ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Negative field-dependent charge mobility in crystalline organic semiconductors with delocalized transport

Andrey Kadashchuk, Robby Janneck, Fei Tong, Ivan I. Fishchuk, Alexander Mityashin, Egon Pavlica, Anna Köhler, Paul Heremans, Cedric Rolin, Gvido Bratina, and Jan Genoe

IMEC, Leuven, Belgium

E-mail: kadash@imec.be

Abstract: Charge-carrier mobility has been investigated by time-of-flight (TOF) transient photocurrent in a lateral transport configuration in highly crystalline thin films of 2,7-dioctyl[1]benzothieno [3,2-b][1] benzothiophene (C₈-BTBT) grown by a zone-casting alignment technique. High TOF mobility has been revealed that it is consistent with the delocalized nature of the charge transport in this material, yet it featured a positive temperature dependence at ( T ge 295,{ ext{K}} ). Moreover, the mobility was surprisingly found to decrease with electric field in the high-temperature region. These observations are not compatible with the conventional band-transport mechanism. We have elaborated an analytic model based on effective-medium approximation to rationalize the puzzling findings. The model considers the delocalized charge transport within the energy landscape formed by long-range transport band-edge variations in imperfect organic crystalline materials and accounts for the field-dependent effective dimensionality of charge transport percolative paths. The results of the model calculations are found to be in good agreement with experimental data.

Keywords: Organic semiconductors ; Thin crystalline films ; C₈-BTBT ; Time-of-flight mobility ; Delocalized charge transport ; Electric field dependence of mobility ; Effective-medium approximation 

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-018-0483-x

Chemical Papers 72 (7) 1685–1695 (2018)