Fine energy‐level modulations of small‐molecule acceptors (SMAs) are realized via subtle chemical modifications on strong electron‐withdrawing end‐groups. The two new SMAs (IT‐M and IT‐DM) end‐capped by methyl‐modified dicycanovinylindan‐1‐one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open‐circuit voltages can be observed in the corresponding devices. Finally, a top power conversion efficiency of 12.05% is achieved.
A nonfullerene‐based polymer solar cell (PSC) that significantly outperforms fullerene‐based PSCs with respect to the power‐conversion efficiency is demonstrated for the first time. An efficiency of >11%, which is among the top values in the PSC field, and excellent thermal stability is obtained using PBDB‐T and ITIC as donor and acceptor, respectively.
Fluorine‐contained polymers, which have been widely used in highly efficient polymer solar cells (PSCs), are rather costly due to their complicated synthesis and low yields in the preparation of components. Here, the feasibility of replacing the critical fluorine substituents in high‐performance photovoltaic polymer donors with chlorine is demonstrated, and two polymeric donors, PBDB‐T‐2F and PBDB‐T‐2Cl, are synthesized and compared in parallel. The synthesis of PBDB‐T‐2Cl is much simpler than that of PBDB‐T‐2F. The two polymers have very similar optoelectronic and morphological properties, except the chlorinated polymer possess lower molecular energy levels than the fluorinated one. As a result, the PBDB‐T‐2Cl‐based PSCs exhibit higher open circuit voltage (Voc) than the PBDB‐T‐2F‐based devices, leading to an outstanding power conversion efficiency of over 14%. This work establishes a more economical design paradigm of replacing fluorine with chlorine for preparing highly efficient polymer donors. A chlorinated polymer donor, PBDB‐T‐2Cl, is synthesized and compared in parallel with its fluorinated counterpart, PBDB‐T‐2F. PBDB‐T‐2Cl exhibits a much simpler synthesis route, which is favorable for future practical application of organic solar cells; in addition, a high power conversion efficiency of 14.4% (with certified PCE of 13.9% by the National Institute of Metrology) and good stability tested over 1000 h is achieved.
Semiconductor‐based photocatalysis attracts wide attention because of its ability to directly utilize solar energy for production of solar fuels, such as hydrogen and hydrocarbon fuels and for degradation of various pollutants. However, the efficiency of photocatalytic reactions remains low due to the fast electron–hole recombination and low light utilization. Therefore, enormous efforts have been undertaken to solve these problems. Particularly, properly engineered heterojunction photocatalysts are shown to be able to possess higher photocatalytic activity because of spatial separation of photogenerated electron–hole pairs. Here, the basic principles of various heterojunction photocatalysts are systematically discussed. Recent efforts toward the development of heterojunction photocatalysts for various photocatalytic applications are also presented and appraised. Finally, a brief summary and perspectives on the challenges and future directions in the area of heterojunction photocatalysts are also provided. Heterojunction photocatalysts attract a lot of attention because of their effectiveness for spatial separation of photogenerated electron–hole pairs. Therefore, various types of heterojunction photocatalyst are applied in different photocatalytic fields, including H2 production, CO2 reduction, and pollutant degradation. The development of heterojunction photocatalysts can lead to significant advancements in the photocatalysis field.
Water electrolysis is considered as the most promising technology for hydrogen production. Much research has been devoted to developing efficient electrocatalysts for hydrogen production via the hydrogen evolution reaction (HER) and oxygen production via the oxygen evolution reaction (OER). The optimum electrocatalysts can drive down the energy costs needed for water splitting via lowering the overpotential. A number of cobalt (Co)‐based materials have been developed over past years as non‐noble‐metal heterogeneous electrocatalysts for HER and OER. Recent progress in this field is summarized here, especially highlighting several important bifunctional catalysts. Various approaches to improve or optimize the electrocatalysts are introduced. Finally, the current existing challenges and the future working directions for enhancing the performance of Co‐implicated electrocatalysts are proposed. Electrochemical water splitting is a well‐established technology with which to produce high‐purity hydrogen. Recent progress in cobalt‐based heterogeneous electrocatalysts for water splitting is reviewed. Strategies to obtain optimized or enhanced performance are introduced through specific examples. The current existing challenges and future working directions for enhancing the performance of Co‐implicated electrocatalysts are discussed.
