Organometal Halide Perovskite Research Articles

Boron nitride-incorporated NiOx as a hole transport material for high-performance p-i-n planar perovskite solar cells

In recent years, organo-metal halide perovskite and p-i-n planar perovskite solar cells (PSCs) based on it have received tremendous attention due to their high efficiency close to silicon, low temperature process, and ease of cost-effective large-scale manufacturing. However, p-i-n planar PSCs have low fill factor and low current density due to poor interface properties, resulting in low performance. In this work, to solve these problems, we introduce boron nitride (BN) as an interface modifier and demonstrate that the BN incorporated NiOx (NiO:BN) is effectively working as hole transport layer of p-i-n planar PSCs. The NiO:BN hole transport layer (HTL) has a deep energy level of highest occupied molecular orbital (HOMO) and smooth surface compared to pristine NiOx, which provide the better energy level alignment and better interface contact between NiO:BN HTL and perovskite, improving charge extraction and transportation and inhibiting recombination of charge. As a result, NiO:BN based p-i-n planar PSCs represent an improved power conversion efficiency of 20.74% and long-term stability in ambient air for 60 days (maintained over 84% of their initial PCE). Therefore, it can be suggested that the NiO:BN HTL is a promising alternative HTL for high performance p-i-n planar PSCs.

Direction-selective electron beam damage to CH3NH3PbI3 based on crystallographic anisotropy

We report that the organometal halide perovskite is selectively damaged by an electron beam depending on its irradiation direction. Using transmission electron microscopy investigation, we have confirmed that CH3NH3PbI3 single crystals are highly tolerant to [] electron beam irradiation while they are easily damaged by [] electron irradiation. We have shown that the direction selectivity of the electron beam damage through the decomposition of the organic components in CH3NH3PbI3 crystals is consistent with the crystallographic arrangement of organic and iodide ions in the crystal.

Toward Efficient and Stable Perovskite Solar Cells: Choosing Appropriate Passivator to Specific Defects

With a certificated record efficiency of 25.2%, organometal halide perovskite (OHP) solar cells have experienced unprecedentedly rapid development in the past decade due to their extraordinary photoelectronic properties. However, because of the rapid processing conditions and complex precursor compositions, there are a large number of defects in polycrystalline OHP films, including point defects and 2D defects along grain boundary and on the surface. Unfortunately, these defects serve as the nonradiative recombination centers and exert negative effects on the degradation and performance of OHP layers, heavily limiting their further application for efficient photovoltaic devices. Herein, the formation origin of various defects as well as their detrimental effects on the efficiency and stability of perovskite solar cells (PSCs) are discussed, and recent passivation strategies for specific defects to minimize defect state density in the perovskite films are summarized. Finally, a brief outlook on the development trend of future passivation engineering is provided for deeper understanding of efficient and stable PSCs.

Addressing the Stability of Lead Halide Perovskites

The rapid rise in efficiencies of lead halide perovskite solar cells has hastened the case for commercialization. One of the key barriers, however, is stability of devices. In this issue of Joule, Zhou et al. studied the degradation mechanism of a FA-Cs mixed cation perovskite-based solar cell with experimental and modeling techniques to show that phase separation into FA-rich and Cs-rich compositions account for the observed degradation.

The Effect of Extended Ball-Milling upon Three-Dimensional and Two-Dimensional Perovskite Crystals Properties

The ball-milling of materials is a mechanical grinding method that has different effects on treated materials, and can be used for the direct synthesis of organometal halide perovskite (OHP) crystals. Herein, the effect of such a process, extended over a large temporal window, is related to the properties of referential three-dimensional (3D) MAPbI3 (MA = methylammonium) and two-dimensional (2D) PEA2PbI4 (PEA = phenylethylammonium) perovskite crystals. For both 2D and 3D systems, the ball-milling induces a reduction of the crystallite dimension, accompanied by a worsening of the overall crystallinity, but without any sign of amorphization. For MAPbI3, an intriguing room temperature structural transition, from tetragonal to cubic, is observed. The processing in both cases impacts on the morphology, with a reduction of the crystal shape quality connected to the particles’ agglomeration tendency. All these effects translate to a “blue shift” of the absorption and emission features, suggesting the use of this technique to modulate the 3D and 2D OHPs’ properties.

