Single-crystalline Perovskite Research Articles

Exploring photoconduction mechanisms in Lead‐Free Cs3Sb2I9 single crystal thin films

The future commercial advancement of lead-halide perovskites (LHPs) faces obstacles due to the existence of harmful lead and the inadequate stability associated with these materials. To tackle this challenge, we have prepared a Cs3Sb2I9 perovskite single-crystalline thin film (Cs3Sb2I9 device) using a technique based on the restricted evaporation of solvents in space, aiming for effective photodetection. The photodetector in the current study shows a responsivity (R) of around 111 mA/W and a detectivity (D∗) of approximately 3.7 × 1012 Jones. While these performance metrics are comparable to other photodetectors, there is a need for additional optimization to match the capabilities of commercial silicon and germanium-based counterparts. The examination of ultrafast transient absorption provides insights into the essential photophysics inherent in Cs3Sb2I9. The synergy between the deformation potential and the Fröhlich effect plays a crucial role in shaping electronic dynamics. This synergy leads to the self-trapping of charge carriers, resulting in the creation of localized polarons within the Cs3Sb2I9 lattice within just some picoseconds. The restriction of carrier mobility within Cs3Sb2I9 arises from the self-capturing and confinement of small polarons (SPs). Furthermore, it was noted that SPs in a localized state could undergo absorption into an elevated state (photon energy ⁓ 1.60 eV). This process effectively facilitates the charge carriers' mobilization to a more dispersed eigenstate. Our research provides essential comprehension into the light-induced processes of lead-free halide perovskites (LFHPs), offering valuable insights for their prospective use in optoelectronics as promising future semiconducting agents.

Supersaturation- and external force-engineered high-quality 2D CsCu2I3 single-crystalline film for heterogeneous integration in photodetectors

Heterogeneous integration of various crystalline materials in electronic and optoelectronic devices have fueled the development of two-dimensional (2D) perovskite single-crystalline (SC) film. However, it is still challenging to synthesize 2D CsCu2I3 SC film due to the uncontrolled nuclei/growth. In the work, the bottleneck for the synthesis of 2D CsCu2I3 SC film can be well tackled by the solution supersaturation and external pressure for the first time, meanwhile, the morphological transformation of CsCu2I3 from dendritic crystal to 2D film are firstly achieved through controlling nucleation driving force. The heterogeneous integration of 2D CsCu2I3 SCs film on various substrates was demonstrated, a self-powered GaN-CsCu2I3 SC film photodetector exhibits high rectification ratio of 1250 (±1 V) with improved responsivity of 460 mA W−1 and EQE of 163 %, which outperforms most reported 2D lead-free halide perovskite film photodetectors. Furthermore, theoretical computational calculation was employed to investigate their crystal structure and electronic distribution, evidencing that 2D CsCu2I3 SC film could facilitate the separation of photo-induced carriers. The study not only shows an in-depth mechanism for perovskite growth, but also advances the development of 2D copper-based perovskite film and hetero-integration, laying the groundwork for future commercial optoelectronics.

Interfacial Engineering for Controlled Crystal Mosaicity in Single-Crystalline Perovskite Films.

Organic-inorganic hybrid perovskites have attracted significant attention for optoelectronic applications due to their efficient photoconversion properties. However, grain boundaries and irregular crystal orientations in polycrystalline films remain issues. This study presents a method for producing crystalline-orientation-controlled perovskite single-crystal films using retarded solvent evaporation. It is shown that single-crystal films, grown via inverse temperature crystallizationwithin a confined space, exhibit enhanced optoelectronic property. Using interfacial polymer layer, this method produces high-quality perovskite single-crystalline films with varying crystal orientations. Density functional theory calculations confirm favorable adsorption energies for (110) surfaces with methylammonium iodide and PbI2 terminations on poly(3-hexylthiophene), and stronger adsorption for (224) surfaces with I and methylammonium terminations on polystyrene, influenced by repulsive forces between the thiophene group and the perovskite surface. The correlation between charge transport characteristics and perovskite single-crystalline properties highlights potential advancements in perovskite optoelectronics, improving device performance and reliability.

Functionalized Single Crystal Perovskite Materials for SERS and Their Potential Detection Applications.

