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Back‐contact architectures offer a promising route to improve the record efficiencies of perovskite solar cells (PSCs) by eliminating parasitic light absorption. However, the performance of back‐contact PSCs is limited by inadequate carrier diffusion in perovskite. Here, we report that perovskite films with a preferred out‐of‐plane orientation show improved carrier dynamic properties. With the addition of guanidine thiocyanate, the films exhibit carrier lifetimes and mobilities increased by 3–5 times, leading to diffusion lengths exceeding 7 μm. The enhanced carrier diffusion results from substantial suppression of nonradiative recombination and improves charge collection. Devices using such films achieve reproducible efficiencies reaching 11.2 %, among the best performances for back‐contact PSCs. Our findings demonstrate the impact of carrier dynamics on back‐contact PSCs and provide the basis for a new route to high‐performance back‐contact perovskite optoelectronic devices at low cost. [ABSTRACT FROM AUTHOR]

All-inorganic lead halide perovskite nanocrystals (NCs) have been widely investigated as highly promising optical gain materials due to their compelling electrical and optical properties. Although many efforts have been carried out, a deep understanding of perovskite NC vertical-cavity surface-emitting lasers (VCSELs) is elusive, which is very important in the development of photoelectronic integrated circuits. Along these lines, in this work, a low lasing threshold (22 μJ/cm2) single-mode VCSEL consisting of CsPbBr3 NCs film and two distributed Bragg reflectors was successfully constructed. The CsPbBr3 NCs were synthesized by using the supersaturated recrystallization method. Interestingly, benefiting from the strong coupling between the active layer and the optical field in the cavity, a single-mode lasing at 527 nm was demonstrated under femtosecond optical pumping. The carrier dynamics of the perovskite NC VCSEL was also thoroughly investigated by performing pump intensity-dependent time-resolved photoluminescence measurements. The typical gain-switching phenomenon was observed with an ultrafast decay of the laser pulse of ∼10 ps. Our work provides valuable insights for the implementation of the CsPbBr3 NC VCSEL for various optoelectronic applications. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have been one of the most promising materials for the photoelectric, electro‐optical, and all‐optical conversion devices, thanks to their excellent energy conversion. To investigate the energy conversion induced by structural symmetry, herein, the carrier dynamics and dielectric properties in MHPs are surveyed and reviewed as the microscopic and macroscopic bridge, respectively. The intrinsic correlations between the structural symmetry broken, carrier dynamics, and energy conversion performance are systematically analyzed by considering the energy band structures and dielectric constants. The internal energy conversion mechanisms are elucidated to pave the way for the perovskite advanced applications. [ABSTRACT FROM AUTHOR]

Pressure‐induced emission (PIE) associated with self‐trapping excitons (STEs) in low‐dimensional halide perovskites has attracted great attention for better materials‐by‐design. Here, using 2D layered double perovskite (C6H5CH2CH2NH3+)4AgBiBr8 as a model system, we advance a fundamental physicochemical mechanism of the PIE from the perspective of carrier dynamics and excited‐state behaviors of local lattice distortion. We observed a pressure‐driven STE transformation from dark to bright states, corresponding a strong broadband Stokes‐shifted emission. Further theoretical analysis demonstrated that the suppressed lattice distortion and enhanced electronic dimensionality in the excited‐state play an important role in the formation of stabilized bright STEs, which could manipulate the self‐trapping energy and lattice deformation energy to form an energy barrier between the potential energy curves of ground‐ and excited‐state, and enhance the electron‐hole orbital overlap, respectively. [ABSTRACT FROM AUTHOR]

In the past 20 years, perovskite-related research has attracted wide attention. The related research into two-dimensional/quasi-two-dimensional perovskite has propelled the research of perovskite materials to a new height. To improve the properties of quasi-2D perovskite, improve the stability of materials, and achieve specific functions, using different types, volumes, and lengths of organic spacers is an essential method. In this paper, quasi-2D perovskites with EDA (ethylene diammonium), PDA (1,3-propanediammonium), and BDA (1,4-butanediammonium) (m = 2–4) as organic spacers were prepared, and the effects of different organic spacers on the 2D perovskite were investigated. The results show that the length of the organic spacer significantly impacts the perovskite’s properties. A shorter organic spacer can effectively reduce the quantum confinement and dielectric confinement in perovskite. It should be noted that if the organic spacer is too short, the stability of the quasi-2D perovskite will be greatly reduced.

Here we develop a microscopic approach aimed at the description of a suite of physical effects related to carrier transport in, and the optical properties of, halide perovskites. Our theory is based on the description of the nuclear dynamics to all orders and goes beyond the common assumption of linear electron-phonon coupling in describing the carrier dynamics and band gap characteristics. When combined with first-principles calculations and applied to the prototypical MAPbI3 system, our theory explains seemingly disparate experimental findings associated with both the charge-carrier mobility and optical absorption properties, including their temperature dependencies. Our findings demonstrate that orbital-overlap fluctuations in the lead-halide structure plays a significant role in determining the optoelectronic features of halide perovskites.

It has been established that the Coulomb interactions can transform the electron gas into a viscous fluid. This fluid is realized in a number of platforms, including graphene and two-dimensional semiconductor heterostructures. The defining characteristic of the electron fluid is the formation of layers of charge carriers that are in local thermodynamic equilibrium, as in classical fluids. In the presence of nonuniformities, whirlpools and nontrivial flow profiles are formed, which have been directly imaged in recent experiments. In this paper, we theoretically study the response of the electron fluid to localized magnetic fields. We find that the electric current is suppressed by viscous vortices in regions where magnetic field is sharply varying, causing strong transport signatures. Experimentally, our considerations are relevant since local magnetic fields can be applied to the system through implanting adatoms or embedding micromagnets in the top-gate. Our theory is essential for the characterization and future applications of electron fluids in hydrodynamic spin transport. [ABSTRACT FROM AUTHOR]