Novel quantum‐dot light‐emitting diodes based on all‐inorganic perovskite CsPbX3 (X = Cl, Br, I) nanocrystals are reported. The well‐dispersed, single‐crystal quantum dots (QDs) exhibit high quantum yields, and tunable light emission wavelength. The demonstration of these novel perovskite QDs opens a new avenue toward designing optoelectronic devices, such as displays, photodetectors, solar cells, and lasers.
Semiconductor‐based photocatalysis is considered to be an attractive way for solving the worldwide energy shortage and environmental pollution issues. Since the pioneering work in 2009 on graphitic carbon nitride (g‐C3N4) for visible‐light photocatalytic water splitting, g‐C3N4‐based photocatalysis has become a very hot research topic. This review summarizes the recent progress regarding the design and preparation of g‐C3N4‐based photocatalysts, including the fabrication and nanostructure design of pristine g‐C3N4, bandgap engineering through atomic‐level doping and molecular‐level modification, and the preparation of g‐C3N4‐based semiconductor composites. Also, the photocatalytic applications of g‐C3N4‐based photocatalysts in the fields of water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection are reviewed, with emphasis on photocatalysis promoted by carbon materials, non‐noble‐metal cocatalysts, and Z‐scheme heterojunctions. Finally, the concluding remarks are presented and some perspectives regarding the future development of g‐C3N4‐based photocatalysts are highlighted. Polymeric g‐C3N4‐based photocatalysts are very attractive due to their unique electronic and physicochemical properties, which make them well suited for various applications, such as photocatalytic water splitting, CO2 reduction, pollutant degradation, organic syntheses, and bacterial disinfection. These unique properties can be achieved by optimized preparation, nanostructural design, and bandgap engineering of g‐C3N4, as well as by the construction of g‐C3N4‐based semiconductor heterojunctions.
Lithium‐sulfur (Li‐S) batteries have attracted tremendous interest because of their high theoretical energy density and cost effectiveness. The target of Li‐S battery research is to produce batteries with a high useful energy density that at least outperforms state‐of‐the‐art lithium‐ion batteries. However, due to an intrinsic gap between fundamental research and practical applications, the outstanding electrochemical results obtained in most Li‐S battery studies indeed correspond to low useful energy densities and are not really suitable for practical requirements. The Li‐S battery is a complex device and its useful energy density is determined by a number of design parameters, most of which are often ignored, leading to the failure to meet commercial requirements. The purpose of this review is to discuss how to pave the way for reliable Li‐S batteries. First, the current research status of Li‐S batteries is briefly reviewed based on statistical information obtained from literature. This includes an analysis of how the various parameters influence the useful energy density and a summary of existing problems in the current Li‐S battery research. Possible solutions and some concerns regarding the construction of reliable Li‐S batteries are comprehensively discussed. Finally, insights are offered on the future directions and prospects in Li‐S battery field. The research status of Li‐S batteries is briefly reviewed based on statistical analysis results. A summary of existing problems in the current Li‐S battery research is concluded with possible solutions and some concerns comprehensively discussed. Perspectives are proposed with respect to more reliable lithium‐sulfur batteries with rationally improved performance.
