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A series of lead-free Rb2ZrCl6:xTe4+ (x = 0%, 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 5.0%, 10.0%) perovskite materials were synthesized through a hydrothermal method in this work. The substitution of Te4+ for Zr in Rb2ZrCl6 was investigated to examine the effect of Te4+ doping on the spectral properties of Rb2ZrCl6 and its potential applications. The incorporation of Te4+ induced yellow emission of triplet self-trapped emission (STE). Different luminescence wavelengths were regulated by Te4+ concentration and excitation wavelength, and under a low concentration of Te4+ doping (x ≤ 0.1%), different types of host STE emission and Te4+ triplet state emission could be achieved through various excitation energies. These luminescent properties made it suitable for applications in information encryption. When Te4+ was doped at high concentrations (x ≥ 1%), yellow triplet state emission of Te4+ predominated, resulting in intense yellow emission, which stemmed from strong exciton binding energy and intense electron-phonon coupling. In addition, a Rb2ZrCl6:2%Te4+@RTV scintillating film was fabricated and a spatial resolution of 3.7 lp/mm was achieved, demonstrating the potential applications of Rb2ZrCl6:xTe4+ in nondestructive detection and bioimaging. [ABSTRACT FROM AUTHOR]

The 2D semiconductors are an ideal platform for exploration of bosonic fluids composed of coupled photons and collective excitations of atoms or excitons, primarily due to large excitonic binding energies and strong light‐matter interaction. Based on first‐principles calculations, it is demonstrated that the phonon polaritons formed by two infrared‐active phonon modes in monolayer MoSi2N4 and WSi2N4 possess ultra‐high confinement factors of around ≈105 and 103, surpassing those of conventional polaritonic thin‐film materials by two orders of magnitude. It is observed that the first bright exciton possesses a substantial binding energies of 750 and 740 meV in these two monolayers, with the radiative recombination lifetimes as long as 25 and 188 ns, and the Rabi splitting of the formed cavity‐exciton polaritons reaching 373 and 321 meV, respectively. The effective masses of the cavity exciton polaritons are approximately 10−5me, providing the potential for high‐temperature quantum condensation. The ultra‐confined and ultra‐low‐loss phonon polaritons, as well as strongly‐coupled cavity exciton polaritons with ultra‐small polaritonic effective masses in these two monolayers, offering the flexible control of light at the nanoscale, probably leading to practical applications in nanophotonics, meta‐optics, and quantum materials. [ABSTRACT FROM AUTHOR]

The optical spectra of transition metal dichalcogenide monolayers are dominated by excitons and trions. Here, we establish the dependence of these optical transitions on the disorder from hyperspectral imaging of h-BN encapsulated monolayer MoSe2. While both exciton and trion energies vary spatially, these two quantities are almost perfectly correlated, with spatial variation in the trion binding energy of only ∼0.18 meV. In contrast, variation in the energy splitting between the two lowest energy exciton states is one order of magnitude larger at ∼1.7 meV. Statistical analysis and theoretical modeling reveal that disorder results from dielectric and bandgap fluctuations, not electrostatic fluctuations. Our results shed light on disorder in high quality TMDC monolayers, its impact on optical transitions, and the many-body nature of excitons and trions. [ABSTRACT FROM AUTHOR]

The first-order phase transition between the liquid and gaseous phases ends at a critical point. Critical opalescence occurs at this singularity. Discovered in 1822, it is known to be driven by diverging fluctuations in the density. During the past two decades, boundaries between the gas-like and liquid-like regimes have been theoretically proposed and experimentally explored. Here, we show that fast cooling of near-critical sulfur hexafluoride (SF6), in presence of Earth's gravity, favors dark opalescence, where visible photons are not merely scattered, but also absorbed. When the isochore fluid is quenched across the critical point, its optical transmittance drops by more than three orders of magnitude in the whole visible range, a feature which does not occur during slow cooling. We show that transmittance shows a dip at 2eV near the critical point, and the system can host excitons with binding energies ranging from 0.5 to 4 eV. The spinodal decomposition of the liquid-gas mixture, by inducing a periodical modulation of the fluid density, can provide a scenario to explain the emergence of this platform for coupling between light and matter. The possible formation of excitons and polaritons points to the irruption of quantum effects in a quintessentially classical context. The first-order phase boundary between the liquid and gaseous phases ends at a critical point where the fluid, kept at thermodynamic equilibrium, displays a turbidity known as 'critical opalescence'. The authors quench a fluid across its critical point, find blackness instead of turbidity, and argue that, out of equilibrium, photons can be absorbed, not merely scattered. [ABSTRACT FROM AUTHOR]

Due to its tunable bandgap, anisotropic behavior, and superior thermoelectric properties, device applications using layered tellurene (Te) are becoming more attractive. Here, we report a thinning technique for exfoliated tellurene nanosheets using thermal annealing in an oxygen environment. We characterize different thinning parameters, including temperature and annealing time. Based on our measurements, we show that controlled layer thinning occurs in the narrow temperature range of 325–350 °C. We also show a reliable method to form β-tellurene oxide (β-TeO2), which is an emerging wide bandgap semiconductor with promising electronic and optoelectronic properties. This wide bandgap semiconductor exhibits a broad photoluminescence (PL) spectrum with multiple peaks covering the range of 1.76–2.08 eV. This PL emission, coupled with Raman spectra, is strong evidence of the formation of 2D β-TeO2. We discuss the results obtained and the mechanisms of Te thinning and β-TeO2 formation at different temperature regimes. We also discuss the optical bandgap of β-TeO2 and show the existence of pronounced excitonic effects evident by the large exciton binding energy in this 2D β-TeO2 system that reach 1.54–1.62 eV for bulk and monolayer, respectively. Our work can be utilized to have better control over the Te nanosheet thickness. It also sheds light on the formation of well-controlled β-TeO2 layered semiconductors for electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Carbon nitrides form a series of polymer semiconductors popular in photocatalysis. In the course of photoresponse, the separation of light-induced electron–hole pairs is one of the critical factors that affect the conversion rate from photoenergy to chemical substance. Exciton binding energy ( E b ) is treated as a classical parameter to evaluate the barrier of exciton dissociation. In this work, we study the electronic and optical nature of two specific members of the carbon nitride family, polymeric carbon nitride (melon) and crystallized poly(triazine imide) (PTI/Li+Cl−) by employing the photoluminescence spectra and density functional theory (DFT) calculations based on the Wannier-Mott exciton module. The results of self-consistent GW computation were applied. The measurement of photoluminescence spectra, by which exciton binding energies are estimated, is likewise discussed. Generally, compared with the results calculated by GW-BSE, the DFT results based on the Wannier-Mott model are closer to the experimental values. From a materials perspective, on the other hand, the exciton binding energy of the melon is lower than that of PTI/Li+Cl−. [ABSTRACT FROM AUTHOR]

