Two-Dimensional Bis(dithiolene)iron(II) Self-Powered UV Photodetectors with Ultrahigh Air Stability

Lateral Heterometal Junction Rectifier Fabricated by Sequential Transmetallation of Coordination Nanosheet

Heterostructures of two-dimensional materials realise novel and enhanced physical phenomena, making them attractive research targets. Compared to inorganic materials, coordination nanosheets have virtually infinite combinations, leading to tunability of physical properties and are promising candidates for heterostructure fabrication. Although stacking of coordination materials into vertical heterostructures is widely reported, reports of lateral coordination material heterostructures are few. Here we show the successful fabrication of a seamless lateral heterojunction showing diode behaviour, by sequential and spatially limited immersion of a new metalladithiolene coordination nanosheet, Zn3 BHT, into aqueous Cu(II) and Fe(II) solutions. Upon immersion, the Zn centres in insulating Zn3 BHT are replaced by Cu or Fe ions, resulting in conductivity. The transmetallation is spatially confined, occurring only within the immersed area. We anticipate that our results will be a starting point towards exploring transmetallation of various two-dimensional materials to produce lateral heterojunctions, by providing a new and facile synthetic route.

A Conductive Two-dimensional Trimetallic FeCoNi-Benzenehexathiol π-d Conjugated Metal-organic Framework for Highly Efficient Oxygen Evolution Reaction

The poor electrically conductivity of metal-organic frameworks (MOFs) is the main factor hinder their application in electrocatalysis field. In this work, we synthesize a conductive two-dimensional (2D) trimetallic π-d conjugated metal-organic framework (MOF) FeCoNi-BHT (BHT = 1,2,3,4,5,6-benzenehexathiol) through coordinating Co, Fe and Ni ions with 1,2,3,4,5,6-benzenehexathiol ligands. FeCoNi-BHT is demonstrated possessing homogeneously dispersed abundant Co-S4, Fe-S4, Ni-S4 single-atom active sites (14.26 wt% of the metal elements) and a large specific surface area (267.05 m2g-1). The room temperature conductivity of FeCoNi-BHT is measured to be 92 S m-1, indicating its metallic behavior. DFT theoretical calculation reveals that the π-d conjugation structure of FeCoNi-BHT is responsible for its metallic behavior. In addition, FeCoNi-BHT exhibits prominent oxygen evolution reaction (OER) activity (an overpotential of 266 mV vs. RHE at 10 mA cm-2 and a Tafel value of 58 mV dec-1) in alkaline media. The combined experimental and DFT studies reveal that the synergistic effect of Co, Fe, Ni sites of FeCoNi-BHT contribute to its prominent OER activity. This work paves a new avenue of developing 2D π-d conjugated MOFs with different metal centers as highly efficient eletrocatalysts.

An Internal-Electrostatic-Field-Boosted Self-Powered Ultraviolet Photodetector

Self-powered photodetectors are of significance for the development of low-energy-consumption and environment-friendly Internet of Things. The performance of semiconductor-based self-powered photodetectors is limited by the low quality of junctions. Here, a novel strategy was proposed for developing high-performance self-powered photodetectors with boosted electrostatic potential. The proposed self-powered ultraviolet (UV) photodetector consisted of an indium tin oxide and titanium dioxide (ITO/TiO₂) heterojunction and an electret film (poly tetra fluoroethylene, PTFE). The PTFE layer introduces a built-in electrostatic field to highly enhance the photovoltaic effect, and its high internal resistance greatly reduces the dark current, and thus remarkable performances were achieved. The self-powered UV photodetector with PTFE demonstrated an extremely high on-off ratio of 2.49 × 10⁵, a responsivity of 76.87 mA/W, a response rise time of 7.44 ms, and a decay time of 3.75 ms. Furthermore, the device exhibited exceptional stability from room temperature to 70 °C. Compared with the conventional ITO/TiO₂ heterojunction without the PTFE layer, the photoresponse of the detector improved by 442-fold, and the light-dark ratio was increased by 8.40 × 10⁵ times. In addition, the detector is simple, easy to fabricate, and low cost. Therefore, it can be used on a large scale. The electrostatic modulation effect is universal for various types of semiconductor junctions and is expected to inspire more innovative applications in optoelectronic and microelectronic devices.

