The diversity of organic cations greatly enriches the species of 2D perovskites; traditional 2D Ruddlesden‐Popper (RP) and Dion‐Jacobson (DJ) perovskites are synthesized by two different organic amines. Here, according to the difference in pKa values between conjugated acids of monoprotonated and biprotonated 4‐(2‐Aminoethyl)pyridine (4AEPy) ions, the 2D perovskites of RP (4AEPy)2PbI4 and DJ (4AEPy)PbI4 from same organic amine is reported, which can realize reversible transformation under the treatment of HI and NH3, respectively. The interaction of N‐H···N hydrogen bond between adjacent organic molecules in (4AEPy)2PbI4 leads to the bending conformation of ethylamine groups, which results in a 2.4 Å reduction in layer spacing compared to typical phenylethylamine lead iodine ((PEA)2PbI4) 2D perovskite. Besides, the ethylamine groups of organic layers in (4AEPy)PbI4 are deeply inserted into octahedral cavities and directly participate in the construction of the conduction band minimum, which leads to a small exciton binding energy of 27.3 meV to generate free charges. The stronger coupling between the organic and inorganic layers and the minor exciton binding energy can promote the DJ phase to possess a more stable structure and better optoelectronic properties. Thus the (4AEPy)PbI4 device displays better light response and X‐ray detection capability with a high sensitivity of 5627 µC Gyair‐1 cm‐2 and the lowest detectable dose rate of 20 nGyair s‐1.

The low-dimensional halide perovskites have attracted increasing attention due to their improved moisture stability, reduced defects, and suppressed ions migration in many optoelectronic devices such as solar cells, light-emitting diodes, X-ray detectors, and so on. However, they are still limited by their large band gap and short charge carriers' diffusion length. Here, we demonstrate that the introduction of metal ions into organic interlayers of two-dimensional (2D) perovskite by cross-linking the copper paddle-wheel cluster-based lead bromide ([Cu(O 2 CÀ (CH 2 ) 3 À NH 3 ) 2 ]PbBr 4 ) perovskite single crystals with coordination bonds can not only significantly reduce the perovskite band gap to 0.96 eV to boost the X-ray induced charge carriers, but can also selectively improve the charge carriers' transport along the out-of-plane direction and blocking the ions motion paths. The [Cu(O 2 CÀ (CH 2 ) 3 À NH 3 ) 2 ]PbBr 4 single-crystal device can reach a record charges/ions collection ratio of 1.69 × 10 18 � 4.7 % μGy air À 1 s, and exhibit a large sensitivity of 1.14 × 10 5 � 7% μC Gy air À 1 cm À 2 with the lowest detectable dose rate of 56 nGy air s À 1 under 120 keV X-rays irradiation. In addition, [Cu-(O 2 CÀ (CH 2 ) 3 À NH 3 ) 2 ]PbBr 4 single-crystal detector exposed to the air without any encapsulation shows excellent X-ray imaging capability with long-term operational stability without any attenuation of 120 days.

All-inorganic perovskite cesium lead triiodide (CsPbI 3 ) has attracted much attention among the perovskite family due to its excellent optoelectronic properties and chemical stability. However, the high-temperature crystallization process makes CsPbI 3 less compatible with commercially flexible substrates, limiting its application into flexible optoelectronics. Here, a cation of 1-(3-aminopropyl)-2pyrrolidinone (APP) is reported that can form 1D (APP)PbI 3 perovskite as templates, and significantly reduce the CsPbI 3 black-phase transition energy with a low annealing temperature of 75 °C, which further enables a flexible (APP)PbI 3 /γ-CsPbI 3 (1D/3D) heterostructure photodetector on ITO/ PET substrate. A high external quantum efficiency (EQE) greater than 2377% is observed along the orientated 1D/3D heterostructure. The high gain and low noise result in a high specific detectivity (D*) over 10 12 Jones under −0.6 V low bias. The optimized device structure brings a high EQE × bandwidth product of 119 kHz under a low driving bias. Due to the high toughness of orientated APP + ions and the face-connected [PbI 3 ] − chains structure as a strong energy absorber, the flexible photodetector also shows excellent phase stability and impressive flexibility, remaining >90% initial responsivity after over 20 000 times bending with potential flexible imaging application in harsh environments.

The low‐dimensional halide perovskites have attracted increasing attention due to their improved moisture stability, reduced defects, and suppressed ions migration in many optoelectronic devices such as solar cells, light‐emitting diodes, X‐ray detectors, and so on. However, they are still limited by their large band gap and short charge carriers’ diffusion length. Here, we demonstrate that the introduction of metal ions into organic interlayers of two‐dimensional (2D) perovskite by cross‐linking the copper paddle‐wheel cluster‐based lead bromide ([Cu(O2C−(CH2)3−NH3)2]PbBr4) perovskite single crystals with coordination bonds can not only significantly reduce the perovskite band gap to 0.96 eV to boost the X‐ray induced charge carriers, but can also selectively improve the charge carriers’ transport along the out‐of‐plane direction and blocking the ions motion paths. The [Cu(O2C−(CH2)3−NH3)2]PbBr4 single‐crystal device can reach a record charges/ions collection ratio of 1.69×1018±4.7 % μGyair−1 s, and exhibit a large sensitivity of 1.14×105±7% μC Gyair−1 cm−2 with the lowest detectable dose rate of 56 nGyair s−1 under 120 keV X‐rays irradiation. In addition, [Cu(O2C−(CH2)3−NH3)2]PbBr4 single‐crystal detector exposed to the air without any encapsulation shows excellent X‐ray imaging capability with long‐term operational stability without any attenuation of 120 days.