Through-Space Charge-Transfer Organogold(III) Complexes Enable High-Performance X-ray Scintillation and Imaging.

Organic scintillators have recently attracted growing attention for X-ray detection in industrial and medical applications. However, these materials still face critical obstacles of low attenuation efficiency and/or inefficient triplet exciton utilization. Here we developed a new category of organogold(III) complexes, Tp-Au-1 and Tp-Au-2, through adopting a through-space interaction motif to realize high X-ray attenuation efficiency and efficient harvesting of triplet excitons for emission. Thanks to the efficient through-space charge transfer process, this panel of complexes achieved higher photoluminescence quantum yield and shorter radiative lifetimes compared with the through-bond reference complexes. Inspiringly, these organogold(III) complexes exhibited polarity-dependent emission origins: thermally activated delayed fluorescence and/or phosphorescence. Under X-ray irradiation, Tp-Au-2 manifested intense radioluminescence together with a record-high scintillation light yield of 77,600 photons MeV-1 for organic scintillators. The resulting scintillator screens demonstrated high-quality X-ray imaging with >16.0 line pairs mm-1 spatial resolution, outstripping most organic and inorganic scintillators. This finding provides a feasible strategy for the design of superior organic X-ray scintillators.

Enhanced Photoluminescence Quantum Yield of Metal Halide Perovskite Microcrystals for Multiple Optoelectronic Applications.

Recently, metal 1halide perovskites have shown compelling optoelectronic properties for both light-emitting devices and scintillation of ionizing radiation. However, conventional lead-based metal halide perovskites are still suffering from poor material stability and relatively low X-ray light yield. This work reports cadmium-based all-inorganic metal halides and systematically investigates the influence of the metal ion incorporation on the optoelectronic properties. This work introduces the bi-metal ion incorporation strategy and successfully enhances the photoluminescence quantum yield (98.9%), improves thermal stability, and extends the photoluminescence spectra, which show great potential for white light emission. In addition, the photoluminescent decay is also modulated with single metal ion incorporation, the charge carrier lifetime is successfully reduced to less than 1 µs, and the high luminescent efficiency and X-ray light yield (41 000 photons MeV-1 ) are maintained. Then, these fast scintillators are demonstrated for high-speed light communication and sensitive X-ray detection and imaging.

Charge-Carrier Dynamics of Evaporated Bismuth-Based Chalcogenide Thin Films Probed with Time-Resolved Microwave Conductivity.

Chalcogenide-based semiconductors are emerging as a set of highly promising candidates for optoelectronic devices, owing to their low toxicity, cost-effectiveness, exceptional stability, and tunable optoelectronic properties. Nonetheless, the limited understanding of charge recombination mechanisms and trap states of these materials is impeding their further development. To fill this gap, we conducted a comprehensive study of bismuth-based chalcogenide thin films and systematically investigated the influence of post-treatments via time-resolved microwave conductivity and temperature-dependent photoluminescence. The key finding in this work is that post-treatment with Bi could effectively enhance the crystallinity and charge-carrier mobility. However, the carrier density also increased significantly after the Bi treatment. On the contrary, post-treatment of evaporated Bi2S3 thin films with sulfur could effectively increase the carrier lifetime and mobility by passivating the trap states on the grain boundaries, which is also consistent with the enhanced radiative recombination efficiency.

Thick-junction perovskite X-ray detectors: processing and optoelectronic considerations.

Metal halide perovskites have attracted increasing attention due to their strong stopping power, defect tolerance, large mobility lifetime product, tunable bandgap and simple single-crystal growth via low-cost solution processes, particularly for ionizing radiation detection. Over the past few years, semiconductor-type X-ray detectors based on a variety of perovskites have been developed, showing impressive progress in achieving high sensitivity and low detection limits. In this study, based on the requirement of material properties for high-performance X-ray detectors, we review various materials used for direct detection and summarize the processing techniques and optoelectronic considerations of thick-junction perovskite X-ray detectors. This review also highlights the key challenges facing perovskite X-ray detectors towards real applications and discusses the opportunities, which are promising to explore and may require more research activities.

