ABSTRACT Metal halide perovskites, in the form of large‐area, hundreds‐of‐micrometer thick polycrystalline films, hold great potential in revolutionizing current X‐ray imaging technologies. However, their monolithic integration with thin‐film transistor (TFT) backplanes is hindered by thermal expansion mismatch, excessive dark current, and buried‐interface defects. Herein, we introduce a multifunctional buried interlayer strategy that simultaneously surmount these obstacles. By engineering a pol