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.

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.

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.

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.

Space-confined growth of metal halide perovskite crystal films

Metal halide perovskites,as a new generation of optoelectronic materials,have attracted a great deal of interest due to their remarkable intrinsic properties.Due to the excellent optoelectronic properties,the perovskite crystals are widely used in lasers,photodetectors,X-ray detectors and solar cells.Considering the device performance and fabrication requirements,proper thickness of the crystal is required to avoid carrier loss and simultaneously ensure sufficient light absorption,which can realize the full potential of its excellent carrier transport property.Thus,the fabrication of perovskite crystal in a thin film with an adjustable thickness is highly desirable.The space-confined method has been demonstrated to be an effective way of preparing perovskite with controlled thickness.In this method,the thickness of perovskite can be regulated flexibly in a geometric confined space.Moreover,the size,quality and architecture of perovskite crystal films are also major concerns for practical photoelectric devices,which can also be optimized by the space-confined method owing to its good adaptability towards various modified strategies.In a word,the space-confined method is not only a simple and conventional way to adjust the thickness of perovskite crystal films,but also provides a platform to optimize their size,quality and architecture through applying appropriate strategies to the confined space.Herein,we review the space-confined growth of perovskite crystal films.Particularly,various modified strategies based on the space-confined method applied to the optimization of thickness,size,quality and architecture are highlighted.Then the stability investigating and component regulating of perovskite crystal films would be also mentioned.Furthermore,the correlation between the perovskite thickness and the device performance is discussed.Finally,several key challenges and proposed solutions of perovskite thin films based on the space-confined method are discussed.

Metal Halide Perovskite for next-generation optoelectronics:progresses and prospects

Metal halide perovskites(MHPs),emerging as innovative and promising semiconductor materials with prominent optoelectronic properties,has been pioneering a new era of light management(ranging from emission,absorption,modulation,to transmission)for next-generation optoelectronic technology.Notably,the exploration of fundamental characteristics of MHPs and their devices is the main research theme during the past decade,while in the next decade,it will be primarily critical to promote their implantation in the next-generation optoelectronics.In this review,we first retrospect the historical research milestones of MHPs and their optoelectronic devices.Thereafter,we introduce the origin of the unique optoelectronic features of MHPs,based on which we highlight the tunability of these features via regulating the phase,dimensionality,composition,and geometry of MHPs.Then,we show that owing to the convenient property control of MHPs,various optoelectronic devices with target performance can be designed.At last,we emphasize on the revolutionary applications of MHPs-based devices on the existing optoelectronic systems.This review demonstrates the key role of MHPs played in the development of modern optoelectronics,which is expected to inspire the novel research directions of MHPs and promote the widespread applications of MHPs in the next-generation optoelectronics.

Chemical regulation of metal halide perovskite nanomaterials for efficient light-emitting diodes

Metal halide perovskite nanomaterials emerged as attractive emitting materials for light-emitting diodes(LEDs) devices due to their high photoluminescence quantum yield(PLQY), narrow bandwidth, high charge-carrier mobility, bandgap tunability, and facile synthesis. In the past few years, it has been witnessed an unprecedented advance in the field of metal halide perovskite nanomaterials based LEDs(Pe LEDs) with a rapid external quantum efficiency(EQE) increase from 0.1% to 14.36%. From the viewpoint of material chemistry, the chemical regulation of metal halide perovskite nanomaterials made a great contribution to the efficiency improvement of Pe LEDs. In this review, we categorize the strategies of chemical regulation as A-site cation engineering, B-site ion doping, X-site ion exchange, dimensional confinement, ligand exchange, surface passivation and interface optimization of transport layers for improving the EQEs of Pe LEDs. We also show the potentials of chemical regulation strategies to enhance the stability of Pe LEDs. Finally, we present insight toward future research directions and an outlook to further improve EQEs and stabilities of Pe LEDs aiming to practical applications.

Recent advances and perspective on the synthesis and photocatalytic application of metal halide perovskite nanocrystals

Metal halide perovskite nanocrystals have attracted great attention of researchers due to their unique optoelectronic properties such as high photoluminescence quantum yield (PLQY), narrow full width at half-maximum (FWHM), long exciton diffusion length and high carrier mobility, which have been widely used in diverse fields including solar cells, photodetectors, light-emitting diodes, and lasers. Very recently, metal halide perovskites have emerged as a new class of materials in photocatalysis due to their promising photocatalytic performance. In this review, we summarize the recent advances on synthesis, modification and functionalization, with a specific focus on the photocatalytic application of metal halide perovskite nanocrystals. Finally, a brief outlook is proposed to point out the challenges in this emerging area. The goal of this view is to introduce the photocatalytic application of the metal halide perovskites and motivate researchers from different fields to explore more potentials in catalysis.

