Low-dimensional Hybrid Perovskites Research Articles

Regulating The Electronic Configuration of Low-Dimensional Hybrid Perovskites via Organic Cations for Self-Powered Ultraviolet Photodetectors.

Ultraviolet photodetectors (UPDs) based on low-dimensional halide perovskites have undergone rapid development. Here, regulation ofthe electronic configuration of low-dimensional hybrid perovskites are reported via organic cations for self-powered UPDs. For the first time, it is determine that the rational design of organic cation phenyl alkylammonium can effectively prevent phonon scattering thus increasing charge carrier extraction in low dimensional lead chlorine perovskite thin-films. As a result, the exciton-binding energy can be reduced to 62.91meV in (PMA)2PbCl4 perovskite films with a charge-carrier mobility of 0.335cm2V-1s-1. The fabricated (PMA)2PbCl4-based self-powered UPDs has achieved a high detectivity of 6.32 × 1013 jones with a low noise current of 0.35pAHz-1/2 under zero bias. A further demonstration of images with high UV to visible light rejection ratio under weak-light illumination of 70nWcm-2 highlights the feasible potential application of low-dimensional perovskite.

Lead-Bromide Hybrid Perovskites with Different Dimensions due to NH<sub>2</sub> Position Variation Pyridine Ligand Methylene Bridge-CH<sub>2</sub>

The hybrid perovskites of amino(methyl) pyridines (AMP) and lead (II) bromide (PbBr2) were synthesised using a reflux method in 40% hydrobromic acid medium in a closed-nitrogen condition. The structural, chemical and optical properties of the as-synthesised compounds were analysed analytically using XRD, FT-IR and UV-Vis. Based on the XRD analysis, all compounds have distinct and evenly spaced diffraction peaks, indicating that they are strongly oriented and well-crystallised. The presence of aromatics and primary amines in mono-substituted pyridinium cation variations was confirmed by the FT-IR analysis. All compounds absorbed strongly in visible spectra at 430 nm, 427 nm and 355 nm, respectively. This study demonstrates that organic-tailoring effects in the shifting of aminomethyl position in the pyridine chain contribute to different dimensionalities of hybrid perovskite frameworks, even when synthesised under the same conditions. The as-synthesised low-dimensional hybrid perovskite can be further utilised as a light-harvester material in Perovskite Solar Cells (PSCs).

Role of Hydrogen Bonding on the Design of New Hybrid Perovskites Unraveled by Machine Learning.

Selecting a set of reactants to accurately design a new low dimensional hybrid perovskite could greatly accelerate the discovery of materials with great potential in photovoltaics, or solid-state lighting. However, this design is challenging as most hybrid metal halides are not perovskites and no feature is clearly associated to the structural characteristics of the inorganic metal halide network. This work first demonstrates that the organic molecules are key parameters to determine the structure type of the inorganic network (i.e., perovskite versus non-perovskite). Then, machine learning (ML) algorithms are used to identify the key features of the organic cations leading to the perovskite structure type. Using a large dataset of hybrid metal halides, this work extracts the organic molecules of all hybrid lead halide compounds, calculates 2756 molecular descriptors and fingerprints for each of these molecules, and are able to predict through ML techniques if a specific organic amine will lead to the perovskite type with an accuracy up to 88.65%. Descriptors related to hydrogen bonding are identified as important features. Thus, a simple but reliable design principle could be demonstrated: the presence of primary ammonium cation is the primary condition to prepare hybrid lead halide perovskites regardless of their dimensionalities.

Ferroelectricity in Hybrid Perovskites.

Ferroelectric ceramics such as PbZrxTi1-xO3 (PZT) are widely applied in many fields, from medical to aerospace, because of their dielectric, piezoelectric, and pyroelectric properties. In the past few years, hybrid organic-inorganic halide perovskites have gradually attracted attention for their optical and electronic properties, including ferroelectricity, and for their low fabrication costs. In this Review, we first describe techniques that are used to quantify ferroelectric figures of merit of a material. We then discuss ferroelectricity in hybrid perovskites, starting from controversies in methylammonium iodoplumbate perovskites and then focusing on low-dimensional perovskites that offer an unambiguous platform to obtain ferroelectricity. Finally, we provide examples of the application of perovskite ferroelectrics in solar cells, LEDs, and X-ray detectors. We conclude that the vast structure-property tunability makes low-dimensional hybrid perovskites promising, but they have yet to offer ferroelectric figures of merit (e.g., saturated polarization) and thermal stability (e.g., Curie temperature) competitive with those of conventional oxide perovskite ferroelectric materials.