A library of large organic cation spacers is available for engineering the performance of layered two‐dimensional (2D) halide perovskite devices. Despite extensive photophysics studies, there remains a research gap over the structure‐function relations in 2D perovskites, especially the underlying factors influencing the Auger recombination (AR) process. Herein, the contributions of exciton binding energy, exciton‐phonon coupling, and defects/film morphology to the AR process in 2D perovskites are examined. Phenyl‐alkyl‐ammonium cations with different lengths of attached alkyl groups, commonly used in blue light‐emitting diodes, are investigated. The findings reveal an order of magnitude higher threshold carrier density for the AR onset as well as a reduced AR in cations with longer alkyl chain length. Although possessing similar exciton binding energies, the exciton‐phonon coupling strength is found to play a major role in reducing the AR rate, with a smaller contribution from the defect states/film morphology. The findings can help provide further guidance on organic spacer cation engineering for highly efficient 2D perovskite light emitters. [ABSTRACT FROM AUTHOR]

An evolutionary algorithm was employed to locate the global minimum of Ti O 2 n nanoparticles with n = 2 – 20. More than 61,000 structures were calculated with a semiempirical method and reoptimized using density functional theory. The exciton binding energy of TiO2 nanoparticles was determined through the fundamental and optical band gap. Frenkel exciton energy scales as E B eV = 8.07 / n 0.85 , resulting in strongly bound excitons of 0.132–1.2 eV for about 1.4 nm nanoparticles. Although the exciton energy decreases with the system size, these tightly bound Frenkel excitons inhibit the separation of photogenerated charge carriers, making their application in photocatalysis and photovoltaic devices difficult, and imposing a minimum particle size. In contrast, the exciton binding energy of rutile is 4 meV, where the Wannier exciton energy scales as E B eV = 13.61 μ / ε 2 . Moreover, the Wannier excitons in bulk TiO2 are delocalized according to the Bohr radii: 3.9 nm for anatase and 7.7 nm for rutile. [ABSTRACT FROM AUTHOR]

We employ quasiparticle path integral molecular dynamics to study how the excitonic properties of model semiconductors are altered by electron–phonon coupling. We describe ways within a path integral representation of the system to evaluate the renormalized mass, binding energy, and radiative recombination rate of excitons in the presence of a fluctuating lattice. To illustrate this approach, we consider Fröhlich-type electron–phonon interactions and employ an imaginary time influence functional to incorporate phonon-induced effects nonperturbatively. The effective mass and binding energies are compared with perturbative and variational approaches, which provide qualitatively consistent trends. We evaluate electron-hole recombination rates as mediated through both trap-assisted and bimolecular processes, developing a consistent statistical mechanical approach valid in the reaction limited regime. These calculations demonstrate how phonons screen electron–hole interactions, generically reducing exciton binding energies and increasing their radiative lifetimes. [ABSTRACT FROM AUTHOR]

Room-temperature Bose–Einstein condensates (BECs) of exciton polaritons have been realized in organic molecular systems owing to strong light–matter interaction, strong exciton binding energy, and low effective mass of a polaritonic particle. These molecular-exciton-polariton BECs have demonstrated their potential in nonlinear optics and optoelectronic applications. In this study, we first demonstrate that molecular-polariton BECs can be utilized for Bose enhancement of excitation-energy transfer (EET) in a molecular system with an exciton donor coupled to a group of exciton acceptors that are further strongly coupled to a single mode of an optical cavity. Similar to the stimulated emission of light in which photons are bosonic particles, a greater rate of EET is observed if the group of acceptors is prepared in the exciton-polariton BEC state than if the acceptors are initially either in their electronic ground states or in a normal excited state with an equal average number of molecular excitations. The Bose enhancement also manifests itself as the growth of the EET rate with an increasing number of exciton polaritons in the BEC. Finally, a generalization to the EET in many-donor-many-acceptor molecular systems is considered, and a permutation-symmetry-based approach to suppress the EET to the huge manifold of dark states in the acceptor group is proposed to facilitate the Bose-enhanced EET to the polariton BEC. [ABSTRACT FROM AUTHOR]

Adsorption‐photocatalysis technology based on covalent organic frameworks (COFs) offers an alternative method for advancing the field of uranium extraction from seawater. When determining the photocatalytic activity of COFs, the binding energy of excitons (Eb) functions is the decisive factor. Nevertheless, the majority of reported COFs have a large Eb, which seriously restricts their application in the field of photocatalysis. Using a practical π‐skeleton engineering strategy, the current study synthesizes three donor‐acceptor olefin‐linked COFs containing amidoxime units in an effort to minimize Eb. Theoretical and experimental results reveal that the construction of planar and continuous π‐electron delocalization channels can significantly reduce Eb and promote the separation of electron‐hole pairs, thereby enhancing the photocatalytic activities. Moreover, the Eb of the TTh‐COF‐AO with a planar π‐skeleton donor is significantly reduced, and exhibits a substantially smaller Eb (38.4 meV). Under visible light irradiation, a high photo‐enhanced uranium extraction capacity of 10.24 mg g−1 is achieved from natural seawater without the addition of sacrificial reagents, which is superior to the majority of olefin‐linked COFs that have been reported to date. This study, therefore, paves the way for the development of tailored, efficient COFs photocatalysts for the extraction of uranium from seawater. [ABSTRACT FROM AUTHOR]

We reported exciton binding-energy determination using tunneling-current spectroscopy of Germanium (Ge) quantum dot (QD) single-hole transistors (SHTs) operating in the few-hole regime, under 405–1550 nm wavelength (λ) illumination. When the photon energy is smaller than the bandgap energy (1.46 eV) of a 20 nm Ge QD (for instance, λ = 1310 nm and 1550 nm illuminations), there is no change in the peak voltages of tunneling current spectroscopy even when the irradiation power density reaches as high as 10 µW/µm2. In contrast, a considerable shift in the first hole-tunneling current peak towards positive VG is induced (ΔVG ≈ 0.08 V at 0.33 nW/µm2 and 0.15 V at 1.4 nW/µm2) and even additional photocurrent peaks are created at higher positive VG values (ΔVG ≈ 0.2 V at 10 nW/µm2 irradiation) by illumination at λ = 850 nm (where the photon energy matches the bandgap energy of the 20 nm Ge QD). These experimental observations were further strengthened when Ge-QD SHTs were illuminated by λ = 405 nm lasers at much lower optical-power conditions. The newly-photogenerated current peaks are attributed to the contribution of exciton, biexciton, and positive trion complexes. Furthermore, the exciton binding energy can be determined by analyzing the tunneling current spectra. [ABSTRACT FROM AUTHOR]

