Search

Four TM1TM2@C9N4 candidates (TM1TM2 = NiRu, FeNi, TiNi, and NiZr) with end-on N2 adsorption configuration, and two candidates (TM1TM2 = TiNi and TiFe) with side-on adsorption configuration, were screened out as high efficiency NRR catalysts.

We combine a polarized material and the rational B-doping concentration to improve the catalytic activity and photo-absorption of g-C3N5 for photocatalytic overall water splitting.

N2 fixation under mild conditions using renewable electricity or solar energy is a promising alternative to the century-old Haber–Bosch process; however, it is generally impeded by the initial hydrogenation and competitive hydrogen evolution reaction. Herein, a new N2 fixation strategy is proposed via directly forming *N2− excited state on metal-free boron-decorated diamond clusters (BDCs). Surface-doped B atoms facilitate the adsorption of N2 and simultaneously suppress H+ due to the repulsion of Lewis acids. Excited state dynamics simulations demonstrate that valence electrons using the valence-band edge of BDCs as springboard are directly excited into the π* orbitals of *N2 under the illumination of ∼4 eV light (far below ∼11 eV for free N2), which not only further improves the selectivity but also forms activated *N2− excited states with sufficient lifetime (∼10 ns) for the initial hydrogenation. This work affords fresh insight to advance photocatalysis for sustainable NH3 production.

In atomically thin two-dimensional van der Waals (2D vdW) heterostructures, spatially separated interlayer excitons play an important role in the optoelectronic performance and show great potential for the exploration of many-body quantum phenomena. A commonly accepted formation mode for interlayer excitons is via a two-step intralayer exciton transfer mechanism, namely, photo-excited intralayer excitons are initially generated in individual sublayers, and photogenerated electrons and holes are then separated into opposite sublayers based on the type-II band alignment. Herein, we expand the concept of interlayer exciton formation and reveal that bright interlayer excitons can be generated in one step by direct interlayer photoexcitation in 2D vdW heterostructures that have strong interlayer coupling and a short photoexcitation channel. First-principles and many-body perturbation theory calculations demonstrate that indium selenide/antimonene and indium selenide/black phosphorus heterostructures are two promising systems that show an exceptionally large interlayer transition probability (>500 Debye2). This study enriches the understanding of interlayer exciton formation and provides a new avenue to acquiring strong interlayer excitons in artificial 2D vdW heterostructures.

Photoexcited carrier dynamics at the interface play a vital role in two-dimensional heterostructure-based photovoltaic and photoelectric devices. This study systematically investigates how the interface morphologies (i.e., alloy and sharp interfaces) control the photogenerated carrier transfer and electron–hole recombination processes in MoSe2/WSe2 lateral heterostructures. It is revealed that both interfaces exhibit a remarkable photogenerated carrier separation rate within a few picoseconds. More surprisingly, the sharp interface exhibits an exceptional long carrier lifetime up to 1 nanosecond, which is longer than that of the alloy interface by a factor of 1.5. This is ultimately attributed to the vanishing interface-coupled states that effectively limit the transition channel and suppress the electron–hole recombination. This study provides insights into the photogenerated carrier dynamics in heterostructure interfaces and sheds light on the rational design of high-performance transition metal dichalcogenide heterostructure-based photovoltaic and photoelectric devices.

Interlayer coupling inducing an anomalous layer number dependent property of carrier lifetimes in Bi2OS2 nanosheet.

Recently, lead halide perovskites with outstanding emission performance have become new candidate materials for light-emitting devices and displays; however, the toxicity of lead and instability of halide perovskites remain significant challenges. Herein, we report the aqueous acid-based synthesis of highly emissive two-dimensional (2D) tin halide perovskites, (octylammonium)2SnX4 (X = Br, I, or mixtures thereof), which displayed a high absolute photoluminescence (PL) quantum yield of near-unity in the solid-state, PL emission centered at 600 nm with a broad bandwidth (136 nm), a large Stokes shift (250 nm), long-lived luminescence (τ = 3.3 μs), and zero overlap between their absorption and emission spectra. Significantly, the stability study of 2D tin halide perovskites monitored by the PL quantum yield showed no changes after 240 days of storage at room temperature under ambient air and humidity conditions. The PL emission of the 2D tin halide perovskites was tuned from yellow to deep red by controlling halide composition. Furthermore, new yellow phosphors with superior optical properties are used to fabricate UV pumped white light emitting diodes (WLEDs). We expect these results to facilitate the development of new environmentally friendly and high-performance phosphors for future lighting and display technologies.

