Jiuxiang Dai

Organic photovoltaics have made great progress due to the rapid development of non-fullerene acceptors. Herein, we summarize the design rules of acceptors with core moiety substituted by various heteroatoms. A comprehensive understanding on the structure–property−performance relationships of these heteroatom-substituted acceptors is also provided.

Abstract

Organic photovoltaics (OPVs) represent one of the most promising photovoltaic technologies owing to their high capacity to convert solar energy to electricity. With the continuous structure upgradation of photovoltaic materials, especially that of non-fullerene acceptors (NFAs), the OPV field has witnessed rapid progress with power conversion efficiency (PCE) exceeding 19%. However, it remains challenging to overcome the intrinsic trade-off between the photocurrent and photovoltage, restricting the further promotion of the OPV efficiency. In this regard, it is urgent to further tailor the structure of NFAs to broaden their absorption spectra while mitigating the energy loss of relevant devices concomitantly. Heteroatom substitution on the fused-ring π-core of NFAs is an efficient way to achieve this goal. In addition to improve the near-infrared light harvest by strengthening the intramolecular charge transfer, it can also enhance the molecular stacking via forming multiple noncovalent interactions, which is favorable for reducing the energetic disorder. Therefore, in this review we focus on the design rules of NFAs, including the polymerized NFAs, of which the core moiety is substituted by various kinds of heteroatoms. We also afford a comprehensive understanding on the structure–property−performance relationships of these NFAs. Finally, we anticipate the challenges restricting the efficiency promotion and industrial utilization of OPV, and provide potential solutions based on the further heteroatom optimization on NFA core-moiety.

Publication date: December 2024

Source: Progress in Materials Science, Volume 146

Author(s): Yuewen Jia, Kelvin Wong, Can Zeng Liang, Ji Wu, Tai-Shung Chung, Sui Zhang

The work reports the synthesis of the superconducting freestanding La_0.8Sr_0.2NiO₂ membranes (Tczero=10.6K${T}_{\mathrm{c}}^{\mathrm{zero}}\ =\ 10.6\mathrm{K}$), emphasizing the crucial roles of the interface engineering in the precursor phase film growth and the quick transfer process in achieving superconductivity. This work offers a new versatile platform for investigating superconductivity in nickelates, such as the pairing symmetry via constructing Josephson tunneling junctions and higher T _c values via high-pressure experiments.

Abstract

The observation of superconductivity in infinite-layer nickelates has attracted significant attention due to its potential as a new platform for exploring high-T _c superconductivity. However, thus far, superconductivity has only been observed in epitaxial thin films, which limits the manipulation capabilities and modulation methods compared to two-dimensional exfoliated materials. Given the exceptionally giant strain tunability and stacking capability of freestanding membranes, separating superconducting nickelates from the as-grown substrate is a novel way to engineer the superconductivity and uncover the underlying physics. Herein, this work reports the synthesis of the superconducting freestanding La_0.8Sr_0.2NiO₂ membranes (Tczero=10.6K${T}_{\mathrm{c}}^{\mathrm{zero}}\ =\ 10.6\ \mathrm{K}$), emphasizing the crucial roles of the interface engineering in the precursor phase film growth and the quick transfer process in achieving superconductivity. This work offers a new versatile platform for investigating superconductivity in nickelates, such as the pairing symmetry via constructing Josephson tunneling junctions and higher T _c values via high-pressure experiments.

This review delves into high-performance thermal interface materials (TIMs) based on 2D materials like graphene/boron nitride, pivotal for heat management in advanced electronics. Focusing on their structural attributes, properties, and applications, it differentiates from other reviews by emphasizing their developmental history, addressing critical challenges, and proposing solutions. Additionally, it introduces other 2D materials-based TIMs, providing insights for future advancements.

Abstract

The challenges associated with heat dissipation in high-power electronic devices used in communication, new energy, and aerospace equipment have spurred an urgent need for high-performance thermal interface materials (TIMs) to establish efficient heat transfer pathways from the heater (chip) to heat sinks. Recently, emerging 2D materials, such as graphene and boron nitride, renowned for their ultrahigh basal-plane thermal conductivity and the capacity to facilitate cross-scale, multi-morphic structural design, have found widespread use as thermal fillers in the production of high-performance TIMs. To deepen the understanding of 2D material-based TIMs, this review focuses primarily on graphene and boron nitride-based TIMs, exploring their structures, properties, and applications. Building on this foundation, the developmental history of these TIMs is emphasized and a detailed analysis of critical challenges and potential solutions is provided. Additionally, the preparation and application of some other novel 2D materials-based TIMs are briefly introduced, aiming to offer constructive guidance for the future development of high-performance TIMs.

