TPD-based polythiophene derivatives with higher Voc for polymer solar cells

Abstract

New D–A copolymers, PTPD-DT and PTPD-DFDT, based on a thieno[3,4-c]pyrrole-4,6-dione (TPD) acceptor unit and 2,2′-bithiophene (DT) or 3,3′-difluoro-2,2′-bithiophene (DFDT) donor units, were designed and synthesized for application as donor materials in polymer solar cells (PSCs). A control polymer PTPD-DT with a similar structure but without fluorine substitution on the 2,2′-bithiophene (DT) unit was also synthesized for comparison. Compared with PTPD-DT, the polymer PTPD-DFDT with fluorine substitution on the DT unit shows a lower HOMO energy level of −5.55 eV, more broad absorption in the wavelength range from 300 to 700 nm, greater coplanarity and crystalline structure. The PSCs based on PTPD-DFDT/PC₇₁BM demonstrated a power conversion efficiency of 5.52%, with a higher open-circuit voltage of 0.96 V. Furthermore, PTPD-DFDT exhibits a simpler molecular structure and easier synthesis steps, which is beneficial for mass production in future.