Ternary-Assisted Sequential Solution Deposition Enables Efficient All-Polymer Solar Cells with Tailored Vertical-Phase Distribution

All-polymer solar cells (all-PSCs) have received attention in recent years for their desirable properties in power conversion efficiency and long-term operational stability. However, it is still a big challenge to acquire an "ideal" vertical-phase distribution of polymer/polymer blends due to the non-ideal molecular conformations and mixing behaviors. Herein, a ternary-assisted sequential solution deposition (SSD) strategy is adopted to regulate the vertical compositional profile of all-PSCs. A favorable acceptor(donor)-enriched phase near the cathode(anode) can be obtained by a ternary-assisted SSD strategy. With such a compositional profile, the exciton yield and carrier density can be enhanced by the vertical component gradient. Remarkably, the non-geminate recombination is suppressed with an improved exciton diffusion length (15.36 nm) that delivers an outstanding power conversion efficiency over 16% of the ternary PM6/PY-IT:PDI-2T SSD devices. This work demonstrates the success of ternary-assisted SSD strategy in reorganizing the vertical-phase distribution, which provides a feasible route for a potential ternary device construction toward efficient all-polymer photovoltaics.