Reliable In Situ Probing of Perovskite Solar Cells Under Space‐Relevant Vacuum‐Thermal Cycling

Perovskite solar cells (PSCs) offer high efficiency and ultralight weight, making them promising for aerospace use. However, their stability under extreme vacuum (10 −8 Pa) and thermal cycling (150 K‐430 K) conditions remains unclear. Here, we present an in situ ultrahigh‐vacuum platform that decouples atmospheric effects and enables direct monitoring of FAPbI 3 films and devices. The absorber shows irreversible decomposition into PbI 2 and volatile organics, with degradation most pronounced during the first cycle. In situ X‐ray photoelectron spectroscopy (XPS)/quadrupole mass spectrometry (QMS) trace ion loss and gas release, while ex situ characterizations confirm structural collapse. Devices retain >80% efficiency after five cycles but exhibit reduced short‐circuit current density ( J SC ) and severe interfacial ion migration (Ag + , Pb 2+ , I – , Ni 2+ ). This study provides critical mechanistic insights into PSC degradation under space stresses and establishes an in situ method yielding reliable degradation data for space‐relevant evaluation.