Organometal Halide Perovskite Research Articles

Global instability index as a crystallographic stability descriptor of halide and chalcogenide perovskites

Crystallographic stability is an important factor that affects the stability of perovskites. The stability dictates the commercial applications of lead-based organometal halide perovskites. The tolerance factor (t) and octahedral factor (μ) form the state-of-the-art criteria used to evaluate the perovskite crystallographic stability. We studied the crystallographic stabilities of halide and chalcogenide perovskites by exploring an effective alternative descriptor, the global instability index (GII) that was used as an indicator of the stability of perovskite oxides. We particularly focused on determining crystallographic reliability by calculating GII. We analyzed the bond valence models of the 243 halide and chalcogenide perovskites that occupied the lowest-energy cubic-phase structures determined by conducting the first-principles-based total energy minimization calculations. The decomposition energy (ΔHD) reflects the thermodynamic stability of the system and is considered as the benchmark that helps assess the effectiveness of GII in evaluating the crystallographic stability of the systems under study. The results indicated that the accuracy of predicting thermodynamic stability was significantly higher when GII (73.6%) was analyzed compared to the cases when t (55%) and μ (39.1%) were analyzed to determine the stability. The results obtained from the machine learning-based data mining method further indicate that GII is an important descriptor of the stability of the perovskite family.

Composition engineering to enhance the photovoltaic performance and to prolong the lifetime for silver bismuth iodide solar cell

Lead, a toxic element in organometal halide perovskite solar cells, has caught lots of attention and has raised public concerns after such perovskite solar cells made rapid progress in their photovoltaic performance. Herein, a series of lead-free light absorber layers with a rudorffite structure were examined in this study. The obscure role of A-site and B-site cation in silver bismuth iodide rudorffite materials has been revealed through their energy diagrams and surface potential analyses. By manipulating the stoichiometric ratio of bismuth and silver at a ratio of 1.1/3, a Ag3BiI6 layer with uniform morphology, high carrier mobility, and a high light response was obtained. The superior optoelectrical properties of the modified Ag3BiI6 active layer directly influenced the photovoltaic performance and the environmental stability of such a device. The photovoltaic device with the modified Ag3BiI6 active layer exhibited a PCE of 2.60%. It also maintained over 80% of its initial PCE after being stored in an ambient environment for over 3,000 h. This result sheds light on how to process silver bismuth iodide materials and extends the knowledge for rudorffite materials.

Facilitate hole transport with thin 2D perovskite capping layer to passivate interface defects of 3D perovskite solar cells using PEABr

Hybrid 2D/3D-perovskites are attracting more interest in the area of organometal halide perovskite solar cells (PSCs) because of their high efficiency and extended environmental stability. The 3D portion in 2D/3D perovskites, serves as an active material with exceptional optoelectronic characteristics (for example excellent light absorption and an extended carrier lifetime), while its 2D counterpart protects against environmental conditions (water and oxygen) and increase the stability of the whole structure. In this study, a hetero-structure 2D/3D is constructed via spin-coating a phenyl-ethyl ammonium bromide (PEABr) solution upon over of (FA0.6MA0.4)PbI3 3D perovskite films. As compared to their 3D analogs, the PSC devices based on optimized 2D/3D hetero-structures display substantial improvements in photovoltaic efficiency due to the passivation of cationic and halide vacancies on the surface of 3D perovskite for better energy level alignments, longer carrier lifetimes, and fewer defects, which facilitate hole transfer and transport to the hole transport layer and reduce interface recombination centers. The extremely-thin film of 2D perovskite on the top of 3D perovskite boots the stability and reduces the crystal imperfection of 3D perovskite. Furthermore, the PEABr-treated perovskite device has a PCE of 20.57% as compared with the control device, which has a PCE of 17.01%.

Cs incorporation via sequential deposition for stable and scalable organometal halide perovskite solar cells

In this study, uniform Cs distribution in an organometal halide perovskite (OHP) film was achieved via sequential deposition method entailing the dissolution of Cs compounds in dimethyl formamide (DMF) with inorganic components, as opposed to using isopropyl alcohol with organic components, and the thermal stability and crystallinity of the OHP film were enhanced by improving the structural stability through Cs incorporation. Additionally, the device performance and thermal stability of OHP solar cells were enhanced by Cs incorporation, which led to fewer defect sites and the suppression of defect generation in OHP films, as confirmed by optical and electrical analysis, improving the overall film quality. The sequential deposition method was more amenable to scaling up than the anti-solvent assisted one-step spin-casting method, as demonstrated by the sequential deposition of the OHP film uniformly over a substrate with size of 8 cm × 8 cm. The uniformly sequentially deposited OHP film was used to create a large-area 1 cm 2 OHP solar cell, which exhibited a high power conversion efficiency (PCE) of 16.77%. Further scalability of the sequentially deposited OHP solar cell was confirmed by highly uniform device performances by three cells on a single substrate with a negligible PCE standard deviation of 0.94%. • The uniform Cs distribution in OHP film is achieved via sequential deposition. • The thermal stability of the OHP film increased through Cs incorporation. • The performance and stability of the PeSCs is improved. • Uniform OHP film with large size is successfully fabricated by sequential deposition. • A p-i-n PeSCs with a size of 1 cm 2 was successfully fabricated.

