From Amorphous to Polycrystalline Rubrene: Charge Transport in Organic Semiconductors Paralleled with Silicon

While progress has been made in the design of organic semiconductors (OSCs) with improved transport properties, the understanding of the mechanisms involved is still limited, hindering further development. In this study, the interplay between structural order and transport considering one single OSC...

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Veröffentlicht in:Advanced functional materials 2022-12, Vol.32 (49), p.n/a
Hauptverfasser: Euvrard, Julie, Gunawan, Oki, Kahn, Antoine, Rand, Barry P.
Format: Artikel
Sprache:eng
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Zusammenfassung:While progress has been made in the design of organic semiconductors (OSCs) with improved transport properties, the understanding of the mechanisms involved is still limited, hindering further development. In this study, the interplay between structural order and transport considering one single OSC, analogous to past research on silicon is investigated. Rubrene (C42H28) is selected as it spans transport mechanisms from thermally activated hopping in its amorphous form to band‐like in highly ordered crystals in the orthorhombic polymorph. Transport characterizations including variable temperature conductivity, advanced Hall effect, and magnetoresistance measurements are performed on rubrene films with varying levels of order (polycrystalline vs amorphous), crystal phase (orthorhombic vs triclinic), and morphologies (platelet‐like vs spherulitic grains). A conductivity tuning range over four orders of magnitude between polycrystalline (platelet‐like) orthorhombic and amorphous films is reported. As observed in silicon, transport in polycrystalline orthorhombic rubrene is limited by energy barriers at grain boundaries. Additionally, a gradual transition from predominantly band‐like to predominantly hopping transport with increasing disorder, reminiscent of observations in silicon is shown. Nevertheless, OSCs differ from covalently bonded silicon by their weak intermolecular interaction. This study highlights that molecular packing must be optimized in OSCs to favor advantageous π‐orbital overlap and optimized transport properties. A comprehensive understanding of the interplay between order, molecular packing, morphology, and charge transport in organic semiconductors is provided, akin to research on silicon decades ago. Results point toward the application of a unified transport model with varying contributions of delocalized and localized carriers. Additionally, it is demonstrated that order alone is insufficient while molecular packing is paramount for optimal transport.
ISSN:1616-301X
1616-3028
DOI:10.1002/adfm.202206438