The past decade has witnessed the rise of low-dimensional materials, such as graphene, transition metal dichalcogenides, black phosphorus, organic–inorganic hybrid perovskites and MXenes. They have received tremendous attention due to their peculiar properties, as compared to their bulk phase. These unique properties have ushered in a paradigm shift in many applied fields and technologies including, but not limited to optoelectronics, catalysis, biomedical research and quantum information sciences. The fundamental processes determining the performance of devices, utilizing the low-dimensional materials, are photogeneration of charge carriers and carrier transport. A detailed understanding of these processes is therefore indispensable to the design and optimization of advanced high-performance low-dimensional materials-based devices for broadband photodetection, high-speed modulation, high-efficiency solar energy harvesting, and energy storage, among others. Herein, we critically review recent advances in studies of photoinduced carrier dynamics in low-dimensional semiconductors and semimetals. Transient carrier generation, trapping and recombination dynamics can be controlled by temperature, charge transfer in hybrid structures, electrical and magnetic field, and stress. Revealing the mechanisms and strategies of their tuning should help design and optimize multifunctional materials to enable high-performance devices. In this review, we do not focus exclusively on the photoinduced species (excitons and charge carriers), but also discuss possible strategies to adjust their properties and their impact on device characteristics. To conclude, we summarize current status, describe existing challenges, and provide a subjective opinion on future opportunities to advance this exciting field. We hope that this review will be appealing to a broad materials physics audience and will be helpful in exploring new physics and discovering theory guided novel materials with robust performance. [ABSTRACT FROM AUTHOR]

Triplet exciton‐based long‐lived phosphorescence is severely limited by the thermal quenching at high temperature. Herein, we propose a novel strategy based on the energy transfer from triplet self‐trapped excitons to Mn2+ dopants in solution‐processed perovskite CsCdCl3. It is found the Mn2+ doped hexagonal phase CsCdCl3 could simultaneously exhibit high emission efficiency (81.5 %) and long afterglow duration time (150 s). Besides, the afterglow emission exhibits anti‐thermal quenching from 300 to 400 K. In‐depth charge‐carrier dynamics studies and density functional theory (DFT) calculation provide unambiguous evidence that carrier detrapping from trap states (mainly induced by Cl vacancy) to localized emission centers ([MnCl6]4−) is responsible for the afterglow emission with anti‐thermal quenching. Enlightened by the present results, we demonstrate the application of the developed materials for optical storage and logic operation applications. [ABSTRACT FROM AUTHOR]

Formamidinium (FA)‐based perovskite promises high power conversion efficiency in photovoltaics while it faces awkward spontaneous yellow phase transition even at ambient conditions. This has spurred intensive efforts which leave a formidable challenge on robust anchoring of the soft perovskite lattice. Present work pioneers the rational design of interfacial ionic‐bonding between halogen‐terminated nano‐MXenes and perovskite for effective retarding of the lattice instability in FA‐based perovskites. The robust heterointerface between perovskite and nano‐MXenes results also in effectively modulating the deep‐energy‐level defects, lowering the interfacial charge transfer barrier, and tuning the work function of perovskite films. Benefiting from these merits, unencapsulated FA‐based perovskite solar cells after the ionic stabilization (champion efficiency up to 24.17%), maintain over 90% of their initial efficiency after operation at maximum power point under continuous illumination for 1000 h, and retain more than 85% of their initial efficiency even after annealing for 1000 h at 85 °C in inert atmosphere. [ABSTRACT FROM AUTHOR]

Halide perovskite quantum dots (PQDs) have exhibited significantly superior nonlinear optical properties compared to traditional semiconductor materials thanks to their peculiar physical and electronic structures. By further improving the nonlinear optical properties of PQDs, it is expected to adapt to ultrafast photonics applications. This work reported the nonlinear optical properties of methylammonium lead bromide-graphene (CH3NH3PbBr3-G) composites synthesized by growing CH3NH3PbBr3 quantum dots directly from a graphene oxide lattice. Our experiments indicate that the combined advantages of the ultrafast charge transport properties from graphene and the strong charge generation efficiency of perovskite can be integrated together. The CH3NH3PbBr3-G composite exhibited enhanced saturable absorption properties with large modulation depth and very low saturation intensity. The transient absorption spectra and carrier dynamics analysis revealed that the enhancement of the saturated absorption properties of the composites mainly arose from the ultrafast charge transfer between G and CH3NH3PbBr3 which promoted the coupling between different states. The results pave the way for the design of optical switches or mode lockers based on saturable absorbers with good performance.

Efficient extraction of photogenerated hot carriers and insight into the involved dynamics are crucial to promoting the photoelectric efficiencies of photovoltaic and photocatalytic devices. Here, we synthesized Cu-doped CdSe quantum dots (Cu-CdSe QDs) as the donor and investigated the ultrafast dynamics of hot electron cooling and electron transfer from Cu-CdSe QDs to benzoquinone (BQ) as the acceptor. The doping of copper ion effectively suppresses the cooling rate of hot electrons in CdSe QDs and extends the lifetime of hot electrons from 0.2 ps to 3.6 ps. The results of steady-state and time-resolved spectroscopy demonstrate that the overall electron transfer efficiency from Cu-CdSe QDs to BQ exceeds 70 %. Dynamical analysis confirms that two electron transfer pathways of hot and band-edge electrons exist in the Cu-CdSe-BQ composites. The hot electron transfer efficiency can reach ∼45 % with a rate constant of 3.90 × 1011 s−1. The band-edge electron transfer efficiency is about 50 %. These findings demonstrate an effective strategy for improving the photoelectric performance of Cu-CdSe-BQ composites by efficiently separating photogenerated carriers and extracting hot electrons. • Copper-ion doped CdSe (Cu-CdSe) QDs with a hot electron lifetime of up to 3.6 ps were synthesized. • The photoelectric composites were constructed using Cu-doped CdSe QDs and benzoquinone (BQ). • The two electron transfer pathways of hot and band-edge electrons exist in the Cu-CdSe-BQ composites. • The CdSe QDs-BQ composites exhibit a high photocurrent response compared to that of pure Cu-CdSe QDs. [ABSTRACT FROM AUTHOR]

