Search

Passivation is one of the most promising concepts to heal defects created at the surface and grain boundaries of polycrystalline perovskite thin films, which significantly deteriorate the photovoltaic performance and stability of corresponding devices. Here, 1,10-phenanthroline, known as a bidentate chelating ligand, is implemented between the methylammonium lead iodide (MAPbI3) film and the hole-transport layer for both passivating the lead-based surface defects (undercoordinated lead ions) and converting the excess/unreacted lead iodide (PbI2) buried at interfaces, which is problematic for the long-term stability, into "neutralized"and beneficial species (PbI2(1,10-phen)x, x = 1, 2) for efficient hole transfer at the modified interface. The defect healing ability of 1,10-phenanthroline is verified with a set of complementary techniques including photoluminescence (steady-state and time-resolved), space-charge-limited current (SCLC) measurements, light intensity dependent JV measurements, and Fourier-transform photocurrent spectroscopy (FTPS). In addition to these analytical methods, we employ advanced X-ray scattering techniques, nano-Fourier transform infrared (nano-FTIR) spectroscopy, and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) to further analyze the structure and chemical composition at the perovskite surface after treatment at nanoscale spatial resolution. On the basis of our experimental results, we conclude that 1,10-phenanthroline treatment induces the formation of different morphologies with distinct chemical compositions on the surface of the perovskite film such that surface defects are effectively passivated, and excess/unreacted PbI2 is converted into beneficial complex species at the modified interface. As a result, an improved power conversion efficiency (20.16%) and significantly more stable unencapsulated perovskite solar cells are obtained with the 1,10-phenanthroline treatment compared to the MAPbI3 reference device (18.03%).

With fascinating photophysical properties and a strong potential to utilize solar energy, metal halide perovskites (MHPs) have become a prominent feature within photocatalysis research. However, the effectiveness of single MHP photocatalysts is relatively poor. The introduction of a second component to form a heterojunction represents a well-established route to accelerate carrier migration and boost reaction rates, thus increasing the photoactivity. Recently, there have been several scientific advances related to the design of MHP-based heterojunction photocatalysts, including Schottky, type II, and Z-scheme heterojunctions. In this Review, we systematically discuss and critically appraise recent developments in MHP-based heterojunction photocatalysis. In addition, the techniques for identifying the type of active heterojunctions are evaluated and we conclude by briefly outlining the ongoing challenges and future directions for promising photocatalysts based on MHP heterojunctions. ispartof: ANGEWANDTE CHEMIE-INTERNATIONAL EDITION vol:61 issue:24 ispartof: location:Germany status: published

Passivation of perovskite films by ionic liquids (ILs)improves the performance (efficiency and stability) of perovskitesolar cells (PSCs). However, the role of ILs in the passivation ofperovskitefilms is not fully understood. Here, we report thereactions of commonly used ILs with the components ofperovskites. The reaction of ILs with perovskite precursors (PbI2and methylammonium iodide or formamidinium iodide) in a 1:1:1molar ratio affords one-dimensional (1D) salts composed of the ILcation interspersed along infinite 1D polymeric [PbI3]-nchains. If the IL is applied in excess, the resulting crystal is composed of sixcations surrounding a discrete [Pb3I12]6-cluster. All the isolated salts were unambiguously characterized by single-crystal X-ray diffraction analysis, which also reveals extensive hydrogen-bonding interactions

The migration of mobile ions has long been considered a source of performance degradation in devices based on halide perovskites, but details regarding the mechanisms and extent of this problem remain scarce. Here we report the finding that differences in electrical potential across the plane of the substrate, induced by electrode edges such as the boundaries of the metallization or the transparent conductive oxide, can play a primary role in behaviour and degradation across a wide range of stability tests. In particular, we observe clear signatures of lateral ion migration in solar cells made using both double and triple cation mixed-halide perovskites, with effects induced by reverse-bias stress, illuminated MPP-tracking, and even as a result of time spent in storage. In their mildest form these effects manifest as patterns of modulated photoluminescence intensity around device boundaries that propagate into surrounding regions as a function of applied bias and time. We show that ionic drift-diffusion models provide a convincing match to these patterns, including their voltage dependence. In the context of MPP-tracking, we observe a severe form of material degradation in our solar cells whose spatial distribution and voltage dependence match models of lateral ion migration with high accuracy. We thereby obtain evidence of an ionically-mediated degradation mode which proceeds at a high rate near device boundaries, but is nonetheless also operative throughout the active area. This connection between "bulk" and "boundary" degradation has multiple implications for both the design of perovskite solar cell and LED devices, as well as for the understanding of their characteristic behaviour in long-term stability testing.

