High-entropy catalysts featuring exceptional properties are,in no doubt,playing an increasingly significant role in aprotic lithium-oxygen batteries.Despite extensive effort devoted to tracing the origin of their unpa...High-entropy catalysts featuring exceptional properties are,in no doubt,playing an increasingly significant role in aprotic lithium-oxygen batteries.Despite extensive effort devoted to tracing the origin of their unparalleled performance,the relationships between multiple active sites and reaction intermediates are still obscure.Here,enlightened by theoretical screening,we tailor a high-entropy perovskite fluoride(KCoMnNiMgZnF_(3)-HEC)with various active sites to overcome the limitations of conventional catalysts in redox process.The entropy effect modulates the d-band center and d orbital occupancy of active centers,which optimizes the d–p hybridization between catalytic sites and key intermediates,enabling a moderate adsorption of LiO_(2)and thus reinforcing the reaction kinetics.As a result,the Li–O2 battery with KCoMnNiMgZnF_(3)-HEC catalyst delivers a minimal discharge/charge polarization and long-term cycle stability,preceding majority of traditional catalysts reported.These encouraging results provide inspiring insights into the electron manipulation and d orbital structure optimization for advanced electrocatalyst.展开更多
Two-dimensional Ruddlesden-Popper(2DRP)perovskites have attracted intense research interest for optoelectronic applications,due to their tunable optoelectronic properties and better environmental stability than their ...Two-dimensional Ruddlesden-Popper(2DRP)perovskites have attracted intense research interest for optoelectronic applications,due to their tunable optoelectronic properties and better environmental stability than their threedimensional counterparts.Furthermore,high-performance photodetectors based on single-crystal and polycrystalline thin-films 2DRP perovskites have shown great potential for practical application.However,the complex growth process of single-crystal membranes and uncontrollable phase distribution of polycrystalline films hinder the further development of 2DRP perovskites photodetectors.Herein,we report a series of high-performance photodetectors based on single-crystal-like phase-pure 2DRP perovskite films by designing a novel spacer source.Experimental and theoretical evidence demonstrates that phase-pure films substantially suppress defect states and ion migration.These highly sensitive photodetectors show I_(light)/I_(dark) ratio exceeding 3×10^(4),responsivities exceeding 16 A/W,and detectivities exceeding 3×10^(13) Jones,which are higher at least by 1 order than those of traditional mixed-phase thinfilms 2DRP devices(close to the reported single-crystal devices).More importantly,this strategy can significantly enhance the operational stability of optoelectronic devices and pave the way to large-area flexible productions.展开更多
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 t...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.展开更多
In the past decade, metal-halide perovskites have attracted increasing attention in optoelectronics, due to their superior optoelectronic properties.However, inherent instabilities of conventional three-dimensional(3D...In the past decade, metal-halide perovskites have attracted increasing attention in optoelectronics, due to their superior optoelectronic properties.However, inherent instabilities of conventional three-dimensional(3D)perovskites over moisture, heat, and light remain a severe challenge before the realization of commercial application of metal-halide perovskites.Interestingly, when the dimensions of metal-halide perovskites are reduced to two dimensions(2D), many of the novel properties will arise, such as enlarged bandgap, high photoluminescence quantum yield, and large exciton binding energy. As a result, 2D metal-halide perovskite-based optoelectronic devices display excellent performance, particularly as ambient stable solar cells with excellent power conversion efficiency(PCE), high-performance light-emitting diodes(LEDs) with sharp emission peak, and high-sensitive photodetectors. In this review, we first introduce the synthesis, structure,and physical properties of 2D perovskites. Then, the 2D perovskite-based solar cells, LEDs, and photodetectors are discussed. Finally, a brief overview of the opportunities and challenges for 2D perovskite optoelectronics is presented.展开更多
Metal halide perovskite solar cells have attracted considerable attention because of their high-power conversion efficiency and costeffective solution-processable fabrication;however,they exhibit poor structural stabi...Metal halide perovskite solar cells have attracted considerable attention because of their high-power conversion efficiency and costeffective solution-processable fabrication;however,they exhibit poor structural stability.Two-dimensional(2D)Ruddlesden-Popper(RP)perovskites could address the aforementioned issue and present excellent stability because of their hydrophobic organic spacer cations.However,the crystallographic orientation of 2D crystals should be perpendicular to the bottom substrates for charges to transport fast and be collected in solar cells.Moreover,controlling the crystallographic orientation of the 2D RP perovskites prepared by the solution process is difficult.Herein,we reviewed the progress of recent research regarding 2D RP perovskite films with the focus on the crystallographic orientation mechanism and orientation controlling methods.Furthermore,the current issues and prospects of 2D RP perovskites in the photovoltaic field were discussed to elucidate their development and application in the future.展开更多