Strain-promoted conductive metal-benzenhexathiolate frameworks for overall water splitting

Designing efficient catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a desirable strategy for overall water splitting and the generation of clean and renewable energies. Herein, the electrocatalytic HER and OER activity of the conductive metal-benzenhexathiolate (M-BHT) frameworks has been evaluated utilizing first-principles calculations. The in-plane π-d conjugation of M-BHT guarantees fast electron transfer during electrocatalytic reactions. Notably, Rh-BHT holds the promise of bifunctional HER/OER activity with the overpotentials of 0.07/0.36 V. Furthermore, the application of strain engineering tailors the adsorption of intermediates and promotes the overall water splitting performance. Rh-BHT with the +1% tensile strain shows the HER/OER overpotential of 0.02/0.37 V. This work not only demonstrates the prospects of conductive metal-organic frameworks in electrocatalysis but also offers new insights into designing efficient catalysts by strain engineering.

Ferro-Pyro-Phototronic Effect in Monocrystalline 2D Ferroelectric Perovskite for High-Sensitive, Self-Powered, and Stable Ultraviolet Photodetector

2D hybrid perovskite ferroelectrics have drawn great attention in the field of photodetection, because the spontaneous polarization-induced built-in electric field can separate electron-hole pairs, and makes self-powered photodetection possible. However, most of the 2D hybrid perovskite-based photodetectors focused on the detection of visible light, and only a few reports realized the self-powered and sensitive ultraviolet (UV) detection using wide bandgap hybrid perovskites. Here, 2D ferroelectric PMA₂PbCl₄ monocrystalline microbelt (MMB)-based PDs are demonstrated. By using the ferro-pyro-phototronic effect, the self-powered Ag/Bi/2D PMA₂PbCl₄ MMB/Bi/Ag PDs show a high photoresponsivity up to 9 A/W under 320 nm laser illumination, which is much higher than those of previously reported self-powered UV PDs. Compared with responsivity induced by the photovoltaic effect, the responsivity induced by the ferro-pyro-phototronic effect is 128 times larger. The self-powered PD also shows fast response and recovery speed, with the rise time and fall time of 162 and 226 μs, respectively. More importantly, the 2D PMA₂PbCl₄ MMB-based PDs with Bi/Ag electrode exhibit significant stability when subjected to high humidity, continuous laser illumination, and thermal conditions. Our findings would shed light on the ferro-pyro-phototronic-effect-based devices, and provide a good method for high-performance UV detection.

2D Layered Material Alloys: Synthesis and Application in Electronic and Optoelectronic Devices

2D layered materials (2DLMs) have come under the limelight of scientific and engineering research and broke new ground across a broad range of disciplines in the past decade. Nevertheless, the members of stoichiometric 2DLMs are relatively limited. This renders them incompetent to fulfill the multitudinous scenarios across the breadth of electronic and optoelectronic applications since the characteristics exhibited by a specific material are relatively monotonous and limited. Inspiringly, alloying of 2DLMs can markedly broaden the 2D family through composition modulation and it has ushered a whole new research domain: 2DLM alloy nano-electronics and nano-optoelectronics. This review begins with a comprehensive survey on synthetic technologies for the production of 2DLM alloys, which include chemical vapor transport, chemical vapor deposition, pulsed-laser deposition, and molecular beam epitaxy, spanning their development, as well as, advantages and disadvantages. Then, the up-to-date advances of 2DLM alloys in electronic devices are summarized. Subsequently, the up-to-date advances of 2DLM alloys in optoelectronic devices are summarized. In the end, the ongoing challenges of this emerging field are highlighted and the future opportunities are envisioned, which aim to navigate the coming exploration and fully exert the pivotal role of 2DLMs toward the next generation of electronic and optoelectronic devices.