The electrocatalytic activity of transition‐metal‐based compounds is strongly related to the spin states of metal atoms. However, the ways for regulation of spin states of catalysts are still limited, and the underlying relationship between the spin states and catalytic activities remains unclear. Herein, for the first time, by taking NiII‐based compounds without high or low spin states for example, it is shown that their spin states can be delocalized after introducing structural distortion to the atomic layers. The delocalized spin states for Ni atoms can provide not only high electrical conductivity but also low adsorption energy between the active sites and reaction intermediates for the system. As expected, the ultrathin nanosheets of nickel‐chalcogenides with structural distortions show dramatically enhanced activity in electrocatalytic oxygen evolution compared to their corresponding bulk samples. This work establishes new way for the design of advanced electrocatalysts in transition‐metal‐based compounds via regulation of spin states. Delocalized spin states in transition‐metal‐based compounds by introducing structural distortion to their confined 2D atomic layers can enhance activity in electrocatalytic oxygen evolution. This work establishes new way for the design of advanced electrocatalysts in transition‐metal‐based compounds via regulation of spin states.
A new fluorinated nonfullerene acceptor, ITIC‐Th1, has been designed and synthesized by introducing fluorine (F) atoms onto the end‐capping group 1,1‐dicyanomethylene‐3‐indanone (IC). On the one hand, incorporation of F would improve intramolecular interaction, enhance the push–pull effect between the donor unit indacenodithieno[3,2‐b]thiophene and the acceptor unit IC due to electron‐withdrawing effect of F, and finally adjust energy levels and reduce bandgap, which is beneficial to light harvesting and enhancing short‐circuit current density (JSC). On the other hand, incorporation of F would improve intermolecular interactions through CF···S, CF···H, and CF···π noncovalent interactions and enhance electron mobility, which is beneficial to enhancing JSC and fill factor. Indeed, the results show that fluorinated ITIC‐Th1 exhibits redshifted absorption, smaller optical bandgap, and higher electron mobility than the nonfluorinated ITIC‐Th. Furthermore, nonfullerene organic solar cells (OSCs) based on fluorinated ITIC‐Th1 electron acceptor and a wide‐bandgap polymer donor FTAZ based on benzodithiophene and benzotriazole exhibit power conversion efficiency (PCE) as high as 12.1%, significantly higher than that of nonfluorinated ITIC‐Th (8.88%). The PCE of 12.1% is the highest in fullerene and nonfullerene‐based single‐junction binary‐blend OSCs. Moreover, the OSCs based on FTAZ:ITIC‐Th1 show much better efficiency and better stability than the control devices based on FTAZ:PC71BM (PCE = 5.22%). Single‐junction binary‐blend nonfullerene polymer solar cells based on fluorinated acceptor ITIC‐Th1 afford power conversion efficiency of 12.1%, which is much higher than those of nonfluorinated ITIC‐Th (8.88%) and PC71BM (5.22%) counterparts under the same condition. Moreover, the nonfullerene devices exhibit better thermal stability than the fullerene devices.
A novel non‐fullerene electron acceptor (ITIC) that overcomes some of the shortcomings of fullerene acceptors, for example, weak absorption in the visible spectral region and limited energy‐level variability, is designed and synthesized. Fullerene‐free polymer solar cells (PSCs) based on the ITIC acceptor are demonstrated to exhibit power conversion efficiencies of up to 6.8%, a record for fullerene‐free PSCs.
Oxygen electrocatalysis, including the oxygen‐reduction reaction (ORR) and oxygen‐evolution reaction (OER), is a critical process for metal–air batteries. Therefore, the development of electrocatalysts for the OER and the ORR is of essential importance. Indeed, various advanced electrocatalysts have been designed for the ORR or the OER; however, the origin of the advanced activity of oxygen electrocatalysts is still somewhat controversial. The enhanced activity is usually attributed to the high surface areas, the unique facet structures, the enhanced conductivities, or even to unclear synergistic effects, but the importance of the defects, especially the intrinsic defects, is often neglected. More recently, the important role of defects in oxygen electrocatalysis has been demonstrated by several groups. To make the defect effect clearer, the recent development of this concept is reviewed here and a novel principle for the design of oxygen electrocatalysts is proposed. An overview of the defects in carbon‐based, metal‐free electrocatalysts for ORR and various defects in metal oxides/selenides for OER is also provided. The types of defects and controllable strategies to generate defects in electrocatalysts are presented, along with techniques to identify the defects. The defect–activity relationship is also explored by theoretical methods. Defects in carbon‐based metal‐free electrocatalysts for the oxygen‐reduction reaction (ORR) and various defects in metal oxide/selenide for the oxygen‐evolution reaction (OER) are reviewed. The existence of defects has a great effect on the properties of catalysts; for example, the charge distribution and the conductibility. The strategies to generate defects, the defect–activity relationship, and the techniques to identify defects are discussed.
