Phase‐Purified and Highly Textured 2D Perovskite ( n = 5) Photodetectors Grown via a Temperature‐Gradient‐Free Thermal‐Pressing‐Casting Strategy for Broadband Response and Weak‐Light Imaging

ABSTRACT Self‐powered photodetectors (SPPDs) with broadband response and high‐resolution weak‐light imaging capabilities are crucial for next‐generation optoelectronics. Quasi‐two‐dimensional (quasi‐2D) Ruddlesden‐Popper perovskites are promising candidates, but their solution‐processed films typically suffer from multiphase coexistence and random crystallographic orientation, which severely impede vertical charge transport. Here, we report a facile temperature‐gradient‐free thermal‐pressing‐casting (TGF‐TPC) strategy to fabricate quasi‐2D (FPEA) 2 MA 4 Pb 5 I 16 perovskite films with a phase‐purified composition and a vertically aligned, highly textured structure. This method simultaneously applies uniform temperature and isostatic pressure, synergistically regulating crystallization thermodynamics and kinetics to suppress phase segregation and promote out‐of‐plane grain growth. The resulting films exhibit reduced trap‐state density, suppressed non‐radiative recombination, efficient vertical charge transport, and favorable interfacial energy alignment. Consequently, planar heterojunction SPPDs demonstrate outstanding optoelectronic performances, e.g., remarkable responsivity, ultralow noise, high specific detectivity, and robust stability. Crucially, they achieve high‐fidelity UV–vis–NIR broadband imaging under an ultralow power density of 50 nW cm −2 . This work provides a simple and scalable processing paradigm to control the microstructure of quasi‐2D perovskites, unlocking their potential for advanced low‐power photodetection and imaging.