Properties Of Halide Perovskites Research Articles

Ultrafast carrier dynamics and transient nonlinear absorption in chalcogenide perovskite BaZrS3

The unique combination of excellent semiconducting properties in halide perovskites and the high stability and nontoxicity of oxide perovskites has led to a recent surge in interest in chalcogenide perovskite BaZrS3 for optoelectronic applications. However, to realize its potential in future device technologies, a comprehensive understanding of photoexcited carrier dynamics and transient optical response is imperative, yet it remains largely unexplored for BaZrS3. In this work, employing transient absorption spectroscopy, we have revealed that photoexcited carriers in epitaxial BaZrS3 nanofilms exhibit two exponential decay components relating to optical phonon cooling and interband recombinations. Meanwhile, our investigation unveils an intriguing transient nonlinear absorption phenomenon in BaZrS3, characterized by the ultrafast switching of the pump-induced transparency (i.e., the saturable absorption) to the absorption enhancement within a timescale commensurate with the measurement resolution (hundreds of femtosecond). This study provides crucial dynamic insights essential for leveraging chalcogenide perovskites, such as BaZrS3, in the development of advanced optoelectronic devices.

Cryogenic Electron-Beam Writing for Perovskite Metasurface.

Halide perovskites (HPs) metasurfaces have recently attracted significant interest due to their potential to not only further enhance device performance but also reveal the unprecedented functionalities and novel photophysical properties of HPs. However, nanopatterning on HPs is critically challenging as they are readily destructed by the organic solvents in the standard lithographic processes. Here, we present a novel, subtle, and fully nondestructive HPs metasurface fabrication strategy based on cryogenic electron-beam writing. This technique allows for high-precision patterning and in situ imaging of HPs with excellent compatibility. As a proof-of-concept, broadband absorption enhanced metasurfaces were realized by patterning nanopillar arrays on CH3NH3PbI3 film, which results in photodetectors with approximately 14-times improvement on responsivity and excellent stability. Our findings highlight the great feasibility of cryogenic electron-beam writing for producing perovskite metasurface and unlocking the unprecedented photoelectronic properties of HPs.

Carriers, Quasi-particles, and Collective Excitations in Halide Perovskites.

Halide perovskites (HPs) are potential game-changing materials for a broad spectrum of optoelectronic applications ranging from photovoltaics, light-emitting devices, lasers to radiation detectors, ferroelectrics, thermoelectrics, etc. Underpinning this spectacular expansion is their fascinating photophysics involving a complex interplay of carrier, lattice, and quasi-particle interactions spanning several temporal orders that give rise to their remarkable optical and electronic properties. Herein, we critically examine and distill their dynamical behavior, collective interactions, and underlying mechanisms in conjunction with the experimental approaches. This review aims to provide a unified photophysical picture fundamental to understanding the outstanding light-harvesting and light-emitting properties of HPs. The hotbed of carrier and quasi-particle interactions uncovered in HPs underscores the critical role of ultrafast spectroscopy and fundamental photophysics studies in advancing perovskite optoelectronics.

Electron Ptychographic Phase Imaging of Beam-sensitive All-inorganic Halide Perovskites Using Four-dimensional Scanning Transmission Electron Microscopy.

Halide perovskites (HPs) are promising candidates for optoelectronic devices, such as solar cells or light-emitting diodes. Despite recent progress in performance optimization and low-cost manufacturing, their commercialization remains hindered due to structural instabilities. While essential to the development of the technology, the relation between the microscopic properties of HPs and the relevant degradation mechanisms is still not well understood. The sensitivity of HPs toward electron-beam irradiation poses significant challenges for transmission electron microscopy (TEM) investigations of structure and degradation mechanisms at the atomic scale. However, technological advances and the development of direct electron cameras (DECs) have opened up a completely new field of electron microscopy: four-dimensional scanning TEM (4D-STEM). From a 4D-STEM dataset, it is possible to extract not only the intensity signal for any STEM detector geometry but also the phase information of the specimen. This work aims to show the potential of 4D-STEM, in particular, electron exit-wave phase reconstructions via focused probe ptychography as a low-dose and dose-efficient technique to image the atomic structure of beam-sensitive HPs. The damage mechanism under conventional irradiation is described and atomically resolved almost aberration-free phase images of three all-inorganic HPs, CsPbBr3, CsPbIBr2, and CsPbI3, are presented with a resolution down to the aperture-constrained diffraction limit.

Prospects for Tin-Containing Halide Perovskite Photovoltaics.

