Solid-solvent hybrid additive for the simultaneous control of the macro- and micro-morphology in non-fullerene-based organic solar cells

Abstract

Most organic solar cells based on a bulk-heterojunction active layer are fabricated with the assistance of high boiling point solvent additives to optimize the phase separation of the donor and acceptor. The macroscopic phase separation can be controlled by this solvent additive. However, the control of the microscopic morphology (e.g., π-π stacking, orientation) of the inside phase is still dependent on the interaction and self-assembly characteristics of each donor and acceptor. In this work, we introduce a solid-solvent hybrid additive on PM6:Y6 solar cells to optimize both the macroscopic phase separation and the microscopic morphology at the same time. For the solvent additive, the well-known 1-CN solvent additive was used. For the solid additive, newly synthesized 3D star-shaped solid additives (Star-A and Star-F), which were delicately designed to achieve adequate electrical properties, electrostatic potential, and geometrical structure, were used to further optimize the microscopic morphology. Grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements showed that the star additives not only induce the dense and enhanced microscopic intermolecular π-π stacking within the phase, but also further optimize the phase separation. By adding only 1% star-series solid additives, a significantly enhanced efficiency was achieved from PM6:Y6 solar cells.