Black materials of CuVP₂S₆ and CuCrP₂S₆, with a narrow bandgap of ≈1.0 eV, are developed as the new photocatalysts, which display high photocatalytic hydrogen evolution (PHE) activity, far exceeding current layered metal phospho–sulfides and other materials. They even show  near-infrared-driven PHE rates of 0.66 and 0.20 mmol h⁻¹ g⁻¹, respectively.

Abstract

The development of new near-infrared-responsive photocatalysts is a fascinating and challenging approach to acquire high photocatalytic hydrogen evolution (PHE) performance. Herein, near-infrared-responsive black CuVP₂S₆ and CuCrP₂S₆ flakes, as well as CuInP₂S₆ flakes, are designed and constructed for PHE. Atom-resolved scanning transmission electron microscopy images and X-ray absorption fine structure evidence the formation of ultrathin single-crystalline sheet-like structure of CuVP₂S₆ and CuCrP₂S₆. The synthetic CuVP₂S₆ and CuCrP₂S₆, with a narrow bandgap of ≈1.0 eV, shows the high light-absorption edge exceeding 1100 nm. Moreover, through the femtosecond-resolved transient absorption spectroscopy, CuCrP₂S₆ displays the efficient charge transfer and long charge lifetime (18318.1 ps), which is nearly 3 and 29 times longer than that of CuVP₂S₆ and CuInP₂S₆, respectively. In addition, CuCrP₂S₆, with the appropriate d-band and p-band, is thermodynamically favorable for the H⁺ adsorption and H₂ desorption by contrast with CuVP₂S₆ and CuInP₂S₆. As a result, CuCrP₂S₆ exhibits high PHE rates of 9.12 and 0.66 mmol h⁻¹ g⁻¹ under simulated sunlight and near-infrared light irradiation, respectively, far exceeding other layered metal phospho–sulfides. This work offers a distinctive perspective for the development of new near-infrared-responsive photocatalysts.

Seeking to understand recent predictions of the exotic state known as “altermagnetism”. The study reports that even when high-quality samples are grown by molecular beam epitaxy, altermagnetic candidates may exhibit richer phenomena than anticipated, which highlights new routes to take advantage of these novel magnetic materials for new applications.

Abstract

The field of spintronics has seen a surge of interest in altermagnetism due to novel predictions and many possible applications. MnTe is a leading altermagnetic candidate that is of significant interest across spintronics due to its layered antiferromagnetic structure, high Neel temperature (T_N  ≈ 310 K) and semiconducting properties. The results on molecular beam epitaxy (MBE) grown MnTe/InP(111) films are presented. Here, it is found that the electronic and magnetic properties are driven by the natural stoichiometry of MnTe. Electronic transport and in situ angle-resolved photoemission spectroscopy show the films are natively metallic with the Fermi level in the valence band and the band structure is in good agreement with first-principles calculations for altermagnetic spin-splitting. Neutron diffraction confirms that the film is antiferromagnetic with planar anisotropy and polarized neutron reflectometry indicates weak ferromagnetism, which is linked to a slight Mn-richness that is intrinsic to the MBE-grown samples. When combined with the anomalous Hall effect, this work shows that the electronic response is strongly affected by the ferromagnetic moment. Altogether, this highlights potential mechanisms for controlling altermagnetic ordering for diverse spintronic applications.

Nature Photonics, Published online: 10 June 2024; doi:10.1038/s41566-024-01454-7

A fully hybrid integrated erbium-doped photonic integrated waveguide laser with wide tuning of 40 nm, side-mode suppression ratio of >70 dB and output power up to 17 mW is demonstrated, achieving not only footprint reduction but also the long-anticipated fibre-laser coherence.

2D metal oxides (2DMOs) have emerged as a new class of ultrathin (0.5–4 nm), wide bandgap materials offering exceptional electrical and optical properties for applications in energy, sensing, and display technologies. This review focuses on the physics of liquid metal printed 2DMOs, including their growth, patterning, crystallinity, doping, and device integration for high-performance flexible electronics.