Two-dimensional(2D) layered perovskites have emerged as potential alternates to traditional three-dimensional(3D)analogs to solve the stability issue of perovskite solar cells. In recent years, many efforts have been ...Two-dimensional(2D) layered perovskites have emerged as potential alternates to traditional three-dimensional(3D)analogs to solve the stability issue of perovskite solar cells. In recent years, many efforts have been spent on manipulating the interlayer organic spacing cation to improve the photovoltaic properties of Dion–Jacobson(DJ) perovskites. In this work, a serious of cycloalkane(CA) molecules were selected as the organic spacing cation in 2D DJ perovskites, which can widely manipulate the optoelectronic properties of the DJ perovskites. The underlying relationship between the CA interlayer molecules and the crystal structures, thermodynamic stabilities, and electronic properties of 58 DJ perovskites has been investigated by using automatic high-throughput workflow cooperated with density-functional(DFT) calculations.We found that these CA-based DJ perovskites are all thermodynamic stable. The sizes of the cycloalkane molecules can influence the degree of inorganic framework distortion and further tune the bandgaps with a wide range of 0.9–2.1 eV.These findings indicate the cycloalkane molecules are suitable as spacing cation in 2D DJ perovskites and provide a useful guidance in designing novel 2D DJ perovskites for optoelectronic applications.展开更多
Two-dimensional(2D) layered organic-inorganic hybrid perovskites have attracted much more attention for some applications than their three-dimensional(3D) perovskite counterparts due to their promising thermal and moi...Two-dimensional(2D) layered organic-inorganic hybrid perovskites have attracted much more attention for some applications than their three-dimensional(3D) perovskite counterparts due to their promising thermal and moisture stabilities.In particular, the 2D perovskite devices have shown better promise for optoelectronic applications.However, tunability of optoelectronic properties is often demanded to improve the device performance.Herein, we adopt a newly method to tune the electronic properties of 2D perovskite by introducing pseudohalide into the structure.In this work, we designed a pseudohalidesubstituted 2D perovskite by substituting the out-of-plane halide with pseudohalide and studied the electronic and excitonic properties of 2D-BA2MX4 and 2D-BA2MX2Ps2(M=Ge^(2+), Sn^(2+), and Pb^(2+);X=I;Ps=NCO, NCS, OCN, SCN, Se CN).We revealed the dependence of electronic properties including band gaps, composition of band edges, bonding characteristics, work functions, effective masses, and exciton binding energies on different pseudohalides substituted in 2D perovskite.Our results indicate that the substitution of pseudohalide in 2D perovskites is energetically favorable and can significantly affect the bonding characteristics as well as the CBM and VBM that often play major role in determining their performance in optoelectronic devices.It is expected that the pseudohalide substitution will be helpful in developing more advanced optoelectronic device based on 2D perovskite by optimizing band alignment and promoting charge extraction.展开更多
Metal halide perovskite nanocrystals(NCs)exhibit impressive optical and electronic properties,making them an important class of functional materials with promising applications in solar cells,light emitting diodes(LED...Metal halide perovskite nanocrystals(NCs)exhibit impressive optical and electronic properties,making them an important class of functional materials with promising applications in solar cells,light emitting diodes(LEDs),photodetectors,and photocatalysts.In addition to the widely studied 0-dimensional(0 D)metal halide perovskite NCs,such as nanocubes,low dimensional perovskites,such as 2 D all-inorganic perovskite(AIP)NCs,subsist with directionally relevant quantum confinement.These anisotropic NCs have the propensity to exhibit interesting optoelectronic properties that are exceedingly difficult to introduce into 0 D systems,yet as of late are largely unexplored.In this review,we discuss the recent synthetic progress of 2 D all-inorganic metal halide perovskite NCs with ABX3 structure.Specifically,we highlight the discrete composition control of the cations(A and B sites)and anions(X site)by dopant incorporation and alloying in 2 D metal halide perovskite NCs.We will also discuss more complex perovskite crystal structures,such as Ruddlesden-Popper double perovskites,and compare these materials to 0 D perovskite systems.Ultimately,our work culminates in the future interests and perspectives of this field with a focus on the wide applicability of 2 D systems and the large variance in structure capable with discrete compositional tuning.展开更多
The high efficiency and low production cost enable the halide perovskite solar cells as a promising technology for the next generation photovoltaics.Nevertheless,the relatively poor stability of the organic–inorganic...The high efficiency and low production cost enable the halide perovskite solar cells as a promising technology for the next generation photovoltaics.Nevertheless,the relatively poor stability of the organic–inorganic halide perovskites hinders their commercial applications.In the past few years,two-dimensional(2D)perovskite has emerged as a more stable alternative to the three-dimensional(3D)counterparts and attracted intense research interests.Although many attempts and advances have been made,it is still ambiguous that whether the 2D perovskites could bring closure to the stability issue.To answer this essential question,a systematic study of the nature of 2D halide perovskites is necessary.Here,we focus on the stability investigations of 2D perovskites from different perspectives,especially light,heat,ion migration and strain.Several remaining challenges and opening problems are also discussed.With further material and device engineering,we believe that the 2D perovskites would promote perovskite solar cells to a promising future.展开更多