The future commercial advancement of lead-halide perovskites (LHPs) faces obstacles due to the existence of harmful lead and the inadequate stability associated with these materials. To tackle this challenge, we have prepared a Cs 3 Sb 2 I 9 perovskite single-crystalline thin film (Cs 3 Sb 2 I 9 device) using a technique based on the restricted evaporation of solvents in space, aiming for effective photodetection. The photodetector in the current study shows a responsivity (R) of around 111 mA/W and a detectivity (D∗) of approximately 3.7 × 1012 Jones. While these performance metrics are comparable to other photodetectors, there is a need for additional optimization to match the capabilities of commercial silicon and germanium-based counterparts. The examination of ultrafast transient absorption provides insights into the essential photophysics inherent in Cs 3 Sb 2 I 9. The synergy between the deformation potential and the Fröhlich effect plays a crucial role in shaping electronic dynamics. This synergy leads to the self-trapping of charge carriers, resulting in the creation of localized polarons within the Cs 3 Sb 2 I 9 lattice within just some picoseconds. The restriction of carrier mobility within Cs 3 Sb 2 I 9 arises from the self-capturing and confinement of small polarons (SPs). Furthermore, it was noted that SPs in a localized state could undergo absorption into an elevated state (photon energy ⁓ 1.60 eV). This process effectively facilitates the charge carriers' mobilization to a more dispersed eigenstate. Our research provides essential comprehension into the light-induced processes of lead-free halide perovskites (LFHPs), offering valuable insights for their prospective use in optoelectronics as promising future semiconducting agents. • Cs 3 Sb 2 I 9 perovskite single-crystalline thin film was prepared using a technique based on the restricted evaporation of solvents in space, aiming for effective photodetection. • The synergy between the deformation potential and the Fröhlich effect plays a crucial role in shaping electronic dynamics. • This synergy leads to the self-trapping of charge carriers, resulting in the creation of localized polarons within the Cs 3 Sb 2 I 9 lattice within just some picoseconds. • The restriction of carrier mobility within Cs 3 Sb 2 I 9 arises from the self-capturing and confinement of small polarons. • This process effectively facilitates the charge carriers' mobilization to a more dispersed eigenstate. [ABSTRACT FROM AUTHOR]

[Display omitted] • GaZnON/CdS type-II heterojunction was prepared by a facile and robust electrostatic assembly method. • Interfacial Ga-S bond is proved as an electron-transfer channel and drives ultrafast carrier dynamics. • The optimal composite photocatalyst reached an impressive hydrogen evolution rate of 14.76 mmol g-1h−1. Constructing heterojunction has been regarded as a valid strategy of photocatalysts to promote the catalytic process. However, beyond the possible synergistic advantage from the component catalysts, the understanding of the interface effect on the photocatalytic process within heterojunction remains challenging. Herein, we prepare a novel GaZnON/CdS heterojunction photocatalyst via a robust electrostatic assembly method. The sulfur atoms in CdS are found to occupy the nitrogen vacancy over the GaZnON surface to form interfacial Ga-S bonds, which is proved as electron-transfer channel between CdS and GaZnON to realize efficient photo-induced carrier separation. The dynamic study quantificationally reveals interfacial electron transfer with a fast transfer rate of 143.8 ns−1. Thereby, the optimal composite photocatalyst reached an impressive hydrogen evolution rate of 14.76 mmol g-1h−1, as well as an impressive AQY of 36.1 % (450 nm). This work expounds the ultrafast carrier dynamics underlying interface bonds within heterojunction for weakened photo-induced carrier recombination. [ABSTRACT FROM AUTHOR]

[Display omitted] • Significance of metal oxides and metal oxide heterostructures in photochemical reactions is summarized. • Roles of oxygen vacancies and other structural defects in metal oxide nanostructures in CO 2 adsorption and photoreduction is provided. Advancements in the design and synthesis of novel metal oxide heterojunctions for CO 2 photoreduction are presented. • The efficiency of CO 2 photoreduction over nanocomposites containing carbonaceous materials such as graphene oxide is addressed. • Strategies to increase the lifetime of photogenerated carriers in semiconductors are included. The main factors determining the selectivity in CO 2 photoreduction are discussed. The current surge in atmospheric CO 2 poses a critical challenge to global climate stability. To combat this, effective strategies for capturing and utilizing CO 2 are imperative. Among the available strategies, photochemical reduction emerges as a highly promising avenue. However, achieving efficient CO 2 reduction with superior product selectivity demands well-designed photocatalysts. In this review, we provide an overview of recent advancements in designing and fabricating metal oxide-based heterojunction nanocatalysts, including novel types such as high-entropy oxides and MXenes, over the past five years, assessing their effectiveness in photocatalytic CO 2 reduction. Emphasis is placed on understanding the roles played by oxygen vacancies and structural defects in enhancing the CO 2 adsorption capacities of metal oxides. Considering the critical role of carrier recombination processes in photocatalytic efficiency, we delve into the formation of junction potential, as well as the separation and recombination of charge carriers at heterojunction interfaces, elucidating their impact on the CO 2 reduction capabilities of metal-oxide heterostructures. Finally, we address the current challenges and prospects of harnessing such heterojunction nanostructures for CO 2 photoreduction. [ABSTRACT FROM AUTHOR]

[Display omitted] • The rotation rate of MA+ can be adjusted by modifying of the relative atomic mass of nitrogen atoms. • The rotational rate of MA+ served as the sole independent variable. • The slower the rotation rate of MA+, the longer the carrier lifetime of perovskite. At room temperature, organic molecules undergo continuous rotation, driven by rotational barriers lower than k B T. However, consensus regarding the impact of organic molecule rotation on carrier dynamics remains elusive, as conventional research methods struggle to distinguish between organic molecule rotation and inorganic frame vibrations. This study successfully achieved the goal of modulating the rotation rate of organic molecules by adjusting the relative atomic mass of nitrogen atoms. In the investigation of carrier dynamics, the rotational rate of organic molecules served as the sole independent variable. The findings indicate that a slower rotation rate correlates with an extended carrier lifetime. This correlation is attributed to the heightened charge separation and reduced motion of nuclei. This research provides valuable insights for prolonging the carrier lifetime of organic–inorganic hybrid perovskites. [ABSTRACT FROM AUTHOR]

Metal halide perovskites (MHPs) have demonstrated great advances for photovoltaic and optoelectronic applications. However, owing to the presence of the synergy from lattice strain, defects of MHPs, and environment, MHPs suffer from phase transitions and degradation, resulting in the restriction of their practical applications and further commercialization. Multiple metal elements can coexist in MHPs to form alloys due to the high tolerance of lattice and the composition replaceability, which provides a novel strategy for improvement of performance and stability. In this review, the recent advances of alloy engineering of MHPs, focusing on the cation and the metal ion (A‐ and B‐site) alloy strategies, are reviewed. The alloy effects on the crystalline structure, optoelectronic properties, ferroelectricity, carrier dynamics, and stability of perovskites are interpreted. Finally, the prospect of this study is the challenges in the MHPs alloy engineering.