Numerical modeling and simulation for augmenting the photovoltaic response of HTL free perovskite solar cells

Organo-metal halide perovskites have drawn a lot of appeal from the research community in recent years because of its application as an absorber in thin-film solar cells. However, the fabrication of multi-layered defect-free planar perovskite solar cell (PSC) structures is a very challenging task. This is because the interface between charge transport layer/perovskite materials promotes hysteresis and recombination leading to poor long term stability. Along with the mechanism of charge transport, the dependence of performance on the material parameters in hole transport layer (HTL)-free PSCs is unclear. Removal of the HTL layer from the standard configuration in PSC degrades the device performance. In this paper, a novel HTL-free PSC employing glass/FTO/TiO2/CH3NH3Pb(I1-xBrx)3/Au contact structure has been investigated using a one-dimensional modeling program AMPS-1D. It was demonstrated that to achieve better photovoltaic performance, the thickness of the absorber should be increased; the acceptor doping concentration should be of the order of ∼ 1017 and the bandgap should be modified to 1.7 eV. Under moderate simulation conditions, if the above factors are satisfied, efficiencies over 17% can be attained.

Controlled Size Growth of Thermally Stable Organometallic Halide Perovskite Microrods: Synergistic Effect of Dual-Doping, Lattice Strain Engineering, Antisolvent Crystallization, and Band Gap Tuning Properties.

Organometallic halide perovskites, as the light-harvesting material, have been extensively used for cost-effective energy production in high-performance perovskite solar cells, despite their poor stability in the ambient atmosphere. In this work, methylammonium lead iodide, CH3NH3PbI3, perovskite was successfully doped with KMnO4 using antisolvent crystallization to develop micrometer-length perovskite microrods. Thus, the obtained KMnO4-doped perovskite microrods have exhibited sharp, narrow, and red-shifted photoluminescence band, as well as high lattice strain with improved thermal stability compared to undoped CH3NH3PbI3. During the synthesis of the KMnO4-doped perovskite microrods, a low boiling point solvent, anhydrous chloroform, was employed as an antisolvent to facilitate the emergence of controlled-size perovskite microrods. The as-synthesized KMnO4-doped perovskite microrods retained the pristine perovskite crystalline phases and lowered energy band gap (∼1.57 eV) because of improved light absorption and narrow fluorescence emission bands (fwhm < 10 nm) with improved lattice strain (∼4.42 × 10–5), Goldsmith tolerance factor (∼0.89), and high dislocation density (∼5.82 × 10–4), as estimated by Williamson–Hall plots. Thus, the obtained results might enhance the optical properties with reduced energy band gap and high thermal stability of doped-perovskite nanomaterials in ambient air for diverse optoelectronic applications. This study paves the way for new insights into chemical doping and interaction possibilities in methylamine-based perovskite materials with various metal dopants for further applications.

Fully Integrated Mechanoluminescent Devices with Nanometer-Thick Perovskite Film as Self-Powered Flexible Sensor for Dynamic Pressure Sensing

Flexible pressure sensors have numerous future applications in artificial electronic skins, foot ulcer detection, structural health monitoring, soft robotics, and wearable technology. We, herein, report an efficient, low-cost manufacturing technique to construct a compact, sensitive, robust yet flexible pressure sensor by fully integrating the mechanoluminescent device with nanometer thick organometal halide perovskite. The mechanoluminescent-perovskite flexible sensor does not require any power source at the sensing location. The sensor was subjected to repeated pressure and generated a distinct electrical current signal corresponding to each pressure cycle. The current intensity increases linearly with the increase of applied pressure on the sensor, which is desirable. Our sensor can detect pressure as low as 11 kPa with a large sensing range and a sensitivity of 0.095 kPa–1. The sensor displays consistent signals over 1000 cycles, which demonstrates its potential as a reliable sensor in practical applications such as structural health monitoring. Our approach of efficiently harvesting mechanoluminescent light via integrated light-absorbing nanometer thick perovskite might open a window for advanced research in self-powered mechanoluminescent-perovskite-based devices.

Pressure Engineered Optical Properties and Carrier Dynamics of FAPbBr3 Nanocrystals Encapsulated by Siliceous Nanosphere

Organo-metallic halide perovskite nanocrystals are widely studied because of their exceptional optoelectronic properties on solar cells, lighting, and display applications. However, their ultrafast...