Taking advantage of the excellent stability and photoelectric properties,two-dimensional(2D)organicinorganic halide perovskites have been widely researched and applied in optoelectronic and photovoltaic devices.The re...Taking advantage of the excellent stability and photoelectric properties,two-dimensional(2D)organicinorganic halide perovskites have been widely researched and applied in optoelectronic and photovoltaic devices.The remarkable properties are attributed to the unique quantum well structures by intercalating large organic ammonium space layers.In this review,we first summarize the crystal structures and growth methods of 2D halide perovskite crystals.Then,the distinctive optical characteristics and enhanced stability under high humidity,phase stability,suppressed ion migration,and high formation energy,are discussed in detail.Furthermore,we discuss orientation control in 2D perovskite films.The applications of 2D perovskites in solar cells,photo detectors and X-ray detectors are discussed in detail.Finally,we propose an outlook and perspectives to overcome the present challenges and broaden this new class of perovskite materials with other 2D nanomaterials.展开更多
Although two-dimensional perovskite devices are highly stable,they also lead to a number of challenges.For instance,the introduction of large organic amines makes crystallization process complicated,causing problems s...Although two-dimensional perovskite devices are highly stable,they also lead to a number of challenges.For instance,the introduction of large organic amines makes crystallization process complicated,causing problems such as generally small grain size and blocked charge transfer.In this work,imprint assisted with methylamine acetate were used to improve the morphology of the film,optimize the internal phase distribution,and enhance the charge transfer of the perovskite film.Specifically,imprint promoted the dispersion of spacer cations in the recrystallization process with the assistance of methylamine acetate,thus inhibited the formation of low-n phase induced by the aggregation of spacer cations and facilitated the formation of 3D-like phase.In this case,the corresponding quasi-2D perovskite solar cells delivered improved efficiency and exhibited superior stability.Our work provides an effective strategy to obtain uniform phase distribution for quasi-2D perovskite.展开更多
Perovskite solar cells(PSCs)have been developed over the past decade as the forefront of the state-of-theart photovoltaic technologies owing to their high efficiency and low cost,where nanostructured functional materi...Perovskite solar cells(PSCs)have been developed over the past decade as the forefront of the state-of-theart photovoltaic technologies owing to their high efficiency and low cost,where nanostructured functional materials play key roles in performance optimization.As a versatile class of two-dimensional(2D)materials,transition metal carbides/nitrides MXenes have gained enormous attentions in PSCs since 2018 due to their superior properties such as excellent metallic conductivity,abundant surface functional groups,tunable work functions,high optical transparency,and mechanical robustness.The explorations of MXenes are of significance in performance promotion and commercialization expansion of devices.As such,this review focuses on the diversified advantages of MXenes,comprehensively summarizing their applications and developments in PSCs as additives,electron/hole transporting layers,interfacial engineering layers,and electrodes in sequence and explaining the relevant mechanisms behind.Simultaneously,the problems emerged from the related studies are considered and the corresponding suggestions like opening up the type of MXenes usage,taking further insight of the modulation of surface termination groups on Fermi levels,understanding the effect on energy level structures of perovskite or other functional layers,and realizing commercialization,etc.are provided for the future in-depth explorations.This review is intended to provide overall perspective of the current status of MXenes and highlight the direction for the future advancements in MXenes design and processes towards efficient,stable,large-area,and low-cost PSCs.展开更多
Two-dimensional(2D)perovskites are known as one of the most promising luminescent materials due to their structural diversity and outstanding optoelectronic properties.Compared with 3D perovskites,2D perovskites have ...Two-dimensional(2D)perovskites are known as one of the most promising luminescent materials due to their structural diversity and outstanding optoelectronic properties.Compared with 3D perovskites,2D perovskites have natural quantum well structures,large exciton binding energy(Eb)and outstanding thermal stability,which shows great potential in the next-generation displays and solidstate lighting.In this review,the fundamental structure,photophysical and electrical properties of 2D perovskite films were illustrated systematically.Based on the advantages of 2D perovskites,such as special energy funnel process,ultrafast energy transfer,dense film and low efficiency roll-off,the remarkable achievements of 2D perovskite light-emitting diodes(PeLEDs)are summarized,and exciting challenges of 2D perovskite are also discussed.An outlook on further improving the efficiency of pure-blue PeLEDs,enhancing the operational stability of PeLEDs and reducing the toxicity to push this field forward was also provided.This review provides an overview of the recent developments of 2D perovskite materials and LED applications,and outlining challenges for achieving the high-performance devices.展开更多
