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.

Impact of Structural Disorder on Excitonic Behaviors and Dynamics in 2D Organic-Inorganic Hybrid Perovskites

Two thin-film 2 D organic-inorganic hybrid perovskites,i.e.,2-phenylethylammonium lead iodide(PEPI)and 4-phenyl-1-butylammonium lead iodide(PBPI)were synthesized and investigated by steady-state absorption,temperature-dependent photoluminescence,and temperature-dependent ultrafast transient absorption spectroscopy.PBPI has a longer organic chain(via introducing extra ethyl groups)than PEPI,thus its inorganic skeleton can be distorted,bringing on structural disorder.The comparative analyses of spectral profiles and temporal dynamics revealed that the greater structural disorder in PBPI results in more defect states serving as trap states to promote exciton dynamics.In addition,the fine-structuring of excitonic resonances was unveiled by temperature-dependent ultrafast spectroscopy,suggesting its correlation with inorganic skeleton rather than organic chain.Moreover,the photoexcited coherent phonons were observed in both PEPI and PBPI,pointing to a subtle impact of structural disorder on the low-frequency Raman-active vibrations of inorganic skeleton.This work provides valuable insights into the optical properties,excitonic behaviors and dynamics,as well as coherent phonon effects in 2 D hybrid perovskites.

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.

Dehydration-triggered structural phase transition-associated ferroelectricity in a hybrid perovskite-type crystal

Since the appearance of Rochelle salt,ferroelectrics have received extensive attention from researchers due to they are playing an important role in sensors,memories,mechanical actuation,and so on.In recent years,with the rapid development of molecular ferroelectrics,high-performance molecular ferroelectrics have become effective complement to inorganic ferroelectrics.However,compared with inorganic ferroelectrics,the family of molecular ferroelectrics is relatively scarce,and exploring highperformance ferroelectric materials through new synthesis strategies has become the trend of molecular ferroelectrics.Here,we successfully transformed non-polar material 1(2-H_(2)PCA)_(2)(H_(2)O)CdCl_(6)(2-H_(2)PCA=2-picolylamine cation)into polar material 2(2-H_(2)PCA)2CdCl_(6)by single-crystal to single-crystal transformation(SCSCT).Meanwhile,2 exhibits clear ferroelectricity with a high-temperature Tc of 378 K,a Ps of 1.18μC/cm^(2)at 300 K.This work not only realizes the purpose of synthesizing ferroelectrics by forming polar structures by SCSCT,but also realizes the reversibility of SCSCT,which provides ideas for the construction and exploration of new molecular ferroelectrics.

X-ray-ultraviolet–visible-near-infrared photoresponsesrealized in a lead-free hybrid perovskite ferroelectricthrough light-induced ferro-pyro-phototronic effect

Due to the built-in electric field induced by spontaneous polarization in hybridperovskite (HP) ferroelectrics, the devices based on them exhibit excellent performancein self-powered photodetection. However, most of the self-poweredphotodetector are made of lead-based HP ferroelectrics and have a relativelynarrow photoresponse waveband. Although lead-free HPs solve the problem oflead toxicity, their optoelectronic performance is inferior to that of lead-basedHPs and photoresponse waveband is limited by its optical band gap, whichhinders their further application. To solve this problem, herein, a lead-free HPferroelectric (HDA)BiI5 (HDA is hexane-1,6-diammonium) with large spontaneouspolarization shows an enhanced photocurrent and achieves x-ray-ultraviolet–visible-near-infrared (x-ray-UV–Vis–NIR) photoresponse through theferro-pyro-phototronic (FPP) effect. The ferroelectric, pyroelectric, and photovoltaiccharacteristics coupled together in a single-phase (HDA)BiI5 ferroelectricis an effective way to improve the performance of the devices. What isparticularly attractive is that the FPP effect not only improves the optoelectronicperformance of (HDA)BiI_(5), but also achieves broadband photoresponsesbeyond its optical absorption range. Especially, the current boosting with anexceptional contrast of 1100% and 2400% under 520 and 637 nm, respectively,which is associated with FPP effect. Meanwhile, single crystal self-poweredphotodetector based on (HDA)BiI5 also exhibit significant FPP effects evenunder high-energy x-ray, which owns an outstanding sensitivity of 170.7 μCGy^(-1) cm^(-2) and a lower detection limit of 266 nGy s^(-1) at 0 V bias. Therefore, it is of great significance to study the coupling of multiple physical effects andimprove device performance based on lead-free HP ferroelectrics.

