Enhanced Short-Wavelength Absorption and Effective Exciton Dissociation in NC₇₀BA-Based Ternary Polymer Solar Cells

A ternary heterojunction strategy was employed to improve the photovoltaic performance of polymer solar cells (PSCs) by harvesting more short-wavelength photons and more efficient exciton dissociation. Ternary PSCs were fabricated by employing the wide-band-gap polymer PBDB-T-2F as the donor, the narrow-band-gap nonfullerene small-molecule IT-4F as the acceptor, and the fullerene derivative NC70BA as the third component to tune the light absorption, enlarge the energy band gap, and improve the charge-carrier dynamics of the ternary photoactive layer. The highest power conversion efficiency (PCE) of 13.90% is achieved in an optimized PBDB-T-2F:IT-4F:NC70BA ratio of 1:1.2:0.25. The introduction of NC70BA has complementary light absorption in the short-wavelength region (from 300 to 450 nm) and optimizes the exciton dissociation. The lowest unoccupied molecular orbital (LUMO) energy level of NC70BA is higher than that of IT-4F, which enlarges the energy band gap and enhances the open-circuit voltage (VOC). A very promising ternary heterojunction strategy with NC70BA as the third component is to develop highly efficient ternary PSCs.