Perovskite light‐emitting diodes (PeLEDs) are promising candidates for displays and solid‐state lighting due to their tunable colors, high conversion efficiency, and low cost. However, the performance of deep blue PeLEDs lags far behind that of near‐infrared, red, and green ones. Here, the ligand concentration on the perovskite surface is regulated by introducing a small organic molecule 3‐(5,9‐dioxa‐13b‐boranaphtho [3,2,1‐d,e] anthracene‐7‐yl)‐9‐phenyl‐9H‐carbazole (BOCzPh) to reduce the defects in the mixed‐halogen perovskite lattice and improve the exciton binding energy of perovskite quantum dots (QDs). Finally, deep blue PeLEDs with an emission peak at 469 nm, a peak external quantum efficiency of 2.8%, and a maximum brightness of 851 cd m−2 are obtained. Owing to the post‐passivation of QDs by BOCzPh molecules, the emission spectra of the mixed‐halide perovskites are stabilized and the luminous efficiency of the devices is improved simultaneously. This work provides a new approach to realize spectrally stable and efficient deep blue PeLEDs. [ABSTRACT FROM AUTHOR]

We develop a theoretical study to evaluate the dynamic of the time-resolved photoemission spectrum arising from the dissociation of exciton steady-states 1s, 2s in a monolayer transition metal dichlacogenides. We discuss the dielectric environment effect on the exciton binding energies. Quantum beat signatures in photoemission intensity demonstrate coherent coupling between 1s and 2s excitons. The beating contribution due to excitonic coherence is also discussed. The periodic oscillations arising from coherent superposition states and quantum beats enable exploration of novel coherent phenomena. [ABSTRACT FROM AUTHOR]

Correlated spectral fluctuations were suggested to coordinate excitation transport inside natural light harvesting complexes. We demonstrate the capacities of 2D line shapes from fifth-order coherent electronic signals (R5-2D) to report on such fluctuations in molecular aggregates and present a stochastic approach to fluctuations in correlated site and bi-exciton binding energies in the optical dynamics of Frenkel excitons. The model is applied to R5-2D line shapes of a homodimer, and we show that the peak tilt dynamics are a measure for site energy disorder, inter-site correlation, and the strength of bi-exciton binding energy fluctuations. [ABSTRACT FROM AUTHOR]

We reported exciton binding-energy determination using tunneling-current spectroscopy of Germanium (Ge) quantum dot (QD) single-hole transistors (SHTs) operating in the few-hole regime, under 405–1550 nm wavelength (λ) illumination. When the photon energy is smaller than the bandgap energy (1.46 eV) of a 20 nm Ge QD (for instance, λ = 1310 nm and 1550 nm illuminations), there is no change in the peak voltages of tunneling current spectroscopy even when the irradiation power density reaches as high as 10 µW/µm2. In contrast, a considerable shift in the first hole-tunneling current peak towards positive VG is induced (ΔVG ≈ 0.08 V at 0.33 nW/µm2 and 0.15 V at 1.4 nW/µm2) and even additional photocurrent peaks are created at higher positive VG values (ΔVG ≈ 0.2 V at 10 nW/µm2 irradiation) by illumination at λ = 850 nm (where the photon energy matches the bandgap energy of the 20 nm Ge QD). These experimental observations were further strengthened when Ge-QD SHTs were illuminated by λ = 405 nm lasers at much lower optical-power conditions. The newly-photogenerated current peaks are attributed to the contribution of exciton, biexciton, and positive trion complexes. Furthermore, the exciton binding energy can be determined by analyzing the tunneling current spectra. [ABSTRACT FROM AUTHOR]

Covalent triazine frameworks (CTF) offer a tunable platform for photocatalytic H2 generation due to their diverse structures, low costs, and precisely tunable electronic structures. However, high exciton binding energy and short lifetimes of photogenerated carriers restrict their application in photocatalytic hydrogen evolution. Herein, a novel phosphorus‐incorporated CTF is introduced to construct a chemically bonded PCTF/WO3 (PCTFW) heterostructure with a precise interface electron transfer channel. The phosphorus incorporation is found to dominantly reduce the exciton binding energy and promote the dissociation of singlet and triplet excitons into free charge carriers due to the regulation of electronic structures. High‐quality interfacial WN bonds improve the interfacial transfer of photogenerated electrons, thus prolonging the lifetime of photogenerated electrons. Femtosecond transient absorption spectroscopy characterizations and DFT calculations further confirm both phosphorus incorporation and Z‐scheme heterojunctions can synergistically boost the in‐built electric field and accelerate the migration and separation of photogenerated electrons. The optimized photocatalytic H2‐evolution rate of resultant PCTFW is 134.84 µmol h−1 (67.42 mmol h−1g−1), with an apparent quantum efficiency of 37.63% at 420 nm, surpassing many reported CTF‐based photocatalysts so far. This work highlights the significance of atom‐level interfacial exciton dissociation, and charge transfer and separation in improving photocatalysis. [ABSTRACT FROM AUTHOR]

Dopant-free lateral p–n junctions in the GaAs/AlGaAs material system have attracted interest due to their potential use in quantum optoelectronics (e.g., optical quantum computers or quantum repeaters) and ease of integration with other components, such as single electron pumps and spin qubits. A major obstacle to integration has been the unwanted charge accumulation at the p–n junction gap that suppresses light emission, either due to enhanced non-radiative recombination or due to inhibition of p–n current. Typically, samples must frequently be warmed to room temperature to dissipate this built-up charge and restore light emission in a subsequent cooldown. Here, we introduce a practical gate voltage protocol that clears this parasitic charge accumulation, in situ at low temperature, enabling the indefinite cryogenic operation of devices. This reset protocol enabled the optical characterization of stable, bright, dopant-free lateral p–n junctions with electroluminescence linewidths among the narrowest (<1 meV; <0.5 nm) reported in this type of device. It also enabled the unambiguous identification of the ground state of neutral free excitons (heavy and light holes) as well as charged excitons (trions). The free exciton emission energies for both photoluminescence and electroluminescence are found to be nearly identical (within 0.2 meV or 0.1 nm). The binding and dissociation energies for free and charged excitons are reported. A free exciton lifetime of 237 ps was measured by time-resolved electroluminescence, compared to 419 ps with time-resolved photoluminescence. [ABSTRACT FROM AUTHOR]