Effect of the magnetic order on the magneto-photocurrent of organo-metal halide perovskites

The optical properties of perovskite materials are spin dependent. Therefore, tuning the spin-exchange energy in perovskite materials can provide a way towards improving their photovoltaic and light-emission performances. In this study, the effect of an externally applied magnetic field on the magneto-photocurrent of hybrid-perovskite-based devices was investigated. We show that a magnetic field can be used to tune the short-range exchange energy of excited states, which results in a negative magneto-photocurrent. Besides, doping perovskite with manganese provides an additional way to tune the long-range spin-exchange energy between the excited states through the formation of polarons. This can lead to an increase of the performance of perovskite-based optoelectronic devices.

Stability enhancement of perovskite solar cells via multi-point ultraviolet-curing-based protection

As efficiency approaches the limit, it becomes more urgent to solve the toxicity and instability of organometal halide perovskite solar cells (PSCs), which asks for enhancement by applying methods that majorly contribute to stability itself to help prevent device from suffering from harmful matters. In this paper, we introduce a simple ultraviolet (UV) curing recipe which contains ethoxylated trimethylolpropane triacrylate (ETPTA) and 2-hydroxy-2-methyl-1-phenyl-1-propanone. ETPTA is polymerized by UV-curing and is applied as additive rather than as encapsulation material to distribute around the perovskite as a cross-linked network. Suitable amount of UV-gel added in perovskite precursor solution and hole transport material solution during device fabrication could promotes the crystallization of perovskite, reduce the diffusion of moisture in hole transport layer and therefore avoid degradation of PSCs. Notable protection happens with a volume percentage of ETPTA no more than 0.5%, especially in ambient conditions with humidity larger than 60%. • UV-gel is introduced through fabrication process and polymerized by UV-curing. • The addition of UV-gel is beneficial to the crystallization of perovskite. • Polymerized UV-gel effectively prevents the degradation of perovskite and device.

Surface Passivation of MAPbBr3 Perovskite Single Crystals to Suppress Ion Migration and Enhance Photoelectronic Performance.

Recently, organometal halide perovskites (OHPs) have achieved significant advancement in photovoltaics, light-emitting diodes, X-ray detectors, and transistors. However, commercialization and practical applications were hindered by the notorious ion migration issue of OHPs. Here, we report a simple solvent-based surface passivation strategy with organic halide salts (methylammonium bromide (MABr) and phenylethylammonium bromide (PEABr)) to suppress the ion migration of MAPbBr3 single crystals. The surface passivation effect is evidenced by the stronger photoluminescence (PL) intensity and extended PL lifetime. Using the pulse voltage and continuous voltage current-voltage measurements, we found that single crystals with surface passivation showed negligible hysteresis on the surface due to the suppression of ion migration. As a result, the dark current stability of coplanar structure devices was significantly improved. Moreover, the vertical structure X-ray detectors with PEABr treatment exhibited a high sensitivity of 15 280 μC Gyair-1 cm-2 and a low detection limit of 87 nGyair s-1 under 5 V bias. The proposed technology would be a versatile tool to improve the performance of perovskite photoelectronic devices.

Improving the Conductivity of the PEDOT:PSS Layers in Photovoltaic Cells Based on Organometallic Halide Perovskites.

Among conductive polymers, PEDOT films find the widest application in electronics. For photovoltaic applications, studies of their optical properties, stability, and electrical conductivity are of greatest interest. However, the PEDOT:PSS transport layers, when used in photovoltaic cells, have a high electrical resistance, which prevents solar cells from increasing their efficiency. One of the promising ways to improve their electrical properties is the use of composite materials based on them, in which the conductivity can be increased by introducing various additives. In this work, conductive polymer films PEDOT:PSS (poly (3,4-ethylenedioxythiophene):polystyrene sulfonate acid) doped with a number of amines (Pentylamine, Octylamine, Diethylamine, Aniline with carbon nanotubes) were obtained and studied. It is shown that, depending on the concentration of dopants, the electrical conductivity of PEDOT:PSS films can be significantly improved. In this case, the light transmission of the films practically does not change. The process of improving the conductivity by treating the surface of the finished film with amines, followed by heat treatment, was studied. It is assumed that the improvement in conductivity is the result of the self-assembly of monolayers of organic molecules on the surface of the PEDOT:PSS film leading to its p-doping due to intermolecular interaction.