This work employs femtosecond transient absorption spectroscopy to investigate the ultrafast carrier dynamics of bound states in In0.14Ga0.86N/GaN quantum wells. The ground state (GS) dynamics usually dominate these characteristics, appearing as a prominent peak in the absorption spectra. It is observed that the excited state also contributes to the overall dynamics, with its signature showing up later. The contributions of both the ground and excited states in the absorption spectra and time-resolved dynamics are decoupled in this work. The carrier density in the GS first increases and then decays with time. The carriers populate the excited state only at a delayed time. The dynamics are studied considering the Quantum-Confined Stark Effect-induced wavelength shift in the absorption. The relevant microscopic optoelectronic processes are understood phenomenologically, and their time constants are extracted. An accurate study of these dynamics provides fundamentally essential insights into the time-resolved dynamics in quantum-confined heterostructures and can facilitate the development of efficient light sources using GaN heterostructures. [ABSTRACT FROM AUTHOR]

Plasmonic perovskite solar cells (PSCs) using core−shell type plasmonic particles are designed, which possess the plasmon resonance in the near‐infrared range. This can selectively strengthen the interaction of the perovskite layer with low‐energy photons. The mesoporous PSCs employing the plasmonic particles have delivered a 10%–15% enhancement of external quantum efficiency in the plasmonic resonance range. This surface‐plasmonic effect has been analyzed using complementary techniques, including selective wavelength excitation and time‐dependent photoluminescence. It is shown that the metal‐based core−shell‐type plasmonic structures in PSCs optimize the scattering and absorption of incident light and the dynamics of photogenerated carriers. Furthermore, both optical and electronic effects increase the power conversion efficiency of PSCs from 17.49% to 19.88%, paving a way toward controlling the thickness of the photoactive layer for advanced devices such as tandem solar cells. [ABSTRACT FROM AUTHOR]

All-inorganic perovskite materials (CsPbX3) have attracted increasing attention due to their excellent photoelectric properties and stable physical and chemical properties. The dynamics of charge carriers affect the photoelectric conversion efficiencies of perovskite materials. Regulating carrier dynamics by changing pressure is interesting with respect to revealing the key microphysical processes involved. Here, ultrafast spectroscopy combined with high-pressure diamond anvil cell technology was used to study the generation and transfer of photoinduced carriers of a Mn-doped inorganic perovskite CsPbBr3 material under pressure. Three components were obtained and assigned to thermal carrier relaxation, optical phonon–acoustic phonon scattering and Auger recombination. The time constants of the three components changed under the applied pressures. Our experimental results show that pressure can affect the crystal structure of Mn-doped CsPbBr3 to regulate carrier dynamics. The use of metal doping not only reduces the content of toxic substances but also improves the photoelectric properties of perovskite materials. We hope that our study can provide dynamic experimental support for the exploration of new photoelectric materials. [ABSTRACT FROM AUTHOR]

The fine-tuning of the growth conditions and post-deposition treatments is of fundamental importance to improve the efficiency of photovoltaic devices based on all-inorganic metal halide perovskites like CsPbBr3. In this work, we used time-resolved terahertz spectroscopy (TRTS) in combination with optical characterization techniques, x-ray diffraction (XRD), and scanning electron microscopy, to probe the different properties induced by a low-temperature (180 °C) annealing treatment on evaporated CsPbBr3 thin-films. We observed a faster build-up and relaxation dynamics in the annealed sample, accompanied by a remarkable decrease of the photoluminescence intensity and minor changes in the photoconductivity and XRD measurements as compared to the as-deposited sample. We estimated for both the samples a mobility of ÎĽ = 1.7 ± 0.5 Ă— 10 2 cm2 Vâˆ'1 sâˆ'1. Our results suggest that the lattice reorganization induced by low-temperature annealing of evaporated CsPbBr3 could lead to a different charge carrier-phonon coupling and to an increased contribution of non-radiative recombination channels. We found that TRTS can be effectively used to follow the changes induced by post-deposition thermal annealing of CsPbBr3. [ABSTRACT FROM AUTHOR]

Metal halide perovskites have become a research highlight in the optoelectronic field due to their excellent properties. The perovskite light-emitting diodes (PeLEDs) have achieved great improvement in performance in recent years, and the construction of quasi-2D perovskites by incorporating large-size organic cations is an effective strategy for fabricating efficient PeLEDs. Here, we incorporate the fluorine meta-substituted phenethylammonium bromide (m-FPEABr) into CsPbBr3 to prepare quasi-2D perovskite films for efficient PeLEDs, and study the effect of fluorine substitution on regulating the crystallization kinetics and phase distribution of the quasi-2D perovskites. It is found that m-FPEABr allows the transformation of low-n phases to high-n phases during the annealing process, leading to the suppression of n = 1 phase and increasing higher-n phases with improved crystallinity. The rational phase distribution results in the formation of multiple quantum wells (MQWs) in the m-FPEABr based films. The carrier dynamics study reveals that the resultant MQWs enable rapid energy funneling from low-n phases to emission centers. As a result, the green PeLEDs achieve a peak external quantum efficiency of 16.66% at the luminance of 1279 cd m−2. Our study demonstrates that the fluorinated organic cations would provide a facile and effective approach to developing high-performance PeLEDs. [ABSTRACT FROM AUTHOR]

Highly photoluminescent, lead‐free perovskites are of interest for displays and solid‐state light‐emitting devices. In this report, streak camera‐based time‐resolved emission and transient absorption spanning visible to deep‐ultraviolet (UV) wavelengths are utilized to study self‐trapped and free exciton dynamics in vacuum‐deposited cesium copper halide thin films of CsCu2I3 and Cs3Cu2I5. Self‐trapped exciton emission of CsCu2I3 exhibits more noticeable changes with time in the peak position and width than Cs3Cu2I5. UV‐to‐blue emission is detectable for both compositions, where free exciton emission is distinct for CsCu2I3. Transient absorption shows loss of ground‐state bleach signals at early time delays for both, and the bleach signal shifts toward higher energy as time delay increases, likely due to strains induced by the newly created self‐trapped excitons. Global analysis performed on the transient absorption results yields time constants in these materials that build an overall dynamic scheme. This work aids in building a complete picture regarding light emission in these promising materials. [ABSTRACT FROM AUTHOR]