Ultrasensitive polarized-light photodetectors based on 2D hybrid perovskite ferroelectric crystals with a low detection limit

Polarized-light photodetectors are the indispensable elements for practical optical and optoelectronic device applications.Two-dimensional(2D)hybrid perovskite ferroelectrics,in which the coupling of spontaneous polarization(P_(s))and light favors the dissociation of photo-induced carriers,have taken a booming position within this portfolio.However,polarized-light photodetectors with a low detectionlimit remain unexplored in this 2D ferroelectric family.In this work,the high-quality individual crystals of a 2D perovskite ferroelectric,BA_(2)CsPb_(2)Br_(7)(1,where BA^(+)is n-butylammonium),were used to fabricate ultrasensitive polarized-light detectors.Its unique bilayered structural motif results in quite strong electric and optical anisotropy with a large absorption ratio of a_(c)/α_(a)≈3.2(λ=405 nm).Besides,the presence of ferroelectric Psalso endows high built-in electric field along the polar c-axis that favors photoelectric activities.Under an extremely low detectable limit of 40 n W/cm^(2),the detector of 1 exhibits a notable dichroism ratio(I_(ph)^(c)/I_(ph)^(a)≈1.5),a large responsivity of~39.5 m A/W and a specific detectivity of~1.2×10^(12)Jones.Moreover,crystal-based devices of 1 also exhibit a fast response speed(~300μs)and excellent anti-fatigue merits.This work highlights great potentials of hybrid perovskite ferroelectrics toward polarized-light photodetection.

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.

Research Advances of Ferroelectric Semiconductors of 2D Hybrid Perovskites toward Photoelectronic Applications

Ferroelectric materials, characterized by the switchable spontaneous polarization(Ps) through reversing the directions of external electric field, exhibit versatile physical attributes that have been extensively used for practical device applications. Two-dimensional(2D) organic-inorganic hybrid perovskites are recently emerging as a robust family of candidate ferroelectrics, termed ferroelectric semiconductors. In particular, the coexistence and/or coupling of ferroelectric polarization with their semiconducting properties enables new physical concepts, thus providing a potential platform for the development of new multifunctional optoelectronic devices. This review primarily describes the structural origin of symmetry breaking for generating ferroelectric orders in 2D hybrid perovskites, and then presents the combination of ferroelectric Ps with other semiconducting optoelectronic activities. Regarding the emergence of new photoelectric behaviors, the prospects for this 2D family of ferroelectric semiconductors are further discussed, along with their development tendency for the future photoelectronic device applications.

Unraveling the mechanochemical synthesis and luminescence in MnⅡ-based two-dimensional hybrid perovskite（C4H9NH3）2PbCl4

The mechanochemical route is a facile and fast way and has received much attention for developing versatile advanced functional materials. Herein, we reported a mechanochemical synthesis for incorporating divalent manganese ions (Mn^Ⅱ) into a two-dimensional (2D) hybrid perovskite (C4H9NH3)2PbCl4. The mild external stimuli originating from the grinding at room temperature enabled the formation of Mn^Ⅱ-doped 2D hybrid perovskites, and rapidly changed the luminescence characteristics. The photoluminescence analyses show that the violet and orange emissions are attributed to (C4H9NH3)2Pb1-xMnxCl4 band-edge emission and the T1→^6A1 transition of Mn^2+ resulting from an efficient energy transfer process, respectively. Site preference and distribution of the doped Mn^2+ cations on the locations of Pb^2+ were analyzed. The formation energy calculated by the density functional theory (DFT) indicates that the Mn^2+ ions can rapidly enter the crystal lattice due to the unique 2D crystal structure of the hybrid perovskite. Such a case of mechanochemical synthesis for the 2D hybrid perovskite motivates many novel emerging materials and the related applications.

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.