Tunable engineering of photo- and electro-induced carrier dynamics in perovskite photoelectronic devices

The last decade has witnessed great progress in photovoltaic technology based on organometal halide perovskites because of their low nonradiative recombination loss, long carrier lifetime, and long diffusion length. The excellent optical properties and easy preparation of organometal halide perovskite-based photovoltaic products enable their wide applications in electro-optical and opto-electrical conversions. In this review, photoinduced free carriers, exciton recombination, and diffusion properties of perovskite photoelectronic devices are discussed. By controlling grain sizes and grain boundaries, suppressing defects, and conducting interfacial charge transfer, their dynamics can be controlled in a versatile manner. The generality and differences in “effective carriers” for device applications, including their electro-optical and opto-electrical conversions, are discussed. In all-optical devices, a strong light-matter interaction causes nonlinear effects, such as two-photon absorption, self-phase modulation, and optical blenching, which enable high-resolution imaging, optical modulation, and optical switching. This review provides a basis for constructing high-performance photoelectronic devices.

Kinetic study on growth of organic lead halide perovskite nanocrystals through water-oil interfacial reaction

Formation of organometal lead halide perovskite nanocrystals (OPNCs) occurs in fast time scales from milliseconds to seconds, thus posing a hurdle to the growth kinetic study of OPNCs. Water-oil interfacial reaction provides an effective approach for retarding the growth of CH3NH3PbBr3 OPNCs. Herein, we investigate systematically the kinetics of CH3NH3PbBr3 NCs in water–oil reaction by in situ optical characterization, and identify the key factors governing the growth of OPNCs. Molecular polarity and viscosity of the solvent are found to be crucial to the diffusion step by affecting the diffusion coefficient of CH3NH3+. Covalent characteristic of the Pb source and molecular structure of the ligands have an impact on the rate-limiting step of PbBr64- formation. In addition, we establish the reaction condition that enables controlled growth of formamidinium lead bromide NCs, thereby demonstrating the application of the growth kinetic in the synthesis of other OPNCs. Kinetic investigation of OPNCs provides a better understanding of their crystallization process that helps guide the development of quantum confined OPNCs for optoelectronic applications.

Dynamics of Strong Coupling Between Free Charge Carriers in Organometal Halide Perovskites and Aluminum Plasmonic States.

We have investigated a strong coupled system composed of a MAPbIxCl3-x perovskite film and aluminum conical nanopits array. The hybrid states formed by surface plasmons and free carriers, rather than the traditional excitons, is observed in both steady-state reflection measurements and transient absorption spectra. In particular, under near upper band resonant excitation, the bleaching signal from the band edge of uncoupled perovskite was completely separated into two distinctive bleaching signals of the hybrid system, which is clear evidence for the formation of strong coupling states between the free carrier–plasmon state. Besides this, a Rabi splitting up to 260 meV is achieved. The appearance of the lower bands can compensate for the poor absorption of the perovskite in the NIR region. Finally, we found that the lifetime of the free carrier–SP hybrid states is slightly shorter than that of uncoupled perovskite film, which can be caused by the ultrafast damping of the SPs modes. These peculiar features on the strong coupled hybrid states based on free charge carriers can open new perspectives for novel plasmonic perovskite solar cells.

Lead-free AgBiI4 perovskite artificial synapses for a tactile sensory neuron system with information preprocessing function

Organometal halide perovskites (OHPs) exhibit great potential in memristors and artificial synaptic devices.

Impact of localized surface plasmon resonance on efficiency of zinc oxide nanowire-based organic-inorganic perovskite solar cells fabricated under ambient conditions.

Organometal halide perovskites as hybrid light absorbers have been investigated and used in the fabrication of perovskite solar cells (PSCs) due to their low-cost, easy processability and potential for high efficiency. Further enhancing the performance of solution processed PSCs without making the device architecture more complex is essential for commercialization. In this article, the overall improvement in the performance of ZnO nanowires (NWs)-based PSCs fabricated under ambient conditions, incorporating Ag nanoparticles (NPs) delivering a device efficiency of up to 9.7% has been demonstrated. This study attributes the origin of the improved photocurrent to the improved light absorption by localized surface plasmon resonance (LSPR) with the incorporation of Ag NPs. These findings represent a basis for the application of metal NPs in photovoltaics and could lead to facile tuning of optical absorption of the perovskite layer giving higher current-density (JSC) and suppressed recombination effects leading to higher open-circuit voltage (VOC).