Subcycle spectral structures and dynamics of high-order harmonic generation (HHG) processes of atoms and molecules driven by intense laser fields on the attosecond time scale have been originally studied theoretically and experimentally. However, the time scale of HHG dynamics in crystals is in the order of sub-femtosecond, and the carrier dynamics of HHG in crystals driven by subcycle laser pulses are largely unexplored. Here we perform a theoretical study of subcycle structures, spectra, and dynamics of HHG of crystals in mid-infrared laser fields subject to excitation by a subcycle laser pulse with a time delay. The HHG spectra as a function of time delay between two laser fields are calculated by using a single-band model for the intra-band carrier dynamics in crystal momentum space and by solving the time-dependent Schrödinger equation in velocity gauge for the treatment of multi-band crystal systems. The results exhibit a complex time-delay-dependent oscillatory pattern, and the enhancement and suppression of the HHG related to subcycle pulse are observed at the given time delay in either single-band or multi-band crystal systems. To understand oscillation structures with respect to the dependence for the subcycle laser fields, the time-frequency characteristics of the HHG as well as the probability density distribution of the radiation are analyzed in detail. [ABSTRACT FROM AUTHOR]

Integration of graphene and quantum dots (QD) is a promising route to improved material and device functionalities. Underlying the improved properties are alterations in carrier dynamics within the graphene/QD heterostructure. In this study, it is shown that graphene functions as a carrier redistribution and supply channel when integrated with InAs QDs. Photoluminescence (PL) spectroscopy provides evidence that graphene modifies the redistribution, escape, and recombination dynamics of carriers in the InAs QD ensemble, which ultimately leads to enhanced radiative recombinations at all temperatures and excitation densities probed. It is also shown that the PL enhancement from the graphene/InAs QD heterostructure is greatest with a thin GaAs cap and at higher temperatures where devices operate. This study advances the understanding of graphene/QD heterostructures and can aid the design of mixed-dimensional optoelectronic devices., (© 2024 2024 The Author(s). Small published by Wiley‐VCH GmbH.)

Carrier dynamics is crucial in semiconductors, and it determines their conductivity, response time, and overall functionality. In flat bands (FBs), carriers with high effective masses are predicted to host unconventional transport properties. The FBs usually overlap with other trivial energy bands, however, making it difficult to accurately distinguish their carrier dynamics. In this paper, we have investigated the flat-band carrier dynamics of excited electrons in Nb 3 Cl 8 , which hosts ideal nonoverlapping FBs near the Fermi level. The optical transition between Hubbard bands is abnormally weakened, exhibiting weak interband absorption and its related slow photoresponse with a time constant of ∼120 s, which are associated with flat-band Mottness-induced large electron effective mass and parity-forbidden transitions. Besides, the localized states created by chlorine vacancies also act as trapping centers for carriers with a time constant of ∼600 s, which are similar to those of the compact localized states of the FB, making the relaxation behavior even more extraordinary. The presence and impacts of atomic defects are confirmed experimentally and theoretically. This work has revealed the abnormal flat-band carrier dynamics of Nb 3 Cl 8 , which is essential for understanding the optical, electrical, and thermal transport properties of flat-band materials.

Prolonging hot carrier cooling, a crucial factor in optoelectronic applications, including hot carrier photovoltaics, presents a significant challenge. High-energy band-nesting excitons within parallel bands offer a promising and underexplored avenue for addressing this issue. Here, we exploit an exceptional D exciton cooling prolongation of 2 to 3 orders of magnitude compared to sub-picosecond in typical transition metal dichalcogenides (TMDs) owing to the complex Coulomb environment and the sequential and mismatch-valley relaxation. Simultaneously, the intervalley scattering upconversion of band-edge excitons with the slow D exciton formation in the metastable Γ valley/hill also reduces the cooling rate. We successfully extract D and C excitons as hot carriers through integrating with various thicknesses of TiO x , achieving the highest efficiency of 98% and 85% at a Ti thickness of 2 nm. Our findings highlight the potential of band-nesting excitons for extending hot carrier cooling time, paving the way for advancements in hot carrier-based optoelectronic devices.

Effective electron supply to produce ammonia in photoelectrochemical nitrogen reduction reaction (PEC NRR) remains challenging due to the sluggish multiple proton-coupled electron transfer and unfavorable carrier recombination. Herein, InP quantum dots decorated with sulfur ligands (InP QDs-S 2- ) bound to MIL-100(Fe) as a benchmark catalyst for PEC NRR is reported. It is found that MIL-100(Fe) can combined with InP QDs-S 2- via Fe─S bonds as bridge to facilitate the electron transfer by experimental results. The formation of Fe─S bonds can facilitate electron transfer from inorganic S 2- ligands of InP QDs to the Fe metal sites of MIL-100(Fe) within 52 ps, ensuring a more efficient electron transfer and electron-hole separation confirmed by the time-resolved spectroscopy. More importantly, the process of photo-induced carrier transfer can be traced by in situ attenuated total reflection surface-enhanced infrared tests, certifying that the effective electron transfer can promote N≡N dissociation and N 2 hydrogenation. As a result, InP QDs-S 2- /MIL-100(Fe) exhibits prominent performance with an outstanding NH 3 yield of 0.58 µmol cm -2 h -1 (3.09 times higher than that of MIL-100(Fe)). This work reveals an important ultrafast dynamic mechanism for PEC NRR in QDs modified metal-organic frameworks, providing a new guideline for the rational design of efficient MOFs photocathodes., (© 2024 Wiley‐VCH GmbH.)

