2D perovskite single crystals have emerged as excellent optoelectronic materials owing to their unique anisotropic properties. However, growing large 2D perovskite single crystals remains challenging and time‐consuming. Here, a new composition of lead‐free 2D perovskite—4‐fluorophenethylammonium bismuth iodide [(F‐PEA)3BiI6] is reported. An oriented bulk 2D wafer with a large area of 1.33 cm2 is obtained by tableting disordered 2D perovskite powders, resulting in anisotropic resistivities of 5 × 1010 and 2 × 1011 Ω cm in the lateral and vertical directions, respectively. Trivalent Bi3+ ions are employed to achieve a stronger ionic bonding energy with I‐ ions, which intrinsically suppress the ion‐migration effect. Thus, the oriented wafer presents good capabilities in both charge collection and ion‐migration suppression under a large applied bias along the out‐of‐plane direction, making it suitable for low‐dosage X‐ray detection. The large‐area wafer shows a sensitive response to hard X‐rays operated at a tube voltage of 120 kVp with the lowest detectable dose rate of 30 nGy s‐1. Thus, the fast tableting process is a facile and effective strategy to synthesize large‐area, oriented 2D wafers, showing excellent X‐ray detection performance and operational stability that are comparable to those of 2D perovskite single crystals.

Solution-processed perovskites as emerging semiconductors have achieved unprecedented milestones in sensor optoelectric devices. Stability along with the device noise issues are the major obstacle for photodetectors to compete with the traditional devices. Here, we demonstrated that L-ascorbic acid (L-AA) as a polyhydroxy ester can coordinate with the amino group of formamidine cations (FA + ) through multiple hydrogen bond interactions to stabilize the perovskite, which protect the FA + ions from nucleophile attack and effectively suppress the degradation of FA + ions, improving the perovskite stability and suppressing the device noise to below 0.3 pA Hz −1/2 with a large linear dynamic range of 239 dB. The dual functions of L-AA enable the perovskite photodetector to have a high detectivity of 10 12 Jones. The selfpowered device works with no energy consumption and maintains an undegraded performance over 1200 h of inspection at ambient conditions, which is promising for infrastructure construction, signal sensing, and real-time information delivery.

Design and development of highly efficient photocatalytic materials are key to employ photocatalytic technology as a sound solution to energy and environment related challenges. This work aims to significantly boost photocatalytic activity through rich indium vacancies (VIn) In2S3 with atomic p–n homojunction through a one‐pot preparation strategy. Positron annihilation spectroscopy and electron paramagnetic resonance reveal existence of VIn in the prepared photocatalysts. Mott–Schottky plots and surface photovoltage spectra prove rich VIn In2S3 can form atomic p–n homojunction. It is validated that p–n homojunction can effectively separate carriers combined with photoelectrochemical tests. VIn decreases carrier transport activation energy (CTAE) from 0.64 eV of VIn‐poor In2S3 to 0.44 eV of VIn‐rich In2S3. The special structure endows defective In2S3 with multifunctional photocatalysis properties, i.e., hydrogen production (872.7 µmol g−1 h−1), degradation of methyl orange (20 min, 97%), and reduction in heavy metal ions Cr(VI) (30 min, 98%) under simulated sunlight, which outperforms a variety of existing In2S3 composite catalysts. Therefore, such a compositional strategy and mechanistic study are expected to offer new insights for designing highly efficient photocatalysts through defect engineering.

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.

Quasi-2D perovskites have been demonstrated to be competitive materials in the photodetection fields due to the enhanced moisture stability by large organic cations. However, as the increasing demands of modern technology, it is still challenging to combine the flexibility with the capability of weak light detection in a low-cost way. Here, amides, carboxylic acids, and anhydrides groups-rich carbonized polymer dots (CPDs) were employed to fill in the perovskite grain boundaries, which can passivate the point defects of perovskite by coordinating with the unbonded Pb atoms, and reduce the leakage current. Weak light detection capability was demonstrated by directly resolving light with an intensity of 10.1 pW cm−2. More importantly, the stretchable polymer chains on CPDs strongly interact with perovskite ions through multiple supramolecular interactions, and extend the stretchable properties to the perovskite/CPDs composites, which can maintain the integral structure stability during the deformation of perovskite crystals and restricted any crack by releasing the film strain. Our fabricated devices show extraordinary flexible stability in the bending-dependent response tests. The viscoelasticity of CPDs improves the bending stability of the flexible quasi-2D perovskite photodetectors, and device performance shows no degradation after bending 10000 times, comparable or even outperforming the dominating flexible photodetectors.