In Situ Growth of Lead‐Free Double Perovskite Micron Sheets in Polymethyl Methacrylate for X‐Ray Imaging

Abstract Pb‐free double‐perovskite (DP) scintillators are highly promising candidates for X‐ray imaging because of their superior optoelectronic properties, low toxicity, and high stability. However, practical applications require Pb‐free DP crystals to be ground and mixed with polymers to produce scintillator films. Grinding can compromise film uniformity and optical properties, thereby affecting imaging resolution. In this study, an in situ fabrication strategy is proposed to facilitate the crystalline growth of Pb‐free Cs 2 AgIn x Bi 1‐x Cl 6 micron sheets in polymethyl methacrylate in a single step. By adjusting the In 3+ /Bi 3+ ratio, Cs 2 AgIn 0.9 Bi 0.1 Cl 6 /PMMA composite films (CFs) with excellent scintillation properties are obtained, including a light yield of up to 32000 photons per MeV and an X‐ray detection limit of 87 nGy air s −1 . This strategy also enabled the production of large Cs 2 AgIn 0.9 Bi 0.1 Cl 6 /PMMA CFs, which demonstrated favorable flexibility and stability, fabricating products with advanced eligibility for commercial applications. The CFs exhibited outstanding performances in X‐ray imaging, producing high‐resolution structures and providing a new avenue for the development of Pb‐free DP materials in fields such as medical imaging and safety detection.