Crafting rational heterojunctions with nanostructured materials is instrumental in fostering effective interfacial charge separation and transport for optoelectronics. Layered halide perovskites (LHPs) that form heterojunctions between organic spacer molecules and inorganic metal halide layers exhibit tunable photophysics owing to their customizable band alignment. However, controlling photogenerated carrier dynamics by strategically designing layered perovskite heterojunctions remains largely unexplored. We combine a data-driven approach with time-domain density functional theory (TD-DFT) and non-adiabatic molecular dynamics (NAMD) to screen and select electronically active spacer dications (A') that introduce a type-II heterojunction in the lead iodide-based Dion-Jacobson phase LHPs. The composition-structure-electronic property correlations reveal that the number of nitrogens in aromatic heterocycles is the key factor in designing electron-accepting spacers in these perovskites. The detailed atomistic simulations validate the design strategy further by modeling (A')PbI 4 perovskites, which incorporate three different screened electroactive A' spacers. The computed excited charge carrier dynamics illustrate the phonon-mediated ultrafast interfacial electron transfer from the inorganic conduction band edge to the lower-lying unoccupied orbitals of spacers, exhibiting photoluminescence quenching in these (A')PbI 4 perovskites. The spatially separated electrons and holes at the type-II heterojunction interface prolong the excited charge carrier lifetime, boosting the carrier transport and exciton dynamics. Our work illustrates a robust in silico approach for designing LHPs with exciting optoelectronic properties originating from their fine-tuned heterojunctions.

Abstract Monolayers of transition metal dichalcogenides are semiconducting materials which offer many prospects in optoelectronics. A monolayer of molybdenum disulfide (MoS2) has a direct bandgap of 1.88 eV. Hence, when excited with optical photon energies below its bandgap, no photocarriers are generated and a monolayer of MoS2 is not of much use in either photovoltaics or photodetection. Here, we demonstrate that large size MoS2 monolayer sandwiched between two graphene layers makes this heterostructure optically active well below the band gap of MoS2. An ultrafast optical pump‐THz probe experiment reveals in real‐time, transfer of carriers between graphene and MoS2 monolayer upon photoexcitation with photon energies down to 0.5 eV. It also helps to unravel an unprecedented enhancement in the broadband transient THz response of this tri‐layer material system. We propose possible mechanism which can account for this phenomenon. Such specially designed heterostructures, which can be easily built around different transition metal dichalcogenide monolayers, will considerably broaden the scope for modern optoelectronic applications at THz bandwidth.

As a novel transition metal dichalcogenide material with high carrier mobility, adjustable band gap and excellent stability, the photocarrier ultrafast dynamics of PtSe2 films with the different thickness is researched by ultrafast transient absorption spectrum and optical pump and terahertz probe spectrum. The experimental results show that the few-layer PtSe2 films present semiconductor phase which exhibits a triple exponential decay process, while multi-layer of PtSe2 films present semi-metallic phase which exhibits a double exponential decay process. And the principle of light response and carrier dynamics of PtSe2 films after excitation is analyzed, one found that the defect state carrier recombination exists in all samples. The carrier relaxation is dominated by Auger exciton–exciton annihilation in few-layer PtSe2 film, and the defect state of multiple-layer PtSe2 film plays a dominant role in the photo carrier relaxation, which is promising to a further application in modulators and detectors for characterizing the transition from semiconductor to semi-metal by controlling its film thickness.

Halide perovskite quantum dots (PQDs) have exhibited significantly superior nonlinear optical properties compared to traditional semiconductor materials thanks to their peculiar physical and electronic structures. By further improving the nonlinear optical properties of PQDs, it is expected to adapt to ultrafast photonics applications. This work reported the nonlinear optical properties of methylammonium lead bromide-graphene (CH3NH3PbBr3-G) composites synthesized by growing CH3NH3PbBr3 quantum dots directly from a graphene oxide lattice. Our experiments indicate that the combined advantages of the ultrafast charge transport properties from graphene and the strong charge generation efficiency of perovskite can be integrated together. The CH3NH3PbBr3-G composite exhibited enhanced saturable absorption properties with large modulation depth and very low saturation intensity. The transient absorption spectra and carrier dynamics analysis revealed that the enhancement of the saturated absorption properties of the composites mainly arose from the ultrafast charge transfer between G and CH3NH3PbBr3 which promoted the coupling between different states. The results pave the way for the design of optical switches or mode lockers based on saturable absorbers with good performance. [ABSTRACT FROM AUTHOR]

Bismuth sulfide (Bi2S3) possesses bandgap of 1.30–1.45 eV, perfectly suitable for light‐harvesting materials in solar cells. Carrier dynamics in the Bi2S3 absorber material are determinant for energy conversion performance of solar cells, yet the carrier dynamics and associated recombination mechanism are rarely studied. Taking advantage of spectroscopic study on Bi2S3 nanocrystals, here new findings are uncovered inherent from the unique crystal structure that causes the energy loss in Bi2S3 materials. One is the trap state emission at near‐infrared region, the other is the ultrafast intrinsic trapping in picosecond scale without saturation at 1019 cm−3 carrier density and various decay rates by adjusting excitation fluence. These observations indicate that photoinduced carriers are likely to be intrinsically trapped due to lattice distortion and display different recombination pathways. This study provides fundamental understanding on the detailed carriers dynamics of Bi2S3 nanocrystals and new insights into the optimization of Bi2S3‐based photovoltaic devices. [ABSTRACT FROM AUTHOR]

Metal halide perovskite, an emerging photosensitive semiconductor, has been widely employed in solar cells, light‐emitting diodes, photodetectors, and lasers owing to its excellent photophysical properties and simple solution preparation processing. However, as a photoactive layer, the higher refractive index and thinner thickness of perovskite film can cause reflection and transmission at the interface, and confine the emitted light within devices, resulting in the poor incident photon absorption and emitted photon extraction. In addition, the intrinsic brittleness of perovskite material restricts its potential applications in flexible optoelectronics. Therefore, great effort has been put into micro‐nano structured perovskite optoelectronics, and the reported reviews mainly focus on the fabrication process of micro‐nano patterned perovskite. Herein, the functionalities of micro‐nano structures in optoelectronics, including improving the light trapping, light extraction, light modulation, carrier dynamics, mechanical robustness, and other novel functionalities, are comprehensively reviewed. The specific applications of these functionalities in perovskite‐based optoelectronic devices are then discussed in detail to provide a better understanding of the photophysical properties of micro‐nano structure functionalized optoelectronics. Finally, promising strategies to promote the multifunctional commercial applications of micro‐nano structured perovskite optoelectronics are provided. [ABSTRACT FROM AUTHOR]

Understanding and optimising the mechanisms of generation and extraction of hot carriers in plasmonic heterostructures is important for applications in new types of photodetectors, photochemistry and photocatalysis, as well as nonlinear optics. Here, we show using transient dynamic measurements that the relaxation of the excited hot-carriers in Au/Pt hetero-nanostructures is accelerated through the transfer pathway from Au, where they are generated, to Pt nanoparticles, which act as a hot-electron sink. The influence of the environment on the dynamics was also demonstrated. The time-resolved photoluminescence measurements confirm the modified hot-electron dynamics, revealing quenching of the photoluminescence signal from Au nanoparticles in the presence of Pt and an increased photoluminescence lifetime. These observations are signatures of the improved extraction efficiency of hot-carriers by the Au/Pt heterostructures. The results give insight into the time-dependent behaviour of excited compound nanoscale systems and provide a way of controlling the relaxation mechanisms involved, with important consequences for engineering nonlinear optical response and hot-carrier-assisted photochemistry.

