A new class of 2D transition metal carbides, carbonitrides and nitrides, termed MXenes, has emerged as a new candidate for many applications in electronics, optoelectronics, and energy storage. Since ...their first discovery in 2011, MXenes have gathered increasingly more interest owing to their unique physical, chemical, and mechanical properties that can be tuned by different surface terminations and transition metals. In particular, the intriguing optical and electrical properties, including transparency, saturable absorption, and high conductivity, grant MXenes various roles in photodetectors, such as transparent electrodes, Schottky contacts, photoabsorbers, and plasmonic materials. Given the solution‐processability, MXenes also hold great potential for large‐scale synthesis, and thus are favored for a number of electronic and photonic device applications. In this review, recent advances in photodetectors based on 2D MXenes are summarized. Despite the fact that such applications have only recently been explored compared with other 2D materials, MXenes have shown promise in low‐cost and high‐performance photodetection.
Since their first discovery in 2011, MXenes have gained ever increasing interest. Despite their intriguing optical and electrical properties for optoelectronics, 2D MXenes have been thus far marginally explored for photodetectors. Nonetheless, the progress over the past few years cannot be ignored. In this review, the recent development of MXene photodetectors is summarized, including simple photoconductors, self‐driven photodetectors, and plasmon‐enhanced photodetectors.
Semiconductor nanocrystals, the so‐called quantum dots (QDs), exhibit versatile optical and electrical properties. However, QDs possess high density of surface defects/traps due to the high ...surface‐to‐volume ratio, which act as nonradiative carrier recombination centers within the QDs, thereby deteriorating the overall solar cell performance. The surface passivation of QDs through the growth of an outer shell of different materials/compositions called “core/shell QDs” has proven to be an effective approach to reduce the surface defects and confinement potential, which can enable the broadening of the absorption spectrum, accelerate the carrier transfer, and reduce exciton recombination loss. Here, the recent research developments in the tailoring of the structure of core/shell QDs to tune exciton dynamics so as to improve solar cell performance are summarized. The role of band alignment of core and shell materials, core size, shell thickness/compositions, and interface engineering of core/thick shell called “giant” QDs on electron–hole spatial separation, carrier transport, and confinement potential, before and after grafting on the carrier scavengers (semiconductor/electrolyte), is described. Then, the solar cell performance based on core/shell QDs is introduced. Finally, an outlook for the rational design of core/shell QDs is provided, which can further promote the development of high‐efficiency and stable QD sensitized solar cells.
Colloidal core/shell quantum dots (QDs) exhibit promising optical and electrical properties. Herein, a comprehensive overview is presented of the recent developments in the engineering of the structure of core/shell QDs to tune exciton dynamics so as to improve the performance of QD‐sensitized solar cells.
Solar‐driven photoelectrochemical (PEC) hydrogen evolution is a promising and sustainable approach to convert solar energy into a fuel that can be stored. Semiconductor quantum dots (QDs) are ...increasingly used in PEC devices due to their broad composition/size/shape tunable absorption spectrum (from ultraviolet to near‐infrared, with significant overlap with the solar spectrum). Despite significant efforts and recent progress, several major challenges remain unresolved in this fast‐developing field. Here, the latest progress in tailoring the materials, structure, and performance of QDs‐based PEC H2 generation, including photoanodes, photocathodes, and tandem PEC systems, is summarized. In particular, recent strategies developed for PEC H2 generation are critically analyzed. Specific features of QDs (e.g., size/shape/composition‐tunable absorption band edge arising from quantum confinement, ease of fabrication through chemical approaches, and multiple exciton generation), charge generation, and charge transfer of photoelectrodes and their implications on the performance of PEC devices are discussed. Future challenges and opportunities working, toward high‐efficiency and stable QDs‐based PEC applications are discussed in the conclusion.
This progress report comprehensively covers the latest progress in tailoring the materials, structure, and performance of quantum dots (QDs) based photoelectrochemical (PEC) hydrogen production from water splitting using solar energy, including photoanodes, photocathodes, and tandem systems. Particular attention is paid to the QDs engineering, PEC configuration, and electron/hole acceptors to tune the charge generation/separation/transfer dynamics, targeted at improving PEC performance.
Abstract
Based on wind speed, direction and power data, an assessment method of wind energy potential using finite mixture statistical distributions is proposed. Considering the correlation existing ...and the effect between wind speed and direction, the angular-linear modeling approach is adopted to construct the joint probability density function of wind speed and direction. For modeling the distribution of wind power density and estimating model parameters of null or low wind speed and multimodal wind speed data, based on expectation–maximization algorithm, a two-component three-parameter Weibull mixture distribution is chosen as wind speed model, and a von Mises mixture distribution with nine components and six components are selected as the models of wind direction and the correlation circular variable between wind speed and direction, respectively. A comprehensive technique of model selection, which includes Akaike information criterion, Bayesian information criterion, the coefficient of determination
R
2
and root mean squared error, is used to select the optimal model in all candidate models. The proposed method is applied to averaged 10-min field monitoring wind data and compared with the other estimation methods and judged by the values of
R
2
and root mean squared error, histogram plot and wind rose diagram. The results show that the proposed method is effective and the area under study is not suitable for wide wind turbine applications, and the estimated wind energy potential would be inaccuracy without considering the influence of wind direction.
