Achieving Narrowed Bandgaps and Blue-Light Excitability in Zero-Dimensional Hybrid Metal Halide Phosphors via Introducing Cation-Cation Bonding

Zero-dimensional(0D)hybrid metal halides,which consist of organic cations and isolated inorganic metal halide anions,have emerged as phosphors with efficient broadband emissions.However,these materials generally have too wide bandgaps and thus cannot be excited by blue light,which hinders their applications for efficient white light-emitting diodes(WLEDs).The key to achieving a blue-light-excitable 0D hybrid metal halide phosphor is to reduce the fundamental bandgap by rational chemical design.In this work,we report two designed hybrid copper(I)iodides,(Ph_(3)MeP)_(2)Cu_(4)I_(6)and(Cy_(3)MeP)_(2)Cu_(4)I_(6),as blue-light-excitable yellow phosphors with ultrabroadband emission.In these compounds,the[Cu_(4)I_(6)]^(2-)anion forms an I6 octahedron centered on a cationic Cu_(4)tetrahedron.The strong cation-cation bonding within the unique cationic Cu_(4)tetrahedra enables significantly lowered conduction band minimums and thus narrowed bandgaps,as compared to other reported hybrid copper(I)iodides.The ultrabroadband emission is attributed to the coexistence of free and self-trapped excitons.The WLED using the[Cu_(4)I_(6)]^(2-)anion-based single phosphor shows warm white light emission,with a high luminous efficiency of 65 Im W^(-1)and a high color rendering index of 88.This work provides strategies to design narrow-bandgap 0D hybrid metal halides and presents two first examples of blue-light-excitable 0D hybrid metal halide phosphors for efficient WLEDs.

Solar Cells Based on All-Inorganic Halide Perovskites:Progress and Prospects

The emergence of perovskite solar cells(PSCs)based on all-inorganic metal halide(IMH)has generated enormous interest in the photovoltaic research community,and the power conversion efficiency(PCE)has exceeded13%.Despite its outstanding performance in thermal stability,PSCs based on IMH still face problems such as the lack of a suitable band gap and the inability to generate large areas.In this review,we will summarize the latest progress of PSCs based on IMH.

Infrared optical absorption of Fr?hlich polarons in metal halide perovskites

The formation of Frohlich polarons in metal halide perovskites,arising from the charge carrier-longitudinal optical(LO)phonon coupling,has been proposed to explain their exceptional properties,but the effective identification of polarons in these materials is still a challenging task.Herein,we theoretically present the infrared optical absorption of Frohlich polarons based on the Huang-Rhys model.We find that multiphonon overtones appear as the energy of the incident photons matches the multiple LO phonons,wherein the average phonon number of a polaron can be directly evaluated by the order of the strongest overtone.These multiphonon structures sensitively depend on the scale of electronic distribution in the ground state and the dimensionality of the perovskite materials,revealing the effective modulation of competing processes between polaron formation and carrier cooling.Moreover,the order of the strongest overtone shifts to higher ones with temperature,providing a potential proof that the carrier mobility is affected by LO phonon scattering.The present model not only suggests a direct way to verify Frohlich polarons but also enriches our understanding of the properties of polarons in metal halide perovskites.

Progress on the controllable synthesis of all-inorganic halide perovskite nanocrystals and their optoelectronic applications

In the past five years,all-inorganic metal halide perovskite(CsPbX3,X=Cl,Br,I)nanocrystals have been intensely studied due to their outstanding optical properties and facile synthesis,which endow them with potential optoelectronic applications.In order to optimize their physical and chemical properties,different strategies have been developed to realize the controllable synthesis of CsPbX3 nanocrystals.In this short review,we firstly present a comprehensive and detailed summary of existed synthesis strategies of CsPbX3 nanocrystals and their analogues.Then,we introduce the regulations of several reaction parameters and their effects on the morphologies of CsPbX3 nanocrystals.At the same time,we provide stability improvement methods and representative applications.Finally,we propose the current challenges and future perspectives of the promising materials.