Growing green and amber emitting InGaN/GaN quantum wells in the zincblende, rather than the wurtzite, crystal phase has the potential to improve efficiency. However, optimization of the emission efficiency of these heterostructures is still required to compete with more conventional alternatives. Photoluminescence time decays were used to assess how the quantum well width and number of quantum wells affect the recombination rates, and temperature dependent photoluminescence was used to determine the factors affecting recombination efficiency. The radiative recombination lifetime was found to be approximately 600 ps and to increase weakly with well width, consistent with a change in the exciton binding energy. The relative efficiency at room temperature was found to increase by a factor of five when the number of wells was increased from one to five. Furthermore, the efficiency increased by factor 2.2 when the width was increased from 2.5 to 7.5 nm. These results indicate that thermionic emission is the most important process reducing efficiency at temperatures in excess of 100 K. Moreover, the weak dependence of the rate of radiative recombination on well width means that increasing well thickness is an effective way of suppressing thermionic emission and thereby increasing efficiency in zincblende InGaN/GaN quantum wells, in contrast to those grown in the wurtzite phase. [ABSTRACT FROM AUTHOR]

In this paper, the exciton binding energy and radiation lifetime in type I and II structures of CdTe/Cd 1 − x ZnxS strained core/shell spherical quantum dots under the hydrostatic pressure have been studied by using the variational method within the continuous dielectric model and effective mass approximation. The results show that for these two structures, the exciton binding energies with and without strain decrease with the increasing core radius but increase with the increasing pressure. The exciton binding energy with strain is smaller than that without strain. For type I structure, the effect of strain is small, and the radiation lifetime decreases monotonically with the increasing pressure. By contrast, for type II structure, the effects of shell radius and strain on the exciton binding energy are obvious, and the radiation lifetime increases first and then decreases with the increasing pressure. [ABSTRACT FROM AUTHOR]

Recent advances in organic photodetectors (OPDs) have enabled high detectivity, high quantum efficiency, and fast response, due to their broad spectral response, easy processing, compatibility with flexible devices, and cooling‐free operations. The advantages of combining ultrathin and self‐powered OPDs are rarely explored, as technological limitations and lack of knowledge on the underlying mechanisms may lead to low light absorption efficiency and carrier recombination issues. Here, a modification layer‐assisted approach is developed to construct ultrathin self‐powered OPDs with enhanced sensitivity and ultrafast response time performance due to efficient exciton dissociation, energy transfer, and charge extraction processes. Specifically, this strategy enables a reduced exciton binding energy (42.4 meV) for efficient dissociation, as well as an increased dielectric constant of the photosensitive layer that shields undesirable lattice binding effects of photogenerated excitons. As a result, a remarkable device responsivity (0.45 A W−1), improved response detectivity (1.25 × 1012 Jones), and enhanced energy transfer efficiency (78.7%) are observed in the modified ultrathin organic photodetector. These findings illustrate a clear correlation between the exciton dissociation process, photogenerated exciton yields, and energy transfer channels, providing essential insight into the design of efficient ultrathin organic photodetectors. [ABSTRACT FROM AUTHOR]

Recently, interlayer and intralayer excitons in transition metal dichalcogenide heterobilayers have been studied both experimentally and theoretically. In spite of a growing interest, these layer-resolved excitons in the presence of external stimuli, such as strain, remain not fully understood. Here, using density-functional theory calculations with many-body effects, we explore the excitonic properties of vertically stacked MoSe2/WSe2 heterobilayer in the presence of in-plane biaxial strain of up to 5%. We calculate the strain dependence of exciton absorption spectrum, oscillator strength, wave function, and binding energy by solving the Bethe–Salpeter equation on top of the standard GW approach. We identify the interlayer and intralayer excitons by analyzing their electron-hole weights and spatial wave functions. We show that with the increase in strain magnitude, the absorption spectrum of the interlayer and intralayer excitons is red-shifted and re-ordered, and the binding energies of these layer-resolved excitons decrease monotonically and almost linearly. We derive the sensitivity of exciton binding energy to the applied strain and find that the intralayer excitons are more sensitive to strain than the interlayer excitons. For instance, a sensitivity of −7.9 meV/% is derived for the intra-MoSe2-layer excitons, which is followed by −7.4 meV/% for the intra-WSe2-layer excitons, and by −4.2 meV/% for the interlayer excitons. Our results indicate that interlayer and intralayer excitons in vertically stacked MoSe2/WSe2 heterobilayer are efficiently tunable by in-plane biaxial strain. [ABSTRACT FROM AUTHOR]

Highlights: The classification of 2D perovskite is summarized, and the preparation methods of 2D perovskite according to the requirements of X-ray detection materials are introduced. We analyzed the advantages and insufficiency of different devices and introduced improvement measures, including ion migration, charge transfer performance, stability, and 2D/3D heterojunctions. Finally, we introduced the potential preponderances of 2D perovskite in the scintillation detection field; meanwhile, the main challenges facing the practical application of 2D perovskite X-ray detectors are analyzed. Metal halide perovskites have recently emerged as promising candidates for the next generation of X-ray detectors due to their excellent optoelectronic properties. Especially, two-dimensional (2D) perovskites afford many distinct properties, including remarkable structural diversity, high generation energy, and balanced large exciton binding energy. With the advantages of 2D materials and perovskites, it successfully reduces the decomposition and phase transition of perovskite and effectively suppresses ion migration. Meanwhile, the existence of a high hydrophobic spacer can block water molecules, thus making 2D perovskite obtain excellent stability. All of these advantages have attracted much attention in the field of X-ray detection. This review introduces the classification of 2D halide perovskites, summarizes the synthesis technology and performance characteristics of 2D perovskite X-ray direct detector, and briefly discusses the application of 2D perovskite in scintillators. Finally, this review also emphasizes the key challenges faced by 2D perovskite X-ray detectors in practical application and presents our views on its future development. [ABSTRACT FROM AUTHOR]

Electroluminescence properties of epitaxially grown n+-ZnO/p-GaN pn+-heterojunctions are investigated as functions of applied bias and temperature. This study reveals the existence of indirect interfacial excitons at sufficiently low temperatures. Electroluminescence feature associated with these excitons redshifts with increasing forward bias. It has been found that the binding energy of these entities can be controlled through applied forward bias and can even be made higher than that of the excitons in ZnO bulk (60 meV). However, the formation of these excitons becomes unsustainable when either the applied bias or the temperature crosses a threshold. This has been explained in terms of leakage and thermal escape of electrons (holes) into the GaN (ZnO) side. Calculations for the band diagram and the binding energy of these spatially indirect electron–hole coulomb-coupled entities are carried out. Theoretical results are found to explain the experimental findings quite well. [ABSTRACT FROM AUTHOR]