Engineering two-/three-dimensional (2D/3D) perovskite solar cells is nowadays a popular strategy for efficient and stable devices. However, the exact function of the 2D/3D interface in controlling the long-term device behavior is still obscure. Here, we reveal a dynamical structural mutation of the 2D/3D interface: the small cations in the 3D cage move towards the 2D layer, which acts as an ion scavenger. If structurally stable, the 2D layer physically blocks the ion movement at the interface boosting the device stability. Otherwise, the 2D layer embeds them, dynamically self-transforming into a quasi-2D structure. The judicious choice of the 2D constituent is decisive in controlling the 2D/3D kinetics and improving the device lifetime, opening a new avenue for perovskite interface design.

In this study, we discuss the underlying mechanism of the current-voltage hysteresis in a hybrid lead-halide perovskite solar cell. We have developed a method based on Kelvin probe force microscopy that enables mapping charge redistribution in an operating device upon a voltage- or light pulse with sub-millisecond resolution. We observed the formation of a localized interfacial charge at the anode interface, which screened most of the electric field in the cell. The formation of this charge happened within 10 ms after applying a forward voltage to the device. After switching off the forward voltage, however, these interfacial charges were stable for over 500 ms and created a reverse electric field in the cell. This reverse electric field directly explains higher photocurrents during reverse bias scans by electric field-assisted charge carrier extraction. Although we found evidence for the presence of mobile ions in the perovskite layer during the voltage pulse, the corresponding ionic field contributed only less than 10% to the screening. Our observation of a time-dependent ion concentration in the perovskite layer suggests that iodide ions adsorbed and became neutralized at the hole-selective spiro-OMeTAD electrode. We thereby show that instead of the slow migration of mobile ions, the formation and the release of interfacial charges is the dominating factor for current-voltage hysteresis.

© The Royal Society of Chemistry 2018. As an important category of perovskite materials, two-dimensional (2D) perovskites are attracting increasing research attention these days. Their possibility of combining high performance and stability for perovskite based optoelectronic devices has triggered a new wave of research. This review mainly focuses on the application of 2D perovskite materials for solar cells. We start with a brief introduction of 2D perovskite structures and their unique properties. The recent progress in 2D perovskite solar cells is summarized in three aspects according to the existing forms of the perovskite materials in the devices. In the end, a short outlook with our opinion is given to indicate the possible development trend for this kind of perovskite material. ispartof: JOURNAL OF MATERIALS CHEMISTRY A vol:6 issue:24 pages:11063-11077 status: published