Metal halide perovskite photodetectors: Material features and device engineering

In recent years, the rapid progress of metal halide perovskite solar cells has been witnessed by the rocketing power conversion efficiency. In addition, perovskites have opened up a great opportunity for high performance photodetectors(PDs), due to their attractive optical and electrical properties. This review summarizes the latest progress of perovskitebased PDs, aiming to give a comprehensive understanding of the material design and device engineering in perovskite PDs.To begin with, the performance parameters and device configurations of perovskite PDs are introduced, which are the basis for the next discussion. Next, various PDs based on perovskites in different morphologies are discussed from two aspects:the preparation method, and device performance. Then, several device engineering strategies to enhance the performance of perovskite-based PDs are highlighted, followed by the introduction of flexible and narrow-band perovskite PDs. Finally,key issues and major challenges of perovskite PDs that need to be addressed in the future are outlined.

Stretchable alkenamides terminated Ti_(3)C_(2)T_(x)MXenes to release strain for lattice-stable mixed-halide perovskite solar cells with suppressed halide segregation

Bandgap-tunable mixed-halide perovskite materials have attracted considerable interest because of their indispensability as top counterparts in tandem solar cells.However,the soft and disordered lattice always suffers from severe phase segregation under illumination,which is particularly susceptible to residual lattice strain.Herein,we report a strain regulation strategy by using alkenamides terminated Ti_(3)C_(2)T_(x)MXenes as an additive into perovskite precursor.Apart from the role of a template for grain growth to obtain high-quality films,the stretchable alkyl chain promotes lattice shrinkage or expansion to form an elastic grain boundary to eliminate the spatially distributed stain and shut down ion migration channels.As a result,the all-inorganic perovskite solar cells based on CsPbIBr_(2)and CsPbI_(2)Br halides achieve prolonged device stability under harsh conditions and the best power conversion efficiencies up to 11.06%and 14.30%,respectively.

Deep Extractive Desulfurization of Gasoline with Ionic Liquids Based on Metal Halide

Ionic liquid [Et3NH]C1-FeCl3/CuCl was synthesized by mixing [Et3NH]Cl, anhydrous FeCl3 and anhydrous CuCl, and the desulfurization activity of this ionic liquid was tested. It exhibited remarkable ability in effective desulfurization of model gasoline （thiophene in n-octane） and fluid catalytic cracking （FCC） gasoline, and the sulfur removal of thiophene in model oil （V（IL）： V（oil）=0.08） could reach 93.9% in 50 min at 50 ℃. Low-sulfur （〈10 μg/g） FCC gasoline could be obtained after three extraction runs at an ionic liquid/oil volume ratio of 0.1, with the yield of FCC gasoline reaching 94.3%. The ionic liquid could be recycled 5 times with merely a slight decrease in activity.

Two-dimensional transition metal dichalcogenides for lead halide perovskites-based photodetectors: band alignment investigation for the case of CsPbBr3/MoSe2

The distinguished electronic and optical properties of lead halide perovskites(LHPs)make them good candidates for active layer in optoelectronic devices.Integrating LHPs and two-dimensional(2 D)transition metal dichalcogenides(TMDs)provides opportunities for achieving increased performance in heterostructured LHPs/TMDs based optoelectronic devices.The electronic structures of LHPs/TMDs heterostructures,such as the band offsets and interfacial interaction,are of fundamental and technological interest.Here CsPbBr3 and MoSe2 are taken as prototypes of LHPs and 2 D TMDs to investigate the band alignment and interfacial coupling between them.Our GGA-PBE and HSE06 calculations reveal an intrinsic type-II band alignment between CsPbBr3 and MoSe2.This type-II band alignment suggests that the performance of CsPbBr3-based photodetectors can be improved by incorporating MoSe2 monolayer.Furthermore,the absence of deep defect states at CsPbBr3/MoSe2 interfaces is also beneficial to the better performance of photodetectors based on CsPbBr3/MoSe2 heterostructure.This work not only offers insights into the improved performance of photodetectors based on LHPs/TMDs heterostructures but it also provides guidelines for designing high-efficiency optoelectronic devices based on LHPs/TMDs heterostructures.

