Bisphosphonate‐Embedded a π‐Conjugated Passivator Enable Efficient and Stable <i>n‐i‐p</i> Perovskite Solar Cells with Low‐Polarity Solvent Processing

Interface passivators play a critical role in improving the efficiency of perovskite solar cells (PSCs). However, the conventional passivators often require processing in high-polarity solvents that can cause additional surface defects on the perovskite film, thereby reducing the efficiency and stability of n-i-p PSCs. Herein, a bisphosphate molecule (named DCTP) is designed and synthesized to simultaneously address solvent compatibility, defect passivation, and hole extraction. DCTP has good solubility in low-polarity solvents such as toluene, chlorobenzene, and chloroform without damaging the perovskite surface. The chlorobenzene-processed DCTP interlayer can sufficiently passivate the defects on the perovskite surface and improve the energy level arrangement at the perovskite/hole transporting layer interface. Meanwhile, the DCTP layer effectively inhibits interlayer diffusion of formamidine (FA⁺), iodide (I^-), and lithium (Li⁺) and ions under thermal stress. As a result, the DCTP-controlled device produces a champion power conversion efficiency (PCE) of 26.07% with excellent reproducibility, compared to 24.28% for the reference device. More importantly, the operational stability of the device is significantly improved. The DCTP-treated device retains 90.1% of its initial PCE after 900 h of maximum power point tracking (MPPT) at 65 °C under the ISOS-L-2I protocol.