Tin-containing metal halide perovskites have enormous potential as photovoltaics, both in narrow band gap mixed tin-lead materials for all-perovskite tandems and for lead-free perovskites. The introduction of Sn(II), however, has significant effects on the solution chemistry, crystallization, defect states, and other material properties in halide perovskites. In this perspective, we summarize the main hurdles for tin-containing perovskites and highlight successful attempts made by the community to overcome them. We discuss important research directions for the development of these materials and propose some approaches to achieve a unified understanding of Sn incorporation. We particularly focus on the discussion of charge carrier dynamics and nonradiative losses at the interfaces between perovskite and charge extraction layers in p-i-n cells. We hope these insights will aid the community to accelerate the development of high-performance, stable single-junction tin-containing perovskite solar cells and all-perovskite tandems.

Pressure-Tuning Photothermal Synergy to Optimize the Photoelectronic Properties in Amorphous Halide Perovskite Cs3 Bi2 I9.

Effective modification of the structure and properties of halide perovskites via the pressure engineering strategy has attracted enormous interest in the past decade. However, sufficient effort and insights regarding the potential properties and applications of the high-pressure amorphous phase are still lacking. Here, the superior and tunable photoelectric properties that occur in the pressure-induced amorphization process of the halide perovskite Cs3 Bi2 I9 are demonstrated. With increasing pressure, the photocurrent with xenon lamp illumination exhibits a rapid increase and achieves an almost five orders of magnitude increment compared to its initial value. Impressively, a broadband photoresponse from 520 to 1650nm with an optimal responsivity of 6.81mA W-1 and fast response times of 95/96ms at 1650nm is achieved upon successive compression. The high-gain, fast, broadband, and dramatically enhanced photoresponse properties of Cs3 Bi2 I9 are the result of comprehensive photoconductive and photothermoelectric mechanisms, which are associated with enhanced orbital coupling caused by an increase in BiI interactions in the [BiI6 ]3- cluster, even in the amorphous state. These findings provide new insights for further exploring the potential properties and applications of amorphous perovskites.

A Review on Halide Perovskite-Based Photocatalysts: Key Factors and Challenges.

A growing number of research articles have been published on the use of halide perovskite materials for photocatalytic reactions. These articles extend these materials' great success from solar cells to photocatalytic technologies such as hydrogen production, CO2 reduction, dye degradation, and organic synthesis. In the present review article, we first describe the background theory of photocatalysis, followed by a description on the properties of halide perovskites and their development for photocatalysis. We highlight key intrinsic factors influencing their photocatalytic performance, such as stability, electronic band structure, and sorption properties. We also discuss and shed light on key considerations and challenges for their development in photocatalysis, such as those related to reaction conditions, reactor design, presence of degradable organic species, and characterization, especially for CO2 photocatalytic reduction. This review on halide perovskite photocatalysts will provide a better understanding for their rational design and development and contribute to their scientific and technological adoption in the wide field of photocatalytic solar devices.

Nonlinear Infrared Photodetection Based on Strong Nondegenerate Two‐Photon Absorption of Perovskite Single Crystal

AbstractHalide perovskites have been recently shown to exhibit strong nonlinear optical properties such as two‐photon absorption, second harmonic generation, etc. In this work, the nondegenerate two‐photon absorption, i.e., when the energies of two photons absorbed are not the same, of methylammonium lead bromide single crystal is studied. It is found that the nondegenerate two‐photon absorption is much stronger than the degenerate two‐photon absorption. For the photon pair ℏω1 = 2.96 eV, ℏω2 = 0.73 eV, the nondegenerate two‐photon absorption coefficient reaches 51.3 cm GW−1, which is around 6 times that of degenerate two‐photon absorption. Taking advantage of the strong nondegenerate two‐photon absorption, a nonlinear infrared pulse photodetector based on the combination of a methylammonium lead bromide single crystal and a silicon photodiode is developed. The infrared femtosecond laser pulses at 1700 nm can be well measured with a resolution on the order of 1 nJ and responsivity of 68 V W−1. These findings provide novel insight for the understanding of nondegenerate nonlinear optical properties in halide perovskites and may open a new avenue for the development of high‐sensitivity infrared photon detection.