Improving the long-term stability of perovskite solar cells is critical to the deployment of this technology. Despite the great emphasis laid on stability-related investigations, publications lack consistency in experimental procedures and parameters reported. It is therefore challenging to reproduce and compare results and thereby develop a deep understanding of degradation mechanisms. Here, we report a consensus between researchers in the field on procedures for testing perovskite solar cell stability, which are based on the International Summit on Organic Photovoltaic Stability (ISOS) protocols. We propose additional procedures to account for properties specific to PSCs such as ion redistribution under electric fields, reversible degradation and to distinguish ambient-induced degradation from other stress factors. These protocols are not intended as a replacement of the existing qualification standards, but rather they aim to unify the stability assessment and to understand failure modes. Finally, we identify key procedural information which we suggest reporting in publications to improve reproducibility and enable large data set analysis., This article is based upon work from COST Action StableNextSol MP1307 supported by COST (European Cooperation in Science and Technology). M.V.K., E.A.K., V.B. and A.O. thank the financial support of the United States – Israel Binational Science Foundation (grant no. 2015757). E.A.K., A.A. and I.V.-F. acknowledge partial support from the SNaPSHoTs project in the framework of the German-Israeli bilateral R&D cooperation in the field of applied nanotechnology. M.S.L. thanks the financial support of National Science Foundation (ECCS, award #1610833). S.C., M.Manceau and M.Matheron thank the financial support of European Union’s Horizon 2020 research and innovation programme under grant agreement no 763989 (APOLO project). F.D.R. and T.M.W. would like to acknowledge the support from the Engineering and Physical Sciences Research Council (EPSRC) through the SPECIFIC Innovation and Knowledge Centre (EP/N020863/1) and express their gratitude to the Welsh Government for their support of the Ser Solar programme. P.A.T. acknowledges financial support from the Russian Science Foundation (project No. 19-73-30020). J.K. acknowledges the support by the Solar Photovoltaic Academic Research Consortium II (SPARC II) project, gratefully funded by WEFO. M.K.N. acknowledges financial support from Innosuisse project 25590.1 PFNM-NM, Solaronix, Aubonne, Switzerland. C.-Q.M. would like to acknowledge The Bureau of International Cooperation of Chinese Academy of Sciences for the support of ISOS11 and the Ministry of Science and Technology of China for the financial support (no. 2016YFA0200700). N.G.P. acknowledges financial support from the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science, ICT Future Planning (MSIP) of Korea under contracts NRF-2012M3A6A7054861 and NRF-2014M3A6A7060583 (Global Frontier R&D Program on Center for Multiscale Energy System). CSIRO’s contribution to this work was conducted with funding support from the Australian Renewable Energy Agency (ARENA) through its Advancing Renewables Program. A.F.N gratefully acknowledges support from FAPESP (Grant 2017/11986-5) and Shell and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation. Y.-L.L. and Q.B. acknowledge support from the National Science Foundation Division of Civil, Mechanical and Manufacturing Innovation under award no. 1824674. S.D.S. acknowledges the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (HYPERION, grant agreement no. 756962), and the Royal Society and Tata Group (UF150033). The work at the National Renewable Energy Laboratory was supported by the US Department of Energy (DOE) under contract DE-AC36-08GO28308 with Alliance for Sustainable Energy LLC, the manager and operator of the National Renewable Energy Laboratory. The authors (J.J.B, J.M.L., M.O.R, K.Z.) acknowledge support from the ‘De-risking halide perovskite solar cells’ program of the National Center for Photovoltaics, funded by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Solar Energy Technology Office. The views expressed in the article do not necessarily represent the views of the DOE or the US Government. H.J.S. acknowledges the support of EPSRC UK, Engineering and Physical Sciences Research Council. V.T. and M.Madsen acknowledge ‘Villum Foundation’ for funding of the project CompliantPV, under project no. 13365. M.Madsen acknowledges Danmarks Frie Forskningsfond, DFF FTP for funding of the project React-PV, no. 8022-00389B. M.G. and S.M.Z. thank the King Abdulaziz City for Science and technology (KACST) for financial support. S.V. acknowledges TKI-UE/Ministry of Economic Affairs for financial support of the TKI-UE toeslag project POP-ART (no. 1621103). RC thanks the grants for Development of New Faculty Staff, Ratchadaphiseksomphot Endowment Fund. A.D.C. gratefully acknowledges funding from the European Union’s Horizon 2020 Research and Innovation Program (grant agreement no. 785219-GrapheneCore2 and no. 764047-ESPResSo). M.L.C. and H.X. acknowledges the support from Spanish MINECO for the grant GraPErOs (ENE2016-79282-C5-2-R), the OrgEnergy Excellence Network CTQ2016-81911- REDT, the Agència de Gestiód’Ajuts Universitaris i de Recerca (AGAUR) for the support to the consolidated Catalonia research group 2017 SGR 329 and the Xarxa de Referència en Materials Avançats per a l’Energia (Xarmae). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant no. SEV-2017-0706) and is funded by the CERCA Programme/Generalitat de Catalunya.

