Benzo[1,2-b:4,5-b′]dithiophenedimides as an Electron-Deficient Building Block for n-Type Polymer Semiconductors

The research on p-type polymer semiconductors has achieved significant progress in terms of material diversity and device performance, while the performance of n-type polymer semiconductors has lagged far behind. The design and synthesis of electron-deficient building blocks are essential for the development of high-performance n-type polymer semiconductors. Herein, we report a new electron-deficient unit, 3,4,7,8-benzo[1,2-b:4,5-b′]dithiophenedimides (BDTI), and its derivative dibromide BDTI, which are further employed to construct BDTI-based donor–acceptor copolymers. These polymers show highly planar backbones and deep lowest unoccupied molecular orbital (LUMO) levels (from −3.62 to −3.95 eV), which facilitate electron injection and transport in their thin films. The highest electron mobility of 0.25 cm2 V–1 s–1 was achieved in a field-effect transistor (FET) using the copolymer containing a fluorinated bithiophene donor. This work demonstrates that BDTI is a promising building block for constructing high-performance n-type polymer semiconductors.