Improved order and transport in C60 thin films grown on SiO2 via use of transient templates

Abstract

The performance of C60 semiconducting films is linked to the degree of crystallinity and ordering, properties that strongly depend on the substrate, and growth conditions. Substrate–molecule interactions can be specifically tailored by employing growth templates to achieve a desired thin film structure. However, the presence of a growth template after the film deposition is usually not desirable as it may change the properties of the layer of interest. The ability to remove a growth template without any disruption to the active layer would be highly beneficial. A simple method of template removal by annealing is presented here. A variety of small organic molecules (perfluoropentacene, [6]phenacene, and α-sexithiophene) were used as a growth template to obtain a high-quality well-ordered C60 thin film. In situ grazing-incidence wide-angle x-ray scattering was employed to study the structural changes of C60 thin films during template removal. While a slight disturbance of the thin film structure was observed during template removal caused by evaporated molecules from the growth template escaping through the C60 layer, the disruption is only temporary. When the annealing process is concluded, only the well-ordered C60 thin film directly on top of SiO2 is left, which is not achievable without the use of a growth template. Improved crystallinity and grain size of such a thin film, when compared to preparation without a growth template, lead to a significant improvement of the charge carrier mobility. Importantly, template removal prevents the formation of undesired ambipolar transistor characteristics.