Ultrathin perovskite solar cells (PSCs), defined as flexible devices with total thicknesses below 10 μm, are promising candidates for next‐generation space photovoltaics owing to their extremely low weight and high mechanical compliance. Although the radiation tolerance of rigid PSCs has been widely studied, that of flexible—particularly ultrathin—PSCs remains insufficiently explored, mainly due to radiation‐induced staining and degradation of conventional plastic substrates under high‐dose gamma‐ray irradiation. Here, we demonstrate 4 μm‐thick ultrathin flexible PSCs fabricated on radiation‐stable parylene/SU‐8 substrates, exhibiting exceptional gamma‐ray tolerance under severe total ionizing dose (TID) conditions. The parylene/SU‐8 substrate preserves optical transparency and mechanical compliance after irradiation, effectively suppressing substrate‐induced staining artifacts. Consequently, the ultrathin PSCs retain 99% of their initial power conversion efficiency after exposure to 890 krad (Si). By comparison with rigid PSCs, we show that irradiation‐induced short‐circuit current loss and fill‐factor enhancement originate from the PSC stack itself rather than from the substrate, with the current reduction being consistent with phase segregation in the perovskite layer. These results highlight radiation‐stable ultrathin substrates and interface design as key enablers for highly radiation‐tolerant ultrathin PSCs for future space applications.
Jinno et al. (Mon,) studied this question.