Chlorine‑Rich Substitution Enabled 2D3D Hybrid Perovskites for High Efficiency and Stability in Sn‑Based Fiber‑Shaped Perovskite Solar Cells

Despite the impressive power conversion efficiency(PCE)beyond 25.5%,perovskite solar cells,especially the Sn-based variants,are poorly stable under normal operating conditions compared with the market-dominant silicon solar cells that can last for over 25 years.2D3D hybrid perovskite materials are one of the best options to overcome the instability chal-lenge without compromising efficiency.Indeed,a record performance of 1 year was reported in Pb-based 2D3D planar per-ovskite devices.However,the reaction between 2 and 3D perovskite molecules requires high temperatures(-300°C)and increased reaction time(-24 h)to achieve high-quality 2D3D hybrid perovskites.Herein,we base on the ability of chlorine to displace iodine from its ionic compounds in solutions to utilize chloride ions as catalysts for speeding up the reaction between iodine-based 2D and 3D perovskite molecules.The approach reduces the reaction time to-20 min and the reaction temperature to-100°C with the formation of high-quality 2D3D hybrid perovskites,free from pure 2D traces.Integrating the synthesized 2D3D hybrid perovskite material with 50%chlorine doping in a fiber-shaped solar cell architecture yielded the highest reported PCE of 11.96%in Sn-based fiber-shaped perovskite solar cells.The unencapsulated and encapsulated fiber-shaped solar cells could maintain 75%and 95.5%of their original PCE,respectively,after 3 months under room light and relative humidity of 35–40%,revealing the champion stability in Sn-based perovskite solar devices.The solar yarn also demonstrated constant energy output under changing light incident angles(0–180°).

Mechanochemistry enables optical-electrical multifunctional response and tunability in two-dimensional hybrid perovskites

Two-dimensional(2D)organic-inorganic hybrid perovskites(OIHPs)have attracted phenomenal attention because of their superior optoelectronic performances.The combination of their structural tunability and material stability offers an unprecedented opportunity to engineer materials with unique functionalities.However,developing a rapid and effective design method for introducing luminescence into dielectric switch and realizing controllable regulation has been an enormous challenge.Thus far,materials with tunable optoelectronic multichannel response have not been successfully implemented.In this study,we successfully developed a facile and effective mechanochemical method for realizing the integration and regulation of luminescence and dielectric switch in 2D perovskites,which is unprecedented for the design of dielectric switching materials.The mild external mechanical stimuli enabled the formation of Mn ion-doped 2D hybrid perovskites(Cyclopropylammonium)2Pb1-xMnxBr4 with excellent dielectric switch and rapidly controllable luminescence of highly efficient blue light,white light,pink light,and orange light.This work will provide a new perspective on the rapid and effective design of multifunctional materials and can inspire the future development of low-cost and high-efficiency electronics.

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.

Tunable phase transition, band gap and SHG properties by halogen replacement of hybrid perovskites [(thiomorpholinium)PbX_(3), X = Cl,Br,I]

By the replacement of halogen anion,three new multifunctional organic-inorganic hybrid perovskites(thiomorpholinium)PbX_(3)(X=Cl,Br,I)were successfully synthesized and underwent reversible struc-tural transformation above room temperature,accompanied by the anomalous change of dielectric con-stant.With the adjustment of the halogen anion from Cl to I in the inorganic skeleton,the space group is transformed from centrosymmetric space group P2_(1)/c((thiomorpholinium)PbCl_(3))to chiral one P2_(1)2_(1)2_(1)((thiomorpholinium)PbBr3,(thiomorpholinium)PbI_(3))at room temperature.The ordered-disordered tran-sition of organic cations and the change of hydrogen bonds with the increase of temperature lead to above-room-temperature phase transitions.Ultraviolet absorption and second-harmonic generation(SHG)measurements confirmed that both the band gap and SHG activity of(thiomorpholinium)PbX_(3)(X=Cl,Br,I)crystals were tunable.The band gaps reveal a broadening trend with 3.532 e V,3.410 e V and 3.175 e V along the Cl→Br→I series.This work provides an effective molecular design for multifunctional organic-inorganic perovskites.

