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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.

The electrochemical nitrogen reduction reaction (eNRR) to NH

Photocatalytic overall water splitting is a potential strategy to address energy crisis and environmental issues. However, it remains a great challenge to design an efficient photocatalyst, which not only possesses large spatial separation of photogenerated electrons and holes (PEH) to suppress recombination, but also can preserve the redox capability to drive the reaction. Herein, we design a new type of sandwich-polarized heterojunction by inserting a polarized semiconductor into the interlayer of the conventional photocatalyst. The inserted sublayer with out-of-plane polarization can induce a large electrostatic potential difference between the top and bottom photocatalytic sublayers. Then, the band edges of the top and bottom sublayers can be shifted to form the type II band alignment. Also, the valence band maximum and conduction band minimum will be located on different photocatalytic sublayers to facilitate the spatial separation of PEH. Simultaneously, different from the conventional type II heterojunction that reduces the redox capability, the electrostatic potential difference also acts as an auxiliary booster to offset the reduced redox potential of PEH. Taking the C

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.

Direct Z-scheme heterostructure photocatalysts possess tremendous potential to solar-driven overall water splitting, but how to rationally design and comprehensively characterize high-efficient dir...

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.

The electrochemiluminescence (ECL) is generally emitted via radiative transition of singlet or triplet excited state (S1 or T1). Herein, an ECL mechanism with the transitions of both S1 and T1 of black phosphorus quantum dots (BPQDs) was found for the first time, and an arginine modification strategy was proposed to passivate the surface oxidation defects of BPQDs, which could modulate the excited states for enhancing the ECL of BPQDs. The Arg modification led to greater spatial overlap of HOMO with LUMO and spectral shift of radiative transitions, and improved the stability of anion radical of BPQDs. The enhanced cathodic ECL was used to construct a sensitive method for conveniently evaluating the inhibiting efficiency of cyclo(RGDyK) to cell surface integrin by using RRGDS peptide modified BPQDs as signal tag. The dual excited states mediated ECL emitters provided a new paradigm for adjustable ECL generation and extended the application of ECL analysis.

Employing size effect to tailor photoabsorption and photoemission properties of quantum dot (QD) nanostructures is a widely used method for optoelectronic and biomedical applications. In this work,...

Employing density-functional theory, G0W0 approach, and solving Bethe–Salpter equation (BSE), we investigate the effects of strain and surface modification (hydrogenation or fluorination) on stability, electronic and optical properties of monolayer GaN. Monolayer GaN is predicted to be an indirect semiconductor with wide gap of 4.44 eV, whose bandgap can be effectively modulated by biaxial strain, ranging from 5.49 eV (δ = −6.5%) to 2.27 eV (δ = +8%). In particular, the compressive strain arouses the structural instability of GaN monolayer. Hydrogenation or fluorination not only eliminates its instability, but also tunes the bandgap from indirect to direct. More attractively, tensile strain can significantly redshift the optical spectra of GaN monolayer into the visible-light region, broadening light harvesting. Hydrogenation or fluorination shifts optical activity to the ultra-violet region. The possibility of tuning the optoelectronic properties via strain and surface modification opens doors to novel application of the promising material.

Two-dimensional quantum dots (2DQDs), as promising photothermal agents (PTAs) in photothermal therapy (PTT) to malignant tumors, have been widely studied experimentally, whereas the superior photoabsorption and photothermal conversion mechanisms remain unclear. In this work, we present the first excited-state dynamics study on the PTT of 2D antimonene (AM) QDs by employing time-dependent density functional theory and ab initio nonadiabatic molecular dynamics calculations. Surprisingly, pristine AMQDs themselves are not good PTAs due to weak photoabsorption and low photothermal conversion performance. The superior PTT capacity of AMQDs actually derives from the spontaneously partial oxidation. The partial oxidation introduces additional band edge states, which not only broaden the optical absorption range but also strengthen the transition dipole moment. More importantly, the oxidation doubles the nonradiative transition rate arising from the increased nonradiative coupling, which greatly promotes the release of photogenerated electron energy and accelerates the photothermal conversion efficiency. The in-depth insight unveiled here should be of fundamental importance and benefit for efficient utilization of 2DQDs in biomedical field.

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.

Photogenerated fully spin-polarized current has attracted considerable attention in spintronics owing to its high efficiency for information processing but low energy consumption. However, the short spin carrier lifetime of the primary materials significantly impedes the practical application of spin-polarized current and presents a major challenge. Here, on the basis of density functional theory and nonadiabatic molecular dynamics simulations, we design two prototypes of two-dimensional (2D) ferromagnetic/nonmagnetic semiconductor heterostructures ($\mathrm{Cr}{\mathrm{I}}_{3}/\mathrm{Mo}{\mathrm{Se}}_{2}$ and $\mathrm{Cr}{\mathrm{Br}}_{3}/\mathrm{Mo}{\mathrm{S}}_{2}$) with demonstrated ultralong photogenerated spin carrier lifetime. It is shown that the photogenerated spin holes can be effectively injected from the ferromagnetic layer to the nonmagnetic layer, and fully spin-polarized electrons will be confined in the ferromagnetic layer due to their type-II spin-polarized channel and large spin-flip gap. More surprisingly, the photogenerated spin carrier lifetime of these heterostructures is up to the time scale of nanoseconds. Such an ultralong spin carrier lifetime is mainly originated from small nonadiabatic coupling induced by weak spin electron-phonon interaction and slow nuclear velocity. Our results provide insights into the design of 2D semiconductor spintronic devices with an ultralong fully spin-polarized current lifetime.

