Organic-inorganic halide perovskites for memristors

Organic-inorganic halides perovskites(OHPs)have drawn the attention of many researchers owing to their astonishing and unique optoelectronic properties.They have been extensively used for photovoltaic applications,achieving higher than 26%power conversion efficiency to date.These materials have potential to be deployed for many other applications beyond photovoltaics like photodetectors,sensors,light-emitting diodes(LEDs),and resistors.To address the looming challenge of Moore’s law and the Von Neumann bottleneck,many new technologies regarding the computation of architectures and storage of information are being extensively researched.Since the discovery of the memristor as a fourth component of the circuit,many materials are explored for memristive applications.Lately,researchers have advanced the exploration of OHPs for memristive applications.These materials possess promising memristive properties and various kinds of halide perovskites have been used for different applications that are not only limited to data storage but expand towards artificial synapses,and neuromorphic computing.Herein we summarize the recent advancements of OHPs for memristive applications,their unique electronic properties,fabrication of materials,and current progress in this field with some future perspectives and outlooks.

Colorless to black switching with high contrast ratio via the electrochemical process of a hybrid organic-inorganic perovskite

Colorless‐to‐black switching has attracted widespread attention for smart windows and multifunctional displays because they are more useful to control solar energy.However,it still remains a challenge owing to the tremendous difficulties in the design of completely reverse absorptions in transmissive and colored states.Herein,we report on an electrochemical device that can switch between colorless and black by using the electrochemical process of hybrid organic–inorganic perovskite MAPbBr_(3),which shows a high integrated contrast ratio of up to 73%from 400 to 800 nm.The perovskite solution can be used as the active layer to assemble the device,showing superior transmittance over the entire visible region in neutral states.By applying an appropriate voltage,the device undergoes reversible switching between colorless and black,which is attributed to the formation of lead and Br_(2)in the redox reaction induced by the electron transfer process in MAPbBr_(3).In addition,the contrast ratio can be modulated over the entire visible region by changing the concentration and the applied voltage.These results contribute toward gaining an insightful understanding of the electrochemical process of perovskites and greatly promoting the development of switchable devices.

Ferroelectric Properties and Applications of Hybrid Organic-Inorganic Perovskites

Hybrid organic-inorganic perovskites （e.g. CH;NH;PbI;） have attracted tremendous attention due to their promise for achieving next-generation cost-effective and high performance optoelectronic devices.These hybrid organic-inorganic perovskites possess excellent optical and electronic properties, including strong light absorption, high carrier abilities, optimized charge diffusion lengths, and reduced charge recombination etc., leading to their widespread applications in advanced solar energy technologies （e.g.high efficiency perovskite solar cells）. However, there is still a lack of investigations regarding fundamental properties such as ferroelectricity in these perovskites.As conventional ferroelectric ceramics are prepared at high temperature and have no mechanically flexibility,low-temperature proceed and flexible perovskite ferroelectrics have become promising candidates and should be exploited for future flexible ferroelectric applications. Here, ferroelectric properties in hybrid organic-inorganic perovskites and several state-of-the-art perovskite ferroelectrics are reviewed. Novel ferroelectric applications of hybrid organic-inorganic perovskites are discussed as well, providing guideline for realizing future high performance and flexible ferroelectric devices.

Giant magneto field effect in up-conversion amplified spontaneous emission via spatially extended states in organic-inorganic hybrid perovskites

Up-conversion lasing actions are normally difficult to realize in light-emitting materials due to small multi-photon absorp-tion cross section and fast dephasing of excited states during multi-photon excitation.This paper reports an easily ac-cessible up-conversion amplified spontaneous emission(ASE)in organic-inorganic hybrid perovskites(MAPbBr3)films by optically exciting broad gap states with sub-bandgap laser excitation.The broad absorption was optimized by adjust-ing the grain sizes in the MAPbBr3 films.At low sub-bandgap pumping intensities,directly exciting the gap states leads to 2-photon,3-photon,and 4-photon up-conversion spontaneous emission,revealing a large optical cross section of multi-photon excitation occurring in such hybrid perovskite films.At moderate pumping intensity(1.19 mJ/cm2)of 700 nm laser excitation,a significant spectral narrowing phenomenon was observed with the full width at half maximum(FWHM)de-creasing from 18 nm to 4 nm at the peak wavelength of 550 nm,simultaneously with a nonlinear increase on spectral peak intensity,showing an up-conversion ASE realized at low threshold pumping fluence.More interestingly,the up-con-version ASE demonstrated a giant magnetic field effect,leading to a magneto-ASE reaching 120%.In contrast,the up-conversion photoluminescence(PL)showed a negligible magnetic field effect(<1%).This observation provides an evid-ence to indicate that the light-emitting states responsible for up-conversion ASE are essentially formed as spatially exten-ded states.The angular dependent spectrum results further verify the existence of spatially extended states which are polarized to develop coherent in-phase interaction.Clearly,using broad gap states with spatially extended light-emitting states presents a new approach to develop up-conversion ASE in organic-inorganic hybrid perovskites.

