance are largely determined by the molecular structure of these compounds, and advances in synthetic routes have led to significant progress in charge mobilities and light conversion and light emission efficiencies over the past several decades. Still, the uncontrolled formation of out-of-equilibrium film microstructures and unfavorable polymorphs during rapid solution processing remains a critical bottleneck facing the commercialization of these materials. This tutorial review provides an overview of the use of nanoconfining scaffolds to impose order onto solution-processed semiconducting films to overcome this limitation. For organic semiconducting small molecules and polymers, which typically exhibit strong crystal growth and charge transport anisotropy along different crystallographic directions, nanoconfining crystallization within nanopores and nanogrooves can preferentially orient the fast charge transport direction of crystals with the direction of current flow in devices. Nanoconfinement can also stabilize high-performance metastable polymorphs by shifting their relative Gibbs free energies via increasing the surface area-to-volume ratio. Promisingly, such nanoconfinement-induced improvements in film and crystal structures have been demonstrated to enhance the performance and stability of emerging optoelectronics that will enable large-scale manufacturing of flexible, lightweight displays and solar cells.
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- Award ID(s):
- 2115193
- PAR ID:
- 10314733
- Date Published:
- Journal Name:
- Chemical Society Reviews
- Volume:
- 50
- Issue:
- 17
- ISSN:
- 0306-0012
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Organic semiconducting small molecules have attracted increasing interest over the last decades because of their versatile, tunable optoelectronic properties and, e.g. , the ease they can be purified compared to polymeric systems. Hence, over the past few decades, a large number of small molecules, such as acenes and thiophenes, have been explored for use in semiconducting devices such as thin-film transistors. However, many of these materials can adopt various molecular arrangements, producing polymorphic structures. As a result, the same material can display vastly different optoelectronic properties. This can, in many cases, lead to a large spread of device performances. Hence, it is critical to establish knowledge- and characterization libraries towards relevant structure/processing/performance interrelations to further advance this interesting class of materials and to open new application platforms. Here, we discuss processing strategies and methodologies that allow the control and assessment of polymorph formation in semiconducting small molecules using 5,11-bis(triethylsilylethynyl)anthradithiophene (TES ADT) as a model material system. We revise how a window into the complex phase behavior of semiconducting small molecules can be obtained, how specific polymorphs can be induced, and how post-deposition treatments can be exploited. Moreover, we illustrate pathways towards patterned structures as needed to fully exploit the touted potential of this interesting class of semiconductors.more » « less
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Abstract Organic solar cells incorporating non‐fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology‐function models. Here, it is confirmed that high‐performing solution‐processed indacenodithienothiophene‐based NFAs, i.e., ITIC and its derivatives ITIC‐M, ITIC‐2F, and ITIC‐Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low‐temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low‐temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low‐temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D1CS00430A