Low-dimensional metal halide perovskites and related optoelectronic applications

Low-dimensional materials have pivotal significance in modern photonic,electronic,and optoelectronic areas due to their unique properties of the scale effect.Metal halide perovskites have revived in the optoelectronic fields recently,drawing intensive attention in photovoltaic devices,light-emitting diodes,lasers,photodetectors,and so on.Compared to their three-dimensional counterparts,the role of low-dimensional perovskites is becoming crucial,requiring a comprehensive understanding and exploration unceasingly.In this review,we examine low-dimensional perovskite of different forms and clarify various synthesis methods with morphological and dimensional control.Additionally,we also summarize potential optoelectronic applications based on their advantageous optical/electrical properties and enhanced mechanical integrity and stability.Finally,we propose a future perspective and possible developing directions in the exploration of novel perovskite-derived materials,new physics,and promising applications.

Recent developments in flexible photodetectors based on metal halide perovskite

Flexible photodetectors(FPDs)have been receiving increasing attention in recent years because of their potential applications in electronic eyes,bioinspired sensing,smart textiles,and wearable devices.Moreover,metal halide perovskites(MHPs)with outstanding optical and electrical properties,good mechanical flexibility,lowcost and low-temperature solution-processed fabrication have become promising candidates as light harvesting materials in FPDs.Herein,we comprehensively review the developments of FPDs based on MHPs reported recently.This review firstly provides an introduction with respect to the performance parameters and device configurations of perovskite photodetectors,followed by the specific requirements of FPDs including substrate and electrode materials.Next,chemical compositions,structures and preparation methods of MHPs are presented.Then,the FPDs on the basis of single-component perovskite and hybrid structure perovskite are discussed,subsequently,self-powered flexible perovskite photodetectors were presented.In the end,conclusions and challenges are put forward in the field of FPDs based on perovskites.

Structural modulation and assembling of metal halide perovskites for solar cells and light-emitting diodes

Metal halide perovskites possess appealing optoelectronic properties and have been widely applied for solar energy harvesting and light emitting.Although perovskite solar cells(PeSCs)and perovskite light-emitting diodes(PeLEDs)have been developed rapidly in recent years,there are still no universal rules for the selection of perovskites to achieve high-performance optoelectronic devices.In this review,the working mechanisms of PeSCs and PeLEDs are first demonstrated with the discussion on the factors which determine the device performance.We then examine the optoelectronic properties of perovskites with structures modulated from 3D,2D,1D to 0D,and analyze the corresponding structure-property relationships in terms of photo-electric and electric-photo conversion processes.Based on the unique optoelectronic properties of structurally modulated perovskites,we put forward the concept of structural assembling engineering that integrate the merits of different types of perovskites within one matrix and elaborate their excellent properties for applications of both PeSCs and PeLEDs.Finally,we discuss the potential challenges and provide our perspectives on the structural assembling engineering of perovskites for future optoelectronic applications.

Self-assembly Behavior of Metal Halide Perovskite Nanocrystals

The self-assembled metal halide perovskite(MHP)nanocrystal superlattices have attracted many researchers due to their exceptional optical and electrical properties.The bottom-up self-assembly can be facile to generate ideal and periodic structures.The superlattices’stability can be improved and the photoluminescence lifetime can be extended by an order of magnitude.However,due to lack of a comprehensive and systematic understanding of the internal interactions on self-assembled processes now,superlattices cannot be obtained controllably and play full use of their advantages.Therefore,gaining a deep insight of interaction forces about self-assemblies is the premise of designing and controlling the degree of self-assembly so as to prepare ideal materials.In this review,the definitions and functions of driving forces including van der Waals forces,electrostatic interactions and hydrogen bonds are discussed.Subsequently,we aim to explore the dominant factors affecting the driving forces,which can make a difference in the process of MHP self-assembly.Based on current researches,we emphasize on three aspects−the core of nanocrystals,surface ligands and solvents−to clarify their critical roles in controlling the driving forces.Finally,the outlooks and perspectives of how to facilitate the MHP self-assembly and their application on blue light emitting diodes are discussed.

High performance solid-state thermoelectric energy conversion via inorganic metal halide perovskites under tailored mechanical deformation

Solid-state thermoelectric energy conversion devices attract broad research interests because of their great promises in waste heat recycling,space power generation,deep water power generation,and temperature control,but the search for essential thermoelectric materials with high performance still remains a great challenge.As an emerging low cost,solution-processed thermoelectric material,inorganic metal halide perovskites CsPb(I_(1–x)Br_(x))_(3) under mechanical deformation is systematically investigated using the first-principle calculations and the Boltzmann transport theory.It is demonstrated that halogen mixing and mechanical deformation are efficient methods to tailor electronic structures and charge transport properties in CsPb(I_(1–x)Br_(x))_(3) synergistically.Halogen mixing leads to band splitting and anisotropic charge transport due to symmetry-breakinginduced intrinsic strains.Such band splitting reconstructs the band edge and can decrease the charge carrier effective mass,leading to excellent charge transport properties.Mechanical deformation can further push the orbital energies apart from each other in a more controllable manner,surpassing the impact from intrinsic strains.Both anisotropic charge transport properties and ZT values are sensitive to the direction and magnitude of strain,showing a wide range of variation from 20%to 400%(with a ZT value of up to 1.85)compared with unstrained cases.The power generation efficiency of the thermoelectric device can reach as high as approximately 12%using mixed halide perovskites under tailored mechanical deformation when the heat-source is at 500 K and the cold side is maintained at 300 K,surpassing the performance of many existing bulk thermoelectric materials.