Efficient p‐Type Doping of Tin Halide Perovskite via Sequential Diffusion for Thermoelectrics

Metal halide perovskites (MHPs) hold great potential in thermoelectric (TE) applications, thanks to their regular and soft lattice in nature. However, the poor electrical conductivity caused by low charge carrier density (<1014 cm−3 for lead‐based MHPs) strongly impedes its TE development. In this scenario, tin halide perovskites (THPs) emerge as promising TE candidates owing to their high background hole densities (>1019 cm−3). However, further electrical doping remains challenging, originating from the limited capability of accommodating heterogeneous dopants and the heavy compensation in THPs. Herein, a novel diffusion‐mediated doping approach is demonstrated to prominently increase the p‐type doping level of THPs by a sequence of air exposure and 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F4TCNQ) surface treatments. In paradigm photovoltaic THP materials—CH(NH2)2SnI3 (namely FASnI3), the electrical conductivity is dramatically increased by 300× from 0.06 to 18 S cm−1 in thin films, leading to a remarkable enhancement of power factor by 25× up to 53 μW m−1 K−2. In contrast, only a slight variation of thermal conductivity is observed after F4TCNQ deposition, which is in accordance with the increase in electrical conductivity, indicating that the lattice structures of FASnI3 remain intact after doping. This study paves an illuminating way to ameliorate TE properties in halide perovskites.

Defect tolerance in halide perovskites: A first-principles perspective

In recent years, the impressive photovoltaic performance of halide perovskites has been commonly attributed to their defect tolerance. This attribution is seemingly intuitive and has been widely promoted in the field, though it has not been rigorously assessed. In this Perspective, we critically discuss the proposition of defect tolerance in halide perovskites based on first-principles calculations. We show that halide perovskites actually do suffer from defect-assisted nonradiative recombination, i.e., they are not defect tolerant. The nonradiative recombination rates in halide perovskites are comparable to or even greater than those in more conventional semiconductors. We note that to obtain accurate defect properties in halide perovskites, the level of theory and computational details are highly important, which was previously not sufficiently recognized. A distinctive feature of halide perovskites is that they can be grown with moderate defect densities using low-cost deposition techniques. But, similar to the case of conventional semiconductors, defect engineering is still key to improving the efficiency of perovskite solar cells.

The Recent Progress on Halide Perovskite-Based Self-Powered Sensors Enabled by Piezoelectric and Triboelectric Effects

Sensors have recently gathered significant attention owing to the rapid growth of the Internet of Things (IoT) technology for the real-time monitoring of surroundings and human activities. Particularly, recently discovered nanogenerator-based self-powered sensors are potential candidates to overcome the existing problems of the conventional sensors, including regular monitoring, lifetime of a power unit, and portability. Halide perovskites (HPs), with an excellent photoactive nature, dielectric, piezoelectric, ferroelectric, and pyroelectric properties, have been potential candidates for obtaining flexible and self-powered sensors including light, pressure, and temperature. Additionally, the photo-stimulated dielectric, piezoelectric, and triboelectric properties of HPs make them efficient entrants for developing bimodal and multimode sensors to sense multi-physical signals individually or simultaneously. Therefore, we provide an update on the recent progress in self-powered sensors based on pyroelectric, piezoelectric, and triboelectric effects of HP materials. First, the detailed working mechanism of HP-based piezoelectric, triboelectric, and pyroelectric nanogenerators—operated as self-powered sensors—is presented. Additionally, the effect of light on piezoelectric and triboelectric effects of HPs, which is indispensable in multimode sensor application, is also systematically discussed. Furthermore, the recent advances in nanogenerator-based self-powered bimodal sensors comprising HPs as light-active materials are summarized. Finally, the perspectives and continuing challenges of HP-based self-powered sensors are presented with some opportunities for future development in self-powered multimode sensors.

The application of halide perovskites in memristors

New neuromorphic architectures and memory technologies with low power consumption, scalability and high-speed are in the spotlight due to the von Neumann bottleneck and limitations of Moore's law. The memristor, a two-terminal synaptic device, shows powerful capabilities in neuromorphic computing and information storage applications. Active materials with high defect migration speed and low defect migration barrier are highly promising for high-performance memristors. Halide perovskite (HP) materials with point defects (such as gaps, vacancies, and inversions) have strong application potential in memristors. In this article, we review recent advances on HP memristors with exceptional performances. First, the working mechanisms of memristors are described. Then, the structures and properties of HPs are explained. Both electrical and photonic HP-based memristors are overviewed and discussed. Different fabrication methods of HP memristor devices and arrays are described and compared. Finally, the challenges in integrating HP memristors with complementary metal oxide semiconductors (CMOS) are briefly discussed. This review can assist in developing HP memristors for the next-generation information technology.

