LAUSR

2D organic–inorganic hybrid perovskites are emerging as the promising alternatives in photodetection, due to their unique merits stemming from intrinsic quantum‐confined structures. Despite great ongoing effects, highly sensitive and ultrafast responding photodetectors of 2D hybrid perovskites remain a huge blank. Here, the first nanosecond‐responsive array photodetector based on 2D perovskite crystals of (PA)2(G)Pb2I7 (where PA = n‐pentylaminium and G = guanidinium) is fabricated, which features a newly tailored bilayer motif with large‐size G cation as “perovskiter” inside the distorted PbI3 perovskite framework. This motif creates a new branch of the intriguing 2D hybrid perovskite family. Strikingly, both high photodetectivities (6.3 × 1012 Jones) and responsivities (≈47 A W−1), as well as low dark current (≈2.4 × 10−11 A), are achieved in this array photodetector. Further, its ultrafast response time (τ) of 3.1 ns is one of the record‐fast merits for 2D hybrid perovskites. Such attributes originate from its strong in‐plane photoresponse related to perovskite network and low dark current inhibited by the hopping barriers of insulating PA bilayers. All these characteristics make (PA)2(G)Pb2I7 a promising candidate for photodetection, and pave the way to explore new 2D hybrid perovskite candidates for future high‐performance optoelectronic devices.