Recent advances in atomic imaging of organic-inorganic hybrid perovskites

Three-dimensional organic-inorganic hybrid perovskites(OHPs)hold a great prospect for photovoltaic applications due to their outstanding electronic and optical properties.These fascinating properties of OHPs in combination with their scalable and low-cost production make OHPs promising candidates for next-generation optoelectronic devices.The ability to obtain atomistic insights into physicochemical properties of this class of materials is crucial for the future development of this field.Recent advances in various scanning probe microscopy techniques have demonstrated their extraordinary capability in real-space imaging and spectroscopic measurements of the structural and electronic properties of OHPs with atomic-precision.Moreover,these techniques can be combined with light illumination to probe the structural and optoelectronic properties of OHPs close to the real device operation conditions.The primary focus of this review is to summarize the recent progress in atomic-scale studies of OHPs towards a deep understanding of the phenomena discovered in OHPs and OHP-based optoelectronic devices.

Advanced Strategies of Passivating Perovskite Defects for High-Performance Solar Cells

Organic–inorganic halide perovskite(OIHP)solar cells have garnered great attention in the last decade since they continuously approach the Shockley–Queisser Limit.Compared with conventional organic and inorganic semiconductors,OIHPs possess the high tolerance on defects due to the dominated intrinsically shallow-level carrier-trapping centers.However,the existence of defects still causes the ion migration,produces the hysteresis effect,and accelerates the film degradation,eventually suppressing the device efficiency and stability.In this Review Article,we summarize recent impressive advance on passivating OIHP defects and discuss the future horizon of exploiting high-efficiency and long-stability OIHP solar cells in terms of defect managements.

The structural, electronic, and optical properties of organic–inorganic mixed halide perovskites CH_3NH_3Pb(I_(1-y)X_y)_3(X = Cl, Br)

Methylammmonium lead iodide perovskites（CH3NH3PbI3） have received wide attention due to their superior optoelectronic properties. We performed first-principles calculations to investigate the structural, electronic, and optical properties of mixed halide perovskites CH3NH3Pb（I（1-y）Xy）3（X = Cl, Br; y = 0, 0.33, 0.67）. Our results reveal the reduction of the lattice constants and dielectric constants and enhancement of band gaps with increasing doping concentration of Cl-/Br-at I-. Electronic structure calculations indicate that the valance band maximum（VBM） is mainly governed by the halide p orbitals and Pb 6 s orbitals, Pb 6 p orbitals contribute the conduction band minimum（CBM） and doping does not change the direct semiconductor material. The organic cation [CH3NH3]~＋does not take part in the formation of the band and only one electron donates to the considered materials. The increasing trends of the band gap with Cl content from y = 0（0.793 eV） to y = 0.33（0.953 eV） then to y = 0.67（1.126 eV）. The optical absorption of the considered structures in the visible spectrum range is decreased but after doping the stability of the material is improving.

Charge Localization Induced by Reorientation of FA Cations Greatly Suppresses Nonradiative Electron-Hole Recombination in FAPbI3 Perovskites:a Time-Domain Ab Initio Study

Recent experiments report the rotation of FA(FA=HC[NH2]2+)cations significantly influence the excited-state lifetime of FAPbI3.However,the underlying mechanism remains unclear.Using ab initio nonadiabatic(NA)molecular dynamics combined with time-domain density functional simulations,we have demonstrated that reorientation of partial FA cations significantly inhibits nonradiative electron-hole recombination with respect to the pristine FAPbI3 due to the decreased NA coupling by localizing electron and hole in different positions and the suppressed atomic motions.Slow nuclear motions simultaneously increase the decoherence time,which is overcome by the reduced NA coupling,extending electron-hole recombination time scales to several nanoseconds and being about 3.9 times longer than that in pristine FAPbI3,which occurs within sub-nanosecond and agrees with experiment.Our study established the mechanism for the experimentally reported prolonged excited-state lifetime,providing a rational strategy for design of high performance of perovskite solar cells and optoelectronic devices.