Homojunction perovskite solar cells: opportunities and challenges

Organometallic halide perovskites have rapidly become promising materials as a result of their outstanding properties in high-efficiency and low-cost next-generation solar cells. Perovskite materials can be adjusted to be p- or n-type by defect engineering through, for example, the self-doping method by controlling the precursor compositions and process conditions. Recently, a p-type perovskite/n-type perovskite homojunction has been proposed and constructed, which provides a possibility for the design of a novel type of perovskite solar cell (PSC). Following a brief overview of the physical fundamentals of perovskite homojunctions, a detailed discussion of the promising progress of recently reported homojunction PSCs is presented here, including theoretical simulations, extrinsic and interfacial doping and graded structures. Furthermore, the opportunities regarding higher doping concentrations, simpler device architectures, ion migration inhibition and device stability are discussed. Finally, an outlook that offers insights into the future development of highly efficient and stable homojunction PSCs is provided.

Experimental and theoretical study of europium-doped organometal halide perovskite nanoplatelets for UV photodetection with high responsivity and fast response.

Herein, we investigate the role of Eu3+ doping on CH3NH3PbBr3 nanoplatelets (NPLs) in terms of their optoelectronic properties and photodetection application through a combined experimental and theoretical approach. The introduction of EuCl3 in the CH3NH3PbBr3 crystal structure by a facile solvothermal method enabled the tuning of the lateral and vertical dimensions of the NSs to form large-area NPLs and finally monolayer nanocrystals. The appearance of low-angle diffraction peaks with Eu doping, which are observed in layered perovskite structures, confirms the formation of quasi-2D NPLs. The bandgap of the Eu-doped mixed halide perovskite systematically increases from 2.39 eV to 2.94 eV with increasing doping concentration. Interestingly, 10 mol% EuCl3 doping in the pure CH3NH3PbBr3 crystal dramatically enhances its absorbance and photosensitivity, resulting in high-performance photodetection. Under 405 nm excitation, the CH3NH3Pb0.9Eu0.1Br2.7Cl0.3 photodetector exhibits self-biased behavior with an on/off ratio >103, which is very significant. The planar device achieves a responsivity as high as 5.29 A W- and a detectivity of 1.06 × 1012 Jones under 405 nm with a power density of 0.14 mW cm-2 at 5 V. In addition, the device exhibits very fast response time with a rise/fall time of 17.5/38.5 μs, which is ∼4 times faster than the pristine CH3NH3PbBr3 counterpart. A linear relationship of photocurrent with light intensity in the CH3NH3Pb0.9Eu0.1Br2.7Cl0.3 photodetector signifies low recombination or charge trapping loss. High-performance photodetection in the Eu-doped device is ascribed to the elimination of trap states and the fast charge transfer process. To obtain better insight into the doped system, DFT analysis of the electronic structure of EuCl3-doped CH3NH3PbBr3 was performed and the results are fully consistent with the experimental findings. It was revealed that EuCl3 doping increases the density of states near the conduction band along with a blue shift in the bandgap as compared to that of the pristine perovskite, which in turn increases the built-in potential of the fabricated device, resulting in self-biased photodetection. This work paves the way for deeper understanding of lanthanide doping in perovskites and self-biased photodetection applications of a new family of Eu-doped mixed halide perovskite nanostructures.

An organometal halide perovskite supported Pt single-atom photocatalyst for H2 evolution

An organometal halide perovskite supported Pt single-atom photocatalyst is developed for efficient H2 evolution with a superb STH of 4.50%.

Role of metal and anions in organo-metal halide perovskites CH3NH3MX3 (M: Cu, Zn, Ga, Ge, Sn, Pb; X: Cl, Br, I) on structural and optoelectronic properties for photovoltaic applications.