Abstract

2D metal oxides (2DMOs) have recently emerged as a high-performance class of ultrathin, wide bandgap materials offering exceptional electrical and optical properties for a wide area of device applications in energy, sensing, and display technologies. Liquid metal printing represents a thermodynamically advantageous strategy for synthesizing 2DMOs by a solvent-free and vacuum-free scalable method. Here, recent progress in the field of liquid metal printed 2D oxides is reviewed, considering how the physics of Cabrera-Mott oxidation gives this rapid, low-temperature process advantages over alternatives such as sol-gel and nanoparticle processing. The growth, composition, and crystallinity of a burgeoning set of 1–3 nm thick liquid metal printed semiconducting, conducting, and dielectric oxides are analyzed that are uniquely suited for the fabrication of high-performance flexible electronics. The advantages and limitations of these strategies are considered, highlighting opportunities to amplify the impact of 2DMO through large-area printing, the design of doped metal alloys, stacking of 2DMO to electrostatically engineer new oxide heterostructures, and implementation of 2D oxide devices for gas sensing, photodetection, and neuromorphic computing.

Author(s): Xiaoming Wang, Jiajing He, Ao Wang, Kun Zhang, Yufei Sheng, Weida Hu, Chaoyuan Jin, Hua Bao, and Yaping Dan

An erbium-doped silicon light-emitting diode functions as a single photon emitter for quantum applications.

[Phys. Rev. Lett. 132, 246901] Published Tue Jun 11, 2024

Publication date: December 2024

Source: Progress in Materials Science, Volume 146

Author(s): Waseem Raza, Attia Shaheen, Noureen Amir Khan, Ki Hyun Kim, Xingke Cai

Comparative analysis summarizes the impact of various ion irradiation parameters (mass, energy, incident angle) on defect formation in supported and freestanding 2D materials. Supported materials exhibit consistently higher defect numbers, attributed to the significant impact of the substrate, which introduces extra defect production due to backscattered ions and sputtered atoms.

Abstract

Understanding the nature, density, and distribution of structural defects is crucial for tailoring the properties of atomically thin two-dimensional (2D) materials, which is paramount for advances in nanotechnology. Ion irradiation emerges as a promising technique for defect engineering of single-atom-thick materials, due to its high controllability, repeatability, and accuracy. The objective is to provide a comprehensive review elucidating the impact of various irradiation parameters, such as ion mass, energy, fluence, and incident angle, on defect formation in 2D materials. However, the presence of the substrate can significantly influence defect yield and the mechanism of formation due to backscattered ions and sputtered substrate atoms. Hence, a thorough comparison of ion beam-induced defects in both freestanding (suspended) and supported (on a substrate) 2D materials, with a focus on substrate effects is conducted. Moreover, a detailed analysis of characterization techniques suitable for each scenario will be provided. This work not only contributes to advancing the current understanding of defect formation and evolution in 2D materials during ion beam irradiation but also offers insights into selecting specific parameters for this process to create desired defects in these materials. Consequently, it has the potential to facilitate the design of nanoscale devices with tailored functionality.

In this work, a compromised tableting engineering is proposed that combines the well-ordered lattice of single crystals with the gradient stability of polycrystalline films. Derived from the energy band regulation and main carrier design, the carrier collection in hole-type Au/gradient tablet/Au device is markedly improved in weak terahertz photothermal detection.

Abstract

Component regulation in perovskite single crystals (SCs) sets the precondition for designing energy band and carrier dynamics, which is essential for exploring functional optoelectronic devices. However, entropy-driven ion diffusion in SCs leads to component homogenization in a few hours, while the gradient films exhibit long-term gradient stability. Therefore, tableting engineering is proposed to introduce appropriate boundaries, ensuring good short-range alignment within the grains and suppressed ion diffusion in the long range. With 6–10 MPa pressure, transverse/longitudinal gradient MAPbX₃ (X = Cl, Br, I) tablets are constructed. Due to the alignment of the valence band maximum from MAPbCl₃ to MAPbBr₃ to MAPbI₃, the hole extraction is significantly promoted. As well, different metal electrodes are utilized to regulate the main carrier types. Hole-type Au/gradient tablet/Au devices show an obvious rectification effect, while electron-type Ag/gradient tablet/Ag devices have near-Ohmic contact. Compared to the electron-type devices, Au/gradient tablet/Au devices show a 3.9-fold improvement in terahertz responsivity to 3.51 µA W⁻¹, a 2.6-fold reduction in noise-equivalent power to 2.22 × 10⁻⁸ W Hz^{−1/ 2}; and a 2.6-fold increase in specific detectivity to 1.89 × 10⁷ Jones. This work demonstrates the tableting engineering to realize stable compositional gradients for energy band regulation in weak-signal THz detection.

Composites obtained by introducing highly insulating mica nanosheets into a polymer matrix while designing a sandwich structure to introduce ferroelectric fillers. The mica nanosheet as a dielectric barrier plays a synergistic role with the increased polarization of barium titanate, and the effective deployment of both with the polymer matrix can improve the energy density of the composite film.