Perovskite Nanocrystal Fluorescence-Linked Immunosorbent Assay Methodology for Sensitive Point-of-Care Biological Test

Summary Quantitative fluorescence immunoassay is a vital and convenient method in point-of-care (POC) testing for food safety and clinical healthcare. However, current marking materials, from organic luciferin to quantum dots, still lack the requirement of increasing need for multiple targets of interest because of their too broad emission. Here, a new label material, perovskite nanocrystals (Pe-NCs), with a narrower photoluminescence spectrum is reported, and a sensitive and quantitative immunoassay method named the perovskite nanocrystal fluorescence-linked immunosorbent assay is preliminarily demonstrated. The key point of realizing water-dispersed and stable Pe-NCs was addressed by functionalizing with hydroxyl groups. The fluorescent probes (perovskite antibody) were constructed via electrostatic adsorption with narrow full-width at half-maximum (∼18 nm), laying the foundation for future study of multi-target detection. Both indirect competitive immunity and sandwich immunoassay were successfully demonstrated. This work provides a possible label material for POC tests and may open up a promising avenue of next-generation immunoassay.

Acetamidinium Cation to Confer Ion Immobilization and Structure Stabilization of Organometal Halide Perovskite Toward Long Life and High‐Efficiency p‐i‐n Planar Solar Cell via Air‐Processable Method

Ion migration in organometal halide perovskite solar cell (OHPSC) and crystal structure evolution of organometal halide perovskites (OHPVSKs) in air are considered as one of the critical factors for unstable performance and of the urgent issues for the reliability of OHPSCs. Herein, a novel cation of acetamidinium (Aa+) with stronger coordinated bond with I− than methylammonium is induced into OHPVSK to stabilize its crystal structure. By incorporating Aa+ ions into OHPVSKs, the power conversion efficiency (PCE) of OHPSC without an encapsulation can maintain higher than 75% of its initial PCE after a 200 h humidity (60–80% relative humidity (RH) in air) or a 24 h thermal stress test (85 °C in dry N2). The Aa–MAPbI3 device exhibits an outstanding efficiency of 20.68%, and over 80% of initial PCE is maintained after a 1300 h damp heat as encapsulated. This novel cation can be easily incorporated into OHPVSK via a hot casting process in air with a high environmental tolerance as compared with that from the conventional coating process, which suffers from sophisticated crystallization steps and a strict processing atmosphere. It extends processing windows for OHPVSK fabrication and provides a promising path toward mass production and further commercialization.

First-Principles Investigation of the Thermal Degradation Mechanisms of Methylammonium Lead Triiodide Perovskite

The poor stability of organometallic halide perovskites, especially CH3NH3PbI3 (MAPbI3), in high-temperature environments is one of the challenges retarding its wider applicability. A better understanding of how MAPbI3 perovskite degrades thermally will allow us to develop strategies to improve its “intrinsic” stability. In this study, we employed first-principles density functional theory to obtain detailed thermal degradation energy landscapes for MAPbI3. We focused on studying two reaction pathways: P1, for proton abstraction from methylammonium (MA) to iodine, and P2, for substitution (SN2) of an iodide anion (I–, as nucleophile) at the carbon atom of MA to yield iodomethane (CH3I) and ammonia (NH3). Our calculations provided kinetic data, allowing us to assess the “intrinsic” (in)stability of MAPbI3 under heat stress and to make sense of the seemingly contradictory experimental results. The I– species is more reactive for reaction P1 but not for P2. The energy of the reaction along pathway P1 increases monotonically with respect to proton abstraction. The reaction along pathway P2 is a two-step process, with a CH3–I–Pb–X intermediate formed in the crystal in conjunction with the release of NH3 gas. Our results suggest that the method of preparation (e.g., iodine-deficient conditions) and the morphology (e.g., improved crystallinity) of MAPbI3 could both influence its thermal stability.

A Potential Checkmate to Lead: Bismuth in Organometal Halide Perovskites, Structure, Properties, and Applications.