The operational instability of perovskite solar cells (PSCs) is known to mainly originate from the migration of ionic species (or charged defects) under a potential gradient. Compositional engineering of the A site cation of the ABX(3) perovskite structure has been shown to be an effective route to improve the stability of PSCs. Here, the effect of size-mismatch-induced lattice distortions on the ion migration energetics and operational stability of PSCs is investigated. It is observed that the size mismatch of the mixed A site composition films and devices leads to a steric effect to impede the migration pathways of ions to increase the activation energy of ion migration, which is demonstrated through multiple theoretical and experimental evidence. Consequently, the mixed composition devices exhibit significantly improved thermal stability under continuous heating at 85 degrees C and operational stability under continuous 1 sun illumination, with an extrapolated lifetime of 2011 h, compared to the 222 h of the reference device.

Halide perovskites are promising semiconductors for inexpensive, high-performance optoelectronics. Despite a remarkable defect tolerance compared to conventional semiconductors, perovskite thin films still show substantial microscale heterogeneity in key properties such as luminescence efficiency and device performance. However, the origin of the variations remains a topic of debate, and a precise understanding is critical to the rational design of defect management strategies. Through a multi-scale investigation - combining correlative synchrotron scanning X-ray diffraction and time-resolved photoluminescence measurements on the same scan area - we reveal that lattice strain is directly associated with enhanced defect concentrations and non-radiative recombination. The strain patterns have a complex heterogeneity across multiple length scales. We propose that strain arises during the film growth and crystallization and provides a driving force for defect formation. Our work sheds new light on the presence and influence of structural defects in halide perovskites, revealing new pathways to manage defects and eliminate losses.

The electronic and optical properties of two-dimensional layered materials allow the miniaturization of nanoelectronic and optoelectronic devices in a competitive manner. Even larger opportunities arise when two or more layers of different materials are combined. Here, we report on an ultrafast energy efficient strategy, using laser irradiation, which allows bulk synthesis of crystalline single-layered lead iodide in the cavities of carbon nanotubes by forming cylindrical van der Waals heterostructures. In contrast to the filling of van der Waals solids into carbon nanotubes by conventional thermal annealing, which favors the formation of inorganic nanowires, the present strategy is highly selective toward the growth of monolayers forming lead iodide nanotubes. The irradiated bulk material bearing the nanotubes reveals a decrease of the resistivity as well as a significant increase in the current flow upon illumination. Both effects are attributed to the presence of single-walled lead iodide nanotubes in the cavities of carbon nanotubes, which dominate the properties of the whole matrix. The present study brings in a simple, ultrafast and energy efficient strategy for the tailored synthesis of rolled-up single-layers of lead iodide (i.e., single-walled PbI2 nanotubes), which we believe could be expanded to other two-dimensional (2D) van der Waals solids. In fact, initial tests with ZnI2 already reveal the formation of single-walled ZnI2 nanotubes, thus proving the versatility of the approach., We acknowledge funding from MINECO (Spain), through MAT2017-86616-R, ENE2017-89210-C2-1-R, and “Severo Ochoa” Programme for Centres of Excellence in R&D (SEV2015-0496, SEV-2013-0295), CERCA programme for funding ICN2 and support from AGAUR of Generalitat de Catalunya through the projects 2017 SGR 1086, 2017 SGR 581 and 2017 SGR 327.D.K. acknowledges financial support from the Ministry of Education, Science, and Technological Development of the Republic of Serbia for postdoctoral research.