Recent advances in metal halide perovskite photocatalysts:Properties,synthesis and applications

As a class of new emerged semiconductors,MHPs exhibit many excellent photoelectronic properties,which are superior to most conventional semiconductor nanocrystals(NCs).Particularly,MHPs have received extensive attention and brought new opportunities for the development of photocatalysis.Over the past few years,numerous efforts have been made to design and prepare MHP-based materials for a wide range of applications in photocatalysis,ranging from photocatalytic H_(2) generation,photocatalytic CO_(2) reduction,photocatalytic organic synthesis and pollutant degradation.In this review,recent advances in the development of MHP-based materials are summarized from the standpoint of photocatalysis.A brief outlook of this field has been proposed to point out some important challenges and possible solutions.This review suggests that the new family of MHP photocatalysts provide a new paradigm in efficient artificial photosynthesis.

Improving the stability of metal halide perovskite solar cells from material to structure

Metal halide perovskites(MHPs) are promising photovoltaic(PV) materials owing to their advantages such as high carrier mobility, excellent absorption coefficient, bandgap tenability, long diffusion length,and low material cost. These qualities have increased the efficiency of MHP solar cells to 23.3%. However,MHPs are hindered by a lack of stability. In addition, the applications of MHP solar cells are restricted by the instability of perovskite materials and devices. In this article, the most urgent stability problems faced by perovskite solar cells are identified, and recent progresses in MHPs are enumerated. The factors affecting the stability of perovskite materials and devices are also discussed. We analyzed the thermal and humid stability of perovskite materials in terms of transporting materials and their interface. In view of these recent advances, future works should focus on the large-scale application of MHP solar cells.

Study on Thermal Expansion Coefficient of Sealing Materials for Ceramic Metal Halide Lamps

With Al2O3, Dy2O3, and SiO2 as starting materials, the basic glass of Al2O3-Dy2O3-SiO2 system was prepared by conventional melting technology, and their thermal expansion coefficients （TECs） at different anneal time were investigated. TECs of the basic glass, which were heat-treated under different temperature, were also investigated. The result showed that TECs of the basic glass gradually approached a fixed value as the anneal time was extended, which suggested that most of the inner stress had been eliminated. After heat treatment, the contents of Dy2O3, Dy2Si2O7, and a new crystal increased up to 1200 ℃ and decreased below 1250 ℃, which was consistent with the TEC change of crystallized samples. This suggests that the crystal has a direct effect on TECs of the crystallized samples.

Strategies and methods for fabricating high quality metal halide perovskite thin films for solar cells

With the development of human society,the problems of environmental deterioration and energy shortage have become increasingly prominent.In order to solve these problems,metal halide perovskite solar cells(PSCs)stand out because of their excellent properties(i.e.,high optical absorption coefficient,long carrier lifetime and carrier diffusion length,adjustable band gap)and have been widely studied.PSCs with low cost,high power conversion efficiency and high stability are the future development trend.The quality of perovskite film is essential for fabricating PSCs with high performance.To provide a full picture of realizing high performance PSCs,this review focuses on the strategies for preparing high quality perovskite films(including antisolvent,Lewis acid-base,additive engineering,scaleable fabrication,strain engineering and band gap adjustment),and therefore to fabricate high performance PSCs and to accelerate the commercialization.

Ionic Interactions in Molecular and Liquid States ofPolyvalent Metal Halides

Progress in the development of phenomenological models for the microscoplc interactions in the halides of polyvalent metals is reviewed, with main attention to neutral and ionized molecular states and to the melts of these materials. The following physical problems are discussed: (1)bond bending in the molecules of the alkaline-earth halides, (2) binding of molecular dimers and halogen transfer reactions relevant to the melts of trivalent metal halides, (3) stability of molecular ions in liquid mixtures of polyvalent metal halides and alkali halides, and (4) stabilityof molecular ions and reduced-valence states in molten cryolite under addition of sodium metal.