Imaging Carrier Transport Properties in Halide Perovskites using Time‐Resolved Optical Microscopy

AbstractHalide perovskites have remarkable properties for relatively crudely processed semiconductors, including large optical absorption coefficients and long charge carrier lifetimes. Thanks to such properties, these materials are now competing with established technologies for use in cost‐effective and efficient light‐harvesting and light‐emitting devices. Nevertheless, the fundamental understanding of the behavior of charge carriers in these materials—particularly on the nano‐ to microscale—has, on the whole, lagged behind empirical device performance. Such understanding is essential to control charge carriers, exploit new device structures, and push devices to their performance limits. Among other tools, optical microscopy and spectroscopic techniques have revealed rich information about charge carrier recombination and transport on important length scales. In this progress report, the contribution of time‐resolved optical microscopy techniques to the collective understanding of the photophysics of these materials is detailed. The ongoing technical developments in the field that are overcoming traditional experimental limitations in order to visualize transport properties over multiple time and length scales are discussed. Finally, strategies are proposed to combine optical microscopy with complementary techniques in order to obtain a holistic picture of local carrier photophysics in state‐of‐the‐art perovskite devices.

Defect proliferation in CsPbBr3 crystal induced by ion migration

Ion migration in halide perovskite materials usually brings an intractable problem in the working stability of solar cells and photoelectrical detectors. The mechanism of ion migration and its impact on physical properties are still open questions. In this work, the ion migration behavior in solution-grown CsPbBr3 crystals was observed by the hysteresis in current–voltage curves and the temperature dependent reversed current–time measurements. Defect proliferation phenomena (new defects of [VCs]− and [PbBr]2+) originating from ion migration were verified by thermally stimulated current spectroscopy. Our results also give evidence that Cs+ ions also participate in the process of ion migration except the widely considered Br− ions. Furthermore, the photoelectric properties of the CsPbBr3 device were found to be seriously deteriorated after the ion migration. Our work demonstrates the strong correlation between the ion migration and physical properties in halide perovskites.

Halide perovskite photocatalysis: progress and perspectives

AbstractOrganic–inorganic metal halide perovskites (HPs) have emerged as new frontier materials for optoelectronic and energy applications. In addition to various well‐known applications, such as solar cells, light‐emitting diodes, photodetectors, and resistive switching memories, HPs can be utilized as efficient photocatalysts for numerous electrochemical reactions, including carbon dioxide (CO2) reduction reactions, hydrogen evolution reaction, photosynthesis, and wastewater treatment. However, the use of HPs toward photo‐driven catalysis remains a tremendous challenge owing to their poor stability in polar solvents. Nevertheless, huge progress has been made to counter this critical issue for improving the performance of HPs as efficient photocatalysts in a wide range of applications. In this review, we first introduce the structures and properties of HPs. Next, we highlight the recent approaches on the fabrication of HPs, including thin films and nanostructures. Strategies for implementing HPs in catalysis systems and their working mechanisms are thoroughly summarized and discussed. Lastly, the current challenges and prospects of the application of HPs toward photocatalytic reactions are fully addressed. © 2020 Society of Chemical Industry

Evidence for Ferroelectricity of All-Inorganic Perovskite CsPbBr3 Quantum Dots

The combination of ferroelectric-optical properties in halide perovskites has attracted tremendous interess because of its potential for optoelectronic and energy applications. However, very few reports focus on the ferroelectricity of all-inorganic halide perovskites quantum dots. Herein, we report a excellent ferroelectricity in CsPbBr3 quantum dots (QDs) with a saturation polarization of 0.25 μC/cm2. Differential scanning calorimetry, X-ray diffraction, and transmission electronic microscopy revealed that the mechanism of ferroelectric-paraelectric switching of CsPbBr3 QDs can be attributed to the phase transition from cubic phase (Pm3̅m) to the orthorhombic phase (Pna21). In the orthorhombic CsPbBr3, the distortion of octahedral [PbBr6]4- structural units and the off-center Cs+ generated the slightly separated centers of positive charge and negative charge, resulting in the ferroelectric properties. The variable-temperature emission spectrum from 328 to 78 K exhibits green luminescence and a gradual red shift due to the phase transition. This finding opens up an avenue to explore the ferroelectric-optical properties of inorganolead halide perovskites for high-performance multifunctional materials.

Effects of compositional engineering and surface passivation on the properties of halide perovskites: a theoretical understanding.