Hybrid organic–inorganic perovskites represent a special class of metal–organic framework where a molecular cation is encased in an anionic cage. The molecule–cage interaction influences phase stability, phase transformations, and the molecular dynamics. We examine the hydrogen bonding in four AmBX3 formate perovskites: [Am]Zn(HCOO)3, with Am+ = hydrazinium (NH2NH3+), guanidinium (C(NH2)3+), dimethylammonium (CH3)2NH2+, and azetidinium (CH2)3NH2+. We develop a scheme to quantify the strength of hydrogen bonding in these systems from first-principles, which separates the electrostatic interactions between the amine (Am+) and the BX3– cage. The hydrogen-bonding strengths of formate perovskites range from 0.36 to 1.40 eV/cation (8–32 kcalmol–1). Complementary solid-state nuclear magnetic resonance spectroscopy confirms that strong hydrogen bonding hinders cation mobility. Application of the procedure to hybrid lead halide perovskites (X = Cl, Br, I, Am+ = CH3NH3+, CH(NH2)2+) shows that these compounds have significantly weaker hydrogen-bonding energies of 0.09 to 0.27 eV/cation (2–6 kcalmol–1), correlating with lower order–disorder transition temperatures.

Кристалізацією з парової фази у закритій системі при тиску парів надстехіометричного йоду одержані монокристали PbI2 з вмістом кадмію 0,001-10 ат. %. Досліджено вплив концентрації кадмію у вихідній шихті і температурного градієнту на швидкість масоперенесення в системі та характеристики кристалів. Введення у систему PbI2-I2 кадмію в діапазоні концентрацій від 0,001 до 0,5 ат. % при оптимальних умовах вирощування чистих кристалів PbI2 зменшує швидкість масоперенесення не більше ніж на 2 %, концентрація Cd у вирощених монокристалах одного порядку з їх вмістом у вихідній шихті. Збільшення вмісту домішки у шихті від 0,5 до 5,5 ат. % зменшує швидкість масоперенесення вдвічі, вміст кадмію у монокристалах у 5 разів нижчий ніж у шихті, розміри монокристалів зменшуються. Зниження температурного градієнту в системі дозволило отримати кристали PbI2 з вмістом кадмію до 10 ат. %. Легування Cd сприяє росту монокристалів переважно у формі пластин і стрічок. За спектрами дифракції Х-променів встановлено, що одержані монокристали PbI2 належать до 4Нполитипу, визначені параметри гратки і об’єм елементарної комірки чистих і легованих кристалів. Встановлено вплив домішки Cd на спектри поглинання PbI2. Зростання вмісту кадмію у кристалах до 3 ат. % супроводжується короткохвильовим зсувом краю власного поглинання і збільшенням ширини забороненої зони. PbI2 single crystals containing cadmium 0.001-10 at. % have been obtained by means of crystallization from vapor phase in an enclosed system with over-stoichiometric iodine vapor pressure. The influence of cadmium concentration in source burden material and the influence of temperature gradient upon the mass-transfer rate in the system and on the crystals’ characteristics have been researched. With addition of cadmium within the concentration range from 0.001 to 0.5 at. % into PbI2-I2 system at optimal growing conditions for pure PbI2 crystals, the mass-transfer rate is decreased by not more than 2 %, while Cd concentration in the single crystals grown remains of the same order as their content in the source material. The increase of dopant content from 0.5 to 5.5 at. % in the source material leads to two-fold decrease of mass-transfer rate compared to its initial value, with cadmium content in single crystals 5 times lower than in the source material and with decreased dimensions of single crystals. To obtain Cd-doped crystals up to 10 at. %, temperature gradient in the system has been decreased. Cd doping facilitates the growth of single crystals mainly in the form of plates and tapes. By means of X-ray diffraction spectra, it has been defined that PbI2 single crystals belong to 4H-polytype. The lattice parameters and the unit cell volume of pure and doped crystals have been determined. The influence of cadmium dopant upon the PbI2 absorption spectra has been defined. Increasing cadmium content in PbI2 crystals to 3 at. % results in a shift of intrinsic absorption edge into the short-wave area and increase of the band gap width.

We report clear room temperature ambipolar transport in ambient-air processed methylammonium lead iodide (MAPbI3) thin-film transistors (TFTs) with aluminum oxide gate-insulators and indium-zinc-oxide source/drain electrodes. The high ionicity of the MAPbI3 leads to p-type and n-type self-doping, and depending on the applied bias we show that simultaneous or selective transport of electrons and/or holes is possible in a single MAPbI3 TFT. The electron transport (n-type), however, is slightly more pronounced than the hole transport (p-type), and the respective channel resistances range from 5&ndash, 11 and 44&ndash, 55 M&Omega, /&mu, m. Both p-type and n-type TFTs show good on-state characteristics for low driving voltages. It is also shown here that the on-state current of the n-type and p-type TFTs is highest in the slightly PbI2-rich and MAI-rich films, respectively, suggesting controllable n-type or p-type transport by varying precursor ratio.

