Electron-Deficient N‑Alkyloyl Derivatives of Thieno[3,4‑c]pyrrole-4,6-dione Yield Efficient Polymer Solar Cells with Open-Circuit Voltages > 1 V

Poly­(benzo­[1,2-b:4,5-b′]­dithiophene–thieno­[3,4-c]­pyrrole-4,6-dione) (PBDTTPD) polymer donors yield some of the highest open-circuit voltages (V_OC, ca. 0.9 V) and fill factors (FF, ca. 70%) in conventional bulk-heterojunction (BHJ) solar cells with PCBM acceptors. Recent work has shown that the incorporation of ring substituents into the side chains of the BDT motifs in PBDTTPD can induce subtle variations in material properties, resulting in an increase of the BHJ device V_OC to ∼1 V. In this contribution, we report on the synthesis of N-alkyloyl-substituted TPD motifs (TPD­(CO)) and show that the electron-deficient motifs can further lower both the polymer LUMO and HOMO levels, yielding device V_OC > 1 V (up to ca. 1.1 V) in BHJ solar cells with PCBM. Despite the high V_OC achieved (i.e., low polymer HOMO), BHJ devices cast from TPD­(CO)-based polymer donors can reach power conversion efficiencies (PCEs) of up to 6.7%, making these promising systems for use in the high-band-gap cell of tandem solar cells.