Multifunctional devices based on 2D organic/inorganic van der Waals heterostructures (2D OIHs) exhibit excellent properties due to extensive and flexible structural tunability. However, how to precisely regulate devices via in situ monitoring technique remains a great challenge, and corresponding development is still in its infancy. In this Letter, we show that Raman spectroscopy can serve as an effective in situ detection strategy to systematically observe the interfacial electron–phonon coupling (IEPC) between substrate and 2D OIHs. Combining non-adiabatic molecular dynamics simulations with ultrafast spectroscopy, we reveal that the different strengths of IEPC between substrates and 2D OIHs can directly modulate the photocarrier lifetimes of inorganic 2D materials, and therefore, indirectly modify the Raman-sensitive photo-induced charge transfer processes at the interface of 2D OIHs. Further in situ Raman evidence demonstrates the unique advantage of Raman spectroscopy with high sensitivity to monitor different substrate-induced IEPC under variable temperature.

By employing first-principles calculations, we investigate the stabilities, quasi-particle band structures, and photocatalytic and optical properties of monolayer boron pnictides. Calculations indicate that monolayer boron pnictides have highly thermal stabilities verified by molecular dynamics, appreciable direct bandgaps, and good optical absorptions in the visible and near-infrared ranges. In addition, the relatively small exciton binding energies are also observed in the three systems, facilitating the separation of photogenerated electrons and holes. More interestingly, monolayer boron phosphide satisfies the criteria of photocatalyst for water splitting, and its photocatalytic performance can be further enhanced by applying biaxial tensile strain. Our researches provide valuable insight for finding monolayer boron pnictides applied in optoelectronics and photocatalytic water splitting.

Solar nitrogen (N2) fixation is the most attractive way for the sustainable production of ammonia (NH3), but the development of a highly active, long-term stable and low-cost catalyst remains a great challenge. Current research efforts for N2 reduction mainly focus on the metal-based catalysts using the electrochemical approach, while metal-free or solar-driven catalysts have been rarely explored. Herein, on the basis of a concept of electron "acceptance-donation", a metal-free photocatalyst, namely, boron (B) atom, decorated on the optically active graphitic-carbon nitride (B/g-C3N4), for the reduction of N2 is proposed by using extensive first-principles calculations. Our results reveal that gas phase N2 can be efficiently reduced into NH3 on B/g-C3N4 through the enzymatic mechanism with a record low onset potential (0.20 V). Moreover, the B-decorated g-C3N4 can significantly enhance the visible light absorption, rendering them ideal for solar-driven reduction of N2. Importantly, the as-designed catalyst is further demonstrated to hold great promise for synthesis due to its extremely high stability. Our work is the first report of metal-free single atom photocatalyst for N2 reduction, offering cost-effective opportunities for advancing sustainable NH3 production.

High carrier mobility and moderate band gap are two key properties of electronic device applications. Two ultrathin two-dimensional (2D) semiconductors, namely, Bi2Te2S and Bi2Te2Se nanosheets, with novel electronic and optical properties are predicted based on first-principles calculations. The Bi2Te2S and Bi2Te2Se monolayers own moderate band gaps (∼0.7 eV) and high electron mobilities (∼20 000 cm2 V–1 s–1), and they can absorb sunlight efficiently through the whole incident solar spectrum. Meanwhile, layer-dependent exponential decay band gaps are also unveiled. The relatively low interlayer binding energies suggest that these monolayers can be easily exfoliated from bulk structures. Their high dynamical and thermal stabilities are further verified by phonon dispersion calculations and ab initio molecular dynamics simulations. The exceptional properties render Bi2Te2X (X = S, Se) monolayers promising candidates in future high-speed (opto)electronic devices.

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.

Efficient carrier separation is the key to the application of photoelectric device. However, photogenerated electron–hole pairs in simplex semiconductors generally occupy the same regions spatially and are easy to recombine. Here we design a graphitic zinc-oxide-based (g-ZnO) intrinsic type-II heterostructure, g-ZnO/blue phosphorus (BP), based on first-principles calculations. The type-II band offsets and large built-in electric field ensure the photogenerated electrons easily migrating from g-ZnO to BP, which significantly enhances the separation of electron–hole pairs. Improved optical absorption is also observed in the heterostructure. Furthermore, the perpendicular external electric field can greatly modulate band edges and achieve a direct band gap at Γ point, which provides further promotion in the separation of carriers.

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.

The mixing of charge states of metal copper catalysts may lead to a much improved reactivity and selectivity toward multicarbon products for CO

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 C