particles directly determines the performance of time resolution, response rate, and counting ability of radiation detectors. For example, dynamic high speed X-ray imaging requires frame rates of 2 ns (GHz) and thus the scintillator with sub-nanosecond response is in urgent demand. [3] Sub-nanosecond scintillator is also highly needed in PET detector module to increase the accidental coincidence rate, without image reconstruction to approaching the recognized goals of 10 ps time resolution. [2,7,8] Some nuclear physics experiments with very high count rates required sub-nanosecond scintillation to avoid signal piling up. [9] BaF 2 , CsCl, and ZnO:Ga scintillators have demonstrated sub-nanosecond response speed, with the short lifetime as 0.8, 0.9, and 0.7 ns, respectively. [10,11] However, BaF 2 and CsCl suffered from longstanding weakness of extra-low light yield (<1500 photons MeV −1 ) due to the inefficient core-valence transitions and also an undesirable slow lifetime component (few microseconds). [10] Besides the low light yield, ZnO: Ga scintillator was also limited by the manufacturing difficulty in bulk crystal and high production cost. [11,12] Therefore, new sub-nanosecond scintillator materials with considerable light yield urgently need to be explored. Perovskite materials have emerged as a new family of radiation scintillators with tunable wavelength andPerovskite materials have demonstrated great potential for ultrafast scintillators with high light yield. However, the decay time of perovskite still cannot be further minimized into sub-nanosecond region, while sub-nanosecond scintillators are highly demanded in various radiation detection, including high speed X-ray imaging, time-of-flight based tomography or particle discrimination, and timing resolution measurement in synchrotron radiation facilities, etc. Here, a rational design strategy is showed to shorten the scintillation decay time, by maximizing the dielectric difference between organic amines and Pb-Br octahedral emitters in 2D organic-inorganic hybrid perovskites (OIHP). Benzimidazole (BM) with low dielectric constant inserted between [PbBr 6 ] 2− layers, resulting in a surprisingly large exciton binding energy (360.3 ± 4.8 meV) of 2D OIHP BM 2 PbBr 4 . The emitting decay time is shortened as 0.97 ns, which is smallest among all the perovskite materials. Moreover, the light yield is 3190 photons MeV −1 , which is greatly higher than conventional ultrafast scintillator BaF 2 (1500 photons MeV −1 ). The rare combination of ultrafast decay time and considerable light yield renders BM 2 PbBr 4 excellent performance in γ-ray, neutron, α-particle detection, and the best theoretical coincidence time resolution of 65.1 ps, which is only half of the reference sample LYSO (141.3 ps).

The luminescent property of 2D perovskite materials promotes their applications in light emitting diodes, phosphor powders, and scintillators. Recently, an interesting extrinsic low‐energy broadband luminescence is hotly investigated. However, the understanding of such emissions is still at the early stage. In this study, based on a modified solvent evaporation method, centimeter‐size (BDA)PbI4 (BDA = NH3C4H8NH32+) single crystals are grown which, besides the band–band emission, show a large Stokes‐shifted broadband luminescence. We find such emission can be effectively excited by sub‐gap photons and conclude defects‐induced shallow traps are the corresponding luminescence centers. Density functional theory (DFT) calculations indicate that in‐plane iodine vacancies can introduce shallow electron traps in the band gap and give rise to the broadband emission.

In recent years, organic–inorganic hybrid halide perovskite materials have been found to have low thermal conductivity and a large Seebeck effect, giving them great potential for thermoelectric applications. More stable single crystals make this possible. In this work, high‐quality MAPbI3 single crystals are prepared using a modified solvent engineering method, and their trap density is as low as 2.5 × 109 cm−3. It is noticed that the reaction between the crystal a metal electrode causes different degrees of doping effect along the vertical direction, leading to an increase in the intrinsic P‐type with Au metal, and forming N‐type semiconductor characteristics with Ag metal. A high Seebeck voltage thermoelectric module is obtained by combining the perovskite single crystal with different conductive characteristics. After device optimization, the thermoelectric potential of the champion module reaches a high voltage of 337 mV at 115 °C, the maximum output power with load reaches about 30 nW, and the theoretical maximum power reaches 65 nW. It is hoped that this research can promote the development of low thermal conductivity perovskite materials in the thermoelectric field.