Subwavelength confinement of light with plasmonics is promising for nanophotonics and optoelectronics. However, it is nontrivial to obtain narrow plasmonic resonances due to the intrinsically high ...optical losses and radiative damping in metallic structures. In this review, a thorough summary of the recent research progress on achieving high‐quality (high‐Q) factor plasmonic resonances is provided, emphasizing the fundamentals and six resonant mode types, including surface lattice resonances, multipolar resonances, plasmonic Fano resonances, plasmon‐induced transparency, guided‐mode resonances, and Tamm plasmon resonances. The applications of high‐Q plasmonic resonances in spectrally selective thermal emission, sensing, single‐photon emission, filtering, and band‐edge lasing are also discussed.
In this review article, the recent research progress on achieving high‐quality (high‐Q) factor plasmonic resonances is thoroughly summarized. Six channels for achieving high‐Q in nanophotonic designs are introduced in detail: surface lattice resonances, multipolar resonances, plasmonic Fano resonances, plasmon‐induced transparency, guided‐mode resonances, and Tamm plasmon resonances. Also, applications of the high‐Q plasmonic resonances are discussed.
All-inorganic Pb-free bismuth (Bi) halogen perovskite quantum dots (PQDs) with distinct structural and photoelectric properties provide plenty of room for selective photoreduction of CO2. However, ...the efficient conversion of CO2-to-CO with high selectivity on Bi-based PQDs driven by solar light remains unachieved, and the precise reaction path/mechanism promoted by the surface halogen-associated active sites is still poorly understood. Herein, we screen a series of nontoxic and stable Cs3Bi2X9 (X = Cl, Br, I) PQDs for selective photocatalytic reduction of CO2-to-CO at the gas–solid interface. Among all the reported pure-phase PQDs, the as-synthesized Cs3Bi2Br9 PQDs exhibited the highest CO2-to-CO conversion efficiency generating 134.76 μmol g–1 of CO yield with 98.7% selectivity under AM 1.5G simulated solar illumination. The surface halogen-associated active sites and reaction intermediates were dynamically monitored and precisely unraveled based on in situ DRIFTS investigation. In combination with the DFT calculation, it was revealed that the surface Br sites allow for optimizing the coordination modes of surface-bound intermediate species and reducing the reaction energy of the rate-limiting step of COOH– intermediate formation from •CO2 –. This work presents a mechanistic insight into the halogen-involved catalytic reaction mechanism in solar fuel production.
Reliable and efficient continuous-wave (CW) lasers have been intensively pursued in the field of optoelectronic integrated circuits. Metal perovskites have emerged as promising gain materials for ...solution-processed laser diodes. Recently, the performance of CW perovskite lasers has been improved with the optimization of material and device levels. Nevertheless, the realization of CW pumped perovskite lasers is still hampered by thermal runaway, unwanted parasitic species, and poor long-term stability. This review starts with the charge carrier recombination dynamics and fundamentals of CW lasing in perovskites. We examine the potential strategies that can be used to improve the performance of perovskite CW lasers from the materials to device levels. We also propose the open challenges and future opportunities in developing high-performance and stable CW pumped perovskite lasers.
Highlights
The controllable fabrication methods, the unique properties, and relative applications of 2D heterostructures were summarized.
The generation and detection of interlayer excitons in 2D ...heterostructures with type II band alignment indicate a longer lifetime and larger binding energy than intralayer excitons.
The advances in magnetic tunneling junctions based on 2D heterostructures can be applied in spintronic devices to realize spin filtering.
With a large number of researches being conducted on two-dimensional (2D) materials, their unique properties in optics, electrics, mechanics, and magnetics have attracted increasing attention. Accordingly, the idea of combining distinct functional 2D materials into heterostructures naturally emerged that provides unprecedented platforms for exploring new physics that are not accessible in a single 2D material or 3D heterostructures. Along with the rapid development of controllable, scalable, and programmed synthesis techniques of high-quality 2D heterostructures, various heterostructure devices with extraordinary performance have been designed and fabricated, including tunneling transistors, photodetectors, and spintronic devices. In this review, we present a summary of the latest progresses in fabrications, properties, and applications of different types of 2D heterostructures, followed by the discussions on present challenges and perspectives of further investigations.
0D perovskite Cs4PbBr6 has attracted considerable attention recently because of its highly efficient green photoluminescence (PL) and highly debated opposing mechanisms: embedded CsPbBr3 nanocrystals ...versus intrinsic Br vacancy states. Here we provide sensitive but noninvasive methods that can not only directly correlate luminescence with the underlying structure, but also distinguish point defects from embedded nanostructures. We first use correlated Raman-PL as a passive structure–property method to identify the difference between emissive and nonemissive Cs4PbBr6 crystals and reveal the existence of CsPbBr3 nanocrystals in emissive Cs4PbBr6. We then employ a diamond anvil cell to probe the response of luminescence centers to hydrostatic pressure. The observations of fast red-shifting, diminishing, and eventual disappearance of both green emission and Raman exclude Br vacancies as possible luminescent centers. The resolution of this long-lasting controversy paves the way for further device applications of low dimensional perovskites, and our techniques are applied to other emerging materials.
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