Volatile Fluorination Additive for Operationally Stable Perovskite/TOPCon Tandem Solar Cells

ABSTRACT Perovskite/silicon tandem solar cells have recently achieved power conversion efficiencies (PCEs) approaching 35.0%, far exceeding the single‐junction limit. However, residual tensile stress in perovskite layers remains a critical challenge, severely impairing photovoltaic performance and operational stability. This stress, originating from solution processing, induces lattice distortion and defect aggregation, thereby enhancing nonradiative recombination and lowering ion migration barriers. To address this issue, we introduce octafluoronaphthalene (OFNA) as a volatile multifunctional additive. Benefiting from synergistic anion–π and hydrogen‐bond interactions, OFNA regulates crystallization kinetics, passivates defects, and relieves residual tensile stress, yielding high‐quality perovskite films with enhanced photothermal stability. As a result, single‐junction perovskite solar cells deliver a PCE of 22.23%, while monolithic perovskite/TOPCon tandems achieve 31.43%, both with markedly improved ISOS‐L‐1 and ISOS‐L‐2 stability.