Optoelectronic devices based on intraband or intersublevel transitions in semiconductors are important building blocks of the current THz technology. Large nanocrystals (NCs) of Mercury telluride (HgTe) are promising semiconductor candidates owing to their intraband absorption peak tunable from 60 THz to 4 THz. However, the physical nature of this THz absorption remains elusive as, in this spectral range, quantum confinement and Coulomb repulsion effects can coexist. Further, the carrier dynamics at low energy in HgTe NCs, which strongly impact the performances of THz optoelectronic devices, is still unexplored. Here, we demonstrate a broad THz absorption resonance centered at ≈4.5 THz and fully interpret its characteristics with a quantum model describing multiple intraband transitions of single carriers between quantized states. Our analysis reveals the absence of collective excitations in the THz optical response of these self-doped large NCs. Furthermore, using optical pump-THz probe experiments, we report on carrier dynamics at low energy as long as 6 ps in these self-doped THz HgTe NCs. We highlight evidence that Auger recombination is irrelevant in this system and attribute the main carrier recombination process to direct energy transfer from the electronic transition to the ligand vibrational modes and to nonradiative recombination assisted by surface traps. Our study opens interesting perspectives for the use of large HgTe NCs for the development of advanced THz optoelectronic devices such as emitters and detectors and for quantum engineering at THz frequencies.

Lead-free halide perovskite single crystals (SCs) offer a compelling alternative for optoelectronic devices due to their superior intrinsic properties. Despite advancements in excellent perovskite SCs, analyzing defects remains crucial. This two-fold approach can both enhance device performance and provide insights into the interactions between light-induced carriers and these defects within the material. This work investigates defects in Cs 3 Bi 2 Br 9 perovskite SCs using photoexcitation. Photocurrent and photocapacitance measurements are employed to analyze these light-induced defects and their influence on the material's properties. The examination of Cs 3 Bi 2 Br 9 SCs properties alongside a gold electrode involves evaluating both bulk and interfacial defect densities. This assessment is carried out by analyzing the capacitive behavior in response to different wavelengths λ R , λ G , and λ B (λ R = 652.54 nm, λ G = 539.06 nm, and λ B = 413.28 nm). The temporary reaction to light of individual crystals indicates the presence of carrier capture and subsequent recombination processes. The analysis of the response to light under different situations offers insights into potential defect origins within SCs of Cs 3 Bi 2 Br 9. This extensive optoelectronic investigation unveils a critical connection between light illumination conditions, carrier transport properties, and overall system efficiency. A comprehensive comprehension of light-triggered defects in perovskites could aid in identifying the source of electrical inefficiency and in the creation of exceptionally effective optoelectronic systems. • Utilizing the slow cooling technique with a sandwich-structured Au electrode, we examined the optoelectrical characteristics of Cs 3 Bi 2 Br 9 SCs. • The analysis of space charge limited current and current-voltage characteristics revealed that our Cs 3 Bi 2 Br 9 SCs possess a low density of traps and display a strong response to light. • Our findings suggest that ion mobility is a more likely explanation for the observed defects in Cs 3 Bi 2 Br 9 SCs compared to changes in dielectric properties. • This work proposes that defects induced by λ G illumination primarily contribute to recombination losses, while defects associated with λ B exposure may act as recombination compensation mechanisms. [ABSTRACT FROM AUTHOR]

Organic-inorganic perovskite single crystals (SCs) are considered promising semiconductors for high-sensitivity X-ray detectors because of their strong X-ray interaction, low-temperature processability, and excellent properties such as long diffusion length, low defect density, and long carrier lifetime. However, the specific pulse response of MAPbBr 3 SC-based X-ray detectors frequently exhibits a tail and over/undershoots at several conditions, which degrades the X-ray image quality; however, no detailed analysis of these characteristics has been reported thus far. For high-resolution X-ray imaging, it is necessary to obtain an ideal pulse response that is free of tails and over/undershoots. In this study, we investigated the specific X-ray responses of solution-grown MAPbBr 3 SC-based X-ray detectors under various externally applied voltages. Based on the study on charge carrier dynamics, we analyzed the origin of the tail and over/undershoots in X-ray pulse response shapes. We theoretically verified that the unideal pulse response in perovskite SC-based X-ray detectors is attributed to the defect states inherent in perovskite SCs. • X-ray responses of MAPbBr 3 single-crystal detectors with different electrodes are investigated. • The specific pulse responses of the detectors show tail and over/undershoots. • Tail and overshoots can be interpreted as de-trapping and trapping, respectively, on shallow traps. • Undershoot is caused by diffusion currents due to the internal fields and unoccupied vacancies. [ABSTRACT FROM AUTHOR]