Room-Temperature Diffusion-Induced Extraction for Perovskite Nanocrystals with High Luminescence and Stability.

Metal halide perovskite nanocrystals (NCs) serve as a kind of ideal semiconductor for luminescence and display applications. However, the optoelectronic performance and stability of perovskite NCs are mainly subjected to current ligand strategies since these ligands exhibit a highly dynamic binding state, which complicates NC purification and storage. Herein, a method named diffusion-induced extraction is developed for crystallization (DEC) at room temperature, in which silicone oil serves as a medium to separate the solvent from perovskite precursors and diethyl ether promotes the nucleation, leading to highly emissive perovskite NCs. The formation mechanism of NCs using this approach is elucidated, and their optoelectronic properties are fully characterized. The resultant NCs ink exhibits a high photoluminescence quantum yield (PLQY) over 90% with a narrow full width at half maximum of 17 nm. The DEC method strengthens the interaction between ligand and NCs via the hydrophobic silicone oil. Therefore, the NCs maintain almost 95% of their initial PLQYs after aging more than seven months in air. The findings will be of great significance for the continued advancement of high PLQY perovskite NCs through a better understanding of formation dynamics. The DEC strategy presents a major step forward for advancing the field of perovskite semiconductor nanomaterials.

Interfacial Engineering of Perovskite Solar Cells with Evaporated PbI2 Ultrathin Layers.

Perovskite solar cells are one of the most promising thin-film photovoltaic techniques, which have an unprecedented progress in the last decade. It is well-recognized in the perovskite community that nonradiative recombination losses and the open-circuit voltage deficit are the dominant limiting factors to further improve the device efficiency. Recently, multiple groups have reported that lead iodide can effectively passivate both perovskite grain boundaries and the interfaces between perovskite and charge transport layers. However, most of the excess PbI2 was processed with solution methods and formed PbI2 grains, which cannot cover perovskite layers completely. It is also very challenging to spin-coat PbI2 layers directly on perovskites, which requires orthogonal solvents. In this work, we deposit additional PbI2 thin layers directly on perovskite thin films via thermal evaporation. The impact of PbI2 layers on the perovskite thin films and devices is systematically investigated. It was found that the evaporated PbI2 thin films can effectively reduce the nonradiative recombination and enhance the device performance. The optimized thickness of the PbI2 layer was determined to be around 10 nm, which results in a relatively high Voc of 1.18 V and power conversion efficiency of 21.52%.

Crystallization of CsPbBr3 single crystals in water for X-ray detection.

Metal halide perovskites have fascinated the research community over the past decade, and demonstrated unprecedented success in optoelectronics. In particular, perovskite single crystals have emerged as promising candidates for ionization radiation detection, due to the excellent opto-electronic properties. However, most of the reported crystals are grown in organic solvents and require high temperature. In this work, we develop a low-temperature crystallization strategy to grow CsPbBr3 perovskite single crystals in water. Then, we carefully investigate the structure and optoelectronic properties of the crystals obtained, and compare them with CsPbBr3 crystals grown in dimethyl sulfoxide. Interestingly, the water grown crystals exhibit a distinct crystal habit, superior charge transport properties and better stability in air. We also fabricate X-ray detectors based on the CsPbBr3 crystals, and systematically characterize their device performance. The crystals grown in water demonstrate great potential for X-ray imaging with enhanced performance metrics.

Layered Perovskites Enhanced Perovskite Photodiodes.

