Photodetectors play an important role in optical communication systems and are essential to achieve high‐fidelity signal transmission. The emerging formamidinium‐based quasi‐2D layered perovskites have attracted attention in the field due to their excellent photoelectric performance and moisture stability. By optimizing film quality and device engineering a high‐performance flexible photodetector based on formamidinium‐based perovskites ((BA)2FAPb2I7) is developed, which shows fast response and excellent air‐stability. By introducing the formamidinium chloride as an additive the quality and the crystallinity of the film are improved. In addition, localized surface plasmonic resonances (LSPRs) are introduced by embedding Au nanostructures on the substrate, the LSPRs, in turn, enhance light and matter interaction, which further increases the performance of the device. The optimized devices show an ultimate response speed ≈9 µs as well as outstanding long‐term environmental stability (environmental conditions > 1000 h). Achieving such high dynamic range and stability is to the best of authors knowledge rarely reported. The device shows the highest responsivity of 2.3 A W−1, detectivity of 3.2 × 1012 Jones, and outstanding flexibility stability. Finally, the prepared photodetector is successfully integrated into an optical communication system and tested. The results suggest that formamidinium‐based quasi‐2D perovskite photodetectors have great potential in optical communication applications.

The development of an efficient fabrication route to achieve high‐resolution perovskite pixel array is key for large‐scale flexible image sensor devices. Herein, a high‐resolution and stable 10 × 10 flexible PDs array based on formamidinium(FA+) and phenylmethylammonium (PMA+) quasi‐2D (PMA)2FAPb2I7 (n = 2) perovskite is demonstrated by developing SiO2‐assisted hydrophobic and hydrophilic treatment process on polyethylene terephthalate substrate. By introducing Au nanoparticles (Au NPs),  the perovskite film quality is improved and grain boundaries are reduced. The mechanism by which Au NPs upgrade the photoelectric quality of perovskite is mainly revealed by glow discharge‐optical emission spectroscopy (GD‐OES) and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS). To further improve the photoelectric performance of the devices, a post‐treatment strategy with formamidinium chloride (FACl) is used . The optimized flexible PDs arrays show excellent optoelectronic properties with a high responsivity of 4.7 A W−1, a detectivity of 6.3 × 1012 Jones, and a broad spectral sensitivity. The device also exhibits excellent electrical stability even under severe bending and excellent flexural strength, as well as excellent environmental stability. Finally, the integrated flexible PDs arrays are used as sensor pixels in an imaging system to obtain high‐resolution imaging patterns, demonstrating the imaging capability of the PDs arrays.