Crystal engineering regulation achieving inverse temperature symmetry breaking ferroelasticity in a cationic displacement type hybrid perovskite system

Ferroelastic hybrid perovskite materials have been revealed the significance in the applications of switches,sensors,actuators,etc.However,it remains a challenge to design high-temperature ferroelastic to meet the requirements for the practical applications.Herein,we reported an one-dimensional organicinorganic hybrid perovskites(OIHP)(3-methylpyrazolium)CdCl_(3)(3-MBCC),which possesses a mmmF2/m ferroelastic phase transition at 263 K.Moreover,utilizing crystal engineering,we replace-CH_(3) with-NH_(2) and-H,which increases the intermolecular force between organic cations and inorganic frameworks.The phase transition temperature of(3-aminopyrazolium)CdCl_(3)(3-ABCC),and(pyrazolium)CdCl_(3)(BCC)increased by 73 K and 10 K,respectively.Particularly,BCC undergoes an unconventional inverse temperature symmetry breaking(ISTB)ferroelastic phase transition around 273 K.Differently,it transforms from a high symmetry low-temperature paraelastic phase(point group 2/m)to a low symmetry high-temperature ferroelastic phase(point group ī)originating from the rare mechanism of displacement of organic cations phase transition.It means that crystal BCC retains in ferroelastic phase above 273 K until melting point(446 K).Furthermore,characteristic ferroelastic domain patterns on crystal BCC are confirmed with polarized optical microscopy.Our study enriches the molecular mechanism of ferroelastics in the family of organic-inorganic hybrids and opens up a new avenue for exploring high-temperature ferroic materials.

Organic-inorganic bismuth （lll）-based material： A lead- free, air-stable and solution-processable light-absorber beyond organolead perovskites

Methylammonium bismuth （III） iodide single crystals and films have been developed and investigated. We have further presented the first demonstration of using this organic-inorganic bismuth-based material to replace lead/tin-based perovskite materials in solution-processable solar cells. The organic-inorganic bismuth-based material has advantages of non-toxicity, ambient stability, and low-temperature solution-processability, which provides a promising solution to address the toxicity and stability challenges in organolead- and organotin-based perovskite solar cells. We also demonstrated that trivalent metal cation-based organic-inorganic hybrid materials can exhibit photovoltaic effect, which may inspire more research work on developing and applying organic-inorganic hybrid materials beyond divalent metal cations （Pb （II） and Sn （II）） for solar energy applications.

Memristors with organic-inorganic halide perovskites

Organic-inorganic halide perovskites(OHPs)have been intensively studied for application in solar cells with high conversion efficiency exceeding 22%.The unique electrical and optical properties of OHPs have led to their use in optoelectronic device applications beyond photovoltaics,such as light-emitting diodes,photodetectors,transistors.New information storage technologies and computing architectures are being researched extensively with the aim of addressing the growing challenge of approaching end of Moore's law and von Neumann bottleneck.As the fourth basic circuit element,memristor is a leading candidate with powerful capabilities in information storage and neuromorphic computing applications.Recently,OHPs have received growing attention as promising materials for memristors.In particular,their mixed ionic-electronic conduction ability paired with light sensitivity provide OHPs with the opportunity to display novel functions such as optical-erase memory,optogenetics-inspired synaptic functions,and lightaccelerated learning capability.This review covers recent advances in OHP-based memristors development including memristive mechanism and analytical models,universal memristive characteristics for memory and neuromorphic computing applications,and novel multi-functionalization.Challenges and future prospects of OHP-based memristors are also discussed.

Recent advances on organic-inorganic hybrid perovskite photodetectors with fast response

In the last decade,optoelectronic devices based on organic-inorganic hybrid perovskite(OIHP)materials,which have unique advantages of direct bandgap,large absorption coefficient,low density of defects,long charge carrier lifetime,diffusion length,and solution processability,have traveled with traditional inorganic semiconductor devices.The state-of-the-art OIHP photodetectors have contributed a comparable performance with Si and III-V compound semiconductor based photodetectors.Large amount of efforts have been focused on improving sensitivity,broadening detection spectra,enlarging linear dynamic range.However,few reports emphasized the important parameter of response speed.In this review,we summarize the progress and applications of OIHP photodetectors with fast response.Based on photovoltaic and photoconductive-type OIHP photodetectors,the working principle and key factors on determining response speed are systematically mentioned.Then,the research progress of response speed,which is composed of resistance-capacitance(RC)time constant and charge carrier transit time is discussed in detail.Subsequently,considering the intrinsic flexibility of perovskite materials,we briefly discuss the flexible photodetectors.Finally,an outlook and potential rules for designing fast-response OIHP photodetectors are further proposed.

