Significant Improvement of Unipolar n-Type Transistor Performances by Manipulating the Coplanar Backbone Conformation of Electron-Deficient Polymers via Hydrogen Bonding.

The development of high-performance unipolar n-type semiconducting polymers still remains a significant challenge. Only a few examples exhibit a unipolar electron mobility over 5 cm V s. In this study, a series of new poly(benzothiadiazole-naphthalenediimide) derivatives with a high unipolar electron mobility (μ) up to 7.16 cm V s in thin-film transistors are reported. The dramatically increased μ is achieved by finely optimizing the coplanar backbone conformation through the introduction of vinylene bridges, which can form intramolecular hydrogen bonds with the neighboring fluorine and oxygen atoms. The hydrogen-bonding functionalities are fused to the backbone to ensure a much more planar conformation of the conjugated π-system, as demonstrated by the density functional theory (DFT)-based calculations. The theoretical prediction is in good agreement with the experimental results. As the coplanarity is promoted by the hydrogen bonding, the thin-film crystallinity and molecular packing strength are also improved, which is evidenced by the synchrotron two-dimensional grazing-incidence wide-angle X-ray scattering (GIWAXS) and atomic force microscopy (AFM) measurements. Notably, the GIWAXS measurements reveal an extremely short π-π stacking distance of 3.40 Å. Overall, this study marks a significant advance in the unipolar n-type semiconducting polymers and offers a general approach for further increasing the electron mobility of semiconducting polymers in organic electronics.