Structural Effects of Electrode Proximity in Vacuum-Deposited Organic Semiconductors Studied by Microfocused X-Ray Scattering

Organic semiconductors have seen widespread application in thin-film devices, such as organic field-effect transistors (OFETs), whose performance is closely linked to the molecular-level microstructure and crystalline orientation. In actual OFETs, the microstructure varies significantly based on the local environment, for example, in the proximity of contact electrodes. This account highlights recent examples where microfocused grazing-incidence wide-angle X-ray scattering (μGIWAXS) maps structural information in between the OFET electrodes. Also shown are results where μGIWAXS is used to study the microstructure of naphthyl end-capped oligothiophenes across interdigitated electrode arrays in a bottom-contact OFET identifying lateral proximity effects of the contact electrodes in terms of crystalline misorientation, crystallite size, and disorder. The results together with those highlighted, classify essential structural parameters on and in between the electrodes and demonstrate capabilities of microfocused X-rays to map microstructures in actual devices. The ideas presented herein bring us toward guidelines for understanding electrode proximity and device performance in molecular semiconductors. It is also believed that they are readily expanded from OFETs to other devices and from small molecules to polymers and other materials.