PF6 - Pseudohalides Anion Based Metal-Free Perovskite Single Crystal for Stable X-Ray Detector to Attain Record Sensitivity

Pyroelectric Photoconductive Diode for Highly Sensitive and Fast DUV Detection

Detecting high-energy photons from the deep ultraviolet (DUV) to X-rays is vital in security, medicine, industry, and science. Wide bandgap (WBG) semiconductors exhibit great potential for detecting high-energy photons. However, the implementation of highly sensitive and high-speed detectors based on WBG semiconductors has been a huge challenge due to the inevitable deep level traps and the lack of appropriate device structure engineering. Here, a sensitive and fast pyroelectric photoconductive diode (PPD), which couples the interface pyroelectric effect with the photoconductive effect based on tailored polycrystal Ga-rich GaOx (PGR-GaOx) Schottky photodiode, is first proposed. The PPD device exhibits ultrahigh detection performance for DUV and X-ray light. The responsivity for DUV light and sensitivity for X-ray are up to 104 A W-1 and 105 µC Gyair -1 cm-2, respectively. Especially, the interface pyroelectric effect induced by polar symmetry in the depletion region of the PGR-GaOx can significantly improve the response speed of the device by 105 times. Furthermore, the potential of the device is demonstrated for imaging enhancement systems with low power consumption and high sensitivity. This work fully excavates the potential of the pyroelectric effect for detectors and provides a novel design strategy to achieve sensitive and high-speed detectors.

Aminoazanium of A-site Cations in Metal-Free Halide Perovskite Single Crystals to Reduce Thermal Expansion for Efficient X-ray Detection

Metal-free perovskites (MFPs) have recently become a newcomer in X-ray detection due to their flexibility and low toxicity characteristics. However, their photoelectronic properties and stability should be further improved mainly through materials design. Here, the aminoazanium of DABCO2+ was developed for the preparation of NDABCO-NH4Br3 (NDABCO = N-amino-N'-diazabicyclo[2.2.2]octonium) single crystals (SCs), and its physical properties, intermolecular interactions, and device performance were systematically explored. Notably, NDABCO-NH4Br3 can achieve improved stability by enlarging defect formation energy and inducing abundant intermolecular forces. Moreover, the slight lattice distortion could ensure the weakening electron-phonon coupling for improving carrier transport. In particular, the slight lattice distortion after the long-chain NDABCO2+ introduction could retard thermal expansion for the preparation of high-quality crystals. Finally, the corresponding X-ray detector delivered a moderate sensitivity of 623.3 μC Gyair-1 cm-2. This work provides a novel strategy through rationally designed organic cations to balance the material stability and device performance.

"One-Click Restart" Recycling of Metal-Free Perovskite X-Ray Detectors

Halide perovskites have shown great potential in X-ray detection due to outstanding optoelectronic properties. However, finding a cost-effective and environmentally sustainable method for handling end-of-life devices has remained challenging. Here, a "One-Click Restart" eco-friendly recycling strategy is introduced for end-of-life perovskite X-ray detectors. This method, utilizing water, allows for the recapture and reuse of both perovskite and conductor materials. The process is straightforward and environmentally friendly, eliminating the need for further chemical treatment, purification, additional additives or catalysts, and complex equipment. A sustainable device cycle is developed by reconstructing flexible perovskite membranes for wearable electronics from recycled materials. Large-scale, flexible membranes made from metal-free perovskite DABCO-N2H5-I3 (DABCO = N-N'-diazabicyclo[2.2.2]octonium) achieve remarkably impressive average sensitivity of 6204 ± 268 µC Gyair -1 cm-2 and a low detection limit of 102.3 nGyair s-1, which makes highly effective for X-ray imaging. The sensitivity of recycled flexible devices not only matches that of single-crystal devices made with fresh materials but also ranks as the highest among all metal-free perovskite X-ray detectors. "One-Click Restart" applies to scalable flexible devices derived from aged single-crystal counterparts, offering significant cost, time, and energy savings compared to their single-crystal equivalents. Such advantages significantly boost future market competitiveness.