Broadband red emission from one-dimensional hexamethonium lead bromide perovskitoid.

Broadband emissions from low-dimensional hybrid perovskites have aroused intense interest. However, the achievement of broadband red emission in lead halide perovskites remains challenging. Herein, we report a one-dimensional (1D) hybrid lead bromide perovskitoid, (HM)Pb2Br6 (HM = hexamethonium), featuring a corrugated "3 × 3" [Pb2Br6]2- chain. The unique structure results in intriguingly red emission peaking at 692 nm, with a PLQY of around 6.24%. Our spectroscopic and computational studies reveal that the red emission derives from self-localized Pb23+, Pb3+ and Br2- species confined within the inorganic lead bromide lattice that function as radiative centres. This finding will benefit the design of perovskite systems for efficient red emission.

Probing Strain-Induced Effects on Performance of Low-Dimensional Hybrid Perovskites for Solar Energy Harvesting.

The application of strain to photovoltaics (PVs), thermoelectrics (TEs), and semiconductors often has substantial impacts on the fundamental properties governing the efficiency of these materials. In this work, we investigate two stable phases of hybrid organic-inorganic two-dimensional (2D) perovskites (2DPKs) and their response to the application of tensile and compressive strain of up to 5%. These 2D MAPbI3 analogues are known to exhibit strongly anisotropic properties and have been put forward as excellent candidates for application in mixed PV-TE devices. Our results, stemming from ab initio density functional theory calculations and investigation of transport properties through the Boltzmann transport equations, further elucidate the key properties contributing to the success of these materials. In particular, both the M1 and M2 phases exhibit stable structures between -5 and 5% biaxial strains. The M2 phase exhibits an excellent 23.8% power conversion efficiency under the application of 5% tensile strain. Furthermore, we analyze the effects of spin-orbit coupling on the band structures of both phases, revealing great potential for spintronic applications with the M2 phase, demonstrating Rashba coefficients up to 3.67 eV Å.

Chiral Ligand-Induced Structural Transformation of Low-Dimensional Hybrid Perovskite for Circularly Polarized Photodetection

Chiral Ligand-Induced Structural Transformation of Low-Dimensional Hybrid Perovskite for Circularly Polarized Photodetection

Near-room-temperature reversible switching of quadratic optical nonlinearities in a one-dimensional perovskite-like hybrid

The switching of quadratic nonlinear optical (NLO) effects between two or more NLO states of solid-state materials represents an intriguing new branch in the field of photoelectrics and optics. While structural phase transitions have shown potential in this field, near-room-temperature reversible NLO switches have rarely been reported. To exploit new NLO switching materials within the structurally flexible class of hybrid perovskites, here, we synthesize a one-dimensional perovskite-like hybrid, (MP)PbBr3 (where MP+ is a 1-methylpyrrolidinium cation), through a facile solution method, which exhibits strong second harmonic generation (SHG) activities with an intensity of ~1.6 times as large as potassium dihydrogen phosphate. Intriguingly, (MP)PbBr3 enables the near-room temperature reversible switching of SHG properties, showing a large NLO switching contrast of up to ~40 between its SHG-active and SHG-inactive phases, beyond most of its liquid counterparts. Further microscopic structural analyses reveal that the dynamic ordering of the organic MP+ cation and inorganic chain-like skeleton triggers its centrosymmetric (P63/mmc) to acentric (P212121) phase transition at 316 K upon cooling, resulting in a crucial contribution to its NLO switching properties. This work illustrates the potential of this material as a candidate for solid-state NLO switches and will promote the development of NLO materials within the family of low-dimensional hybrid perovskites.