Constructing van der Waals (vdW) semiconductor heterostructures is a possible approach to optimize the optoelectronic properties, and understanding photogenerated charge carrier dynamics at vdW heterostructure interfaces is of crucial importance. By using time-dependent ab initio nonadiabatic molecular dynamics simulations, we study the dynamics of photogenerated electrons at a BP/InSe heterostructure interface and observethe highly efficient separation of photogenerated electron–hole pairs at the interface. Instead of direct tunneling, the ultrafast transfer of excited electrons is significantly promoted by an adiabatic mechanism related to thermally excited nuclear motions stemming from strong e–p coupling and phonon excitation, and a small energy difference of donor–acceptor states. The internal quantum efficiency for charge separation can reach up to 99.6% and improved optical absorption is also observed in this heterostructure, making the BP/InSe heterostructure a compelling optoelectronic material.

Inspired by natural photosynthesis, direct Z-scheme heterostructures are considered as promising photocatalysts for solar-driven water splitting and attract ever-growing interest. Herein, based on density functional theory and nonadiabatic molecular dynamics calculations, we predict a Janus MoSSe/WSeTe heterostructure as a potential direct Z-scheme photocatalyst for hydrogen evolution. Our calculations show that photogenerated carriers can transfer at the interface via a traditional type II path or Z-scheme path depending on stacking configurations. Surprisingly, introducing surface chalcogen vacancies can not only effectively switch the charge transfer path from type II to Z-scheme, but also increase the time difference between electron (hole) transfer and interlayer carrier recombination with a time scale of 25 ps (37.4 ps), one order of magnitude longer than that of 2595 fs (1531 fs) in intrinsic Z-scheme. This is ascribed to the introduced defect trap states strongly modulating the competition between charge separation and interlayer e–h recombination. These properties make MoSSe/WSeTe heterostructures a compelling direct Z-scheme candidate for photocatalytic hydrogen evolution.

For atomically thin two-dimensional materials, van der Waals interlayer coupling is a crucial factor to tune or produce novel physicochemical properties. In terms of photocatalysis, however, researching into the interlayer coupling effect is still in its infancy, especially that involving excited state dynamics. Here, by performing many-body perturbation theory and ab initio nonadiabatic molecular dynamics, we find that metal-free few-layer graphitic C3N4 (g-C3N4) possesses a better photocatalytic hydrogen evolution performance due to interlayer coupling compared with ultrathin monolayer g-C3N4. Specifically, few-layer g-C3N4 activates the electronic transition channel around the Fermi level and transforms dark excitation to bright excitation, which broadens the solar light absorption region. Meanwhile, few-layer g-C3N4 can effectively weaken the strong binding energy between nitrogen and hydrogen by means of intralayer charge transfer, and can enhance the activity of hydrogen evolution reactive sites. Furthermore, the interlayer coupling tends to localize photogenerated electrons at the reactive sites, which can provide more active electrons to participate in the catalytic reaction.

Two-dimensional (2D) semiconductors with desirable band gaps and high carrier mobility are highly sought after for future application in nanoelectronics. Herein, by means of first-principles calculations, we predict that a new 2D material, namely a Bi2OS2 nanosheet, possesses not only a tunable direct band gap, but also ultra-high electron mobility (up to 26 570 cm2 V−1 s−1). More interestingly, an anomalous layer-dependent band gap is revealed, derived from the synergetic effect of the quantum confinement and intrinsic surface electron states. 2D Bi2OS2 also exhibits excellent absorption over the entire solar spectrum and the absorption coefficient is comparable to that of inorganic–organic hybrid perovskite solar cells. Moreover, the Bi2OS2 monolayer maintains good structural integrity up to 1000 K and has a relatively small exfoliation energy from its layered bulk. The excellent electronic and optical properties, together with high stability and great experimental possibility, render 2D Bi2OS2 a promising material for future nanoelectronic and optoelectronic applications.