Environmentally Benign Electrophilic Halogenation of Naphthalenes by H₂O₂—Alkali Metal Halides in An Aqueous Cationic Micellar Media

An efficient and greener protocol for the synthesis of 1-halo-naphthols by the action of hydrogen peroxide and alkali metal halides in aqueous micellar media is been described in the present work. This is an environmentally clean and safe procedure, which involved insitu generation of the active halogen in presence of alkali halides. Cationic surfactants such as cetyltrimethylammoniumbromide (CTAB) and cetyltrimethylammoniumchloride (CTAC) were found to facilitate efficiency of halogenation in aqueous media.

Microstructured hydroxyl environments and Raman spectroscopy in selected basic transition-metal halides

Raman vibrational spectra of the selected basic （hydroxyl OH and deuteroxyl OD） transition-metal halides, geomet- rically frustrated material series α-, β-, γ-Cu2（OH）3Cl, α-Cu2（OH）3Br, β-Ni2（OH）3Cl, β-Co2（OH）3Cl, β-Co2（OH）3Br, γ-Cu2（OD）3Cl, and β-Co2（OD）3Cl are measured at room temperature and analysed to investigate the relationship be- tween the microstructured OH environments and their respective Raman spectra. Among these selected samples, the last two are used to determine the OH stretching vibration region （3600 cm-1-3300 cm-1） and OH bending vibra- tion region （1000 cm-1-600 cm-1） of OH systems in the spectra. Through the comparative analysis of the distances d（metal-O）, d（O-halogen）, and d（OH）, the strong metal-O interaction and trimeric hydrogen bond （Car, C8 or C1 symmetry） are found in every material, but both determine simultaneously an ultimate d（OH）, and therefore an OH stretching vibration frequency. According to the approximately linear relationship between the OH stretching vibration frequency and d（OH）, some unavailable d（OH） are guessed and some doubtful d（OH） are suggested to be corrected. In addition, it is demonstrated in brief that the OH bending vibration frequency is also of importance to check the more detailed crystal microstructure relating to the OH group.

Temperature-dependent self-trapped exciton emission in Cu(I) doped zinc-based metal halides from well-resolved excited state structures

Zero-dimensional metal halides are of unique structures and tunable photoluminescence properties,showing great potential applications such as light-emitting diodes(LEDs)and sensing.Herein,we successfully synthesized Cu^(+)doped(MA)_(2)ZnCl_(4)metal halides by a slow evaporation solvent method.The introduction of Cu^(+)results in sky-blue self-trapped exciton emission in(MA)_(2)ZnCl_(4) at 486 nm at room temperature,and a photoluminescence quantum yield is as high as 54.9%.Interestingly,at low temperatures,Cu^(+)-doped(MA)_(2)ZnCl_(4) exhibits two emission peaks located at 482 and 605 nm,respectively.This temperaturedependent dual emission indicates two excited state structures that exist on the triplet excited-state potential energy surface.In addition,the temperature sensor we fitted has good performance(Sr=1.65%·K^(−1)),which is the first attempt in Cu^(+) doped Znbased metal halides.Our work enriches the family of sky-blue metal halides and provides a promising strategy for building skyblue LEDs.

Low-Dimensional Halide Perovskites and Their Advanced Optoelectronic Applications