Molecular engineering towards efficientwhite-light-emitting perovskite

Low-dimensional hybrid perovskites have demonstrated excellent performance as white-light emitters. The broadband white emission originates from self-trapped excitons (STEs). Since the mechanism of STEs formation in perovskites is still not clear, preparing new low-dimensional white perovskites relies mostly on screening lots of intercalated organic molecules rather than rational design. Here, we report an atom-substituting strategy to trigger STEs formation in layered perovskites. Halogen-substituted phenyl molecules are applied to synthesize perovskite crystals. The halogen-substituents will withdraw electrons from the branched chain (-R-NH3+) of the phenyl molecule. This will result in positive charge accumulation on -R-NH3+, and thus stronger Coulomb force of bond (-R-NH3+)-(PbBr42−), which facilitates excitons self-trapping. Our designed white perovskites exhibit photoluminescence quantum yield of 32%, color-rendering index of near 90 and chromaticity coordinates close to standard white-light. Our joint experiment-theory study provides insights into the STEs formation in perovskites and will benefit tailoring white perovskites with boosting performance.

Naphthalenediimide/Formamidinium-Based Low-Dimensional Perovskites

Low-dimensional hybrid perovskites have emerged as promising materials for optoelectronic applications. Although these materials have already demonstrated enhanced stability as compared to their three-dimensional perovskite analogues, their functionality has been limited by the insulating character of the organic moieties that primarily play a structure-directing role. This is particularly the case for the layered (2D) perovskite materials based on formamidinium lead iodide (FAPbI3) that remain scarce. We demonstrate a low-dimensional hybrid perovskite material based on a SPbI4 composition incorporating an electroactive naphthalenediimide (NDI) moiety as an organic spacer (S) between the perovskite slabs and evidence the propensity of the spacer to stabilize the α-FAPbI3 perovskite phase in hybrid low-dimensional SFAn–1PbnI3n+1 perovskite compositions. This has been investigated by means of solid-state nuclear magnetic resonance spectroscopy in conjunction with molecular dynamics simulations and density functional theory calculations. Theoretical calculations suggest an electronic contribution of the organic spacer to the resulting optoelectronic properties, which was confirmed by transient absorption spectroscopy. We have further analyzed these materials by time-resolved microwave conductivity measurements, revealing challenges for their application in photovoltaics.

Layered Hybrid Formamidinium Lead Iodide Perovskites: Challenges and Opportunities.

ConspectusHybrid halide perovskite materials have become one of the leading candidates for various optoelectronic applications. They are based on organic-inorganic structures defined by the AMX3 composition, were A is the central cation that can be either organic (e.g., methylammonium, formamidinium (FA)) or inorganic (e.g., Cs+), M is a divalent metal ion (e.g., Pb2+ or Sn2+), and X is a halide anion (I-, Br-, or Cl-). In particular, FAPbI3 perovskites have shown remarkable optoelectronic properties and thermal stabilities. However, the photoactive α-FAPbI3 (black) perovskite phase is not thermodynamically stable at ambient temperature and forms the δ-FAPbI3 (yellow) phase that is not suitable for optoelectronic applications. This has stimulated intense research efforts to stabilize and realize the potential of the α-FAPbI3 perovskite phase. In addition, hybrid perovskites were proven to be unstable against the external environmental conditions (air and moisture) and under device operating conditions (voltage and light), which is related to various degradation mechanisms. One of the strategies to overcome these instabilities has been based on low-dimensional hybrid perovskite materials, in particular layered two-dimensional (2D) perovskite phases composed of organic layers separating hybrid perovskite slabs, which were found to be more stable toward ambient conditions and ion migration. These materials are mostly based on SxAn-1PbnX3n+1 composition with various mono- (x = 1) or bifunctional (x = 2) organic spacer cations that template hybrid perovskite slabs and commonly form either Ruddlesden-Popper (RP) or Dion-Jacobson (DJ) phases. These materials behave as natural quantum wells since charge carriers are confined to the inorganic slabs, featuring a gradual decrease in the band gap as the number of inorganic layers (n) increases from n = 1 (2D) to n = ∞ (3D). While various layered 2D perovskites have been developed, their FA-based analogues remain under-represented to date. Over the past few years, several research advances enabled the realization of FA-based layered perovskites, which have also demonstrated a unique templating effect in stabilizing the α-FAPbI3 phase. This, for instance, involved the archetypical n-butylammonium and 2-phenylethylammonium organic spacers as well as guanidinium, 5-ammonium valeric acid, iso-butylammonium, benzylammonium, n-pentylammonium, 2-thiophenemethylammonium, 2-(perfluorophenyl)ethylammonium, 1-adamantylmethanammonium, and 1,4-phenylenedimethanammonium. FAPbBr3-based layered perovskites have also demonstrated potential in various optoelectronic applications, yet the opportunities associated with FAPbI3-based perovskites have attracted particular attention in photovoltaics, stimulating further developments. This Account provides an overview of some of these recent developments, with a particular focus on FAPbI3-based layered perovskites and their utility in photovoltaics, while outlining challenges and opportunities for these hybrid materials in the future.

