Metal halide semiconductors have huge potential on X‐ray detection, due to their high atomic number, adjustable photoluminescence wavelength, superior stability, and simple fabrication process. Here, cesium lead halide nanocrystals (CsPbX3 NCs) are fabricated on paper substrate as scintillator screen for the first time. By means of all‐solution processed spray‐coating method with optimization of polymethyl methacrylate, large‐area (>600 cm2) and low‐cost (0.0975 dollar cm−2) flexible scintillator screens are obtained with high resolution (≈5 lp mm−1), low detection limit (2.97 μGy s−1), high light yield (≈30000 photons/MeV), and fast response speed (<15 ms). The screen can achieve high‐resolution X‐ray non‐distortion imaging for non‐planar objects and realize battery check and safety monitoring at a broad range of photon energy (10–160 keV). In addition, real‐time dose rates can be easily estimated through counting the luminous arcs of the designed visible indicator. More important, the screen shows remarkable tolerance to high‐dose X‐ray radiation (tolerance over 60 Gyair continuous radiation with only 3% performance degradation), water soaking (2000 h), and conventional storage (over 300 days without apparent deterioration under ambient conditions). Hence, this work may provide huge potential in the field of medical diagnosis, non‐planar detection, and safety monitoring in the future.

The continuous advancement of the Internet of Things (IoT) and photovoltaic technology has promoted the development of indoor photovoltaics (IPVs) that powers wireless devices. Nowadays, the CsPbX 3 perovskite has received widespread attention because of its high power conversion efficiency (PCE) in an indoor environment and suitable band gap for IPVs. In this work, we regulated the thickness of the photoactive layer (to optimize the carrier transport process without affecting indoor absorption) and bromine substitution (to adjust the band gap and improve the quality of the film) to reduce trap-assisted carrier recombination. A CsPbI 2.7 Br 0.3 perovskite cell with excellent performance was obtained, which is superior to c-Si cells in a low-light environment. The optimized device achieved PCE values of 32.69 and 33.11% under a 1000 lux fluorescent lamp and white lightemitting diode (WLED) illumination. The J−V hysteresis of the device is also effectively suppressed. Moreover, it has a steady-state output power of 7.76 μW (0.09 cm 2 , and can be enhanced by enlarging the areas), which can meet the consumption of many small wireless devices. It is worth noting that the optimized device has excellent applicability to be used in a complex indoor environment.

Two‐dimensional (2D) CsPbI3 is developed to conquer the phase‐stability problem of CsPbI3 by introducing bulky organic cations to produce a steric hindrance effect. However, organic cations also inevitably increase the formation energy and difficulty in crystallization kinetics regulation. Such poor crystallization process modulation of 2D CsPbI3 leads to disordered phase‐arrangement, which impedes the transport of photo‐generated carriers and worsens device performance. Herein, a type of C3N quantum dots (QDs) with ordered carbon and nitrogen atoms to manipulate the crystallization process of 2D CsPbI3 for improving the crystallization pathway, phase‐arrangement and morphology, is introduced. Combination analyses of theoretical simulation, morphology regulation and femtosecond transient absorption (fs‐TA) characterization, show that the C3N QDs induce the formation of electron‐rich regions to adsorb bulky organic cations and provide nucleation sites to realize a bi‐directional crystallization process. Meanwhile, the quality of 2D CsPbI3 film is improved with lower trap density, higher surface potential, and compact morphology. As a result, the power conversion efficiency (PCE) of the optimized device (n = 5) boosts to an ultra‐high value of 15.63% with strengthened environmental stability. Moreover, the simple C3N QDs insertion method shows good universality to other bulky organic cations of Ruddlesden‐Popper and Dion‐Jacobson, providing a good modulation strategy for other optoelectronic devices.

The two-dimensional (2D) Ruddlesden–Popper (RP) CsPbI3 with hydrophobic organic spacers can significantly improve the environmental and phase stability of photovoltaic devices by suppressing ion migration and inducing steric hindrance. However, due to the multiple-quantum-well structure, these spacer cations lead to weak interactions in 2D RP CsPbI3, which seriously affect the carrier transport. Here, a novel N–H-group-rich phenylhydrazine spacer, namely, PHA, was developed for 2D RP CsPbI3 perovskite solar cells (PSCs). A series of characterizations confirm that the 2D perovskites using PHA spacers enhanced the N–H···I hydrogen-bonding interaction between the organic spacer cations and the [PbI6]4– inorganic layer and accelerated the crystallization rate of the perovskite film, which was beneficial to the preparation of high-quality films with preferred vertical orientation, large grain size, and dense morphology. Meanwhile, the trap state density of the as-prepared 2D RP perovskite films is significantly reduced to enable efficient charge carrier transport. As a result, the (PHA)2Cs4Pb5I16 PSCs achieved a performance of 16.23% with good environmental stability. This work provides a simple organic spacer selection scheme to realize interaction optimization in 2D RP CsPbI3 to develop efficient and stable PSCs.