Surface Passivation toward Multiple Inherent Dangling Bonds in Indium Phosphide Quantum Dots

Indium phosphide (InP) quantum dots (QDs) have become the most recognized prospect to be less-toxic surrogates for Cd-based optoelectronic systems. Due to the particularly dangling bonds (DBs) and the undesirable oxides, the photoluminescence performance and stability of InP QDs remain to be improved. Previous investigations largely focus on eliminating P-DBs and resultant surface oxidation states; however, little attention has been paid to the adverse effects of the surface In-DBs on InP QDs. This work demonstrates a facile one-step surface peeling and passivation treatment method for both In- and P-DBs for InP QDs. Meanwhile, the surface treatment may also effectively support the encapsulation of the ZnSe shell. Finally, the generated InP/ZnSe QDs display a narrower full width at half-maximum (fwhm) of ∼48 nm, higher photoluminescence quantum yields (PLQYs) of ∼70%, and superior stability. This work enlarges the surface chemistry engineering consideration of InP QDs and considerably promotes the development of efficient and stable optoelectronic devices.

Molecularly thin, two-dimensional all-organic perovskites

Recently, the emergence of all-organic perovskites with three-dimensional (3D) structures has expanded the potential applications of perovskite materials. However, the synthesis and utilization of all-organic perovskites in 2D form remain largely unexplored because the design principle has not been developed. We present the successful synthesis of a metal-free 2D layered perovskite, denoted as the Choi-Loh van der Waals phase (CL-v phase), with the chemical formula A2B2X4, where A represents a larger-sized cation compared to B and X denotes an anion. The CL-v phase exhibits a van der Waals gap enabled by interlayer hydrogen bonding and can be exfoliated or grown as molecularly thin 2D organic crystals. The dielectric constants of the CL-v phase range from 4.8 to 5.5 and we demonstrate their potential as gate dielectrics for thin-film transistors.

Dimensionality Engineering of Organic-Inorganic Halide Perovskites for Next-Generation X-Ray Detector

The next-generation X-ray detectors require novel semiconductors with low material/fabrication cost, excellent X-ray response characteristics, and robust operational stability. The family of organic-inorganic hybrid perovskites (OIHPs) materials comprises a range of crystal configuration (i.e., films, wafers, and single crystals) with tunable chemical composition, structures, and electronic properties, which can perfectly meet the multiple-stringent requirements of high-energy radiation detection, making them emerging as the cutting-edge candidate for next-generation X-ray detectors. From the perspective of molecular dimensionality, the physicochemical and optoelectronic characteristics of OIHPs exhibit dimensionality-dependent behavior, and thus the structural dimensionality is recognized as the key factor that determines the device performance of OIHPs-based X-ray detectors. Nevertheless, the correlation between dimensionality of OIHPs and performance of their X-ray detectors is still short of theoretical guidance, which become a bottleneck that impedes the development of efficient X-ray detectors. In the review, the advanced studies on the dimensionality engineering of OIHPs are critically assessed in X-ray detection application, discussing the current understanding on the "dimensionality-property" relationship of OIHPs and the state-of-the-art progresses on the dimensionality-engineered OIHPs-based X-ray detector, and highlight the open challenges and future outlook of this field.

Molecular Design of Layered Hybrid Silver Bismuth Bromine Single Crystal for Ultra-Stable X-Ray Detection With Record Sensitivity

Nowadays, weak interlayer coupling and unclear mechanism in layered hybrid silver bismuth bromine (LH-AgBiBr) are the main reasons for limiting its further enhanced X-ray detection sensitivity and stability. Herein, the design rules for LH-AgBiBr and its influence on X-ray detection performance are reported for the first time. Although shortening amine size can enhance interlayer coupling, its detection performance is severely hampered by its easier defect formation caused by enlarged micro strain. In contrast, an appropriate divalent amine design endows the material with improved interlayer coupling and released micro strain, which benefits crystal stability and mechanical hardness. Another contribution is to increase material density and dielectric constant; thus, enhancing X-ray absorption and carrier transport. Consequently, the optimized parallel device based on BDA2 AgBiBr8 achieves a record sensitivity of 2638 µC Gyair -1 cm-2 and an ultra-low detection limit of 7.4 nGyair s-1 , outperforming other reported LH-AgBiBr X-ray detectors. Moreover, the unencapsulated device displays remarkable anti-moisture, anti-thermal (>150 °C), and anti-radiation (>1000 Gyair ) endurance. Eventually, high-resolution hard X-ray imaging is demonstrated by linear detector arrays under a benign dose rate (1.63 µGyair s-1 ) and low external bias (5 V). Hence, these findings provide guidelines for future materials design and device optimization.