We report on the scintillation properties of undoped PbI2, and PbI2 doped with La, Cu, Ag, and Te. X-ray luminescence spectra were recorded at 7 K and the time responses for 80 ps pulses of X-rays were recorded from 14 K to 150 K. Samples were irregularly shaped crystal pieces that ranged from 300 to 1000 mm in size. We found that at 14 K the undoped samples had a fast emission at 520 nm (0.18 eV below the band edge) and a total light output of about 40,000 photons/MeV. 10% of this light appears in the first ns, which is 5 times greater than LSO and 1.5 times greater than LaBr3:Ce. 50% of the light appears in the first 100 ns. The luminosity decreased dramatically as the temperature was increased above 40 K, consistent with a non-radiative path that has an activation energy of 3.8 meV. Doping with the donor La 3 þ only slightly changed these scintillation properties. Doping with the donor La 3 þ and the deep acceptors Cu þ ,A g þ , and Te 2– produced primarily slow donor–acceptor emissions at peak wavelengths of 605, 653, and 800 nm, respectively. The luminosity of the samples doped with La 3 þ and Cu þ depended strongly on the La 3 þ concentration, demonstrating its role as an electron donor. First-principles band structure calculations showed (1) that the donor level depth of an isolated iodine vacancy is about 0.8 eV, too deep to explain the 520 nm emission wavelength, and (2) that a donor– acceptor pair consisting of a spatially associated iodine vacancy donor and a lead vacancy acceptor has shallower donor and acceptor depths that are consistent with the 520 nm emission wavelength.

Some semiconductor materials such as lead iodide (PbI 2 ) have applications in the detection of ionizing radiation at room temperature using the direct detection method. In this work we investigate lead iodide films deposited by thermal evaporation. The morphology, structure, and electric properties were investigated as a function of deposition height, i.e. the distance between evaporation-boat and substrates. The results show a morphology of vertical leaves and X-ray diffraction shows just one preferential orientation along the direction 110. Energy dispersive spectroscopy reveals that the films are not stoichiometric, with excess iodine atoms. Electrical resistivity of about 10 8 Ω cm was measured. This is smaller than for the bulk due to structural defects. The values of activation energy for electric transport increase from 0.52 up to 1.1 eV with decreasing deposition height, what indicates that the best film is the one deposited at the shortest distance. Exposure under X-ray mammographic energy shows a linear behavior up to 500 mR. No variation in sensibility was observed between 22 and 30 kVp.

Lead iodide has been recognized as a promising material for room temperature radiation detectors. It has a wide band-gap (∼ 2.3 eV), high atomic numbers (82, 53) and it is environmentally very stable compared to mercuric iodide. Electrical and optical properties of lead iodide grown crystals purified under the influence of selected rare earth elements have been investigated. Photo-luminescence and capacitance-voltage measurements have been performed using different rare earth elements.

We employ flash infrared annealing to investigate the phase transition of formamidinium lead triiodide (FAPbI(3)) thin films for their solar cell applications. Measuring the enthalpy changes of the FAPbI(3) composition at different heating rates allows us to calculate an activation energy of 1.8 eV for the black perovskite phase transition. We explore different heating regimes for triggering the phase transformation and analyze the evolution of the microstructure with an empirical calculation of the average crystal growth velocity required to form a compact film on the micron and submicron scales. The films were then optoelectronically and structurally correlated by mapping the typical spherulite microstructure of grain domains, indicating a direct relationship between film homogeneity and higher crystal growth rate. Accordingly, we manufactured highly stable black FAPbI(3)-based perovskite solar cells using the optimal film crystallization processing parameters, with an annealing time of just 640 ms. We achieve a power conversion efficiency (PCE) of 18.5% using the champion device in the absence of any additives, incurring merely a 10% loss in the PCE during maximum power point tracking for 1500 h under full solar intensity exposure of the devices.