Metal halide perovskites are crystalline materials originally developed out of scientific curiosity. They have shown great potential as active materials in optoelectronic applications. In the last 6 years, their certified photovoltaic efficiencies have reached 22.1%. Compared to bulk halide perovskites, low-dimensional ones exhibited novel physical properties. The photoluminescence quantum yields of perovskite quantum dots are close to 100%. The external quantum efficiencies and current efficiencies of perovskite quantum dot light-emitting diodes have reached 8% and 43 cd A^(-1),respectively, and their nanowire lasers show ultralow-threshold room-temperature lasing with emission tunability and ease of synthesis. Perovskite nanowire photodetectors reached a responsivity of 10 A W^(-1)and a specific normalized detectivity of the order of 10^(12 )Jones. Different from most reported reviews focusing on photovoltaic applications, we summarize the rapid progress in the study of low-dimensional perovskite materials, as well as their promising applications in optoelectronic devices. In particular, we review the wide tunability of fabrication methods and the state-of-the-art research outputs of low-dimensional perovskite optoelectronic devices. Finally, the anticipated challenges and potential for this exciting research are proposed.

Achieving tunable long persistent luminescence in metal organic halides based on pyridine solvent

The research of long persistent luminescence(LPL)materials has yield brilliant results in many fields.However,the efforts are still needed for the regulation of the LPL performance.In this work,a series of LPL metal organic halides with rich halogen-bond interactions,Py-CdX_(2)(X=Cl,Br,I)were synthesized through self-assembly by Cd X_(2)and pyridine solvent.The steady-state emission redshifted and phosphorescence lifetime declined as the halogen atoms are aggravated.Three halides exhibit adjustable emission from blue to green and multiple phosphorescence from green to yellow at room temperature by changing the excitation wavelengths.Surprisingly,Py-CdX_(2)can emit the visible color-tunable LPL from green to yellow after removing different excitation sources at ambient conditions.Combing the results of theoretical calculation and experimental analysis,it is found that heavy atom effect and the rich intermolecular halogen bond help realize LPL and multiple triplet states originated from the pyridine ring and the halogens.

Realizing efficient emission and triple-mode photoluminescence switching in air-stable tin(IV)-based metal halides via antimony doping and rational structural modulation

Recently,many lead-free metal halides with diverse structures and highly efficient emission have been reported.However,their poor stability and single-mode emission color severely limit their applications.Herein,three homologous Sb^(3+)-doped zero-dimensional(0D)air-stable Sn(IV)-based metal halides with different crystal structures were developed by inserting a single organic ligand into SnCl_(4)lattice,which brings different optical properties.Under photoexcitation,(C_(25)H_(22)P)SnC_(l5)@Sb⋅CH_(4O)(Sb^(3+)−1)does not emit light,(C_(25)H_(22)P)_(2)SnC_(l6)@Sb-α(Sb^(3+)−2α)shines bright yellow emission with a photoluminescence quantum yield(PLQY)of 92%,and(C_(25)H_(22)P)_(2)SnC_(l6)@Sb-β(Sb^(3+)−2β)exhibits intense red emission with a PLQY of 78%.The above three compounds show quite different optical properties should be due to their different crystal structures and the lattice distortions.Particularly,Sb^(3+)−1 can be successfully converted into Sb^(3+)−2αunder the treatment of C_(25)H_(22)PCl solution,accompanied by a transition from nonemission to efficient yellow emission,serving as a“turn-on”photoluminescence(PL)switching.Parallelly,a reversible structure conversion between Sb^(3+)−2αand Sb^(3+)−2βwas witnessed after dichloromethane or volatilization treatment,accompanied by yellow and red emission switching.Thereby,a triple-mode tunable PL switching of off-onI-onII can be constructed in Sb^(3+)-doped Sn(IV)-based compounds.Finally,we demonstrated the as-synthesized compounds in fluorescent anticounterfeiting,information encryption,and optical logic gates.

Ion migration in 3D metal halide perovskite field effect transistors

3D perovskite materials are advancing rapidly in the field of photovoltaics and light-emitting diodes,but the development in field effect transistors(FETs)is limited due to their intrinsic ion migration.Ion migration in perovskite FETs can screen the electric field of the gate and affect its modulation,as well as influence the charge carriers transport,leading to non-ideal device characteristics and lower device stability.Here,we provide a concise review that explains the mechanism of ion migration,summarizes the strategies for suppressing ion migration,and concludes with a discussion of the future prospects for 3D perovskite FETs.