Dithienothiapyran: An Excellent Donor Block for Building High-Performance Copolymers in Nonfullerene Polymer Solar Cells.

In this work, a new but excellent donor block dithienothiapyran (DTTP) was developed for constructing highly efficient wide band gap copolymer donors. Compared to dithienopyran (DTP), DTTP features weaken electron-donating ability and more planar-conjugated backbones. Polymer-fluorinated benzotriazole (FBTA) based on DTTP exhibits lower highest occupied molecular orbital level (-5.30 vs -5.21 eV), higher molar extinction coefficient (1.54 × 105 vs 8.65 × 104 M-1 cm-1), and better crystallinity than -FBTA based on DTP, thus producing a higher device performance of 10.51% in binary blend nonfullerene polymer solar cells (NF-PSCs) blended with IT-M. To improve the absorption strength of PDTTP-FBTA: devices in the shorter wavelength range and further optimize the blend morphology, a small molecule of , which has strong absorption at short wavelength (300-600 nm), was incorporated. Finally, the performance of the ternary blends was successfully enhanced to 11.57% and a very high fill factor of 76.5%. Our work provided a new but excellent donor block for building high-performance conjugated copolymers to achieve highly efficient NF-PSCs.