Two extended hybrid conjugated systems based on a triphenylamine(TPA) core with two and three peripheral 1,4-dithiafulvenes(DTF) units coded WH-2 and WH-3 as hole-transporting materials(HTMs) applied in perovskite sol...Two extended hybrid conjugated systems based on a triphenylamine(TPA) core with two and three peripheral 1,4-dithiafulvenes(DTF) units coded WH-2 and WH-3 as hole-transporting materials(HTMs) applied in perovskite solar cells(PSCs) are synthesized by facile one-step reaction in good yield over 75%. DTF unit as electron donor can enhance the electron donating ability and the fusion of benzenic ring of TPA with DTF unit may lead to reinforced intermolecular interactions in the solid state. In addition,WH-2 and WH-3 exhibit a pyramid shape containing partial planarity and quasi three-dimensionality features, which is also conducive to enhancing the π-π stacking of molecules in the solid state. The above-mentioned structural characteristics make the two HTMs have good hole mobilities. As a result,WH-2 and WH-3 obtained the high intrinsic hole mobilities of 4.69 × 10^(-4)and 2.18 × 10^(-3)cm^(2)V^(-1)s^(-1)respectively. Finally, the power conversion efficiencies(PCEs) of PSCs with WH-2 and WH-3 as cost-effective dopant-free HTMs are 15.39% and 19.22% respectively and the PCE of PSC with WH-3 is on a par with that of PSC with Li-TFSI/t-BP doped Spiro-OMe TAD(19.67%).展开更多
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 combin...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.展开更多
Using time-dependent terahertz spectroscopy, we investigate the role of mixed-cation and mixed-halide on the ultrafast photoconductivity dynamics of two different methylammonium(MA) lead-iodide perovskite thin films. ...Using time-dependent terahertz spectroscopy, we investigate the role of mixed-cation and mixed-halide on the ultrafast photoconductivity dynamics of two different methylammonium(MA) lead-iodide perovskite thin films. It is found that the dynamics of conductivity after photoexcitation reveals significant correlation on the microscopy crystalline features of the samples. Our results show that mixed-cation and lead mixed-halide affect the charge carrier dynamics of the lead-iodide perovskites. In the(5-AVA)_(0.05)(MA)_(0.95) PbI_(2.95) Cl_(0.05)/spiro thin film, we observe a much weaker saturation trend of the initial photoconductivity with high excitation fluence, which is attributed to the combined effect of sequential charge carrier generation, transfer, cooling and polaron formation.展开更多
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 ...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.展开更多
The underwater X-ray imaging technology development is significant to subaqueous target reconnaissance/detection/identification, subfluvial archaeology,submerged resource exploration, etc. As the core of X-ray imaging...The underwater X-ray imaging technology development is significant to subaqueous target reconnaissance/detection/identification, subfluvial archaeology,submerged resource exploration, etc. As the core of X-ray imaging detection, the scintillator has been plagued by inherent moisture absorption and decomposition, and strict requirements for seamless packaging and waterproofing.Here, we designed a manganese-doped two-dimensional(2D) perovskite scintillator modified by hydrophobic longchain organic amine through the combination of component and doping engineering. The modified perovskites show high water repellency that can be used as an underwater X-ray scintillator. X-ray images of aquatic organisms or other objects with a high spatial resolution of10 lp·mm^(-1) at a big view field(32 mm × 32 mm) were obtained by scintillation screen. This hydrophobic perovskite scintillator based on molecular design is of great promise in underwater X-ray nondestructive testing technology development.展开更多
By combining temperature-dependent x-ray diffraction(XRD) with temperature-dependent Raman scattering, we have characterized the structural transitions and lattice dynamics of the hybrid organic–inorganic perovskite ...By combining temperature-dependent x-ray diffraction(XRD) with temperature-dependent Raman scattering, we have characterized the structural transitions and lattice dynamics of the hybrid organic–inorganic perovskite CH3NH3PbI3.The XRD measurements cover distinct phases between 15 K and 370 K and demonstrate a general positive thermal expansion.Clear anomalies are found around the transition temperatures.The temperature evolution of the lattice constants reveals that the transition at 160 K/330 K is of the first-/second-order type.Raman measurements uncover three strong lowfrequency modes, which can be ascribed to the vibration of the Pb/I atoms.The temperature evolution of the modes clearly catches these transitions at 160 K and 330 K, and confirms the transition types, which are exactly consistent with the XRD results.The present study may set an experimental basis to understand the high conversion efficiency in methylammonium lead iodide.展开更多
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 p...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.展开更多
基金P.G.acknowledges the financial support from the Youth Foundation of Shandong Natural Science Foundation(No.ZR2023OB230)National Natural Science Foundation(No.22309035)Double First-class Discipline Construction Fund Project of Harbin Institute of Technology at Weihai(No.2023SYLHY11).
文摘High-entropy catalysts featuring exceptional properties are,in no doubt,playing an increasingly significant role in aprotic lithium-oxygen batteries.Despite extensive effort devoted to tracing the origin of their unparalleled performance,the relationships between multiple active sites and reaction intermediates are still obscure.Here,enlightened by theoretical screening,we tailor a high-entropy perovskite fluoride(KCoMnNiMgZnF_(3)-HEC)with various active sites to overcome the limitations of conventional catalysts in redox process.The entropy effect modulates the d-band center and d orbital occupancy of active centers,which optimizes the d–p hybridization between catalytic sites and key intermediates,enabling a moderate adsorption of LiO_(2)and thus reinforcing the reaction kinetics.As a result,the Li–O2 battery with KCoMnNiMgZnF_(3)-HEC catalyst delivers a minimal discharge/charge polarization and long-term cycle stability,preceding majority of traditional catalysts reported.These encouraging results provide inspiring insights into the electron manipulation and d orbital structure optimization for advanced electrocatalyst.
