(Invited) Influence of the Semiconductor Thin Film Morphologies on Dntt Organic Electronic Devices Performances

In this work, we have studied the growth of DNTT semiconductor thin films on two different dielectric materials relating the ordered DNTT thin film structure to the OTFTs' electrical characteristics. OTFTs have been fabricated with Bottom Gate Top Contact (BGTC) configuration using thermal SiO2 or a double layer of SiO2/CytopTM as gate dielectrics. Semiconductor thin films, with thicknesses ranging from 3 nm to 50 nm, were detailed analyzed with high resolution AFM and XRD measurements (Fig. 1a, b, c, d) for different growth conditions to understand the morphologies of the films starting by the very first ordered layers of DNTT semiconductors. Our measurements show that DNTT molecules on SiO2 and Cytop pack into ordered structures placing themselves with their long axis perpendicular to the plane of the substrate (edge-on). However, in the case of DNTT on SiO2, a portion of ordered molecules can lie horizontally on the substrate (face-on). This causes an increase of defective states for the majority carriers in the conductive channel of the transistor, with a consequent reduction of the field-effect mobility (Fig. 1a, b). Numerical simulations were performed to analyze the effects of different semiconductor film morphologies on the electrical characteristics of the OTFTs. We also show that the morphological semiconductor differences lead to better performances for organic phototransistors based on DNTT/Cytop interface [8].