Using density functional and many-body perturbation theories, we explore the strain and electric field effects on the electronic structures and optical properties of hexagonal arsenene (β-As) and antimonene (β-Sb). The calculations show that they can transform from indirect into direct bandgap semiconductors, and even semimetals under biaxial tensile strain and an electric field perpendicular to the layer. In particular, under a stronger electric field, their bandgaps gradually close owing to the field-induced motion of nearly free electron states. More interestingly, increasing the strain can significantly red-shift the optical absorption spectra and even enhance the optical absorption in the energy region of 1.2–2.2 eV (including infrared and partial visible light). Under a stronger electric field, their optical absorptions are enhanced and a large exciton binding energy can be retained. Such dramatic characteristics in the electronic structures and optical properties suggest great potential of β-As and β-Sb for novel electronic and optoelectronic devices.

Gold–sulfur interfaces, including self-assembled monolayers of thiol molecules on gold surfaces, thiolate-protected gold nanoclusters, and gold sulfide complexes, have attracted intensive interest due to their promising applications in electrochemistry, bioengineering, and nanocatalysis. Herein, we predict two hitherto unreported two-dimensional (2D) Au6S2 monolayer polymorphs, named as G-Au6S2 and T-Au6S2. The global-minimum G-Au6S2 monolayer can be viewed as a series of [–S–Au–]n and [–Au4–]n chains packed together in parallel. The metastable T-Au6S2 monolayer resembles the widely studied T-MoS2 monolayer structure with each Mo atom substituted with an octahedral Au6 cluster, while the S atom is bonded with three Au atoms in a μ3 bridging mode. The G-Au6S2 monolayer is predicted to be metallic. The T-Au6S2 monolayer is predicted to be a semiconductor with a direct bandgap of 1.48 eV and high carrier mobility of 2721 cm2 V−1 s−1, ∼10 times higher than that of semiconducting H-MoS2. Moreover, the T-Au6S2 monolayer can absorb sunlight efficiently over almost the entire solar spectrum. These properties render the G- and T-Au6S2 monolayers promising materials for advanced applications in microelectronics and optoelectronics.

Nitrogen-doped graphene quantum dots (N-GQDs) hold promising application in electronics and optoelectronics because of their excellent photo-stability, tunable photoluminescence and high quantum yield. However, the absorption and emission mechanisms have been debated for years. Here, by employing time-dependent density functional theory, we demonstrate that the different N-doping types and positions give rise to different absorption and emission behaviors, which successfully addresses the inconsistency observed in different experiments. Specifically, center doping creates mid-states, rendering non-fluorescence, while edge N-doping modulates the energy levels of excited states and increases the radiation transition probability, thus enhancing fluorescence strength. More importantly, the even hybridization of frontier orbitals between edge N atoms and GQDs leads to a blue-shift of both absorption and emission spectra, while the uneven hybridization of frontier orbitals induces a red-shift. Solvent effects on N-GQDs are further explored by the conductor-like screening model and it is found that strong polarity of the solvent can cause a red-shift and enhance the intensity of both absorption and emission spectra.

Layered semiconductors with broad photoabsorption, a long carrier lifetime and high carrier mobility are of crucial importance for high-performance optoelectronic and photovoltaic devices; however it is hard to satisfy these requirements simultaneously in a system due to the opposite dependence on the layer thickness. Herein, by means of ab initio time-domain nonadiabatic molecular dynamic simulations, we find a new mechanism in Bi2OS2 nanosheets inducing an anomalous layer-dependent property of carrier lifetimes, which makes the few layered Bi2OS2 a possible system for fulfilling the above requirements concurrently. It is revealed that the interlayer dipole-dipole interaction in few layered Bi2OS2 effectively breaks the two-fold degenerate orbitals of [BiS2] layers, which not only cuts down the overlap of the electron and hole wave functions, but also accelerates the electron decoherence process. This significantly suppresses the electron-hole recombination and prolongs the photogenerated carrier lifetime of few layered Bi2OS2. The mechanism unveiled here paves a possible way for developing advanced optoelectronic and photovoltaic devices through engineering interlayer dipole-dipole coupling.