Uncovering the Mechanism of Poly(ionic‐liquid)s Multiple Inhibition of Ion Migration for Efficient and Stable Perovskite Solar Cells

Abstract Longevity is a key constraint for hybrid perovskite based photovoltaics. Here it is demonstrated that ion migration‐induced degradation can be eliminated by incorporation of multifunctional poly(ionic‐liquid)s (PILs) additives, resulting in ultrastable perovskite solar cells (PVSCs). The presence of PILs suffices to construct an “ionic polymer network,” providing the functionalities of defect passivation and ion immobilization by concurrently forming a physical barrier and chemical bonding. Compared with the defect passivation effect for the imidazolium‐based PIL (PIL‐Im) case, the quaternary ammonium‐based PIL (PIL‐Am) shows a higher interaction energy with the perovskite due to the stronger electronic coupling ascribed to the additional complexation, which endows the corresponding perovskite with higher migration energy for iodide ions. As a result, the power conversion efficiency (PCE) of anion‐cation‐mixed hybrid n‐i‐p PVSCs with PIL‐Am is remarkably improved from 20.26% to 22.22%. Specifically, the PILs‐modified device perfectly retains its dark current characteristics upon a cooling (−40 °C)–heating (85 °C) process. The unencapsulated PIL‐Am stabilized PVSC maintains 80% of the initial PCE under AM 1.5G light soaking for nearly 1500 h. The corresponding device also displays pronounced stability under thermal stress or realistic operation conditions.