Graphene-Induced Enhancement of n-Type Mobility in Perylenediimide Thin Films

Organic thin-film transistor transfer characteristics and time-of-flight (TOF) photoconductivity measurements were used to investigate the effect of the addition of liquid-phase exfoliated graphene nanoflakes (GNs) on the electron mobility in thin films of N,N'-bis(1H,1H-perfluorobutyl)dicyanoperylenecarboxydiimide (PDIF-CN2). Transfer characteristics measurements reveal that the charge carrier mobility of PDIF-CN2 increases by almost 3 orders of magnitude via blending with GNs. TOF photocurrent measurements confirm that the GNs improve the charge carrier transport in PDIF-CN2. We have found a strong dependence of the TOF-determined electron mobility on the excitation wavelength and obtained a maximum mobility of 0.17 cm(2)/(V s) for charge carriers produced in GN:PDIF-CN2 blends using a photon energy of 5.9 eV. This value is in good agreement with the field-effect mobility of 0.2 cm(2)/(V s) determined from transfer characteristics.