Introducing\nNoncovalent Interactions in Conjugated\nPolymers to Enhance Backbone Coplanarity and Aggregation at the Interface\nto Improve Carrier Mobility

In\norganic field-effect transistors (OFETs), the high carrier mobility\nof conjugated polymers (CPs) is significantly influenced by the maintenance\nof excellent coplanarity and aggregation, especially at the interface\nbetween the organic semiconductor and dielectric layer. Unfortunately,\nCPs typically exhibit poor coplanarity due to the single bond rotations\nbetween donor and acceptor units. Furthermore, there is relatively\nlittle research on the coplanarity of CPs at the interface. Herein,\nwe propose a strategy of introducing noncovalent interactions to enhance\nthe coplanarity of the backbone and promote the aggregation of the\npolymer at the interface, which should lead to significant enhancements\nin carrier mobility. The idea is proved by incorporating different\nvolume fractions of oleic acid (OA) into poly(indacenodithiophene-<i>co</i>-benzothiadiazole) (IDTBT). OA can form hydrogen bonds,\nwhich has been verified by Fourier transform infrared spectroscopy\n(FT-IR). OA promotes the migration of IDTBT toward the interface,\nthereby enhancing aggregation, as verified by film-depth-dependent\nlight absorption spectroscopy (FLAS) and contact angle (CA) experiments.\nThe results from film-depth-dependent Raman spectroscopy (FRS), two-dimensional\ngrazing incidence wide-angle X-ray scattering (2D GIWAXS), atomic\nforce microscopy (AFM), and density functional theory (DFT) calculations\nsuggest that films treated with OA exhibit enhanced backbone coplanarity\nand aggregation at the interface, resulting in an increase in carrier\nmobility to 4.24 ± 0.11 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> with the addition of OA.