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Two‐dimensional (2D) intrinsic vacancy semiconductors possess great application prospects in optoelectronics fields, originating from abundant intrinsic vacancy structures and exceptional physical properties. Understanding the structure‐activity relationship between vacancies and physical/photoelectric properties is significant for building advanced photoelectric devices. However, limited by the increasing instability of 2D structure induced by intrinsic vacancies, the precise synthesis of 2D intrinsic vacancy semiconductors faces great challenges. Here, high‐quality 2D intrinsic vacancy semiconductor α‐Ga2Se3 is synthesized via low‐pressure and space‐confined physical vapor deposition. The vacancy structures induce an intermediate energy level and a super‐bandgap photoluminescence (PL) peak, which are verified by temperature‐dependent PL spectra. Furthermore, the vacancy energy level favorably endows 2D α‐Ga2Se3‐based photodetector with a UV‐vis‐NIR super‐bandgap photoresponse, excellent ultraviolet detection ability (photoresponsivity (41.86 A W−1), epitaxial quantum efficiency (1.42 × 104%), and detectivity (6.69 × 1011 Jones) @365 nm), fast photoresponse (20 ms), and superior photocurrent‐light power‐fitting factors. In addition, 2D α‐Ga2Se3‐based phototransistor displays p‐type transport behavior with a responsivity of 105 A W−1@365 nm at a gate voltage of −40 V. This work suggests a bright future of 2D intrinsic vacancy semiconductors in tailoring physical properties and enabling sophisticated device functionality. [ABSTRACT FROM AUTHOR]

2D perovskites have attracted wide attention for optoelectronic applications because of their unique layer structure and tunable outstanding optical/electrical properties. In addition, 2D Cs3Bi2Br9 nanoflakes possess large effective atomic number, high resistivity, high density as well as excellent stability, rendering it a promising material for X‐ray detection. Nevertheless, it is full of challenges to synthesize 2D Cs3Bi2Br9 nanoflakes by conventional inversion temperature crystallization (ITC) strategy due to the existence of Br‐ vacancies in the Cs3Bi2Br9 crystal nucleus. Herein, an Ag+ assisted ITC (SAITC) strategy to grow 2D Cs3Bi2Br9 nanoflakes is proposed. The synthesis mechanism revealed by both experiments and theoretical calculations can be mainly ascribed to the passivated Br− vacancies and enhanced structure stability by adding Ag+ which can effectively prevent the oxidation of 2D Cs3Bi2Br9 nanoflakes from growth of hybrid crystals. The synthesized high‐crystallinity 2D Cs3Bi2Br9 nanoflakes possess direct bandgap characteristic, and the mobility lifetime can reach 9.8 × 10−4 cm2 V−1. Excitingly, the fabricated device based on 2D Cs3Bi2Br9 nanoflakes demonstrates ultrahigh sensitivity of detecting X‐ray (1.9 CGyair−1cm−2) at very low driven voltage (0.5 V) due to the photoconductive gain mechanism. The 2D Cs3Bi2Br9 nanoflakes synthesized by SAITC method have great potential for developing highly sensitive optoelectronic devices. [ABSTRACT FROM AUTHOR]

The unique intermolecular van der Waals force in emerging two‐dimensional inorganic molecular crystals (2DIMCs) endows them with highly tunable structures and properties upon applying external stimuli. Using high pressure to modulate the intermolecular bonding, here we reveal the highly tunable charge transport behavior in 2DIMCs for the first time, from an insulator to a semiconductor. As pressure increases, 2D α‐Sb2O3 molecular crystal undergoes three isostructural transitions, and the intermolecular bonding enhances gradually, which results in a considerably decreased band gap by 25 % and a greatly enhanced charge transport. Impressively, the in situ resistivity measurement of the α‐Sb2O3 flake shows a sharp drop by 5 orders of magnitude in 0–3.2 GPa. This work sheds new light on the manipulation of charge transport in 2DIMCs and is of great significance for promoting the fundamental understanding and potential applications of 2DIMCs in advanced modern technologies. [ABSTRACT FROM AUTHOR]