Increasing energy demands and environment awareness have promoted extensive research on the development of alternative energy conversion and storage technologies with high efficiency and environmental friendliness. Among them, water splitting is very appealing, and is receiving more and more attention. The critical challenge of this renewable‐energy technology is to expedite the oxygen evolution reaction (OER) because of its slow kinetics and large overpotential. Therefore, developing efficient electrocatalysts with high catalytic activities is of great importance for high‐performance water splitting. In the past few years, much effort has been devoted to the development of alternative OER electrocatalysts based on transition‐metal elements that are low‐cost, highly efficient, and have excellent stability. Here, recent progress on the design, synthesis, and application of OER electrocatalysts based on transition‐metal elements, including Co, Ni, and Fe, is summarized, and some invigorating perspectives on the future developments are provided. Developing efficient oxygen‐evolution electrocatalysts with high catalytic activities is of great importance for high‐performance water splitting. Recent progress in the design, synthesis, and application of OER electrocatalysts based on transition‐metal elements, including Co, Ni, and Fe, is summarized, and some invigorating perspectives on future developments are discussed.
Metal−organic frameworks (MOFs), also known as coordination polymers, represent an interesting type of solid crystalline materials that can be straightforwardly self‐assembled through the coordination of metal ions/clusters with organic linkers. Owing to the modular nature and mild conditions of MOF synthesis, the porosities of MOF materials can be systematically tuned by judicious selection of molecular building blocks, and a variety of functional sites/groups can be introduced into metal ions/clusters, organic linkers, or pore spaces through pre‐designing or post‐synthetic approaches. These unique advantages enable MOFs to be used as a highly versatile and tunable platform for exploring multifunctional MOF materials. Here, the bright potential of MOF materials as emerging multifunctional materials is highlighted in some of the most important applications for gas storage and separation, optical, electric and magnetic materials, chemical sensing, catalysis, and biomedicine. Metal−organic frameworks, as an emerging type of solid crystalline materials, can be straightforwardly self‐assembled through the coordination of metal ions/clusters with organic linkers. The functions of MOFs can not only originate from their porosities, but can also be generated from metal ions/clusters, organic linkers/metalloligands, or a variety of guest species, making MOFs a highly versatile and tunable platform to develop multifunctional materials for their broad applications
“United we stand, divided we fall.”–Aesop.Aggregation‐induced emission (AIE) refers to a photophysical phenomenon shown by a group of luminogenic materials that are non‐emissive when they are dissolved in good solvents as molecules but become highly luminescent when they are clustered in poor solvents or solid state as aggregates. In this Review we summarize the recent progresses made in the area of AIE research. We conduct mechanistic analyses of the AIE processes, unify the restriction of intramolecular motions (RIM) as the main cause for the AIE effects, and derive RIM‐based molecular engineering strategies for the design of new AIE luminogens (AIEgens). Typical examples of the newly developed AIEgens and their high‐tech applications as optoelectronic materials, chemical sensors and biomedical probes are presented and discussed. “United we stand, divided we fall!” Aggregate formation changes non‐emissive luminogens to efficient emitters – this process is referred to as aggregation‐induced emission (AIE). The AIE effect is caused by the restriction of intramolecular motions of luminogens in aggregate state. The AIE materials have found a wide variety of high‐tech applications in the areas of optoelectronics, chemosensors, and biomedical probes.