Metal-Free Hydrazinium Halide Perovskitoid Single Crystals for X-ray Detection

Metal-free perovskitoids (MFPs) with N2H5+ as B-site component possess higher crystal density and hydrogen bonding networks and have been recently expanded into X-ray detection. However, research on this material is in its infancy and lacks an understanding of the function of halide components on physical properties and device performance. Here, N2H5-based MFP single crystals (SCs) with different halides are fabricated, and the influence of halides on the crystal structure, band nature, charge transport characteristics, and final device performance is actively explored. Based on theory and experiments, the tolerance factor and octahedral factor jointly determine the octahedral composition. Further, halides with different electronegativities and ionic radii also affect octahedral distortion and energy band bending, further influencing carrier transport and device performance. Finally, a sensitivity of 1284 μC Gyair-1 cm-2 and low detection limits (LoD) of 5.62 μGyair s-1 were obtained by the Br-based device due to its superior physical properties.

Metal-Free Perovskites for X-Ray Detection

Metal-free perovskites are a promising class of materials for X-ray detection due to their unique structural, optical, and electrical properties. Here, we first delve into the stoichiometry and geometric argument of metal-free perovskites. Followed, the alternative A/B/X ions and hydrogen-bonding are clearly introduced to further optimize the materials' stability and properties. Finally, we provide a comprehensive overview of their potential applications for flexible X-ray images and prospects for metal-free perovskite development. In conclusion, metal-free perovskite is a promising material for X-ray detection. Its stoichiometric and geometric parameters, ion, and hydrogen bond selection, and application prospects are worthy of further study.

An interfacial toughening strategy for high stability 2D/3D perovskite X-ray detectors with a carbon nanotube thin film electrode

Single-crystalline metal halide perovskite materials hold great promise for developing next-generation low-dose X-ray detection. To bring this new technology into reality, it is important to improve the durability of perovksite detectors by suppressing the well-known corrosion and ion diffusion problems at the perovskite/electrode interface. For imaging application, it is also imperative to develop new assembling approaches to realise non-planar interconnection between thick perovskite crystals and thin-film transistor (TFT) backplanes. Herein, a flexible and mechanically robust carbon nanotube (CNT) film was proposed to replace noble metal electrodes. The proposed CNT film, whose binder contains a carboxyl group, can form solid contact with a phenethylamine-based two-dimensional (2D) perovskite via amide coupling, thus toughening the perovskite-electrode interface. The resulting CNT/2D-3D perovskite detector shows an applaudable low dark current, high sensitivity, a low dose detection limit and excellent stability, retaining 98% of its initial sensitivity after storage for three months. Moreover, the flexible CNT films are also beneficial for making non-planar interconnection between thick perovskite crystals and TFT backplanes. The proposed flexible CNT thin film electrode thus provides a facile route towards realising a low-dose, high-resolution and highly stable perovskite X-ray detector.

Two-Dimensional Metal Halides for X-Ray Detection Applications

Metal halide perovskites have recently emerged as promising candidates for the next generation of X-ray detectors due to their excellent optoelectronic properties. Especially, two-dimensional (2D) perovskites afford many distinct properties, including remarkable structural diversity, high generation energy, and balanced large exciton binding energy. With the advantages of 2D materials and perovskites, it successfully reduces the decomposition and phase transition of perovskite and effectively suppresses ion migration. Meanwhile, the existence of a high hydrophobic spacer can block water molecules, thus making 2D perovskite obtain excellent stability. All of these advantages have attracted much attention in the field of X-ray detection. This review introduces the classification of 2D halide perovskites, summarizes the synthesis technology and performance characteristics of 2D perovskite X-ray direct detector, and briefly discusses the application of 2D perovskite in scintillators. Finally, this review also emphasizes the key challenges faced by 2D perovskite X-ray detectors in practical application and presents our views on its future development.