Abstract

Dielectric polymer composites exhibit great application prospects in advanced pulse power systems and electric systems. However, the decline of breakdown strength by loading of single high dielectric constant nanofiller hinders the sustained increase in energy density of the composites. Here, a sandwich-structured nanocomposite prepared with mica nanosheets as the second filler exhibits decoupled modulation of dielectric constant and breakdown strength. The traditional layered clay mineral mica is exfoliated into nanosheets and filled into polyvinylidene difluoride (PVDF), which shows a special depolarization effect in the polymer matrix. In Kelvin probe microscopy characterization and thermally stimulated depolarization current indicates that the mica nanosheets provided space charge traps for the polymer matrix and effectively suppressed the carrier motion. A sandwich structure composite material with mica nanosheets as the central layer has achieved a high energy density of 11.48 J cm⁻³, 2.4 times higher than the pure PVDF film. This is due to the fact that randomly oriented distribution of nanosheets in a polymer matrix provide better current blocking. This work provides an effective method to improve the energy density of dielectric polymer composites by synergistically introducing insulating nanosheets and high dielectric constant nanofillers.

The Bi₂O₂S nanosheets with varied concentrations of O vacancies and Se doping are prepared. Rich defects cause enhanced nonlinear optical absorption and faster carrier relaxation processes, as the introduced defect levels can serve as the additional absorption cross-sections and fast relaxation channels. Based on the rich-defect Bi₂O₂S as saturable absorbers, high-performance mode-locked laser pulses in ≈1 µm are successfully constructed.

Abstract

Low-dimensional bismuth oxychalcogenides have shown promising potential in optoelectronics due to their high stability, photoresponse, and carrier mobility. However, the relevant studies on deep understanding for Bi₂O₂S is quite limited. Here, comprehensive experimental and computational investigations are conducted in the regulated band structure, nonlinear optical (NLO) characteristics, and carrier dynamics of Bi₂O₂S nanosheets via defect engineering, taking O vacancy (OV) and substitutional Se doping as examples. As the OV continuously increased to ≈35%, the optical bandgaps progressively narrow from ≈1.21 to ≈0.81 eV and NLO wavelengths are extended to near-infrared regions with enhanced saturable absorption. Simultaneously, the relaxation processes are effectively accelerated from tens of picoseconds to several picoseconds, as the generated defect energy levels can serve as both additional absorption cross-sections and fast relaxation channels supported by theoretical calculations. Furthermore, substitutional Se doping in Bi₂O₂S nanosheets also modulate their optical properties with the similar trends. As a proof-of-concept, passively mode-locked pulsed lasers in the ≈1.0 µm based on the defect-rich samples (≈35% OV and ≈50% Se-doping) exhibit excellent performance. This work deepens the insight of defect functions on optical properties of Bi₂O₂S nanosheets and provides new avenues for designing advanced photonic devices based on low-dimensional bismuth oxychalcogenides.

Persistent luminescence materials have currently drawn increasing attention in optical encryption technologies due to the distinctive properties. Herein, a controlled synthesis method is proposed based on defect structure regulation and a series of porous Al₂O₃ persistent phosphors is obtained with different luminous intensities, lifetime, and wavelengths, offering a new approach to high-security information encryption.

Abstract

Optical encryption technologies based on persistent luminescence material have currently drawn increasing attention due to the distinctive and long-lived optical properties, which enable multi-dimensional and dynamic optical information encryption to improve the security level. However, the controlled synthesis of persistent phosphors remains largely unexplored and it is still a great challenge to regulate the structure for optical properties optimization, which inevitably sets significant limitations on the practical application of persistent luminescent materials. Herein, a controlled synthesis method is proposed based on defect structure regulation and a series of porous persistent phosphors is obtained with different luminous intensities, lifetime, and wavelengths. By simply using diverse templates during the sol–gel process, the oxygen vacancy defects structures are successfully regulated to improve the optical properties. Additionally, the obtained series of porous Al₂O₃ are utilized for multi-color and dynamic optical information encryption to increase the security level. Overall, the proposed defect regulation strategy in this work is expected to provide a general and facile method for optimizing the optical properties of persistent luminescent materials, paving new ways for broadening their applications in multi-dimensional and dynamic information encryption.

Nature, Published online: 12 June 2024; doi:10.1038/d41586-024-01750-w

The accidental discovery could be used to make lenses, or even as a glue.

Nature, Published online: 12 June 2024; doi:10.1038/s41586-024-07434-9

We have implemented a two-site Kitaev chain in a two-dimensional electron gas by coupling quantum dots through Andreev bound states in a superconductor–semiconductor hybrid region.