and technologies in improving their charge-transport properties have been explored and practiced from molecular design, [9,10] synthetic method, [11,12] purification, [13,14] thin film microstructural optimization, [15,16] device configuration and fabrication, [17−20] to device interface engineering. [21−23] To be blunt, however, the carrier mobilities and device stability of polymer semiconductors nowadays are generally not adequate for the requirements of next-generation organic electronics. For example, the polymer semiconductors with carrier mobilities greater than 10 cm 2 V −1 s −1 are still few so far and almost all of them are thiophene-flanked diketopyrrolopyrrolebased copolymers (Table S1, Supporting Information). More importantly, the ambipolar or n-type polymer semiconductors with electron mobility exceeding 10 cm 2 V −1 s −1 are quite rare, although they are of great importance for fabricating polymer field-effect transistors (PFETs) and complementary metal-oxidesemiconductor-like circuits toward commercial high-grade electronics. [17,24−27] Nevertheless, the obtained fundamental understandings on charge-carrier transport mechanism in the exploring process still shows us invaluable guidelines for constructing high-mobility polymer semiconductors and PFETs. One fundamental understanding is "intrachain charge-carrier transport along the conjugated backbone chains is much faster than interchain charge-carrier transport, and the key limitation Polymer semiconductors with mobilities exceeding 10 cm 2 V −1 s −1 , especially ambipolar and n-type polymer semiconductors, are still rare, although they are of great importance for fabricating polymer field-effect transistors (PFETs) toward commercial high-grade electronics. Herein, two novel donor−acceptor copolymers, PNFFN-DTE and PNFFN-FDTE, are designed and synthesized based on the electron-deficient bisisoindigo (NFFN) and electron-rich dithienylethylenes (DTE or FDTE). The copolymer PNFFN-DTE, containing NFFN and DTE, possesses a partially locked polymeric conjugated backbone, whereas PNFFN-FDTE, containing NFFN and FDTE, has a fully locked one. Fluorine atoms in FDTE not only induce the formation of additional CH•••F hydrogen bonds, but also lower frontier molecular orbitals for PNFFN-FDTE. Both PNFFN-DTE and PNFFN-FDTE form more ordered molecular packing in thin films prepared from a polymer solution in bicomponent solvent containing 1,2-dichlorobenzene (DCB) and 1-chloronaphthalene (with volume ratio of 99.2/0.8) than pure DCB. The two copolymers-based flexible PFETs exhibit ambipolar charge-transport properties. Notably, the bicomponent solvent-processed PNFFN-FDTE-based PFETs afford a high electron mobility of 16.67 cm 2 V −1 s −1 , which is the highest electron-transport mobility for PFETs reported so far. The high electron mobility of PNFFN-FDTE is attributed to its fully locked conjugated backbone, dense molecular packing, and much matched LUMO energy level.

This review highlights the recent structural evolution of lactam- and imide-functionalized polymers applied in organic field-effect transistors and organic solar cells.