Halide perovskite solar cells have demonstrated high power conversion efficiency. Compositional engineering and surface passivation technologies have been drawing great attention to enhance their energy conversion efficiency and moisture resistance. In this study, the density functional theory method was employed to understand the effects of compositional engineering at the A site of perovskites and the 3-butenoic acid-based passivation layer on the structural, electronic and optical properties of halide perovskites. Our results suggest that the electronic and optical properties of CsPbI3 can be tuned by the mixing of caesium and FA cations. Moreover, the calculation of adsorption energies on mixed-cation Cs1-xFAxPbI3(001) surfaces reveals that the much stronger adsorption strength of 3-butenoic acid facilitates blocking of the interaction of surfaces with water molecules. Meanwhile, the calculated results indicate that adopting such an organic molecule as a passivation layer does not compromise their excellent electronic and optical properties. Our theoretical understanding of the A cation engineering and organic molecule-based surface passivation will be beneficial to the improvement of the overall performance of perovskite solar cells.

Structures and Properties of Methylammonium Iodide Precursors of Halide Perovskites and Implications for Solar Cells: an Ab-Initio Investigation

Halide perovskite materials based on the prototypical CH3NH3PbI3 received much attention in recent years, with applications ranging from solar cells to light-emitting diodes. However, many fundamental aspects of the halide perovskite materials remain elusive at the moment, such as the structures and impacts of the methyl ammonium precursors on the halide perovskite properties. In this manuscript, we take one step back to theoretically investigate the monomer and dimer structures of methylammonium iodide, a precursor for the synthesis of the halide perovskite CH3NH3PbI3 via the first principles calculations, in order to provide a more complete view of the halide perovskite structures. The calculations show that the hydrogen bonds are found to be the major factor that stabilizes the methylammonium iodide monomers and dimers, while the dimeric structure exhibits geometry with each iodine atom shared by two neighbouring hydrogen atoms in the methylammonium cation molecules. The hydrogen bonds in the methylammonium iodide are proposed to be correlated with the three-dimensional halide perovskite buildup, and the formation of the hydrogen bond that is available in the halide perovskite framework could be “historically” traced back as early as the precursor preparation. The manuscript addresses the importance of the hydrogen bonds in the synthesis and the crystal formation of halide perovskite materials, and anticipates the necessity of the fundamental theoretical understanding of the structures from the halide perovskite precursors to the halide perovskite frameworks.

Slow Hot-Carrier Cooling in Halide Perovskites: Prospects for Hot-Carrier Solar Cells.

Rapid hot-carrier cooling is a major loss channel in solar cells. Thermodynamic calculations reveal a 66% solar conversion efficiency for single junction cells (under 1 sun illumination) if these hot carriers are harvested before cooling to the lattice temperature. A reduced hot-carrier cooling rate for efficient extraction is a key enabler to this disruptive technology. Recently, halide perovskites emerge as promising candidates with favorable hot-carrier properties: slow hot-carrier cooling lifetimes several orders of magnitude longer than conventional solar cell absorbers, long-range hot-carrier transport (up to ≈600 nm), and highly efficient hot-carrier extraction (up to ≈83%). This review presents the developmental milestones, distills the complex photophysical findings, and highlights the challenges and opportunities in this emerging field. A developmental toolbox for engineering the slow hot-carrier cooling properties in halide perovskites and prospects for perovskite hot-carrier solar cells are also discussed.

Organic-Inorganic Hybrid Halide Perovskites for Memories, Transistors, and Artificial Synapses.

Fascinating characteristics of halide perovskites (HPs), which cannot be seen in conventional semiconductors and metal oxides, have boosted the application of HPs in electronic devices beyond optoelectronics such as solar cells, photodetectors, and light-emitting diodes. Here, recent advances in HP-based memory and logic devices such as resistive-switching memories (i.e., resistive random access memory (RRAM) or memristors), transistors, and artificial synapses are reviewed, focusing on inherently exotic properties of HPs: i) tunable bandgap, ii) facile majority carrier control, iii) fast ion migration, and iv) superflexibility. Various fabrication techniques of HP thin films from solution-based methods to vacuum processes are introduced. Up-to-date work in the field, emphasizing the compositional flexibility of HPs, suggest that HPs are promising candidates for next-generation electronic devices. Taking advantages of their unique electrical properties, low-cost and low-temperature synthesis, and compositional and mechanical flexibility, HPs have enormous potential to provide a new platform for future electronic devices and explosively intensive studies will pave the way in finding new HP materials beyond conventional silicon-based semiconductors to keep up with "More-than-Moore" times.