Recently, two-dimensional layered perovskites have emerged as effective additives for stabilizing conventional three-dimensional metal halide perovskites. With the addition of layered perovskites, the perovskite-based devices also exhibited enhanced optoelectronic properties, such as reduced nonradiative recombination and ionic migration, strengthened crystallinity, and anisotropic charge transport. However, the influence of the large organic cations on the performance metrics of the photodiodes is not fully understood. In this work, we systematically investigate the device performance and related optoelectronic features of the layered perovskite-enhanced perovskite photodiodes. In particular, with the addition of large organic cations to the FA0.83Cs0.17PbI3 perovskite matrix, the devices exhibited reduced dark current and noise, increased detectivity of >1013 Jones, and a consistent high speed of <100 ns. More importantly, the layered perovskite-enhanced photodiodes exhibited less hysteresis and higher breakdown voltages.

Evaporated Perovskite Thick Junctions for X-Ray Detection.

X-ray detection is widely utilized in our daily life, such as in medical diagnosis, security checking, and environmental monitoring. However, most of the commercial X-ray detectors are based on inorganic semiconductors, e.g., Si, CdTe, and Ge, which require complex and costly fabrication processes. Metal halide perovskites have recently emerged as a set of promising candidates for ionizing radiation detection, owing to the high attenuation coefficient, long carrier lifetime, and excellent charge transport properties. Perovskite single crystals have been successfully implemented in X-ray detection, but the fragile single crystals limit the device fabrication and the integration with a read-out circuit. In addition, it is hard to reach inch-size single crystals for real application. Flexible devices based on perovskite films or composite films have also been reported, but either the thickness or charge transport properties are limited by the solution processes. In this work, we introduced thermal co-evaporation to deposit highly efficient formamidinium lead iodide perovskite films. Considering the trade-off between X-ray absorption and charge transport, we optimized the active layer thickness and achieved large-area and flexible X-ray detectors with state-of-the-art device performance, including extremely low dark current and noise, fast response, and high sensitivity of 142.1 µC Gyair-1 cm-2.

Correction to "Monitoring the Hierarchical Evolution from a Double-Stranded Helix to a Well-Defined Microscopic Morphology Based on a Turbine-like Aromatic Molecule".

[This corrects the article DOI: 10.1021/acsomega.0c01443.].

Monitoring the Hierarchical Evolution from a Double-Stranded Helix to a Well-Defined Microscopic Morphology Based on a Turbine-like Aromatic Molecule.

1H-Indazolo[1,2-b]phthalazine-5,10-dione IPDD with an approximate turbine-like spatial structure, primary assembled double-stranded helices at the first level, was predicted by quantum chemical calculations and confirmed by atomic force microscopy. The higher-dimensional hierarchical architectures including fibrils, helical fibers, spherical shells, and porous prismatic structures were observed in sequence by the scanning electron microscopy technique. The final porous prismatic structures sensitive to NH3 vapors have the potential to be applied in gas sensing and absorbing materials.

Comparison of waxy and normal potato starch remaining granules after chemical surface gelatinization: pasting behavior and surface morphology.

To understand the contribution of granule inner portion to the pasting property of starch, waxy potato starch and two normal potato starches and their acetylated starch samples were subjected to chemical surface gelatinization by 3.8 mol/L CaCl2 to obtain remaining granules. Native and acetylated, original and remaining granules of waxy potato starch had similar rapid visco analyzer (RVA) pasting profiles, while those of two normal potato starches behaved obviously different from each other. All remaining granules had lower peak viscosity than the corresponding original granules. Contribution of waxy potato starch granule's inner portion to the peak viscosity was significant more than those of normal potato starches. The shell structure appearing on the remaining granule surface for waxy potato starch was smoother and thinner than that for normal potato starches as observed by scanning electron microscopy, indicating a more regular structure of shell and a more ordered packing of shell for waxy potato starch granules. The blocklet size of waxy potato starch was smaller and more uniform than those of normal potato starches as shown by atomic force microscopy images of original and remaining granules. In general, our results provided the evidence for the spatial structure diversity between waxy and normal potato starch granules: outer layer and inner portion of waxy potato starch granule had similar structure, while outer layer had notably different structure from inner portion for normal potato starch granule.