The remarkable optoelectronic properties and considerable performance of the organo lead‐halide perovskites (PVKs) in various optoelectronic applications grasp tremendous scientific attention. However, the existence of the toxic lead in these compounds is threatening human health and remains a major concern in the way of their commercialization. To address this issue, numerous nontoxic alternatives have been reported. Among these alternatives, bismuth‐based PVKs have emerged as a promising substitute because of similar optoelectronic properties and extended environmental stability. This work communicates briefly about the possible lead‐alternatives and explores bismuth‐based perovskites comprehensively, in terms of their structures, optoelectronic properties, and applications. A brief description of lead‐toxification is provided and the possible Pb‐alternatives from the periodic table are scrutinized. Then, the classification and crystal structures of various Bi‐based perovskites are elaborated on. Detailed optoelectronic properties of Bi‐based perovskites are also described and their optoelectronic applications are abridged. The overall photovoltaic applications along with device characteristics (i.e., V OC, J SC, fill factor, FF, and power conversion efficiency, PCE), fabrication method, device architecture, and operational stability are also summarized. Finally, a conclusion is drawn where a brief outlook highlights the challenges that hamper the future progress of Bi‐based optoelectronic devices and suggestions for future directions are provided.

Improved Chemical Stability of Organometal Halide Perovskite Solar Cells Against Moisture and Heat by Ag Doping.

Organometal halide perovskite (OHP) solar cells have been intensively studied because of their promising optoelectronic features, which has resulted in high power conversion efficiencies >23 %. Although OHP solar cells exhibit high power conversion efficiencies, their relatively poor stability is a significant obstacle to their practical use. We report that the chemical stability of OHP solar cells with respect to both moisture and heat can be improved by adding a small amount of Ag to the precursor. Ag doping increases the size of the OHP grains and reduces the size of the amorphous intergranular regions at the grain boundaries, and thereby hinders the infiltration of moisture into the OHP films and their thermal degradation. Quantum mechanical simulation reveals that Ag doping increases the energies of both the hydration reaction and heat-induced vacancy formation in OHP crystals. This procedure also improves the power conversion efficiencies of the resulting solar cells.

Facile synthesis of ultrastable organometal halide perovskite nanocomposites using superhydrophobic fumed silica as matrix

Organometal halide perovskite (OMHP) nanocrystals (NCs) have emerged as promising low-cost optoelectronic materials. However, the poor stability of OMHP NCs has greatly hindered their practical applications. Herein, we report a facile synthesis method of ultrastable OMHP nanocomposites by blending the precursor solution of OMHP and superhydrophobic fumed silica. The superhydrophobic surface of silica affords the perfect framework for the growing of nanocrystals. The OMHP composites with emission colour varying from blue to red were conveniently achieved via adjusting the halide element and content. The superhydrophobic fume silica not only improves the water resistance of the OMHP nanocomposites, but also increases their heat and light stability. The applications as phosphor for fabricating green and white light LEDs were demonstrated.

(Invited) Functional Additives for Halide Perovskites Tailored Deposition for Highly Efficient Light-Emitting and Photovoltaic Devices

The control over Organometal Halide Perovskites (OHPs) formation is a fundamental requirement foreseeing the exploitation of these outstanding, eclectic materials in optoelectronics. OHPs, extensively used in solar cells and light emitting diodes (PeLEDs) are deposited from solution on a target substrate and formed throughout a self-assembly process of their chemical precursors [1][2]. The resulting polycrystalline film shows often a far from ideal behaviour, due to unsuitable morphology and high defect density, direct consequences of a scarcely controllable assembly. We present here the exploitation of a tailored biopolymer, starch, as beneficial additional component of formamidinium (FA)- and methylammonium (MA)-based tri-iodide perovskite films. We prove how the macromolecule by establishing specific supramolecular interactions with OHPs precursors allows the deposition of an optimal film via single-step deposition method. Noticeably this is a fundamental technological advantage in comparison to standard multistep deposition approaches. Furthermore, it allows a fine tuning of i) solution viscosity (making it compatible with different large area deposition techniques), of ii) perovskite grain size and of iii) film thickness, parameters that all depends to the polymer:perovskite:solvent relative concentrations. Very importantly the presence of the biopolymer is also improving the stability of the polycrystalline film thanks to two fundamental properties. The polymer being an electronic insulator reduce the impact of the internal electric field over OHPs mobile ions; in addition the polymer is also permeable to ions (ionic conductor), thus by buffering those prevent ions migration/segregation across perovskite grains, one of the most important material degradation mechanism under device working conditions.We validated our approach by embedding these composites in photovoltaic (PV) and light-emitting (PeLED) devices. As result we obtained an inverted, planar, low-temperature processed solar cell showing a remarkable 17% efficiency [3] and a highly efficient LED (EQE of ~5%) exhibiting outstanding radiance values above 200 W/sr·m2 obtained at very high currents (about 1000 mA/cm2) which are among the highest reported radiances for NIR PeLEDs [4].