Nowadays, realizing miniaturized nonlinear optical (NLO) device is crucial to meet the growing needs in on-chip nanophotonics as well as compact integrated devices. The strong optical nonlinearities, ultrafast photoexcitation dynamics, available exciton effects as well as without lattice matching make two-dimensional (2D) layered materials potential candidates for integrated and nano-scale NLO devices. Herein, a novel and inversion symmetry broken 2D layered SnP2S6 with strong second-harmonic and third-harmonic response has been reported for the first time. The second-order susceptibility (χ(2)) of SnP2S6 flakes can reach up to 4.06 × 10−9 m·V−1 under 810 nm excitation wavelength, which is around 1–2 orders of magnitude higher than that of most reported 2D materials. In addition, the NLO response of 2D SnP2S6 can break through the limitation of odd/even layers and exhibit broadband spectral response. Moreover, since the second-harmonic signal is closely related to structure variation, the second-harmonic response in 2D SnP2S6 is extremely sensitive to polarization angle and temperature, which is beneficial to some specific applications. The excellent NLO response in 2D SnP2S6 provides a new arena for realizing miniaturized NLO devices in the future. [ABSTRACT FROM AUTHOR]

The capacitive behavior of AC-AC supercapacitor (AC=activated carbon) at −18 °C are greatly improved by using an acid redox electrolyte comprising p-phenylenediamine. By introducing p-phenylenediamine into 38 % H2SO4 solution, the energy density at −18 °C is remarkably elevated to the level achievable at 23 °C in 38 % H2SO4. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals (vdW) materials, featuring relaxed phase-matching conditions and highly tunable optical nonlinearity, endow them with potential applications in nanoscale nonlinear optical (NLO) devices. Despite significant progress, fundamental questions in 2D NLO materials remain, such as how structural distortion affects second-order NLO properties, which call for advanced regulation and in situ diagnostic tools. Here, by applying pressure to continuously tune the displacement of Nb atoms in 2D vdW NbOI 2 , we effectively modulate the polarization and achieve a 3-fold boost of the second-harmonic generation (SHG) at 2.5 GPa. By introducing a Peierls distortion parameter, λ, we establish a quantitative relationship between λ and SHG intensity. Importantly, we further demonstrate that the SHG enhancement can be achieved under ambient conditions by anionic substitution to tune the distortion in NbO(I 1- x Br x ) 2 ( x = 0-1) compounds, where the chemical tailoring simulates the pressure effects on the structural optimization. Consequently, NbO(I 0.60 Br 0.40 ) 2 with λ = 0.17 exhibits a giant SHG of over 2 orders of magnitude higher than that in monolayer WSe 2 , reaching the record-high value among reported 2D vdW NLO materials. This work unambiguously demonstrates the correlation between Peierls distortion and SHG property and, more broadly, opens new paths for the development of advanced NLO materials by manipulating the structure distortions.

The unique intermolecular van der Waals force in emerging two-dimensional inorganic molecular crystals (2DIMCs) endows them with highly tunable structures and properties upon applying external stimuli. Using high pressure to modulate the intermolecular bonding, here we reveal the highly tunable charge transport behavior in 2DIMCs for the first time, from an insulator to a semiconductor. As pressure increases, 2D α-Sb 2 O 3 molecular crystal undergoes three isostructural transitions, and the intermolecular bonding enhances gradually, which results in a considerably decreased band gap by 25 % and a greatly enhanced charge transport. Impressively, the in situ resistivity measurement of the α-Sb 2 O 3 flake shows a sharp drop by 5 orders of magnitude in 0-3.2 GPa. This work sheds new light on the manipulation of charge transport in 2DIMCs and is of great significance for promoting the fundamental understanding and potential applications of 2DIMCs in advanced modern technologies., (© 2022 Wiley-VCH GmbH.)