The rising demand for radiation detection materials in many applications has led to extensive research on scintillators. The ability of a scintillator to absorb high-energy (kiloelectronvolt-scale) X-ray photons and convert the absorbed energy into low-energy visible photons is critical for applications in radiation exposure monitoring, security inspection, X-ray astronomy and medical radiography. However, conventional scintillators are generally synthesized by crystallization at a high temperature and their radioluminescence is difficult to tune across the visible spectrum. Here we describe experimental investigations of a series of all-inorganic perovskite nanocrystals comprising caesium and lead atoms and their response to X-ray irradiation. These nanocrystal scintillators exhibit strong X-ray absorption and intense radioluminescence at visible wavelengths. Unlike bulk inorganic scintillators, these perovskite nanomaterials are solution-processable at a relatively low temperature and can generate X-ray-induced emissions that are easily tunable across the visible spectrum by tailoring the anionic component of colloidal precursors during their synthesis. These features allow the fabrication of flexible and highly sensitive X-ray detectors with a detection limit of 13 nanograys per second, which is about 400 times lower than typical medical imaging doses. We show that these colour-tunable perovskite nanocrystal scintillators can provide a convenient visualization tool for X-ray radiography, as the associated image can be directly recorded by standard digital cameras. We also demonstrate their direct integration with commercial flat-panel imagers and their utility in examining electronic circuit boards under low-dose X-ray illumination.

Supporting Information Materials and MethodsChemicals and reagents. Lead bromide (≥ 98%), lead iodide (99.999% trace metal basis), DMF (anhydrous, 99.8%) and GBL (≥ 99%) were purchased from Sigma Aldrich. MABr, FABr and FAI were purchased from Dyesol Limited (Australia). All salts and solvents were used as received without any further purification. MAPbBr 3 , FAPbBr 3 and FAPbI 3 single crystals were grown by Inverse Temperature Crystallization (ITC) technique from 1 M solution of PbBr 2 /MABr in DMF, 1 M solution PbBr 2 /FABr in DMF:GBL (1:1 v/v) and 0.8 M solution of PbI 2 /FAI in GBL, respectively, as it was previously reported by Saidaminov et al. 1,2Powder X-ray diffraction was performed on a Bruker AXS D8 diffractometer using Cu-Kα radiation.

So-called zero-dimensional perovskites, such as Cs 4 PbBr 6 , promise outstanding emissive properties. However, Cs 4 PbBr 6 is mostly prepared by melting of precursors that usually leads to a coformation of undesired phases. Here, we report a simple low-temperature solution-processed synthesis of pure Cs 4 PbBr 6 with remarkable emission properties. We found that pure Cs 4 PbBr 6 in solid form exhibits a 45% photoluminescence quantum yield (PLQY), in contrast to its three-dimensional counterpart, CsPbBr 3 , which exhibits more than 2 orders of magnitude lower PLQY. Such a PLQY of Cs 4 PbBr 6 is significantly higher than that of other solid forms of lower-dimensional metal halide perovskite derivatives and perovskite nanocrystals. We attribute this dramatic increase in PL to the high exciton binding energy, which we estimate to be ∼353 meV, likely induced by the unique Bergerhoff−Schmitz−Dumont-type crystal structure of Cs 4 PbBr 6 , in which metal-halide-comprised octahedra are spatially confined. Our findings bring this class of perovskite derivatives to the forefront of color-converting and light-emitting applications.

A rapid, low‐temperature, and solution‐based route is developed for growing large‐sized cesium lead halide perovskite single crystals under ambient conditions. An ultralow minority carrier concentration was measured in CsPbBr3 (≈108 holes per cm3, much lower than in any other lead halide perovskite and crystalline silicon), which enables to realize self‐powered photodetectors with a high ON/OFF ratio (105).

Defect passivation and surface modification of hybrid perovskite films are essential to achieving high power conversion efficiency (PCE) and stable perovskite photovoltaics. Here, we demonstrate a facile strategy that combines high PCE with high stability in CH 3 NH 3 PbI 3 (MAPbI 3 ) solar cells. The strategy utilizes inorganic perovskite quantum dots (QDs) to distribute elemental dopants uniformly across the MAPbI 3 film and attach ligands to the film's surface. Compared with pristine MAPbI 3 films, MAPbI 3 films processed with QDs show a reduction in tail states, smaller trap-state density, and an increase in carrier recombination lifetime. This strategy results in reduced voltage losses and an improvement in PCE from 18.3% to 21.5%, which is among the highest efficiencies for MAPbI 3 devices. Ligands introduced with the aid of the QDs render the perovskite film's surface hydrophobic-inhibiting moisture penetration. The devices maintain 80% of their initial PCE under 1-sun continuous illumination for 500 h and show improved thermal stability.

Lead halide perovskite solar cells (PSCs) have advanced rapidly in performance over the past decade. Single-crystal PSCs based on micrometers-thick grain-boundary-free films with long charge carrier diffusion lengths and enhanced light absorption (relative to polycrystalline films) have recently emerged as candidates for advancing PSCs further toward their theoretical limit. To date, the preferred method to grow MAPbI3 single-crystal films for PSCs involves solution processing at temperatures ≳120 °C, which adversely affects the films’ crystalline quality, especially at the surface, primarily because of methylammonium iodide loss at such high temperatures. Here we devise a solvent-engineering approach to reduce the crystallization temperature of MAPbI3 single-crystal films (<90 °C), yielding better quality films with longer carrier lifetimes. Single-crystal MAPbI3 inverted PSCs fabricated with this strategy show markedly enhanced open-circuit voltages (1.15 V vs 1.08 V for controls), leading to power conversion efficiencies of up to 21.9%, which are among the highest reported for MAPbI3-based devices.

Hybrid perovskite crystals have emerged as an important class of semiconductors because of their remarkable performance in optoelectronics devices. The interface structure and chemistry of these crystals are key determinants of the device’s performance. Unfortunately, little is known about the intrinsic properties of the surfaces of perovskite materials because extrinsic effects, such as complex microstructures, processing conditions, and hydration under ambient conditions, are thought to cause resistive losses and high leakage current in solar cells. We reveal the intrinsic structural and optoelectronic properties of both pristinely cleaved and aged surfaces of single crystals. We identify surface restructuring on the aged surfaces (visualized on the atomic-scale by scanning tunneling microscopy) that lead to compositional and optical bandgap changes as well as degradation of carrier dynamics, photocurrent, and solar cell device performance. The insights reported herein clarify the key variables involved in the performance of perovskite-based solar cells and fabrication of high-quality surface single crystals, thus paving the way toward their future exploitation in highly efficient solar cells.

Much recent attention has been devoted towards unraveling the microscopic optoelectronic properties of hybrid organic-inorganic perovskites. Here we investigate by coherent inelastic neutron scattering spectroscopy and Brillouin light scattering, low frequency acoustic phonons in four different hybrid perovskite single crystals: MAPbBr_{3}, FAPbBr_{3}, MAPbI_{3}, and α-FAPbI_{3} (MA: methylammonium, FA: formamidinium). We report a complete set of elastic constants characterized by a very soft shear modulus C_{44}. Further, a tendency towards an incipient ferroelastic transition is observed in FAPbBr_{3}. We observe a systematic lower sound group velocity in the technologically important iodide-based compounds compared to the bromide-based ones. The findings suggest that low thermal conductivity and hot phonon bottleneck phenomena are expected to be enhanced by low elastic stiffness, particularly in the case of the ultrasoft α-FAPbI_{3}.