Progress in organic-inorganic hybrid halide perovskite single crystal:growth techniques and applications

As a new generation of solution-processable optoelectronic materials, organic-inorganic hybrid halide perovskites have attracted a great deal of interest due to their high and balanced carrier mobility, long carrier dif- fusion length and large light absorption coefficient. These materials have demonstrated wide applications in solar cell, light-emitting diode, laser, photodetector, catalysis and other fields. Comparing with their polycrystalline film counter- part, perovskite single crystals have low trap density and no grain boundaries and thus are anticipated to possess much better optoelectronic performances. Herein, we review the key progress in the development of organic-inorganic halide perovskite single crystals. Particularly, the crystal growth techniques and applications of these advanced materials are highlighted.

Transmission electron microscopy of organic-inorganic hybrid perovskites:myths and truths

Organic-inorganic hybrid perovskites(OIHPs)have attracted extensive research interest as a promising candidate for efficient and inexpensive solar cells.Transmission electron microscopy(TEM)characterizations that can benefit the fundamental understanding and the degradation mechanism are widely used for these materials.However,their sensitivity to the electron beam illumination and hence structural instabilities usually prevent us from obtaining the intrinsic information or even lead to significant artifacts.Here,we systematically investigate the structural degradation behaviors under different experimental factors to reveal the optimized conditions for TEM characterizations of OIHPs by using low-dose electron diffraction and imaging techniques.We find that a low temperature(-180°C)does not slow down the beam damage but instead induces a rapid amorphization for OIHPs.Moreover,a less severe damage is observed at a higher accelerating voltage.The beam-sensitivity is found to be facetdependent that a(100)exposed CH3NH3PbI3(MAPbI3)surface is more stable than a(001)surface.With these guidance,we successfully acquire the atomic structure of pristine MAPbI3 and identify the characterization window that is very narrow.These findings are helpful to guide future electron microscopy characterizations of these beam-sensitive materials,which are also useful for finding strategies to improve the stability and performance of the perovskite solar cells.

Organic-inorganic hybrid Sn-based perovskite photodetectors with high external quantum efficiencies and wide spectral responses from 300 to 1000 nm

Organic-inorganic hybrid perovskites are ideal materials for photodetection owing to their high charge carrier mobility, long charge carrier diffusion length, low dark current density and sharp absorption edge. However, a relatively small band gap(1.6 e V) limits their photonharvesting efficiency in the near-infrared region. In the present work, we demonstrate a hybrid methylamine iodide and Pb-Sn binary perovskite as the light absorption layer in photodetectors. Experimentally, the wavelength of photoresponse onset for the photodetectors can be extended to as great as 1,000 nm when the Sn content of the hybrid perovskite is increased to 30 mol%. In addition, the photodetectors exhibit a photoresponsivity of 0.39 A W^-1, a specific detectivity of 7×10^12 Jones, a fast photoresponse with rise and decay time constants and an external quantum efficiency greater than 50% in the wavelength range of350–900 nm, with a maximum value of about 80% at 550 nm.

Partially reversible photochromic behavior of organic-inorganic perovskites with copper(II) chloride

We report that the ultraviolet （UV） light induced photochromic behavior of layered organic-inorganic perovskite material of （C4H9NH3）2CuCl4, changed from yellow to brown after irradiation with UV light （10 mW/cm^2） and partially recovered through storage in the dark. （C4H9NH3）2CuCl4 exhibited two distinct absorption bands centered at 286 nm （band Ⅰ） and 384 nm （band Ⅱ）, which were attributed to the photo-induced exciton formed in 2D inorganic layers sandwiched by organic layers. The blue shift of band Ⅰ from 287 to 269 nm as well as the decrease of the intensity of band Ⅰ and band Ⅱ could be found when samples were irradiated under UV light for different length of time. The simultaneous weakening of the intensity of the N-H...Cl hydrogen bond as well as the vibration of the long Cu-Cl bond in the distorted CuCl6^4- octahedron could be detected from the Fourier transform infrared （FTIR） spectra, which resulted the change of charge distribution of the dissymmetric Cl-Cu...Cl bond and the resulting photochromic behavior.

