A Thieno[2,3‑<i>b</i>]pyridine-Flanked Diketopyrrolopyrrole Polymer as an n‑Type Polymer Semiconductor for All-Polymer Solar Cells and Organic Field-Effect Transistors

A novel fused heterocycle-flanked diketopyrrolopyrrole (DPP) monomer, thieno­[2,3-<i>b</i>]­pyridine diketopyrrolopyrrole (TPDPP), was designed and synthesized. When copolymerized with 3,4-difluorothiophene using Stille coupling polymerization, the new polymer pTPDPP-TF possesses a highly planar conjugated polymer backbone due to the fused thieno­[2,3-<i>b</i>]­pyridine flanking unit that effectively alleviates the steric hindrance with both the central DPP core and the 3,4-difluorothiophene repeat unit. This new polymer exhibits a high electron affinity (EA) of −4.1 eV and was successfully utilized as an n-type polymer semiconductor for applications in organic field-effect transistors (OFETs) and all polymer solar cells. A promising n-type charge carrier mobility of 0.1 cm² V^–1 s^–1 was obtained in bottom-contact, top-gate OFETs, and a power conversion efficiency (PCE) of 2.72% with a high open-circuit voltage (<i>V</i>_OC) of 1.04 V was achieved for all polymer solar cells using PTB7-Th as the polymer donor.