(Invited) A Chiral Switchable Photovoltaic Ferroelectric Semiconductor

Symmetry is an essential knob in designing and engineering physical properties of materials. In this talk, I will discuss our efforts on searching ferroelectric semiconductors that lack mirror symmetry. I will present the discovery of a previously unknown low-dimensional hybrid perovskite material with electric field-switchable pyroelectricity and optical chirality. This discovery will facilitate the exploration of phenomena such as electric field and chiral enantiomer–dependent Rashba-Dresselhaus splitting and circular photogalvanic effects.

One-Dimensional (NH=CINH3)3PbI5 Perovskite for Ultralow Power Consumption Resistive Memory.

Organic-inorganic hybrid perovskites (OIHPs) have proven to be promising active layers for nonvolatile memories because of their rich abundance in earth, mobile ions, and adjustable dimensions. However, there is a lack of investigation on controllable fabrication and storage properties of one-dimensional (1D) OIHPs. Here, the growth of 1D (NH=CINH3)3PbI5 ((IFA)3PbI5) perovskite and related resistive memory properties are reported. The solution-processed 1D (IFA)3PbI5 crystals are of well-defined monoclinic crystal phase and needle-like shape with the length of about 6 mm. They exhibit a wide bandgap of 3 eV and a high decomposition temperature of 206°C. Moreover, the (IFA)3PbI5 films with good uniformity and crystallization were obtained using a dual solvent of N,N-dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). To study the intrinsic electric properties of this anisotropic material, we constructed the simplest memory cell composed of only Au/(IFA)3PbI5/ITO, contributing to a high-compacted device with a crossbar array device configuration. The resistive random access memory (ReRAM) devices exhibit bipolar current-voltage (I-V) hysteresis characteristics, showing a record-low power consumption of ~0.2 mW among all OIHP-based memristors. Moreover, our devices own the lowest power consumption and "set" voltage (0.2 V) among the simplest perovskite-based memory devices (inorganic ones are also included), which are no need to require double metal electrodes or any additional insulating layer. They also demonstrate repeatable resistance switching behaviour and excellent retention time. We envision that 1D OIHPs can enrich the low-dimensional hybrid perovskite library and bring new functions to low-power information devices in the fields of memory and other electronics applications.

Implicit Tandem Organic–Inorganic Hybrid Perovskite Solar Cells Based on Internal Dye Sensitization: Robotized Screening, Synthesis, Device Implementation, and Theoretical Insights

Low-dimensional hybrid perovskite materials offer significantly improved stability as well as an extensive compositional space to explore. However, they suffer from poor photovoltaic performance as compared to the 3D perovskite materials because of poor charge-transport properties. Herein, we present the concept of internal dye-sensitized hybrid perovskite compounds involving five novel low-dimensional perovskite-type materials 1–5 incorporating triarylmethane, phenazinium and near-infrared (NIR) cyanine cationic dyes, respectively. The synthesis characterization and theoretical analysis of these compounds are presented. Theoretical calculations provide interesting insights into the effects of these dyes on the band structure of the low-dimensional anionic metal-halides and especially highlight compound 1 as a promising photovoltaic candidate. Solar cell investigation of devices based on 1 were conducted. The results show an average power conversion efficiency (PCE) of about 0.1%, which is among the highest reported for a 1D material despite the use of undoped Spiro-OMeTAD as the hole-transport material (HTM). Incident photon-to-electron efficiency (IPCE) spectra confirm the contribution of the dye to the overall photocurrent of the solar cell. Moreover, examination of solar cell devices based on the bismuth-based compound 5 resulted in PCEs in the range of 0.1%. This illustrates the potential of this concept to be exploited for lead-free photovoltaics. Finally automated robotized screening of low-dimensional hybrid perovskite materials through the screening robot PROTEUS has emerged as a powerful tool in the search for novel perovskite-like materials. Our work highlights that the use of cationic dyes could induce interesting sensitizing properties to low-dimensional metal-halide chains and may therefore provide inspiration and new design strategies for the synthesis of new lead-free photovoltaic materials

Guanine-Stabilized Formamidinium Lead Iodide Perovskites.