Fluorographene (FG) is a promising graphene-derived material with a large bandgap. Currently existing predictions of its fundamental gap (Δf) and optical gap (Δopt) significantly vary when compared with experiment. We provide here an ultimate benchmark of Δf for FG by many-body GW and fixed-node diffusion Monte Carlo (FNDMC) methods. Both approaches independently arrive at Δf ≈ 7.1 ± 0.1 eV. In addition, the Bethe–Salpeter equation enabled us to determine the first exciton binding energy, Eb = 1.92 eV. We also point to the possible misinterpretation problem of the results obtained for gaps of solids by FNDMC with single-reference trial wave functions of Bloch orbitals. We argue why instead of Δopt, in the thermodynamic limit, such an approach results in energy differences that rather correspond to Δf, and we also outline conditions when this case actually applies. [ABSTRACT FROM AUTHOR]

The substrate effect is an important issue in the properties of two-dimensional transition metal dichalcogenides (2D TMDs). Quantitatively determining the dependence of the photoluminescence (PL) emission properties and the excitonic behavior of single-layer 2D materials in a specific dielectric environment would provide helpful guidance for the rational design of substrates for high performance 2D TMD PL emission devices. Here, using a WSe2 monolayer on different substrates as a model system, it is demonstrated that the PL emission intensities can drastically change depending on the substrate effect. From the analysis of the excitonic behavior, the results reveal that the spectral weight between the neutral and charged excitons in the PL spectra is significantly modified by the substrate types, and the weight factor is dependent on the laser excitation density. The charged exciton binding energy is obviously negatively related to the substrate dielectric constant. Furthermore, the change trends of the binding energy of the monolayer WSe2 on different substrates are basically the same for the increase of the excitation density. These results suggest that the choice of the substrate plays a significant role in the modulation of the PL properties and exciton states of atomically thin WSe2; hence, substrate engineering should be carefully considered in the design of future 2D devices. [ABSTRACT FROM AUTHOR]

Strong Coulomb interaction in atomically thin transition metal dichalcogenides makes these systems particularly promising for studies of excitonic physics. Of special interest are the manifestations of the charged excitons, also known as trions, in the optical properties of two-dimensional semiconductors. In order to describe the optical response of such a system, the exciton interaction with resident electrons should be explicitly taken into account. In this paper, we demonstrate that this can be done in both the trion (essentially, few-particle) and Fermi-polaron (many-body) approaches, which produce equivalent results, provided that the electron density is sufficiently low and the trion binding energy is much smaller than the exciton one. Here, we consider the oscillator strengths of the optical transitions related to the charged excitons, fine structure of trions, and Zeeman effect, as well as photoluminescence of trions illustrating the applicability of both few-particle and many-body models. [ABSTRACT FROM AUTHOR]

Disintegration and formation of excitons in graphene nanodots are investigated within the framework of mean-field approximation to the Hubbard model. Optically active excitons are found to be disintegrated in the non-magnetic nanodots and are shown to form only when the system enters into the antiferromagnetic state. As the Hubbard parameter U / t exceeds a critical value, the nanodot is found to undergo a phase transition from the non-magnetic to an antiferromagnetic phase. Before the phase transition, both optical and quasiparticle gaps are found to be nearly independent of the interaction strength. After the phase transition, however, the quasiparticle gap is revealed to increase more rapidly than the optical gap, which eventually leads to a positive binding energy of the bright exciton in the antiferromagnetic nanodot. The understanding of this extraordinary disintegration and formation of excitons in different magnetic phases of graphene nanodots is believed to be of paramount importance for their potential optoelectronic applications. [ABSTRACT FROM AUTHOR]

Siligraphene belonging to the family of two-dimensional (2D) materials has great potential in optoelectronics due to its considerable excitonic effects. In this study, the strain effects on the electronic structure and the real-space exciton wave functions of g - SiC 7 are investigated using the first-principles calculations based on the ab initio many-body perturbation theory. Alongside the increase (decrease) of the bandgap with compressive (tensile) strain, our results show that the exciton in the siligraphene monolayer under in-plane biaxial compressive strains is much more localized than that in the case of tensile one, leading to the higher and lower exciton binding energies, respectively. Moreover, the π ↦ π and π ↦ σ exciton state transition emerges when applying the compressive and tensile strains, respectively. Overall, our study reveals that a desirable way to dissociate the electron-hole coupling and to reduce the electron-hole recombination process is applying "in-plane biaxial tensile strain," making g - SiC 7 an excellent potential functional 2D semiconductor in optoelectronics. [ABSTRACT FROM AUTHOR]

In mini-review, deals with the theory of exciton quasimolecules in a nanosystem consisting of double quantum dots of germanium synthesized in a silicon matrix. An exciton quasimolecule was formed as a result of the interaction of two spatially indirect excitons. It is shown that, depending on the distance D between the surfaces of the quantum dots, spatially indirect excitons and of exciton quasimolecules was formed in the nanosystem. The binding energy of the singlet ground state of the exciton quasimolecule has been gigantic exceeding the binding energy of the biexciton in a silicon single crystal by almost two orders of magnitude. The emergence of a band of localized electron states in the band gap of the silicon matrix was found. This band of localized electron states appeared as a result of the splitting of electron levels in the chain of germanium quantum dots. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have shown great potential for lighting. However, their low stability under irradiation/thermal stress and/or ambient storage conditions are critical for light‐emitting diodes (LEDs). Among the stabilization strategies, ligand surface modification is effective toward stable perovskites, but the dynamic ligand adsorption/desorption process on the surface is a limiting factor. Herein, a new family of biogenic and amphiphilic capping agents, phosphatidyl‐L‐serine (Ptd‐L‐Ser), combining stronger multibinding motifs compared to conventional capping agents has led to superior CsPbBr3 (CsPbBr3‐Ptd‐L‐Ser) with significantly enhanced stability upon storage/heating/water, keeping excellent photoluminescence quantum yields of ≈80% over half year. Spectroscopic/theoretical studies reveal that the origin of this behavior is the increased exciton binding energy associated to the versatility of multiple bindings. This results in CsPbBr3‐Ptd‐L‐Ser nanocrystals‐based green‐LEDs featuring excellent stabilities of >700 h (20 mA) and >200 h (100 mA) that strongly contrast with the reference devices with pristine CsPbBr3 nanocrystals (120 h (20 mA) and 27 h (100 mA)). White LEDs (WLEDs) with chromaticity coordinates of (0.34, 0.33) and high luminous efficiency of 76 lm W–1, keeping stable over weeks, are further demonstrated under continuous operational conditions, thereby suggesting CsPbBr3‐Ptd‐L‐Ser nanocrystals can be a potential candidate for commercial WLED technology. [ABSTRACT FROM AUTHOR]