Hybrid perovskites have attracted enormous attention in the next generation resistive switching (RS) memristor for the artificial synapses, owing to their ambipolar charge transport, long diffusion length, and tunable visible bandgap. However, the variable switch, limited reproducibility, and poor endurance are the obstacles to the practical application of the perovskite memristors. Herein, we reported a multilevel RS nonvolatile memory based on a 3D trigonal HC(NH2)(2)PbI3 (& alpha;-FAPbI(3)) perovskite layer modified by 1-cyanobutyl-3-methylimidazolium chloride ([CNBmim]Cl) and sandwiched between ITO and Au electrodes (Au/[CNBmim]Cl/& alpha;-FAPbI(3)/SnO2/ITO). In contrast to the bare memristor with failure switching from low resistance state (LRS) to high resistance state (HRS), the memristor device based on the & alpha;-FAPbI(3) modified with [CNBmim]Cl (Target device) shows the retention time over 10(4) s with On/Off ratio (>10(2)) and endurance up to 550 cycles. The stable RS cycle benefits from the accelerated electrons de-trapping from the reduced defects and fast charge separation in the interface of & alpha;-FAPbI(3)/electrode, leading to the rupture of conductive filaments and transition of LRS to HRS. As a two-terminal analog synaptic device, the target device can realize random handwritten digit recognition with an impressive accuracy of 89.3% on the condition of low learning phases (500 training cycles).

Perovskite solar cells are one of the most promising photovoltaic technologies, although their molecular level design and stability toward environmental factors remain a challenge. Layered 2D Ruddlesden-Popper perovskite phases feature an organic spacer bilayer that enhances their environmental stability. Here, the concept of supramolecular engineering of 2D perovskite materials is demonstrated in the case of formamidinium (FA) containing A(2)FA(n-1)Pb(n)I(3n+1) formulations by employing (adamantan-1-yl)methanammonium (A) spacers exhibiting propensity for strong Van der Waals interactions complemented by structural adaptability. The molecular design translates into desirable structural features and phases with different compositions and dimensionalities, identified uniquely at the atomic level by solid-state NMR spectroscopy. For A(2)FA(2)Pb(3)I(10), efficiencies exceeding 7% in mesoscopic device architectures without any additional treatment or use of antisolvents for ambient temperature film deposition are achieved. This performance improvement over the state-of-the-art FA-based 2D perovskites is accompanied by high operational stability under humid ambient conditions, which illustrates the utility of the approach in perovskite solar cells and sets the basis for advanced supramolecular design in the future.

Mixed-halide perovskites are highly promising materials for tandem solar cells. The phenomenon of phase segregation, however hinders their application. Here, we combine Fourier-Transform photocurrent spectroscopy with photoluminescence and current density-voltage (J-V) measurements to study the effect of light soaking on such materials and devices. At first, we observe a gradual formation of an I-rich phase, which correlates with an increase in deep defect level concentration. We attribute these deep defects to charged iodide interstitials and associate phase segregation with iodide migration through interstitial positions. Upon further light soaking, the second less I-rich phase forms, while the deep level concentration simultaneously decreases. An empirical model describing the phase segregation mechanism is proposed to rationalize these observations. Further, we point to an important role of grain size in determining the degree and terminal phase of segregation.

PbI2 semiconductor quantum wires have been synthesized in the interlayer space of montmorillonite organic modified clays by simple intercalation reactions. The experimental results showed that the quantum wires have been retained within the lamellar space of layer silicates exhibiting a well-defined diameter and narrow length distribution. The synthetic procedure involves chemical reactions within the clay interlayer, which are achieved through a slow mass transport between the clay platelets via a low solubility path between two different lead iodide phases. The structure and properties of the hybrid composites have been studied by means of X-ray diffraction, energy dispersive spectroscopy, Transmission electron microscopy, optical absorption and photoluminescence experiments. The experimental techniques have verified that the resultant organo-clay-semiconductor composite contains within the clay platelets nano sized low dimensional semiconductor species in the form of wires that exhibit well defined energy gap absorption peaks, which are blue shifted due to quantum confinement phenomena. Journal of Optoelectronics and Advanced Materials

