Zwitterionic Bioinspired Acceptor-Acceptor (A₁-A₂) Type Interlayers for Organic Solar Cells

The design of interlayer materials featuring precisely matched electronic properties with the active layer materials and robust thickness tolerance is crucial for advancing organic solar cell (OSC) performance and commercialization. Zwitterionic polymers have been investigated extensively as interlayer materials in organic electronics. However, sulfobetaine (SB) has been the most widely adopted zwitterionic chains, while other cation-anion combinations remain largely unexplored, and the contribution of the anionic groups in zwitterions is still a mystery. Here, we explored a bioinspired zwitterionic interlayer material, engineered through the synergistic integration of fluorinated phosphatidylcholine-based polar side chains and an acceptor-acceptor (A₁-A₂) conjugated backbone. Such a synchronous side chain/backbone "surgery" simultaneously achieves deep frontier molecular orbital energy levels aligned with state-of-the-art electron acceptors, suppressed parasitic absorption, highly ordered molecular packing, and reduced hydrophilicity. The resulting interlayer material, PDITz-PC, demonstrates strong work function modification, superior electrical properties, and excellent interfacial contact. In OSCs, PDITz-PC enables impressive power conversion efficiencies (PCEs) for both small area (0.04 cm²) and large area (0.6 cm²) devices across various active layer systems, accompanied by significantly improved operational device stability, attributed to enhanced exciton dissociation, improved charge transport, and suppressed charge recombination. Notably, PDITz-PC exhibits good thickness tolerance, solar cells retaining 92% of the peak PCE even at an interlayer thickness of 115 nm. This work highlights the critical need to synchronize interlayer design with advancements in active-layer materials via the harmonized engineering of side chains and backbones, offering a strategic route to achieving high-performance, durable, and scalable organic photovoltaics.