Abstract

• The structure of organic semiconductor layers strongly affects the performance of the organic semiconductor-based devices such as organic thin film transistors (OTFTs), organic field effect transistors (OFETs), organic light emitting diodes (OLEDs) and organic photovoltaic cells (OPVs). The layer structure such as preferred orientation is controlled by the heteroepitaxial growth of organic molecules on different type of substrates. The -conjugated organic semiconductor materials were deposited on single crystal sapphire substrate by vacuum thermal evaporation. The heteroepitaxial growth of π-conjugated n-type semiconductor of N, N'-dioctyl3,4,9,10-perylenedicarboximide (PTCDI-C8) and p-type semiconductor of 2,7-dioctyl [1] benzothieno [3,2-b][1] benzothiophene (C8-BTBT) on single crystal Al2O3 sapphire substrates were investigated by X-ray diffraction analysis and atomic force microscopy observation. The (001) out-of-plane orientation of organic layers were developed on single crystal sapphire substrates for all prepared samples irrespective of the deposited organic materials we used in this research. The needle-shape PTCDI-C8 grains and layer-by-layer islands growth of C8-BTBT layers on (0001) C-sapphire substrate were observed in AFM observation. The PTCDI-C8 and C8- BTBT layers showed characteristic of its absorption spectra.