基金Shenzhen-Hong Kong-Macao Science and Technology Innovation Project(Category C),Grant/Award Number:SGDX2020110309360100Fundo para o Desenvolvimento das Ciências e da Tecnologia,Grant/Award Numbers:FDCT-0044/2020/A1,0034/2021/APD+3 种基金Guangdong-Hong Kong-Macao Joint Laboratory of Optoelectronic and Magnetic Functional Materials,Grant/Award Number:2019B121205002Natural Science Foundation of Guangdong Province,Grant/Award Number:2019A1515012186National Natural Science Foundation of China,Grant/Award Numbers:61935017,62175268,62105292UM's research fund,Grant/Award Numbers:MYRG2018-00148-IAPME,MYRG2020-00151-IAPME。
文摘Two-dimensional Ruddlesden-Popper(2DRP)perovskites have attracted intense research interest for optoelectronic applications,due to their tunable optoelectronic properties and better environmental stability than their threedimensional counterparts.Furthermore,high-performance photodetectors based on single-crystal and polycrystalline thin-films 2DRP perovskites have shown great potential for practical application.However,the complex growth process of single-crystal membranes and uncontrollable phase distribution of polycrystalline films hinder the further development of 2DRP perovskites photodetectors.Herein,we report a series of high-performance photodetectors based on single-crystal-like phase-pure 2DRP perovskite films by designing a novel spacer source.Experimental and theoretical evidence demonstrates that phase-pure films substantially suppress defect states and ion migration.These highly sensitive photodetectors show I_(light)/I_(dark) ratio exceeding 3×10^(4),responsivities exceeding 16 A/W,and detectivities exceeding 3×10^(13) Jones,which are higher at least by 1 order than those of traditional mixed-phase thinfilms 2DRP devices(close to the reported single-crystal devices).More importantly,this strategy can significantly enhance the operational stability of optoelectronic devices and pave the way to large-area flexible productions.
基金Natural Science Foundation of Hebei Province(China),Grant/Award Numbers:B2020203013,B2021203016Science and Technology Project of Hebei Education Department(China),Grant/Award Number:QN2020137+3 种基金Cultivation Project for Basic Research Innovation of Yanshan University(China),Grant/Award Number:2021LGZD015Subsidy for Hebei Key Laboratory of Applied Chemistry after Operation Performance(China),Grant/Award Number:22567616HNatural Science Foundation of Heilongjiang Province(China),Grant/Award Number:LH2022B025Fundamental Research Funds for the Provincial Universities of Heilongjiang Province(China),Grant/Award Number:KYYWF10236190104。
文摘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.
基金financially supported by the National Key Research and Development Program of China (No. 2016YFB0700702)research start-up funding from Guangxi University of Science and Technology (No. 03190219)
文摘In the past decade, metal-halide perovskites have attracted increasing attention in optoelectronics, due to their superior optoelectronic properties.However, inherent instabilities of conventional three-dimensional(3D)perovskites over moisture, heat, and light remain a severe challenge before the realization of commercial application of metal-halide perovskites.Interestingly, when the dimensions of metal-halide perovskites are reduced to two dimensions(2D), many of the novel properties will arise, such as enlarged bandgap, high photoluminescence quantum yield, and large exciton binding energy. As a result, 2D metal-halide perovskite-based optoelectronic devices display excellent performance, particularly as ambient stable solar cells with excellent power conversion efficiency(PCE), high-performance light-emitting diodes(LEDs) with sharp emission peak, and high-sensitive photodetectors. In this review, we first introduce the synthesis, structure,and physical properties of 2D perovskites. Then, the 2D perovskite-based solar cells, LEDs, and photodetectors are discussed. Finally, a brief overview of the opportunities and challenges for 2D perovskite optoelectronics is presented.
基金This work was financially supported by the National Key Research and Development Program of China(No.2017YFE0119700)the National Natural Science Found-ation of China(Nos.51961135107,51774034,and 51772026).
文摘Metal halide perovskite solar cells have attracted considerable attention because of their high-power conversion efficiency and costeffective solution-processable fabrication;however,they exhibit poor structural stability.Two-dimensional(2D)Ruddlesden-Popper(RP)perovskites could address the aforementioned issue and present excellent stability because of their hydrophobic organic spacer cations.However,the crystallographic orientation of 2D crystals should be perpendicular to the bottom substrates for charges to transport fast and be collected in solar cells.Moreover,controlling the crystallographic orientation of the 2D RP perovskites prepared by the solution process is difficult.Herein,we reviewed the progress of recent research regarding 2D RP perovskite films with the focus on the crystallographic orientation mechanism and orientation controlling methods.Furthermore,the current issues and prospects of 2D RP perovskites in the photovoltaic field were discussed to elucidate their development and application in the future.
基金supported by the National Natural Science Foundation of China (Grant No. 62004080)the Postdoctoral Innovative Talents Supporting Program (Grant No. BX20190143)the China Postdoctoral Science Foundation (Grant No. 2020M670834)。
文摘Two-dimensional(2D) layered perovskites have emerged as potential alternates to traditional three-dimensional(3D)analogs to solve the stability issue of perovskite solar cells. In recent years, many efforts have been spent on manipulating the interlayer organic spacing cation to improve the photovoltaic properties of Dion–Jacobson(DJ) perovskites. In this work, a serious of cycloalkane(CA) molecules were selected as the organic spacing cation in 2D DJ perovskites, which can widely manipulate the optoelectronic properties of the DJ perovskites. The underlying relationship between the CA interlayer molecules and the crystal structures, thermodynamic stabilities, and electronic properties of 58 DJ perovskites has been investigated by using automatic high-throughput workflow cooperated with density-functional(DFT) calculations.We found that these CA-based DJ perovskites are all thermodynamic stable. The sizes of the cycloalkane molecules can influence the degree of inorganic framework distortion and further tune the bandgaps with a wide range of 0.9–2.1 eV.These findings indicate the cycloalkane molecules are suitable as spacing cation in 2D DJ perovskites and provide a useful guidance in designing novel 2D DJ perovskites for optoelectronic applications.