Lithium–sulfur (Li–S) batteries with high energy density and long cycle life are considered to be one of the most promising next‐generation energy‐storage systems beyond routine lithium‐ion batteries. Various approaches have been proposed to break down technical barriers in Li–S battery systems. The use of nanostructured metal oxides and sulfides for high sulfur utilization and long life span of Li–S batteries is reviewed here. The relationships between the intrinsic properties of metal oxide/sulfide hosts and electrochemical performances of Li–S batteries are discussed. Nanostructured metal oxides/sulfides hosts used in solid sulfur cathodes, separators/interlayers, lithium‐metal‐anode protection, and lithium polysulfides batteries are discussed respectively. Prospects for the future developments of Li–S batteries with nanostructured metal oxides/sulfides are also discussed. Nanostructured metal oxides and sulfides are considered as polysulfide anchoring sites in working Li–S batteries for the battery's high sulfur utilization and long life span. The relationships between the intrinsic properties of the metal oxide/sulfide hosts and the electrochemical performances of Li–S batteries are reviewed.
Flexible and stretchable physical sensors that can measure and quantify electrical signals generated by human activities are attracting a great deal of attention as they have unique characteristics, such as ultrathinness, low modulus, light weight, high flexibility, and stretchability. These flexible and stretchable physical sensors conformally attached on the surface of organs or skin can provide a new opportunity for human-activity monitoring and personal healthcare. Consequently, in recent years there has been considerable research effort devoted to the development of flexible and stretchable physical sensors to fulfill the requirements of future technology, and much progress has been achieved. Here, the most recent developments of flexible and stretchable physical sensors are described, including temperature, pressure, and strain sensors, and flexible and stretchable sensor-integrated platforms. The latest successful examples of flexible and stretchable physical sensors for the detection of temperature, pressure, and strain, as well as their novel structures, technological innovations, and challenges, are reviewed first. In the next section, recent progress regarding sensor-integrated wearable platforms is overviewed in detail. Some of the latest achievements regarding self-powered sensor-integrated wearable platform technologies are also reviewed. Further research direction and challenges are also proposed to develop a fully sensor-integrated wearable platform for monitoring human activity and personal healthcare in the near future.
Organic–inorganic hybrid perovskites have cemented their position as an exceptional class of optoelectronic materials thanks to record photovoltaic efficiencies of 22.1%, as well as promising demonstrations of light‐emitting diodes, lasers, and light‐emitting transistors. Perovskite materials with photoluminescence quantum yields close to 100% and perovskite light‐emitting diodes with external quantum efficiencies of 8% and current efficiencies of 43 cd A−1 have been achieved. Although perovskite light‐emitting devices are yet to become industrially relevant, in merely two years these devices have achieved the brightness and efficiencies that organic light‐emitting diodes accomplished in two decades. Further advances will rely decisively on the multitude of compositional, structural variants that enable the formation of lower‐dimensionality layered and three‐dimensional perovskites, nanostructures, charge‐transport materials, and device processing with architectural innovations. Here, the rapid advancements in perovskite light‐emitting devices and lasers are reviewed. The key challenges in materials development, device fabrication, operational stability are addressed, and an outlook is presented that will address market viability of perovskite light‐emitting devices. Perovskites have sparked a revolution in photovoltaics, and their excellent optoelectronic properties hold the potential to trigger a similar advance in the field of light emission. The versatility of organic–inorganic hybrid perovskites as emitters and gain media is explored, device performance/architectures, processing conditions, and working mechanisms are analyzed, and the main barriers toward market viability are addressed.
A single‐junction polymer solar cell with an efficiency of 10.1% is demonstrated by using deterministic aperiodic nanostructures for broadband light harvesting with optimum charge extraction. The performance enhancement is ascribed to the self‐enhanced absorption due to collective effects, including pattern‐induced anti‐reflection and light scattering, as well as surface plasmonic resonance, together with a minimized recombination probability.
Solution‐processed CsPbBr3 quantum‐dot light‐emitting diodes with a 50‐fold external quantum efficiency improvement (up to 6.27%) are achieved through balancing surface passivation and carrier injection via ligand density control (treating with hexane/ethyl acetate mixed solvent), which induces the coexistence of high levels of ink stability, photoluminescence quantum yields, thin‐film uniformity, and carrier‐injection efficiency.