Research progress on hybrid organic-inorganic perovskites for photo-applications

Hybrid organic-inorganic perovskite materials have attracted significant atte ntion of most re searchers in recently years,which is ascribed to the superior photoelectric properties,such as the suitable band gaps for harvesting sunlight,and exhibit high optical adsorption,high charge-carrier lifetimes and long diffusion lengths.The photodetectors,light-emitting diodes,solar cells and photocatalysts represent the remarkable applications for the hybrid organic-inorganic perovskite materials.Herein,we review the recent progress of hybrid organic-inorganic perovskite-based photodetectors,light-emitting diodes,solar cells and photocatalysts.The challenges and outlook for the hybrid organic-inorganic perovskitebased photodetectors,light-emitting diodes,solar cells and photocatalysts are considered.

Unconventional solution-phase epitaxial growth of organic-inorganic hybrid perovskite nanocrystals on metal sulfide nanosheets

Epitaxial heterostructures based on organicinorganic hybrid perovskites and two-dimensional materials hold great promises in optoelectronics, but they have been prepared only via solid-state methods that restricted their practical applications. Herein, we report cubic-phased MAPbBr3(MA=CH3NH3+) nanocrystals were epitaxially deposited on trigonal/hexagonal-phased MoS2 nanosheets in solution by facilely tuning the solvation conditions. In spite of the mismatched lattice symmetry between the square MAPbBr3(001) overlayer and the hexagonal MoS2(001) substrate, two different aligning directions with lattice mismatch of as small as 1% were observed based on the domainmatching epitaxy. This was realized most likely due to the flexible nature and absence of surface dangling bonds of MoS2 nanosheets. The formation of the epitaxial interface affords an effective energy transfer from MAPbBr3 to MoS2, and as a result, paper-based photodetectors facilely fabricated from these solution-dispersible heterostructures showed better performance compared to those based on MoS2 or MAPbBr3 alone. In addition to the improved energy transfer and light adsorption, the use of MoS2 nanosheets provided flexible and continuous substrates to connect the otherwise discrete MAPbBr3 nanocrystals and achieved the better film forming ability. Our work suggests that the scalable preparation of heterostructures based on organic-inorganic hybrid perovskites and 2D materials via solution-phase epitaxy may bring about more opportunities for expanding their optoelectronic applications.

The chemistry and physics of organic-inorganic hybrid perovskite quantum wells

Organic-inorganic hybrid two dimensional(2D)lead halide perovskites(LHPs)are tunable quantum wells that exhibit a set of intriguing structural and physical properties including soft and dynamic lattices,organic-inorganic epitaxial heterointerfaces,quantum and dielectric confinements,strong light-matter interactions,and large spin-orbit coupling,which enable promising perspectives for optoelectronics,ferroelectrics,and spintronics.While the properties of 2D LHPs bear some resemblance of the3D LHPs,they are often drastically altered due to the reduced dimensionality and the complex interactions between organic and inorganic components.In this review,we discuss the influences of the reduced dimensionality and the organic-inorganic interplays on the structural stability and distortion of the inorganic lattices,inversion symmetry of the crystal structure,electronic band structures,excitonic physics,and carrier-phonon interactions in 2D LHPs.An emphasis is placed on the relationships between the crystal structures and photophysical properties.Future perspectives on the opportunities of hybrid quantum wells are provided.

Targeted Management of Perovskite Film by Co(Ⅱ)Sulfophenyl Porphyrin for Efficient and Stable Solar Cells

In the lead halide perovskite solar cells(PSCs),the redox reaction of I-and Pb^(2+) ions in perovskite materials under the fabrication and operation processes causes the formation of defects to destroy the cell efficiency and long-term stability.Herein,we have employed a Co(Ⅱ)sulfophenyl porphyrin(CoTPPS)to modify the perovskite film.The sulfonic group could coordinate with Pb2+to efficiently passivate the uncoordinated Pb^(2+).Additionally,Co^(2+) ions in CoTPPS could react with I^(2) generated under the thermal and light stress to yield the Co^(3+) and I^(-),thus achieving the regeneration of I^(-) in perovskite film.Therefore,the CoTPPS could realize the targeted management of the imperfections in perovskite film.As a result,the modified PSCs reveal the remarkably enhanced cell perfor-mance.More importantly,the CoTPPS modified device retains 75%of its initial efficiency value storing at 85℃for 2000 h and about 70%of its efficiency when being continuously illuminated at a simulated sunlight for 1200 h.This strategy tackles the chemical reaction and inhibits the defect generation,thus improving the operational stability and efficiency of PSCs.