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. A vertical compositional gradient within the active layer with a donor‐enriched active‐anode interface and an acceptor‐enriched active‐cathode interface can be achieved by sequential solution deposition treatment in PM6/PY‐IT:PDI‐2T device. As a result, charge transfer properties and exciton diffusion length are promoted with suppressed non‐geminate recombination to deliver an outstanding power conversion efficiency of 16% in the all‐polymer solar cells, which are verified with transient absorption, time‐resolved photoluminescence, and capacitance‐voltage measurements.