Recent advances in detection and diagnostic tools have improved understanding and identification of plant physiological and biochemical processes. Effective and safe Surface Enhanced Raman Spectroscopy (SERS) can find objects quickly and accurately. Raman enhancement amplifies the signal by 1014-1015 to accurately quantify plant metabolites at the molecular level. This paper shows how to use functionalized perovskite substrates for SERS. These perovskite substrates have lots of surface area, intense Raman scattering, and high sensitivity and specificity. These properties eliminate sample matrix component interference. This study identified research gaps on perovskite substrates' effectiveness, precision, and efficiency in biological metabolite detection compared to conventional substrates. This article details the synthesis and use of functionalized perovskites for plant metabolites measurement. It analyzes their pros and cons in this context. The manuscript analyzes perovskite-based SERS substrates, including single-crystalline perovskites with enhanced optoelectronic properties. This manuscript aims to identify this study gap by comprehensively reviewing the literature and using it to investigate plant metabolite detection in future studies.

Structural degeneracy and formation of crystallographic domains in epitaxial LaFeO3 films revealed by machine-learning assisted 4D-STEM

Structural domains and domain walls, inherent in single crystalline perovskite oxides, can significantly influence the properties of the material and therefore must be considered as a vital part of the design of the epitaxial oxide thin films. We employ 4D-STEM combined with machine learning (ML) to comprehensively characterize domain structures at both high spatial resolution and over a significant spatial extent. Using orthorhombic LaFeO3 as a model system, we explore the application of unsupervised and supervised ML in domain mapping, which demonstrates robustness against experiment uncertainties. The results reveal the consequential formation of multiple domains due to the structural degeneracy when LaFeO3 film is grown on cubic SrTiO3. In situ annealing of the film shows the mechanism of domain coarsening that potentially links to phase transition of LaFeO3 at high temperatures. Moreover, synthesis of LaFeO3 on DyScO3 illustrates that a less symmetric orthorhombic substrate inhibits the formation of domain walls, thereby contributing to the mitigation of structural degeneracy. High fidelity of our approach also highlights the potential for the domain mapping of other complicated materials and thin films.

Hybrid Molecular Beam Epitaxy for Single-Crystalline Oxide Membranes with Binary Oxide Sacrificial Layers.

The advancement in thin-film exfoliation for synthesizing oxide membranes has led to possibilities for creating artificially assembled heterostructures with structurally and chemically incompatible materials. The sacrificial layer method is a promising approach to exfoliate as-grown films from a compatible material system, allowing for their integration with dissimilar materials. Nonetheless, the conventional sacrificial layers often possess an intricate stoichiometry, thereby constraining their practicality and adaptability, particularly when considering techniques such as molecular beam epitaxy (MBE). This is where easy-to-grow binary alkaline-earth-metal oxides with a rock salt crystal structure are useful. These oxides, which include (Mg, Ca, Sr, Ba)O, can be used as a sacrificial layer covering a much broader range of lattice parameters compared to conventional sacrificial layers and are easily dissolvable in deionized water. In this study, we show the epitaxial growth of the single-crystalline perovskite SrTiO3 (STO) on sacrificial layers consisting of crystalline SrO, BaO, and Ba1-xCaxO films, employing a hybrid MBE method. Our results highlight the rapid (≤5 min) dissolution of the sacrificial layer when immersed in deionized water, facilitating the fabrication of millimeter-sized STO membranes. Using high-resolution X-ray diffraction, atomic-force microscopy, scanning transmission electron microscopy, impedance spectroscopy, and scattering-type near-field optical microscopy (SNOM), we demonstrate single-crystalline STO membranes with bulk-like intrinsic dielectric properties. The employment of alkaline earth metal oxides as sacrificial layers is likely to simplify membrane synthesis, particularly with MBE, thus expanding the research and application possibilities.