In this Letter, we present the experimental observation of trilayer exciton emission in the WSe2/WS2/MoS2 heterostructures by photoluminescence spectroscopy at a low temperature of ∼10 K. It is found that the trilayer exciton has a lower exciton binding energy than that in the WSe2/MoS2 heterobilayer due to the insertion of monolayer WS2, which is manifested by the blueshift of this trilayer exciton peak relative to the bilayer exciton. Through the measurements of the exciton peak position as a function of excitation power, the trilayer excitons exhibited the density-dependent repulsive interaction among them, and the reduction of binding energy ∼8 meV is deduced. Moreover, the trilayer exciton has a longer lifetime than the bilayer exciton, resulting from the reduction of electron–hole wavefunction overlap. [ABSTRACT FROM AUTHOR]

Devices operating with excitons have promising prospects for overcoming the dilemma of response time and integration in current generation of electron‐ or/and photon‐based elements and devices. In combination with the advantages of emerging twistronics and valleytronics, the atomically thin transition metal dichalcogenide semiconductors open up new opportunities for pursuing practical excitonic devices, where the strong exciton binding energy enables operating exciton at room temperature. The essential and foremost step toward exciton devices is the control of spatiotemporal exciton flux, which is density‐dependent and affected by the complex many‐body interactions. It can be effectively controlled by the strain, electric field, electron‐doping, and local dielectric environment. Intriguingly, exotic phenomena such as exciton condensation, electron‐hole liquid, exciton Hall effects, and exciton halo effects can be occurred in 2D exciton system, providing new possibilities for excitonic devices. Up to now, the proof‐of‐principle of room temperature exciton devices, including excitonic switching and transistor, exciton guides, and excitonic nanolaser, have been realized. Here the authors review the recent advances in molding 2D exciton flux from basic principle, manipulation, exotic phenomena to promising applications and discuss the opportunities and challenges in pushing the frontiers of room temperature excitonic devices. [ABSTRACT FROM AUTHOR]

In this study, we investigated the exciton binding energy and interband transition between the electron and heavy-hole for the single and double quantum wells which have different hyperbolic-type potential functions subject to electric, magnetic, and non-resonant intense laser fields. The results obtained show that the geometric shapes of the structure and the applied external fields are very effective on the electronic and optical properties. In the absence of the external fields, the exciton binding energy is a decreasing function of increasing well sizes except for the strong confinement regime. Therefore, for all applied external fields, the increase in the well widths produces a red-shift at the absorption peak positions. The magnetic field causes an increase in the exciton binding energy and provides a blue-shift of the absorption peak positions corresponding to interband transitions. The effect of the electric field is quite pronounced in the weak confinement regime, it causes localization in opposite directions of the quantum wells of the electron and hole, thereby weakening the Coulomb interaction between them, causing a decrease in exciton binding energy, and a red-shift of the peak positions corresponding to the interband transitions. Generally, an intense laser field causes a decrease in the exciton binding energy and produces a red-shift of the peak positions corresponding to interband transitions. [ABSTRACT FROM AUTHOR]

A theory of exciton quasimolecules (formed from spatially separated electrons and holes) in a nanosystem consisting of double quantum dots (QDs) of germanium synthesized in a silicon matrix is presented. It is shown that the binding energy of the singlet ground state of the quasimolecule of an exciton is considerably larger than the binding energy of biexciton in a silicon single crystal by almost two orders of magnitude. It is shown that the exciton quasimolecule formation is of the threshold character and possible in a nanosystem, where D is the distance between the surfaces of QD that satisfies the following condition: (1) (2) DC C1 D D (where (1) DC and (2) DC are some critical distances). Using the variational method, we obtain the binding energy of the exciton quasimolecule singlet ground state of the system as a function of the distance between the surfaces of QD D, and the QD radius a. It is shown that the convergence of two QDs up to a certain critical value of the distance between the surfaces of QD DC leads to the effective overlapping of the electron wave functions and the appearance of exchange interactions. As a result, the exciton quasimolecules can be formed from the QDs. It is shown that the existence of such a critical distance DC arises from the quantum size effects. Dimensional quantization of electrons and holes motion leads to the following fact: as the distance between the surfaces of the QD DC decreases, the decrease in the energies of interaction of the electrons and holes entering into the Hamiltonian of the exciton quasimolecule cannot compensate for the increase in the kinetic energy of the electrons and holes. At larger values of the distance between the surfaces of the QD D, (2) D2 DC, the exciton quasimolecule breaks down into two excitons (consisting of spatially separated electrons and holes), localized over the QD surfaces. The fact that the energy of the ground state of singlet excitonic quasimolecule is in the infrared range of the spectrum, presumably, allows us to use a quasimolecule for the development of new elements of silicon infrared nanooptoelectronics. [ABSTRACT FROM AUTHOR]

Half‐light and half‐matter exciton polaritons have demonstrated profound impacts on coherent quantum phenomena. Two‐dimensional (2D) organic−inorganic perovskite semiconductors, exhibiting large exciton binding energy and spin‐based behavior, are an excellent platform for the study of exciton polaritons at room temperature. However, the implementation of these fascinating coherent phenomena is still constrained by the lack of an understanding of the crucial polariton–polariton interaction effects. Here, an experimental observation of spin‐dependent polariton–polariton interactions in a prototype 2D organic−inorganic perovskite microcavity by circularly polarization‐resolved transient absorption (TA) measurements is reported. A power‐dependent blue shift of the lower polariton bands with the same spin is clearly revealed, whereas the energy band of the polariton bands with the opposite spin is almost not changed. Spectacularly, it is found that the energy band blue shift mainly takes place before the spin depolarization, which provides accurate evidence for the spin‐dependent polariton–polariton interactions. Furthermore, the strong coherent polariton–phonon coupling of perovskite microcavity has also been detected firstly in ultrafast TA dynamics. These results demonstrate that microcavity polaritons inheriting the matter properties from their excitonic constituents exhibit strong nonlinear interactions and pave the way for realizing coherent quantum phenomena at room temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] Earth-abundant g-C 3 N 4 is a promising photocatalyst for CO 2 reduction, but its practical application is severely limited by the excitonic effect of g-C 3 N 4 derived from strong binding energy and lack of electron-enriched active sites. Herein, we design a novel 2D/2D Schottky junction photocatalysts comprising of Ti 3 C 2 T x -modified defective g-C 3 N 4 nanosheets with carbon vacancy (denoted as Ti 3 C 2 T x /V c -CN) by a self-assembly method. The carbon vacancies in g-C 3 N 4 promote exciton dissociation into free charge, while the formed Schottky junctions between Ti 3 C 2 T x and V c -CN further enables a directional charge transfer, thus providing an electron-rich catalytic surface for the CO 2 reduction. Thanks to the synergy of promoted exciton dissociation and directional electron transfer, the optimal 20% Ti 3 C 2 T x /V c -CN display a high CO evolution rate of 20.54 µmol·g−1·h−1 under visible light irradiation, which is 7.4 times higher than that of bare CN. This work highlights the synergy of the promoted exciton dissociation and directional electron transfer in the activity enhancement of photocatalytic CO 2 reduction. [ABSTRACT FROM AUTHOR]