Methylammonium metal halide perovskites have recently been explored for new uses due to their unique and exciting optoelectronic properties. Their exceptional electronic properties have often been attributed to the overlap between the metal cation s and halogen p states. In this study, density functional theory calculations have been carried out based on the orthorhombic phase of the organometal trihalide perovskite CH3NH3MX3 (M: Cu, Zn, Ga, Ge, Sn, Pb; X: Cl, Br, I) to systematically investigate the effects of the metal cation and halogen anion on the structural, electronic, and optical properties for solar cell applications. The calculated lattice parameters agree well with previously obtained experimental and theoretical results. All of these perovskites are direct band gap compounds at the G symmetry point, except CH3NH3GaX3. The band gap increases from iodide to chloride and also with the metal cation size, from Ge to Pb or Cu to Zn. Furthermore, metal halide perovskites show blue shifts in their optical absorption spectra with an increase in metal cation size. Among the studied examples, CH3NH3GaBr3 and CH3NH3CuCl3 absorb a wide range of light, from UV to the visible region, and possess very unusual high dielectric constants and refractive indices. Our calculations reveal that CH3NH3SnI3, CH3NH3GeI3, and CH3NH3ZnI3 are favorable candidates for lead-free photovoltaic applications.

Optical humidity sensors based on lead-free Cu-based perovskite nanomaterials.

Organometallic halide perovskite materials possess unique and tunable optical properties with a wide range of optoelectronic applications. However, these materials suffer from humidity-driven degradation in ambient atmospheres. In this paper we investigate stable copper-based perovskite nanocrystals for potential use in humidity sensors, specifically examining their unique humidity-dependent optical properties and reversibility. We controlled stoichiometric ratios of Cu-based perovskites and demonstrated that (methylammonium)2CuBr4 nanocrystals showed excellent reversible physisorption of water molecules. These perovskite nanocrystals exhibited reversible hydro-optical properties, including transparency changes in response to variations in relative humidity under ambient conditions. The perovskite nanomaterial humidity sensor was highly reliable and stable, with a linear correlation in a relative humidity range of 7% to 98%. Accordingly, the lead-free Cu-based perovskite materials developed herein have the potential to be employed as real-time, self-consistent humidity sensors.

Insertion of metal cations into hybrid organometallic halide perovskite nanocrystals for enhanced stability: eco-friendly synthesis, lattice strain engineering, and defect chemistry studies.

In this work, we developed a facile and environmentally friendly synthesis strategy for large-scale preparation of Cr-doped hybrid organometallic halide perovskite nanocrystals. In the experiment, methylammonium lead bromide, CH3NH3PbBr3, was efficiently doped with Cr3+ cations by eco-friendly method at low temperatures to grow crystals via antisolvent-crystallization. The as-synthesized Cr3+ cation–doped perovskite nanocrystals displayed ∼45.45% decrease in the (100) phase intensity with an enhanced Bragg angle (2θ) of ∼15.01° compared to ∼14.92° of pristine perovskites while retaining their cubic (221/Pm-cm, ICSD no. 00-069-1350) crystalline phase of pristine perovskites. During synthesis, an eco-friendly solvent, ethanol, was utilized as an antisolvent to grow nanometer-sized rod-like crystals. However, Cr3+ cation-doped perovskite nanocrystals display a reduced crystallinity of ∼67% compared to pristine counterpart with ∼75% crystallinity with an improved contact angle of ∼72° against water in thin films. Besides, as-grown perovskite nanocrystals produced crystallite size of ∼48 nm and a full-width-at-half-maximum (FWHM) of ∼0.19° with an enhanced lattice-strain of ∼4.52 × 10−4 with a dislocation-density of ∼4.24 × 1014 lines per m2 compared to pristine perovskite nanocrystals, as extracted from the Williamson–Hall plots. The as-obtained stable perovskite materials might be promising light-harvesting candidates for optoelectronic applications in the future.

Ambient fabrication of efficient triple cation perovskite-based near-infrared light-emitting diodes

In addition to their widespread use as an outstanding light-harvesting material, solution-based organometallic halide perovskites have also recently emerged as a promising material for light-emitting diode (LED) applications. However, their stability under an ambient environment remains a challenge. Triple cation perovskites offer an appealing solution as it reduces the sensitivity to the processing conditions and improves the purity of the perovskite films. This work describes a facile ambient-processed thiocyanate-doped triple-cation perovskite Csx(MA0.17FA0.83)Pb(100-x)(I0.83Br0.17)3 used for high-performance perovskite-based LEDs with peak emission at 750 nm. Using the perovskite film tailoring technique by mixing DMF (N,N-Dimethylmethanamide) with perovskite precursor, we are able to reduce the perovskite grain size and optimize the film thickness while preserving its crystalline structure. With optimized processing techniques, we achieve a ∼90% improvement of the perovskite LEDs external quantum efficiency (EQE) from ∼3.1% to ∼5.9%. We believe this triple cation perovskite synthesis approach and film tailoring technique yields excellent device performances and constitutes a significant step towards low-cost and efficient LEDs.