Correlating charge transport to structure in deconstructed diketopyrrolopyrrole oligomers: A case study of a monomer in field-effect transistors

Copolymers based on diketopyrrolopyrrole (DPP) cores have attracted a lot of attention because of their high p-type as well as n-type carrier mobilities in organic field-effect transistors (FETs) and high power conversion efficiencies in solar cell structures. We report the structural and charge transport properties of n-dialkyl side-chain-substituted thiophene DPP end-capped with a phenyl group (Ph-TDPP-Ph) monomer in FETs which were fabricated by vacuum deposition and solvent coating. Grazing-incidence X-ray diffraction (GIXRD) from bottom-gate, bottom-contact FET architectures was measured with and without biasing. Ph-TDPP-Ph reveals a polymorphic structure with pi-conjugated stacking direction oriented in-plane. The unit cell comprises either one monomer with a = 20.89 angstrom, b = 13.02 angstrom, c = 5.85 angstrom, alpha = 101.4 degrees, beta = 90.6 degrees, and gamma = 94.7 degrees for one phase (TR1) or two monomers with a = 24.92 angstrom, b = 25.59 angstrom, c = 5.42 angstrom, alpha = 80.3 degrees, beta = 83.5 degrees, and gamma = 111.8 degrees for the second phase (TR2). The TR2 phase thus signals a shift from a coplanar to herringbone orientation of the molecules. The device performance is sensitive to the ratio of the two triclinic phases found in the film. Some of the best FET performances with p-type carrier mobilities of 0.1 cm(2)/V s and an on/off ratio of 10(6)are for films that comprise mainly the TR1 phase. GIXRD from in operando FETs demonstrates the crystalline stability of Ph-TDPP-Ph

In situ–Directed Growth of Organic Nanofibers and Nanoflakes: Electrical and Morphological Properties

Organic nanostructures made from organic molecules such as para-hexaphenylene (p-6P) could form nanoscale components in future electronic and optoelectronic devices. However, the integration of such fragile nanostructures with the necessary interface circuitry such as metal electrodes for electrical connection continues to be a significant hindrance toward their large-scale implementation. Here, we demonstrate in situ–directed growth of such organic nanostructures between pre-fabricated contacts, which are source–drain gold electrodes on a transistor platform (bottom-gate) on silicon dioxide patterned by a combination of optical lithography and electron beam lithography. The dimensions of the gold electrodes strongly influence the morphology of the resulting structures leading to notably different electrical properties. The ability to control such nanofiber or nanoflake growth opens the possibility for large-scale optoelectronic device fabrication

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