Introducing Noncovalent Interactions in Conjugated Polymers to Enhance Backbone Coplanarity and Aggregation at the Interface to Improve Carrier Mobility

Abstract

In organic field-effect transistors (OFETs), the high carrier mobility of conjugated polymers (CPs) is significantly influenced by the maintenance of excellent coplanarity and aggregation, especially at the interface between the organic semiconductor and dielectric layer. Unfortunately, CPs typically exhibit poor coplanarity due to the single bond rotations between donor and acceptor units. Furthermore, there is relatively little research on the coplanarity of CPs at the interface. Herein, we propose a strategy of introducing noncovalent interactions to enhance the coplanarity of the backbone and promote the aggregation of the polymer at the interface, which should lead to significant enhancements in carrier mobility. The idea is proved by incorporating different volume fractions of oleic acid (OA) into poly(indacenodithiophene-co-benzothiadiazole) (IDTBT). OA can form hydrogen bonds, which has been verified by Fourier transform infrared spectroscopy (FT-IR). OA promotes the migration of IDTBT toward the interface, thereby enhancing aggregation, as verified by film-depth-dependent light absorption spectroscopy (FLAS) and contact angle (CA) experiments. The results from film-depth-dependent Raman spectroscopy (FRS), two-dimensional grazing incidence wide-angle X-ray scattering (2D GIWAXS), atomic force microscopy (AFM), and density functional theory (DFT) calculations suggest that films treated with OA exhibit enhanced backbone coplanarity and aggregation at the interface, resulting in an increase in carrier mobility to 4.24 ± 0.11 cm² V^–1 s^–1 with the addition of OA.