Employing halogen-halogen interaction to construct high-temperature hybrid perovskite phase transition materials

Organic-inorganic hybrid perovskites(OIHPs)materials with high phase transition temperature(T_(p))have been widely studied in the field of molecular switches,solar energy and electric power.At present,the OIHPs with high T_(p)are generally constructed through molecular design,which can be applied to a wide temperature range.Here,three one-dimensional(1D)OIHPs[R-Cl EQ]PbCl_(3)(T_(p)=442 K),[R-Cl EQ]PbBr_(3)(T_(p)=499 K)and[R-Cl EQ]PbI_(3)(T_(p)above m.p.)(R-Cl EQ=(R)-N-chloroethyl-3-quinuclidinol)with different T_(p)are obtained by regulating the halogen-halogen interaction and hydrogen bonding in the system.Especially in[R-Cl EQ]Pb X_(3)(X=Cl,Br and I)crystal system,all the halogen bonds tend to form at approximately 180°angles and the strength of halogen bonding is found to be increased from 1.59×10^(-3)Hartree to 2.35×10^(-3)Hartree with increased atom number from Cl to I.The synergistic effect of halogen bonding and hydrogen bonding provide a useful strategy for the design OIHPs phase transition materials with high T_(p).

A Simple Deposition Method for Self-Assembling Single Crystalline Hybrid Perovskite Nanostructures

A sequential deposition method is developed, where the hybrid organic-inorganic halide perovskite （CH3NH3Pb （I1-xBrx）3 ） is synthesized using precursor solutions containing CH3NH3I and PbBr2 with different mole ratios and reaction times. The perovskite achieved here is quite stable in the atmosphere for a relatively long time without noticeable degradation, and the perovskite nanowires are proved to be single crystalline structure, based on transmission electron microscopy.Furthermore, strong red photoluminescence from perovskite is observed in the wavelength range from 746nm to 770nm with the increase of the reaction time, on account of the exchanges between I- ions and Br- ions in the perovskite crystal. Lastly, the influences of concentration and reaction time of the precursor solutions are discussed, which are important for evolution of hybrid perovskite from nanocuboid to nanowire and nanosheet.

Highly Efficient White-Light Emission Induced by Carboxylic Acid Dimers in a Layered Hybrid Perovskite

Broadband white-light emission in metal halides has been intensely explored because of their facile solution processability,structural adjustability,and high color rendering index.However,the most reported quantum yields for white-light emission remain low despite great efforts.Herein,we report a metal-halide layered perovskite,(HOOC_(4)H_(9)NH_(3))_(2)PbBr_(4),showing the typical white-light emission with a highly enhan ced quantumyield up to 21.2% compared to previously reported noncarboxyl layered hybrid perovskites(0.5-9%).Notably,mechanistic studies reveal that the distinctive carboxylic acid dimers largely increase the structure rigidity and in consequence reduce the nonradiative recombination induced by stretching vibration.To the best of our knowledge,this strategy is important in hybrid perovskites,which is effective and propagable to acquire prominent photoluminescence.This work will shed light on the design of highly emissive white-light materials involving intense intermolecular interaction and promote their potential in displaying application.

Intrinsic Instability of the Hybrid Halide Perovskite Semiconductor CH3NH3PbI3

The organic-inorganic hybrid perovskite CH3NH3PbI3 has attracted significant interest for its high performance in converting solar light into electrical power with an efficiency exceeding 20%. Unfortunately, chemical stability is one major challenge in the development of CH3NH3PbI3 solar cells. It was commonly assumed that moisture or oxygen in the environment causes the poor stability of hybrid halide perovskites, however, here we show from the first-principles calculations that the room-temperature tetragonal phase of CH3NH3PbI3 is thermodynamically unstable with respect to the phase separation into CH3NH3I ＋ PbI2, i.e., the disproportionation is exothermic, independent of the humidity or oxygen in the atmosphere. When the structure is distorted to the low-temperature orthorhombie phase, the energetic cost of separation increases, but remains small. Contributions from vibrational and configurational entropy at room temperature have been considered, but the instability of CH3NH3PbI3 is unchanged. When I is replaced by Br or CI, Pb by Sn, or the organic cation CH3NH3 by inorganic Cs, the perovskites become more stable and do not phase-separate spontaneously. Our study highlights that the poor chemical stability is intrinsic to CH3NH3PbI3 and suggests that element-substitution may solve the chemical stability problem in hybrid halide perovskite solar cells.

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.