基金funded by the National Key Research and Development Program of China (2017YFA0204800/2016YFA0202403)the Fundamental Research Funds for the Central Universities (2018CBLZ006)+5 种基金the National Natural Science Foundation of China (61604091 and 61674098)the 111 Project (B14041)the Changjiang Scholar and Innovative Research Team (IRT_14R33)the Chinese National 1000 Talents Plan program (1110010341)the China Postdoctoral Science foundation (2018M633455)the Fundamental Research Funds for the Central Universities (GK201903055)
文摘Two-dimensional(2D) layered organic-inorganic hybrid perovskites have attracted much more attention for some applications than their three-dimensional(3D) perovskite counterparts due to their promising thermal and moisture stabilities.In particular, the 2D perovskite devices have shown better promise for optoelectronic applications.However, tunability of optoelectronic properties is often demanded to improve the device performance.Herein, we adopt a newly method to tune the electronic properties of 2D perovskite by introducing pseudohalide into the structure.In this work, we designed a pseudohalidesubstituted 2D perovskite by substituting the out-of-plane halide with pseudohalide and studied the electronic and excitonic properties of 2D-BA2MX4 and 2D-BA2MX2Ps2(M=Ge^(2+), Sn^(2+), and Pb^(2+);X=I;Ps=NCO, NCS, OCN, SCN, Se CN).We revealed the dependence of electronic properties including band gaps, composition of band edges, bonding characteristics, work functions, effective masses, and exciton binding energies on different pseudohalides substituted in 2D perovskite.Our results indicate that the substitution of pseudohalide in 2D perovskites is energetically favorable and can significantly affect the bonding characteristics as well as the CBM and VBM that often play major role in determining their performance in optoelectronic devices.It is expected that the pseudohalide substitution will be helpful in developing more advanced optoelectronic device based on 2D perovskite by optimizing band alignment and promoting charge extraction.
基金support from Syracuse University under the Collaboration for Unprecedented Success and Excellence(CUSE)Grant(SD-10-2020)ACS Petroleum Research Fund under Award Number 59861-DNI5NSF CAREER under Award Number CHE-1944978。
文摘Metal halide perovskite nanocrystals(NCs)exhibit impressive optical and electronic properties,making them an important class of functional materials with promising applications in solar cells,light emitting diodes(LEDs),photodetectors,and photocatalysts.In addition to the widely studied 0-dimensional(0 D)metal halide perovskite NCs,such as nanocubes,low dimensional perovskites,such as 2 D all-inorganic perovskite(AIP)NCs,subsist with directionally relevant quantum confinement.These anisotropic NCs have the propensity to exhibit interesting optoelectronic properties that are exceedingly difficult to introduce into 0 D systems,yet as of late are largely unexplored.In this review,we discuss the recent synthetic progress of 2 D all-inorganic metal halide perovskite NCs with ABX3 structure.Specifically,we highlight the discrete composition control of the cations(A and B sites)and anions(X site)by dopant incorporation and alloying in 2 D metal halide perovskite NCs.We will also discuss more complex perovskite crystal structures,such as Ruddlesden-Popper double perovskites,and compare these materials to 0 D perovskite systems.Ultimately,our work culminates in the future interests and perspectives of this field with a focus on the wide applicability of 2 D systems and the large variance in structure capable with discrete compositional tuning.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 61805263 and 62104234)。
文摘The high efficiency and low production cost enable the halide perovskite solar cells as a promising technology for the next generation photovoltaics.Nevertheless,the relatively poor stability of the organic–inorganic halide perovskites hinders their commercial applications.In the past few years,two-dimensional(2D)perovskite has emerged as a more stable alternative to the three-dimensional(3D)counterparts and attracted intense research interests.Although many attempts and advances have been made,it is still ambiguous that whether the 2D perovskites could bring closure to the stability issue.To answer this essential question,a systematic study of the nature of 2D halide perovskites is necessary.Here,we focus on the stability investigations of 2D perovskites from different perspectives,especially light,heat,ion migration and strain.Several remaining challenges and opening problems are also discussed.With further material and device engineering,we believe that the 2D perovskites would promote perovskite solar cells to a promising future.