The properties of efficient solar cells fabricated with triple-cation perovskite placed between a mesoporous titania layer and a spiro-OMeTAD layer are studied by using devices either prepared under water-free drybox conditions or fabricated under ambient room humidity. The morphological studies indicate that the content of unreacted PbI2 phase in the perovskite structure is much higher near the interface with titania than near the interface with spiro-OMeTAD. The stationary emission spectra and transient bleach peaks of perovskites show additional long-wavelength features close to the titania side. Time-resolved techniques ranging from femtoseconds to seconds reveal further differences in charge dynamics at both interfaces. The population decay is significantly faster at the titania side than at the spiro-OMeTAD side for the cells prepared under ambient conditions. An increased hole injection rate correlates with higher photocurrent seen in the devices prepared under drybox conditions. The charge recombination loss on the millisecond time scale is found to be slower at the interface with titania than at the interface with spiro-OMeTAD. The ideality factor of the cells is found to increase with increasing DMSO content in the precursor solution, indicating a change in recombination mechanism from bulk to surface recombination. We also found that the charge dynamics are not uniform within the whole perovskite layer. This feature has significant implications for understanding the operation and optimizing the performance of solar devices based on mixed cation perovskites.

As a result of their attractive optoelectronic properties, metal halide APbI(3)perovskites employing formamidinium (FA(+)) as the A cation are the focus of research. The superior chemical and thermal stability of FA(+)cations makes alpha-FAPbI(3)more suitable for solar-cell applications than methylammonium lead iodide (MAPbI(3)). However, its spontaneous conversion into the yellow non-perovskite phase (delta-FAPbI(3)) under ambient conditions poses a serious challenge for practical applications. Herein, we report on the stabilization of the desired alpha-FAPbI(3)perovskite phase by protecting it with a two-dimensional (2D) IBA(2)FAPb(2)I(7)(IBA=iso-butylammonium overlayer, formed via stepwise annealing. The alpha-FAPbI(3)/IBA(2)FAPb(2)I(7)based perovskite solar cell (PSC) reached a high power conversion efficiency (PCE) of close to 23 %. In addition, it showed excellent operational stability, retaining around 85 % of its initial efficiency under severe combined heat and light stress, that is, simultaneous exposure with maximum power tracking to full simulated sunlight at 80 degrees C over 500 h.

Organic-inorganic tin(II) halide perovskites have emerged as promising alternatives to lead halide perovskites in optoelectronic applications. While they suffer from considerably poorer performance and stability in comparison to their lead analogues, their performance improvements have so far largely been driven by trial and error efforts due to a critical lack of methods to probe their atomic-level microstructure. Here, we identify the challenges and devise a Sn-119 solid-state NMR protocol for the determination of the local structure of mixed-cation and mixed-halide tin(II) halide perovskites as well as their degradation products and related phases. We establish that the longitudinal relaxation of Sn-119 can span 6 orders of magnitude in this class of compounds, which makes judicious choice of experimental NMR parameters essential for the reliable detection of various phases. We show that Cl/Br and I/Br mixed-halide perovskites form solid alloys in any ratio, while only limited mixing is possible for I/CI compositions. We elucidate the degradation pathways of Cs-, MA-, and FA-based tin(II) halides and show that degradation leads to highly disordered, qualitatively similar products, regardless of the A-site cation and halide. We detect the presence of metallic tin among the degradation products, which we suggest could contribute to the previously reported high conductivities in tin(II) halide perovskites. Sn-119 NMR chemical shifts are a sensitive probe of the halide coordination environment as well as of the A-site cation composition. Finally, we use variable-temperature multifield relaxation measurements to quantify ion dynamics in MASnBr(3) and establish activation energies for motion and show that this motion leads to spontaneous halide homogenization at room temperature whenever two different pure-halide perovskites are put in physical contact.