The effects of confinement potentials of the first and second materials, core size and first shell thickness on the confinement of electron, electron-donor atom, and exciton in cylindrical core/shell/shell quantum dot (CSSQD) are studied taking into account the finite confinement potential model. The confinement of charge carriers in CSSQD with two finite confinement potentials models of the barrier materials are studied. Within the effective mass and parabolic band approximation, the 3D time-independent Schrödinger equation has been resolved. To obtain the ground state quasiparticles energies, we have used the variational technique. Our results show that the donor atom and exciton binding energy, as well as the electron energy, strongly depend on the core radius, first shell thickness, confinement potentials of the barrier materials, and their structures (A and B). Moreover, the confinement potential effect of the first material on the energies is more pronounced when their thickness is large and the core radius is small. So, the external potential effect is more significant when the first shell thickness and potential are small. Also, The binding energy of an on-center (off-center) donor atom is greater (weaker) than that of the exciton, whatever the structure of the confinement potential. In addition, the transition from a type-A to a type-B confinement system has been observed. The findings might be used to modify the electronic and excitonic properties in nanomaterials science. [ABSTRACT FROM AUTHOR]

The biexciton is a quasi‐particle created from two free excitons and can be applied for basic quantum operations, entangled light sources, and lasers. 2D lead‐halide layered perovskites (LPs) naturally form organic–inorganic quantum wells (QWs), leading to high exciton binding energy and tunable band‐gaps dependent on the QW thickness of . Although excitonic lasing has been reported for thicker LP‐QWs, biexciton emissions and lasers from phase‐pure LP‐QWs as a function of remain largely unexplored. Here, a facile solution growth method for fabricating single‐crystalline flakes (SCFs) of LP‐QWs of (PEA)2(MA)n−1PbnI3n+1 (PEA = phenylethylammonium, = 1, 2, and 3) is reported. Further, multicolor amplified spontaneous emissions from biexciton states of (PEA)2(MA)n−1PbnI3n+1 ( = 1, 2, and 3) SCFs are demonstrated at 541 (green), 588 (yellow), 627 nm (red) with thresholds of 35.4, 15.1, and 5.8 µJ cm−2 at 20 K, respectively. In order to offer cavities for these single‐crystalline flakes, they are exfoliated into smaller flakes. Multimode lasing is shown at 586 and 627 nm for = 2 and 3 with threshold of 10.5 and 4.8 µJ cm−2, respectively. The results of this study not only enrich the basic understanding of many‐body excitonic interactions in 2D LPs but also provide insights for developing solution‐processed multicolor lasers. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenide (TMDCs) monolayers make an excellent component in optoelectronic devices such as photodetectors and phototransistors. Selenide‐based TMDCs, specifically molybdenum diselenide (MoSe2) monolayers with low defect densities, show much faster photoresponses compared to their sulfide counterpart. However, the typically low absorption of the atomically thin MoSe2 monolayer and high exciton binding energy limit the photogeneration of charge carriers. Yet, integration of light‐harvesting materials with TMDCs can produce increased photocurrents via energy transfer. In this article, it is demonstrated that the interaction of cesium lead bromide (CsPbBr3) nanocrystals with MoSe2 monolayers results into an energy transfer efficiency of over 86%, as ascertained from the quenching and decay dynamics of the CsPbBr3 nanocrystals emission. Notably, the increase in the MoSe2 monolayer emission in the heterostructure accounts only for 33% of the transferred energy. It is found that part of the excess energy generates directly free carriers in the MoSe2 monolayer, as a result of the transfer of energy into the exciton continuum. The efficiency of the heterostructure via enhanced photocurrents with respect to the single material unit is proven. These results demonstrate a viable route to overcome the high exciton binding energy typical for TMDCs, as such having an impact on optoelectronic processes that rely on efficient exciton dissociation. [ABSTRACT FROM AUTHOR]

We offer a new iterative method for exciton theory and develop a theory of exciton states arising in a plane resonant-tunnelling nanostructure based on semiconducting nitrides. Our approach takes into account the contributions of internal electric fields arising in its layers and employs both iterative and variational methods. We compare our method with the other techniques known in the exciton theory on example of a nanosystem representing a separate cascade of quantum cascade detector, which has been earlier implemented experimentally. The electron and hole spectra, the spectra of excitons and their binding energies, as well as the intensities of electron–hole transitions are calculated as functions of geometric parameters of the nanostructure. Particular cases of light-hole and heavy-hole excitons are analyzed. [ABSTRACT FROM AUTHOR]

Efficient charge generation contributes greatly to the high performance of organic photovoltaic devices. The mechanism of charge separation induced by heterojunction has been widely accepted. However, how and why free charge carriers can generate in homogenous polymer domains remains to be explored. In this work, the extended tight-binding SSH model, combined with the non-adiabatic molecular dynamics simulation, is used to construct the model of a polymer array in an applied electric field and simulate the evolution of an excited state. It is found that under a very weak external electric field 5.0 × 10−3 V/Å, the excited state can evolve directly into spatially separated free charges at the femtosecond scale, and the efficiency is up to 97%. The stacking structure of the polymer array leads to intermolecular electron mutualization and forms intermolecular coupling. This interaction tends to delocalize the excited states in organic semiconductors, competing with the localization caused by electron–phonon coupling. Excitons within the homogenous polymer domains have lower binding energy, less energy dissipation, and ultrafast charge separation. Therefore, the initial excited state can evolve directly into free carriers under a very weak electric field. This finding provides a reasonable explanation for ultrafast charge generation in pure polymer phases and is consistent with the fact that delocalization always coexists with ultrafast charge generation. Moreover, the devices based on homogenous polymer domains are supposed to be stress-sensitive and performance-anisotropic since the above two interactions have contrary effects and work in perpendicular directions. This work is expected to bring inspiration for the design of organic functional materials and devices. [ABSTRACT FROM AUTHOR]