Recent advances on two-dimensional metal halide perovskite x-ray detectors

In recent years,two-dimensional metal halide perovskites(MHPs)have attracted increased attention for radiation detection and imaging.Their detection efficiencies are almost comparable to three-dimensional(3D)perovskites.Meanwhile,they demonstrate superior stability to 3D perovskites.The pursuit of high-quality,phase-pure and lead-free two-dimensional MHP materials and large-area fabrication capability for x-ray detectors are among the research hotspots.In this review,we first give a brief introduction of the crystallographic structure,optoelectronic characteristics and preparation methods of high-quality two-dimensional perovskites.In addition,we overview the general working principles of direct and indirect x-ray detection processes and the corresponding performance metrics from the perspective of detection and imaging.Furthermore,we provide a comprehensive discussion on the recent advances in 2D perovskite x-ray detectors and imaging devices.Finally,we pinpoint several major obstacles of 2D x-ray detectors that should be overcome in the near future.

Metal halide perovskites quantum dots:Synthesis and modification strategies for solar CO_(2)conversion

In the past few years,environmental and energy challenges arising from extensive burning of fossil fuels and CO_(2)emission have become the increasingly severe issue.One effective solution to address these problems is the reduction of CO_(2)into valuable solar fuels such as CO,CH_(4),and HCO_(2)H through the semiconductor-based pho-tocatalysis technology.Metal halide perovskites quantum dots(MHPs QDs)represent a new generation of pho-tosensitizers that possess excellent photoelectric properties and have been attracting enormous attention in the field of photocatalytic CO_(2)reduction.This review provides a concise introduction on different types and prep-aration methods of MHPs QDs and discusses the specific applications especially photocatalytic CO_(2)reduction mechanism of MHPs QDs.Furthermore,future opportunities and challenges for constructing high-performance MHPs QDs-based photocatalysts are further elucidated.We anticipate that our review could provide enriched information on the photocatalytic application of MHPs QDs toward solar-to-fuel conversion.

Room-Temperature Persistent Luminescence in Metal Halide Perovskite Nanocrystals for Solar-Driven CO_(2)Bioreduction

The rapid crystal growth of metal halide perovskite(MHP)nanocrystals inevitably leads to the generation of abundant crystal defects in the lattice.Here,defects-mediated long-lived charges and accompanying room-temperature persistent luminescence are demonstrated to be a general phenomenon in MHP nanocrystals.Density functional theory calculations suggest that the collaboration of Schottky and point defects enables upward cascading depletion for electron transfer in MHP nanocrystals,leading to the generation of long-lived photoexcited charges with lifetimes over 30 min.The excellent optical properties including the presence of long-lived charges,high charge separation efficiency,and broad absorption in the visible region make MHPs ideal candidates for both photocatalysis and photobiocatalysis.The MHPs were further integrated with enzymes to construct a light-driven biosynthetic system for the selective production of fine chemicals from CO_(2)with solar energy.The biosynthetic system can produce formate with a quantum yield of 3.24%,much higher than that of plants(∼0.2-1.6%).These findings will benefit the understanding of the optoelectronic properties of MHPs and further provide opportunities for the development of biosynthetic systems for solar-to-chemical synthesis.

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.

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.

Flexible perovskite light-emitting diodes for display applications and beyond

The flexible perovskite light-emitting diodes(FPeLEDs),which can be expediently integrated to portable and wearable devices,have shown great potential in various applications.The FPeLEDs inherit the unique optical properties of metal halide perovskites,such as tunable bandgap,narrow emission linewidth,high photoluminescence quantum yield,and particularly,the soft nature of lattice.At present,substantial efforts have been made for FPeLEDs with encouraging external quantum efficiency(EQE)of 24.5%.Herein,we summarize the recent progress in FPeLEDs,focusing on the strategy developed for perovskite emission layers and flexible electrodes to facilitate the optoelectrical and mechanical performance.In addition,we present relevant applications of FPeLEDs in displays and beyond.Finally,perspective toward the future development and applications of flexible PeLEDs are also discussed.

Self-assembly of perovskite nanocrystals:From driving forces to applications

Self-assembly of metal halide perovskite nanocrystals(NCs)into superlattices can exhibit unique collective properties,which have significant application values in the display,detector,and solar cell field.This review discusses the driving forces behind the self-assembly process of perovskite NCs,and the commonly used self-assembly methods and different self-assembly structures are detailed.Subsequently,we summarize the collective optoelectronic properties and application areas of perovskite superlattice structures.Finally,we conclude with an outlook on the potential issues and future challenges in developing perovskite NCs.