Effect of the Electron Transport Layer on the Photovoltaic Properties of Hybrid Organic Inorganic Perovskites Solar Cells: Cross-Section of Optics, Morphology, Composition and Quality

Ever since their dawn in 2009 1, hybrid organic–inorganic perovskite materials have been experiencing an ever increase in research investment to finally emerge as a strong alternative for high power conversion efficiency (PCE) photovoltaic devices at low costs. One of the main challenges that is currently impeding the upscaling of these solar cells is the phenomenon of hysteresis on their j–V response that has been correlated with slow ion migration which, in turn, affects their photovoltaic properties. Although hysteresis has been described to some extent of detail, the precise role of the external contacts remains under debate. Furthermore, there has been a great deal of focus on materials and interface design while less attention has been given to optical aspects of these cells. Our work highlights the role of electron transport layer (ETL) of different compositions and synthesized through various routes on the hysteresis response of these systems. We show that there’s a clear correlation between thickness, morphology and composition of the ETL on the photovoltaic response these systems. To better elucidate such a response, we have utilized photoluminescence, electroluminescence, absorption and kelvin probe force microscopy to get a substantial grasp of the optoelectronic phenomena occurring at the interfaces in perovskite solar cells.Acknowledgments: This research was supported by a Hydro-Quebec/NSERC CRD grant and the McGill Sustainability Systems Initiative (MSSI).1- Kojima, A., Teshima, K., Shirai, Y. and Miyasaka, T., 2009. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. Journal of the American Chemical Society, 131(17), pp.6050-6051.

Electrochemical Deposition of Organometallic Halide Perovskite Single-Crystal Particles with Density Gradients and Their Stability, Fluorescence, and Photoelectrochemical Properties

Organometallic halide perovskites have gained immense scientific interest because of their unique optoelectronic properties that can benefit applications such as solar cells, lasers, and light-emit...

Effect of preheated, delayed annealing process on the ultrafast carriers dynamics of perovskite films using ultrafast absorption spectroscopy

Abstract Organic halogenated perovskite material, as an optical material with great development potential, shows excellent application value in the field of solar cells. Solar cells based on organometal halide perovskites possess photoelectricity efficiencies exceeding 25.2%, however, they suffer from oxidization and degradation. In this paper, we present a fabrication technique based on the preheating treatment and delayed annealing to obtain high quality perovskite films. Using the femtosecond transient absorption (TA) spectroscopy, we investigate the transport and lifetime of internal carriers of perovskite films prepared by the preheating treatment and delayed annealing process. The experimental results show that the perovskite film obtained by the preheated treatment is easier to control the carrier recombination rate than the perovskite film obtained by the conventional method. Furthermore, perovskite film with delayed annealing 1 h has a shorter transport time of carriers from the perovskite layer to the hole transport layer, effectively avoiding the direct recombination of carriers. The novel method put forward in this work enables the stabilization and high efficiency of perovskite solar cells.

Zero-power optoelectronic synaptic devices

Abstract Synaptic devices for neuromorphic computing have been recently on the fast track of development. One of the most prominent features of synaptic devices is their potentially ultra-low energy consumption. However, relatively large energy has always been consumed to induce the postsynaptic current (PSC) of a synaptic device up to now. Here, we demonstrate that synaptic devices can work without electrical power supply by taking advantage of the photovoltaic effect during optical stimulation. The optoelectronic synaptic devices with zero-power consumption are fabricated by using the hybrid structure of organometal halide perovskite and silicon nanocrystals (Si NCs). A series of important synaptic functionalities including excitatory PSC, paired-pulse facilitation (PPF), spike-number-dependent plasticity (SNDP), spike-rate-dependent plasticity (SRDP) and dynamic filtering are all successfully mimicked. In addition, arithmetic computing such as addition, subtraction, multiplication and division is realized with the current zero-power-consumption optoelectronic synaptic devices.