基金funded by the National Key Research and Development Program of China(2017YFA0204800)the National Natural Science Foundation of China(91733301/61674098/51901190)+3 种基金the DNL Cooperation Fund CAS(DNL180311)the 111 Project(B14041)the Changjiang Scholars,Innovative Research Team(IRT_14R33)the China Postdoctoral Science Foundation(2020M673336)。
文摘Taking advantage of the excellent stability and photoelectric properties,two-dimensional(2D)organicinorganic halide perovskites have been widely researched and applied in optoelectronic and photovoltaic devices.The remarkable properties are attributed to the unique quantum well structures by intercalating large organic ammonium space layers.In this review,we first summarize the crystal structures and growth methods of 2D halide perovskite crystals.Then,the distinctive optical characteristics and enhanced stability under high humidity,phase stability,suppressed ion migration,and high formation energy,are discussed in detail.Furthermore,we discuss orientation control in 2D perovskite films.The applications of 2D perovskites in solar cells,photo detectors and X-ray detectors are discussed in detail.Finally,we propose an outlook and perspectives to overcome the present challenges and broaden this new class of perovskite materials with other 2D nanomaterials.
基金support from the National Natural Science Foundation of China(NSFC)(52163019,22005131,52173169 and U20A20128)support from the Natural Science Foundation of Jiangxi Province(20224ACB214006)。
文摘Although two-dimensional perovskite devices are highly stable,they also lead to a number of challenges.For instance,the introduction of large organic amines makes crystallization process complicated,causing problems such as generally small grain size and blocked charge transfer.In this work,imprint assisted with methylamine acetate were used to improve the morphology of the film,optimize the internal phase distribution,and enhance the charge transfer of the perovskite film.Specifically,imprint promoted the dispersion of spacer cations in the recrystallization process with the assistance of methylamine acetate,thus inhibited the formation of low-n phase induced by the aggregation of spacer cations and facilitated the formation of 3D-like phase.In this case,the corresponding quasi-2D perovskite solar cells delivered improved efficiency and exhibited superior stability.Our work provides an effective strategy to obtain uniform phase distribution for quasi-2D perovskite.
基金supported by the National Key R&D Program of China (2021YFA0716404)the National Natural Science Foundation of China (51872043,51732003,11974129)+1 种基金the“111”project (B13013)the Jilin Province Development and Reform Commission (2022C040-1)。
文摘Perovskite solar cells(PSCs)have been developed over the past decade as the forefront of the state-of-theart photovoltaic technologies owing to their high efficiency and low cost,where nanostructured functional materials play key roles in performance optimization.As a versatile class of two-dimensional(2D)materials,transition metal carbides/nitrides MXenes have gained enormous attentions in PSCs since 2018 due to their superior properties such as excellent metallic conductivity,abundant surface functional groups,tunable work functions,high optical transparency,and mechanical robustness.The explorations of MXenes are of significance in performance promotion and commercialization expansion of devices.As such,this review focuses on the diversified advantages of MXenes,comprehensively summarizing their applications and developments in PSCs as additives,electron/hole transporting layers,interfacial engineering layers,and electrodes in sequence and explaining the relevant mechanisms behind.Simultaneously,the problems emerged from the related studies are considered and the corresponding suggestions like opening up the type of MXenes usage,taking further insight of the modulation of surface termination groups on Fermi levels,understanding the effect on energy level structures of perovskite or other functional layers,and realizing commercialization,etc.are provided for the future in-depth explorations.This review is intended to provide overall perspective of the current status of MXenes and highlight the direction for the future advancements in MXenes design and processes towards efficient,stable,large-area,and low-cost PSCs.
基金This work was supported by the National Natural Science Foundation of China(Grant No.21661010)the Guangxi Natural Science Foundation(Grant No.2017GXNSFGA198005).
文摘Two-dimensional(2D)perovskites are known as one of the most promising luminescent materials due to their structural diversity and outstanding optoelectronic properties.Compared with 3D perovskites,2D perovskites have natural quantum well structures,large exciton binding energy(Eb)and outstanding thermal stability,which shows great potential in the next-generation displays and solidstate lighting.In this review,the fundamental structure,photophysical and electrical properties of 2D perovskite films were illustrated systematically.Based on the advantages of 2D perovskites,such as special energy funnel process,ultrafast energy transfer,dense film and low efficiency roll-off,the remarkable achievements of 2D perovskite light-emitting diodes(PeLEDs)are summarized,and exciting challenges of 2D perovskite are also discussed.An outlook on further improving the efficiency of pure-blue PeLEDs,enhancing the operational stability of PeLEDs and reducing the toxicity to push this field forward was also provided.This review provides an overview of the recent developments of 2D perovskite materials and LED applications,and outlining challenges for achieving the high-performance devices.
基金the Sichuan Science and Technology Program (2019YJ0162)the National Natural Science Foundation of China (21402023, 51773027)the National Key R@D Program of China (2017YFB0702802) for financial support。
文摘Two extended hybrid conjugated systems based on a triphenylamine(TPA) core with two and three peripheral 1,4-dithiafulvenes(DTF) units coded WH-2 and WH-3 as hole-transporting materials(HTMs) applied in perovskite solar cells(PSCs) are synthesized by facile one-step reaction in good yield over 75%. DTF unit as electron donor can enhance the electron donating ability and the fusion of benzenic ring of TPA with DTF unit may lead to reinforced intermolecular interactions in the solid state. In addition,WH-2 and WH-3 exhibit a pyramid shape containing partial planarity and quasi three-dimensionality features, which is also conducive to enhancing the π-π stacking of molecules in the solid state. The above-mentioned structural characteristics make the two HTMs have good hole mobilities. As a result,WH-2 and WH-3 obtained the high intrinsic hole mobilities of 4.69 × 10^(-4)and 2.18 × 10^(-3)cm^(2)V^(-1)s^(-1)respectively. Finally, the power conversion efficiencies(PCEs) of PSCs with WH-2 and WH-3 as cost-effective dopant-free HTMs are 15.39% and 19.22% respectively and the PCE of PSC with WH-3 is on a par with that of PSC with Li-TFSI/t-BP doped Spiro-OMe TAD(19.67%).