Formamidinium (FA) lead iodide perovskite materials feature promising photovoltaic performances and superior thermal stabilities. However, conversion of the perovskite α-FAPbI3 phase to the thermodynamically stable yet photovoltaically inactive δ-FAPbI3 phase compromises the photovoltaic performance. A strategy is presented to address this challenge by using low-dimensional hybrid perovskite materials comprising guaninium (G) organic spacer layers that act as stabilizers of the three-dimensional α-FAPbI3 phase. The underlying mode of interaction at the atomic level is unraveled by means of solid-state nuclear magnetic resonance spectroscopy, X-ray crystallography, transmission electron microscopy, molecular dynamics simulations, and DFT calculations. Low-dimensional-phase-containing hybrid FAPbI3 perovskite solar cells are obtained with improved performance and enhanced long-term stability.

Fluorination of Organic Spacer Impacts on the Structural and Optical Response of 2D Perovskites.

Low-dimensional hybrid perovskites have triggered significant research interest due to their intrinsically tunable optoelectronic properties and technologically relevant material stability. In particular, the role of the organic spacer on the inherent structural and optical features in two-dimensional (2D) perovskites is paramount for material optimization. To obtain a deeper understanding of the relationship between spacers and the corresponding 2D perovskite film properties, we explore the influence of the partial substitution of hydrogen atoms by fluorine in an alkylammonium organic cation, resulting in (Lc)2PbI4 and (Lf)2PbI4 2D perovskites, respectively. Consequently, optical analysis reveals a clear 0.2 eV blue-shift in the excitonic position at room temperature. This result can be mainly attributed to a band gap opening, with negligible effects on the exciton binding energy. According to Density Functional Theory (DFT) calculations, the band gap increases due to a larger distortion of the structure that decreases the atomic overlap of the wavefunctions and correspondingly bandwidth of the valence and conduction bands. In addition, fluorination impacts the structural rigidity of the 2D perovskite, resulting in a stable structure at room temperature and the absence of phase transitions at a low temperature, in contrast to the widely reported polymorphism in some non-fluorinated materials that exhibit such a phase transition. This indicates that a small perturbation in the material structure can strongly influence the overall structural stability and related phase transition of 2D perovskites, making them more robust to any phase change. This work provides key information on how the fluorine content in organic spacer influence the structural distortion of 2D perovskites and their optical properties which possess remarkable importance for future optoelectronic applications, for instance in the field of light-emitting devices or sensors.

Tuning Hot Carrier Cooling Dynamics by Dielectric Confinement in Two-Dimensional Hybrid Perovskite Crystals

Hot carrier (HC) cooling is a critical photophysical process that significantly influences the optoelectronic performance of hybrid perovskite-based devices. The hot carrier extraction at the device interface is very challenging because of its ultrashort lifetime. Here, ultrafast transient reflectance spectroscopy measurements and time-domain ab initio calculations show how the dielectric constant of the organic spacers can control and slow the HC cooling dynamics in single-crystal 2D Ruddlesden-Popper hybrid perovskites. We find that (EA)2PbI4 (EA = HOC2H4NH3+) that correspond to a high dielectric constant organic spacer has a longer HC cooling time compared to that of (AP)2PbI4 (AP = HOC3H6NH3+) and (PEA)2PbI4 (PEA = C6H5C2H4NH3+). The slow HC relaxation process in the former case can be ascribed to a stronger screening of the Coulomb interactions, a small nonradiative internal conversion within the conduction bands, as well as a weak electron-phonon coupling. Our findings provide a strategy to prolong the hot carrier cooling time in low-dimensional hybrid perovskite materials by using organic spacers with reduced dielectric confinement.

High performance low-dimensional perovskite solar cells based on a one dimensional lead iodide perovskite

One-dimensional perovskites enable high performance low-dimensional perovskite solar cells.

Low-dimensional hybrid perovskites as high performance anodes for alkali-ion batteries

Molecularly engineered low-dimensional hybrid perovskites are demonstrated as anode materials for alkali-ion batteries. The electrochemical performance can be dramatically improved by tuning the dimensionality of halide-perovskites from 3D to 2D to 1D.