The dielectric environment of atomically thin monolayer (ML) of semiconducting transition metal dichalcogenides affects both the electronic bandgap and the excitonic binding energy in the ML. We investigate the effect of the environment on the in-plane magnetic field brightening of neutral and charged dark exciton emissions in the WSe2 ML. The monolayers placed in three dielectric environments are studied, in particular, the ML encapsulated in hexagonal BN (hBN) flakes, the ML deposited on a hBN layer, and the ML embedded between the hBN flake and SiO2/Si substrate. We observe that the brightening rates of the neutral and charged dark excitons depend on the dielectric environment, which may be related to the variation of the level of carrier concentration in the ML. Moreover, the surrounding media, characterized by different dielectric constants, weakly influence the relative energies of the neutral and charged dark excitons in reference to the bright ones. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have been propelled into the limelight over the past decade due to the rapid‐growing power conversion efficiency (PCE). However, the internal defects and the interfacial energy level mismatch are detrimental to the device performance and stability. In this study, it is demonstrated that a small amount of indium (In3+) ions in mixed cation and halide perovskites can effectively passivate the defects, improve the energy‐level alignment, and reduce the exciton binding energy. Additionally, it is confirmed that In3+ ions can significantly elevate the initial carrier temperature, slow down the hot‐carrier cooling rate, and reduce the heat loss before carrier extraction. The device with 1.5% of incorporated In3+ achieves a PCE of 22.4% with a negligible hysteresis, which is significantly higher than that of undoped PSCs (20.3%). In addition, the unencapsulated PSCs achieve long‐term stability, which retain 85% of the original PCE after 3,000 h of aging in dry air. The obtained results demonstrate and promote the development of practical, highly efficient, and stable hot‐carrier‐enhanced PSCs. [ABSTRACT FROM AUTHOR]

Although large exciton binding energies of typically 0.6–1.0 eV are observed for monolayer transition metal dichalcogenides (TMDs) owing to strong Coulomb interaction, multilayered TMDs yield relatively low exciton binding energies owing to increased dielectric screening. Recently, the ideal carrier-multiplication threshold energy of twice the bandgap has been realized in multilayered semiconducting 2H-MoTe2 with a conversion efficiency of 99%, which suggests strong Coulomb interaction. However, the origin of strong Coulomb interaction in multilayered 2H-MoTe2, including the exciton binding energy, has not been elucidated to date. In this study, unusually large exciton binding energy is observed through optical spectroscopy conducted on CVD-grown 2H-MoTe2. To extract exciton binding energy, the optical conductivity is fitted using the Lorentz model to describe the exciton peaks and the Tauc–Lorentz model to describe the indirect and direct bandgaps. The exciton binding energy of 4 nm thick multilayered 2H-MoTe2 is approximately 300 meV, which is unusually large by one order of magnitude when compared with other multilayered TMD semiconductors such as 2H-MoS2 or 2H-MoSe2. This finding is interpreted in terms of small exciton radius based on the 2D Rydberg model. The exciton radius of multilayered 2H-MoTe2 resembles that of monolayer 2H-MoTe2, whereas those of multilayered 2H-MoS2 and 2H-MoSe2 are large when compared with monolayer 2H-MoS2 and 2H-MoSe2. From the large exciton binding energy in multilayered 2H-MoTe2, it is expected to realize the future applications such as room-temperature and high-temperature polariton lasing. [ABSTRACT FROM AUTHOR]

D‐π‐A type 4‐((9‐phenylcarbazol‐3‐yl)ethynyl)‐N‐dodecyl‐1,8‐naphthalimide (CZNI) with a large dipole moment of 8.49 D and A‐π‐A type bis[(4,4′‐1,8‐naphthalimide)‐N‐dodecyl]ethyne (NINI) with a negligible dipole moment of 0.28 D, were smartly designed and synthesized to demonstrate the evidence of a molecular dipole as the dominant mechanism for controlling charge separation of organic semiconductors. In aqueous solution, these two novel naphthalimides can self‐assemble to form nanoribbons (NRs) that present significantly different traces of exciton dissociation dynamics. Upon photoexcitation of NINI‐NRs, no charge‐separated excitons (CSEs) are formed due to the large exciton binding energy, accordingly there is no hydrogen evolution. On the contrary, in the photoexcited CZNI‐NRs, the initial bound Frenkel excitons are dissociated to long‐lived CSEs after undergoing ultrafast charge transfer within ca. 1.25 ps and charge separation within less than 5.0 ps. Finally, these free electrons were injected into Pt co‐catalysts for reducing protons to H2 at a rate of ca. 417 μmol h−1 g−1, correspondingly an apparent quantum efficiency of ca. 1.3 % can be achieved at 400 nm. [ABSTRACT FROM AUTHOR]

D‐π‐A type 4‐((9‐phenylcarbazol‐3‐yl)ethynyl)‐N‐dodecyl‐1,8‐naphthalimide (CZNI) with a large dipole moment of 8.49 D and A‐π‐A type bis[(4,4′‐1,8‐naphthalimide)‐N‐dodecyl]ethyne (NINI) with a negligible dipole moment of 0.28 D, were smartly designed and synthesized to demonstrate the evidence of a molecular dipole as the dominant mechanism for controlling charge separation of organic semiconductors. In aqueous solution, these two novel naphthalimides can self‐assemble to form nanoribbons (NRs) that present significantly different traces of exciton dissociation dynamics. Upon photoexcitation of NINI‐NRs, no charge‐separated excitons (CSEs) are formed due to the large exciton binding energy, accordingly there is no hydrogen evolution. On the contrary, in the photoexcited CZNI‐NRs, the initial bound Frenkel excitons are dissociated to long‐lived CSEs after undergoing ultrafast charge transfer within ca. 1.25 ps and charge separation within less than 5.0 ps. Finally, these free electrons were injected into Pt co‐catalysts for reducing protons to H2 at a rate of ca. 417 μmol h−1 g−1, correspondingly an apparent quantum efficiency of ca. 1.3 % can be achieved at 400 nm. [ABSTRACT FROM AUTHOR]

Solution‐processed metal halide perovskites have the advantages of a tunable bandgap, excellent charge transport properties, and suitable exciton binding energy. They therefore emerge as promising semiconductors for efficient perovskite solar cells (PSCs) and bright perovskite light‐emitting diodes (PLEDs). In addition, these devices possess a similar planar–heterojunction architecture, thus novel dual‐functional perovskite light‐emitting solar cells (PLESCs) that can realize electrical‐to‐optical and optical‐to‐electrical conversion on one device are developed. To date, high‐performance PLESCs with 17.2% electroluminescence external quantum efficiency and 25.2% power conversion efficiency are achieved using a holistic optimization approach. However, a comprehensive review focusing on dual‐functional PLESCs with discussion on their development and limitations, remains lacking. Herein, the rapid progress in PLESCs, including 0D quantum dot, 2D Ruddlesden–Popper, and 3D bulk perovskite devices, is reviewed. First, the fundamental understanding of the device structure and working principle of PLESCs is overviewed. Second, the state‐of‐the‐art developments for simultaneously achieving high‐efficiency PSCs and PLEDs, focusing on defect passivation, interface optimization, energy level alignment, and dimensional control, are comprehensively summarized. Finally, the authors offer some perspectives for future trends in the development of promising PLESCs, which can provide guidelines for this emerging field. [ABSTRACT FROM AUTHOR]