Influences of Conjugation Length on Organic Field-Effect Transistor Performances and Thin Film Structures of Diketopyrrolopyrrole-Oligomers
Journal
ACS Applied Materials and Interfaces
Journal Volume
10
Journal Issue
10
Pages
8869-8876
Date Issued
2018
Author(s)
Huang, Y.-F.
Chang, S.-T.
Wu, K.-Y.
Wu, S.-L.
Ciou, G.-T.
Chen, C.-Y.
Liu, C.-L.
Abstract
Here, two diketopyrrolopyrrole (DPP)-based oligomers, DPP-4T and DPP-6T, are studied to reveal the influences of conjugation length on thin-film morphology and organic field-effect transistor (OFET) performances. PDMS-assisted crystallization in a solvent-annealing chamber is applied to prepare crystal arrays of DPP-4T and DPP-6T to optimize the quality of charge channels for OFET characterizations. To deliver insights into microstructure and morphology of thin films, a characterization procedure for determining molecular packing in thin film and crystallinity of the crystal arrays is presented via grazing incidence wide-angle X-ray scattering, electron diffraction, and lattice simulation software package (Cerius2). With the lattice parameters derived from analyses of grazing incidence wide-angle X-ray scattering (GIWAXS) and electron diffraction (ED), the lattice modeling results indicate that the inferior organic field-effect transistor (OFET) performances of DPP-6T are attributed to longer π-stacking distance. Also, less-ordered molecular arrangement and lower continuity of crystalline domains, both of which are revealed from crystallinity results, lead to lower mobility of DPP-6T. In this case, longer conjugated backbones with more conformational degrees of freedom thus cause inherent crystal defects during the crystal growth process, despite the potential to enhance intermolecular π-orbital overlap. Therefore, to achieve better OFET performance, suitable backbone length makes conjugated oligomers give high intermolecular π-orbital overlap and low density of structural disorder, which are the priorities for constructing good charge channel.
Type
journal article