Indium tin oxide (ITO) has important application in photoelectronic and photonic devices, demanding effective approach and appropriate parameters to modulate the ITO properties. The effects of laser annealing at 1064 nm with different pulse width (875 ps, 10 ns, and 300 ns) on optical and nonlinear optical properties of ITO films were investigated. Compared with 875 ps and 10 ns, laser annealing at 300 ns significantly improved the near-infrared transmittance of ITO films. The change arises from the elimination of oxygen vacancies and reduction of tin oxides, resulting in the decrease of carrier concentration. Finite element simulations indicate that laser annealing with pulse width of 875 ps and 10 ns have high instantaneous peak temperatures of 1128.5 K and 783 K, respectively, while the temperature accumulation between pulses is negligible. On the contrary, the laser annealing with a pulse width of 300 nshas lower peak transient temperature of 343 K but high static residence temperature of 973 K. The results reveal that the modification of ITO films depends more on the static average temperature rather than the instantaneous peak temperature. The modulation of carrier dynamics in both amplitude and temporal domain was demonstrated after 300 ns laser annealing, achieving ultrafast transient response approximately 150 fs. This work provides theoretical and experimental basis for us to select suitable laser conditions for directional annealing of ITO film to make it suitable for the applications of broad optical spectrum photovoltaic devices or ultrafast optical exchange for high-speed data processing. • Laser annealing (LA) is shown for three pulse widths at approximately 0.2 J/cm2. • LA at 300 ns significantly improves the near-infrared transparency due to the reduction of carrier absorption. • Tailorable amplitude and time scale of carrier transient response are achieved by LA, with ultrafast response time 150 fs. • The modification of ITO properties depends on the static temperature rather than transient peak temperature. [ABSTRACT FROM AUTHOR]

TMDs based heterostructure have drawn much attention for its potential application in photoelectric devices benefiting from the rapid and effective carrier separation and ultra-long interlayer exciton lifetime. Recent studies on carrier dynamics of TMDs based heterostructures are mainly focused on the transfer process of photo-generated carriers across the interface and lifetime of interlayer exciton but little attention is paid on the dynamics of hot carriers. Here, the carrier dynamics of hot carriers in MoS2/WS2 heterostructure is investigated by transient absorption spectra. Rapid separation of electron and hole is observed. More importantly, hot carriers of C exciton, which contribute to the absorption of most of the visible light, could compensate for the carrier loss in the band edge exciton energy band through the intervalley transfer process. This re-injection process of hot carriers of C exciton could compensate for carrier depletion in photoelectric devices, thus may greatly improve the light utilization in optoelectronic devices. [ABSTRACT FROM AUTHOR]

Van der Waals heterojunctions are fast‐emerging quantum structures fabricated by the controlled stacking of two‐dimensional (2D) materials. Owing to the atomically thin thickness, their carrier properties are not only determined by the host material itself, but also defined by the interlayer interactions, including dielectric environment, charge trapping centers, and stacking angles. The abundant constituents without the limitation of lattice constant matching enable fascinating electrical, optical, and magnetic properties in van der Waals heterojunctions toward next‐generation devices in photonics, optoelectronics, and information sciences. This review focuses on the charge and energy transfer processes and their dynamics in transition metal dichalcogenides (TMDCs), a family of quantum materials with strong excitonic effects and unique valley properties, and other related 2D materials such as graphene and hexagonal‐boron nitride. In the first part, we summarize the ultrafast charge transfer processes in van der Waals heterojunctions, including its experimental evidence and theoretical understanding, the interlayer excitons at the TMDC interfaces, and the hot carrier injection at the graphene/TMDCs interface. In the second part, the energy transfer, including both Förster and Dexter types, are reviewed from both experimental and theoretical perspectives. Finally, we highlight the typical charge and energy transfer applications in photodetectors and summarize the challenges and opportunities for future development in this field. [ABSTRACT FROM AUTHOR]

Stacking growth of the InGaAs quantum dots (QDs) on top of a carrier injection layer is a very useful strategy to develop QD devices. This research aims to study the carrier injection effect in hybrid structures with a layer of In0.4Ga0.6As surface quantum dots (SQDs), coupled to an injection layer of either one layer of In0.4Ga0.6As buried QDs (BQDs) or an In0.15Ga0.85As quantum well (QW), both through a 10 nm GaAs thin spacer. Spectroscopic measurements show that carrier capture and emission efficiency for SQDs in the BQD injection structure is better than that of the QW injection, due to strong physical and electrical coupling between the two QD layers. In the case of QW injection, although most carriers can be collected into the QW, they then tunnel into the wetting layer of the SQDs and are subsequently lost to surface states via non-radiative recombination. Therefore, the QW as an injection source for SQDs may not work as well as the BQDs for stacking coupled SQDs structures. [ABSTRACT FROM AUTHOR]

Bismuth vanadate (BiVO4) is one of the extensively studied semiconductors in solar water splitting reactions. Due to its inherent properties, much of the utilization of BiVO4 in water splitting is focused on the modified form rather than in native or pure form. Because the pure BiVO4 suffers from numerous limitations and thus structural and chemical modifications are crucial for increasing the solar water splitting efficiency. Primarily, the presence of polarons, low bulk charge transport efficiency, poor water oxidation capability, and stability hinder the water splitting efficiency. The current research developments indicate that the essential modification in BiVO4 via doping is vital and widely implemented for achieving higher photoelectrochemical (PEC) water splitting activity. Recently, the doping strategy in BiVO4 has shifted beyond the single element doping to the co-doping strategy (involving multiple dopants) to further boost the water splitting efficiency that provides extended advantages. In this review, the advancements of co-doping strategies implemented in BiVO4 and their influence on structural, optical, chemical, band edge properties, and stability were summarized. Importantly, future challenges and perspectives are discussed that are beneficial in selecting dopants and designing fabrication strategies to yield highly efficient and optimized BiVO4 for enhanced solar water splitting reactions.

Abstract Van der Waals heterojunctions are fast‐emerging quantum structures fabricated by the controlled stacking of two‐dimensional (2D) materials. Owing to the atomically thin thickness, their carrier properties are not only determined by the host material itself, but also defined by the interlayer interactions, including dielectric environment, charge trapping centers, and stacking angles. The abundant constituents without the limitation of lattice constant matching enable fascinating electrical, optical, and magnetic properties in van der Waals heterojunctions toward next‐generation devices in photonics, optoelectronics, and information sciences. This review focuses on the charge and energy transfer processes and their dynamics in transition metal dichalcogenides (TMDCs), a family of quantum materials with strong excitonic effects and unique valley properties, and other related 2D materials such as graphene and hexagonal‐boron nitride. In the first part, we summarize the ultrafast charge transfer processes in van der Waals heterojunctions, including its experimental evidence and theoretical understanding, the interlayer excitons at the TMDC interfaces, and the hot carrier injection at the graphene/TMDCs interface. In the second part, the energy transfer, including both Förster and Dexter types, are reviewed from both experimental and theoretical perspectives. Finally, we highlight the typical charge and energy transfer applications in photodetectors and summarize the challenges and opportunities for future development in this field.