(Invited) Confined and Free-Standing Perovskite Nanowires for X-Ray Detection

Metal halide perovskites (MHPs) have shown excellent results in many applications, including X-ray scintillation detection. Nanowires could offer improved sensitivity by exploiting nanophotonic light guiding, and the MHP stability could be improved by growing nanowires physically protected in anodized aluminum oxide (AAO). We use a one-step solution low-temperature method to grow arrays of long single-crystalline CsPbBr3 nanowires in an AAO template. The diameters can be adjusted by the AAO template, ranging from 30 to 360 nm, and the length can be controlled up to 15 μm (Fig 1(a)) [1]. The nanowires show excellent stability, with no obvious lack in photoluminescence after months of storage in air. The X-ray scintillation shows no systematic degradation over 2 weeks of continuous X-ray exposure, but an unexpected positive correlation with room humidity. The excellent stability allows tomographic 3D X-ray imaging at better than 3 μm resolution [2].Surprisingly, we find that free-standing CsPbBr3 nanowires can be obtained by the same method (Fig 1(b)) [3]. The length of the vertically aligned nanowires is controlled from 1 to 20 μm with the precursor amount. The nanowires are single-crystalline and exhibit excellent photoluminescence and clear light guiding (Fig 1(c)). Lithography methods for MHPs have been limited because of their solubility in polar solvents. However, we show that o-xylene can be used in a perovskite-compatible electron beam lithography (EBL) process based on nonpolar solvents [4]. Combining these results, we demonstrate single nanowire devices with excellent photoresponse. Recently, we have developed a gas-phase halide exchange method based on HCl or Cl2 to convert the green-emitting CsPbBr3 to blue-emitting CsPb(BrxCl1-x)3. [5]. Using the aforementioned EBL process, we selectively convert segments of nanowires to CsPb(BrxCl1-x)3 and create axially heterostructured nanowires (Fig 1(d)).1 Z. Zhang, H. Dierks, N. Lamers et al., "Single-Crystalline Perovskite Nanowire Arrays for Stable X-ray Scintillators with Micrometer Spatial Resolution" ACS Applied Nano Materials 5 (1), 881 (2022) http://doi.org/10.1021/acsanm.1c035752 H. Dierks, Z. Zhang, N. Lamers, and J. Wallentin, "3D X-ray microscopy with a CsPbBr3 nanowire scintillator" Nano Res. 16 (1), 1084 (2023) https://doi.org/10.1007/s12274-022-4633-73 Z. Zhang, N. Lamers, C. Sun, C. Hetherington, I. G. Scheblykin, and J. Wallentin, "Free-Standing Metal Halide Perovskite Nanowire Arrays with Blue-Green Heterostructures" Nano Lett. 22 (7), 2941 (2022) http://doi.org/10.1021/acs.nanolett.2c001374 N. Lamers, Z. Zhang, and J. Wallentin, "Perovskite-Compatible Electron-Beam-Lithography Process Based on Nonpolar Solvents for Single-Nanowire Devices" ACS Applied Nano Materials 5 (3), 3177 (2022) http://doi.org/10.1021/acsanm.2c001885 N. Lamers, Z. Zhang, I. G. Scheblykin, and J. Wallentin, "Multisegment Heterostructured CsPb(Br1-xClx)3 Perovskite Nanowires using Gas-Phase Anion Exchange" In review (2023) Figure 1

Anisotropic exciton–polaritons in 2D single-crystalline PEA2PbBr4 perovskites at room temperature

Two-dimensional (2D) single-crystalline perovskites are a suitable material for investigating the strong exciton–photon interaction due to the large exciton binding energy. Here, we grow high-quality 2D single-crystalline PEA2PbBr4 thin film in situ in between a pair of distributed Bragg reflectors and construct an anisotropic exciton–polariton microcavity. Clear evidence for strong exciton–photon coupling is observed and represented by a large coupling strength of 211.8 meV. The observed transverse electric–transverse magnetic splitting at the point where the in-plane wave vector is zero indicates crystal birefringence. The effective refractive indices for these two orthogonal polarization directions are derived to have a large difference, corresponding to a material index difference of 0.28, and then an in-plane refractive index ellipse is built for the material. This work shows that the 2D anisotropic perovskite microcavity can not only behave as a platform for characterizing the anisotropic properties of a material but also as a promising room-temperature polaritonic device.

Ultrafast photoinduced carrier dynamics in single crystalline perovskite films

Carrier dynamic processes in CsPbBr3 single crystalline perovskite, including hot carrier cooling, defect state trapping and carrier recombination, were studied using micro-region transient absorption technique.

Epitaxy growth of MAPbBrxCl3−x single-crystalline perovskite films toward spectral selective detection in both broadband and narrowband ranges

Single-crystalline perovskite films with continuous variable bandgaps were grown by liquid phase epitaxy. The planar-type photodetectors present two kind detection mode of broadband and narrowband by manipulating the light incident direction.

