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Design strategies for organic semiconductors beyond the molecular formula

Abstract

Organic semiconducting materials based on polymers and molecular systems containing an electronically delocalized structure are the basis of emerging optoelectronic technologies such as plastic solar cells and flexible transistors. For isolated molecules, guidelines exist that rely on the molecular formula to tailor the frontier (highest occupied or lowest unoccupied) molecular orbital energy levels and optical absorption profiles. Much less control can be achieved over relevant properties, however, as one makes the transition to the ensemble behaviour characteristic of the solid state. Polymeric materials are also challenging owing to the statistical description of the average number of repeat units. Here we draw attention to the limitations of molecular formulae as predictive tools for achieving properties relevant to device performances. Illustrative examples highlight the relevance of organization across multiple length scales, and how device performances — although relevant for practical applications — poorly reflect the success of molecular design.

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Figure 1: Beyond the molecular level.
Figure 2: Molecular weight characteristics substantially influence performance in polymer electronic devices.
Figure 3: Methods for controlling intra- and intermolecular order and the influence on thin-film morphology or electronic properties.
Figure 4: Device performance of polymer and molecular samples with identical structures and similar molecular weight characteristics vary widely as a result of different processing conditions.

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Acknowledgements

Work done at UCSB has been supported through the NSF (DMR 1005546). We gratefully thank Peter Allen for assistance with image preparation.

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Correspondence to Klaus Müllen or Guillermo C. Bazan.

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Henson, Z., Müllen, K. & Bazan, G. Design strategies for organic semiconductors beyond the molecular formula. Nature Chem 4, 699–704 (2012). https://doi.org/10.1038/nchem.1422

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