基金support from MOE Tier 2 grants (MOE2017T2-1-056, MOE2016-T2-2-020 and R-143-000-A75-114)
文摘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.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11604202,11674213,61735010 and 51603119the Young Eastern Scholar under Grant Nos QD2015020 and QD2016027+3 种基金the Shanghai Rising-Star Program under Grant No18QA1401700the ‘Chen Guang’ Project under Grant Nos 16CG45 and 16CG46the Shanghai Municipal Education Commissionthe Shanghai Education Development Foundation
文摘Using time-dependent terahertz spectroscopy, we investigate the role of mixed-cation and mixed-halide on the ultrafast photoconductivity dynamics of two different methylammonium(MA) lead-iodide perovskite thin films. It is found that the dynamics of conductivity after photoexcitation reveals significant correlation on the microscopy crystalline features of the samples. Our results show that mixed-cation and lead mixed-halide affect the charge carrier dynamics of the lead-iodide perovskites. In the(5-AVA)_(0.05)(MA)_(0.95) PbI_(2.95) Cl_(0.05)/spiro thin film, we observe a much weaker saturation trend of the initial photoconductivity with high excitation fluence, which is attributed to the combined effect of sequential charge carrier generation, transfer, cooling and polaron formation.
基金supported by the Special Funds for Major State Basic ResearchNational Natural Science Foundation of China(NSFC)+6 种基金Project of Shanghai Municipality(16520721600)supported by NSFC under Grant No 91233121Shanghai Rising-Star Program(14QA1401500)CC of ECNUsupported by the Royal Society,the ERC and EPSRC under Grant Nos EP/M009580/1 and EP/K016288/1supported by the National Key Research and Development Program of China under Grant No 2016YFB0700700the National Natural Science Foundation of China under Grant Nos 51672023,11634003 and U1530401
文摘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.
基金financially supported by the National Natural Science Foundation of China (NSFC)(Nos.22175007 and 21975007)the National Natural Science Foundation for Outstanding Youth Foundation+1 种基金the Fundamental Research Funds for the Central Universities (No.YWF-22-K-101)the National Program for Support of Top-notch Young Professionals and the 111project (Nos.B14009)。
文摘The underwater X-ray imaging technology development is significant to subaqueous target reconnaissance/detection/identification, subfluvial archaeology,submerged resource exploration, etc. As the core of X-ray imaging detection, the scintillator has been plagued by inherent moisture absorption and decomposition, and strict requirements for seamless packaging and waterproofing.Here, we designed a manganese-doped two-dimensional(2D) perovskite scintillator modified by hydrophobic longchain organic amine through the combination of component and doping engineering. The modified perovskites show high water repellency that can be used as an underwater X-ray scintillator. X-ray images of aquatic organisms or other objects with a high spatial resolution of10 lp·mm^(-1) at a big view field(32 mm × 32 mm) were obtained by scintillation screen. This hydrophobic perovskite scintillator based on molecular design is of great promise in underwater X-ray nondestructive testing technology development.
基金Project supported by the National Natural Science Foundation of China(Grant No.11774419)the Ministry of Science and Technology of China(Grant Nos.2016YFA0300504 and 2017YFA0302904)
文摘By combining temperature-dependent x-ray diffraction(XRD) with temperature-dependent Raman scattering, we have characterized the structural transitions and lattice dynamics of the hybrid organic–inorganic perovskite CH3NH3PbI3.The XRD measurements cover distinct phases between 15 K and 370 K and demonstrate a general positive thermal expansion.Clear anomalies are found around the transition temperatures.The temperature evolution of the lattice constants reveals that the transition at 160 K/330 K is of the first-/second-order type.Raman measurements uncover three strong lowfrequency modes, which can be ascribed to the vibration of the Pb/I atoms.The temperature evolution of the modes clearly catches these transitions at 160 K and 330 K, and confirms the transition types, which are exactly consistent with the XRD results.The present study may set an experimental basis to understand the high conversion efficiency in methylammonium lead iodide.
基金This work was supported by the 973 Program and China National Key Basic Research Program(2016YFA0301100,2016YFA0302000,and 2018YFA0306201)National Science Foundation of China(11774063 and 11727811)+2 种基金Science and Technology Commission of Shanghai Municipality(19XD1434600,2019SHZDZX01 and 19DZ2253000)Air Force Office of Scientific Research(AFOSR)under the grant number FA 9550-15-1-0064,AOARD(FA2386-15-1-4104)National Science Foundation(NSF-1911659).
文摘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.