Strong anisotropic second-order nonlinear optical responses in 0D lead-free chiral perovskite single-crystalline microwire arrays

New 0D Bi-based perovskite single-crystalline microwire arrays were realized by a capillary-bridge confined technique and exhibit excellent second-order NLO performance.

Electrical and Optoelectrical Dual-Modulation in Perovskite-Based Vertical Field-Effect Transistors

Organolead trihalide perovskites have drawn a great deal of interest for application in electronic and optoelectronic devices owing to their exceptional physical properties. However, the majority of reported perovskite field-effect transistors (FETs) demonstrates unsatisfactory performance, such as poor mobility, low on/off ratio, and low current density, which remains a significant obstacle for their potential applications. In this work, we report a vertical FET (VFET) composed of a single-crystalline MAPbBr3 perovskite Schottky junction, which effectively modulates the intrinsic carrier characteristics and enhances the performance of the device by reducing channel length and weakening the electrostatic screening effect. The device exhibits excellent performance with a high on/off ratio (104), high carrier mobility (23.4 cm2 V–1 s–1), and current density of 2.69 A cm–2 at room temperature. Importantly, the regulation of the drain voltage plays a similar role to that of the gate voltage in our device, which is attributed to the doping of perovskite with regulation of the source contact/perovskite Schottky junction. With the drain modulation, a superior photoresponse with enhanced responsivity of 16 A W1– and a low dark current are simultaneously obtained under light illumination, leading to a high detectivity of 1014 Jones. Our research may open up new possibilities for perovskite electronics, such as logic applications for various flexible, wearable, and disposable devices.

Spraying Perovskite Intermediate Enabling Inch‐Scale Microwire Film Fabrication for Integration Compatible Efficient‐Photodetectors Array

AbstractMetal halide perovskite microwires (MWs) have emerged as promising photoactive materials for highly efficient photodetectors (PDs). However, large‐scale MWs film fabrication is still a formidable challenge for achieving integration compatible perovskite PDs arrays, owing to precipitation and structure crushing of MWs during deposition and annealing. Herein, a strategy of fabrication of inch‐scale perovskite MWs films is presented by depositing perovskite intermediate suspension through spray‐coating, which addresses the trade‐off present between the high flatness of MWs film and its large‐scale fabrication. The single crystalline perovskite MWs weave a film with high enough flatness rendering narrow performance distribution of high efficiency on the 7 × 7 PDs arrays. The formamidinium lead iodide (FAPbI3) PDs arrays show average responsivity and detectivity of (1.60 ± 0.46) A W−1 and (1.49 ± 0.50) × 1012 Jones. The methanaminium lead iodide (MAPbI3) PDs arrays show average responsivity and detectivity of (0.065 ± 0.046) A W−1 and (2.54 ± 0.77) × 1011 Jones. The champion PDs based on FAPbI3 MWs film and MAPbI3 MWs film show detectivity of 1.26 × 1013 and 9.67 × 1011 Jones, which are much higher than that of corresponding polycrystalline films and located on the top ranking of similar devices.

Epitaxial Perovskite Single-Crystalline Heterojunctions for Filter-Free Ultra-Narrowband Detection with Tunable Spectral Responses.

Narrowband photodetectors (NPDs) with the capability of detecting light within a selective wavelength range are in high demand for numerous emerging applications such as imaging systems, machine vision, and optical communication. Halide perovskite materials have been developed for eliminating the current complex filtering systems in NPDs due to their beneficial properties, while currently NPDs using perovskite materials are limited by hardly fully eliminated short wavelength response, low charge collection efficiency (CCE), complex fabrication process, and so forth. Herein, a series of perovskite single-crystalline heterojunctions (PSCHs) with a structure of Bi-MAPbX3/MAPbY3 are fabricated by liquid phase epitaxy for filter-free narrowband detection. By varying the halide component in the PSCH, the PSCH-based NPDs can realize continuously tunable spectral response range from blue to NIR regions and ultra-narrow full width at half-maximum (FWHM) of <20 nm. Specifically, the PSCH-based NPD with a high CCE under a large electric filed shows a high spectra rejection ratio of >1000, a fast response speed with rise/fall time of ∼160/∼225 μs, and long-term stability more than 3 months in ambient air. This work provides a simple strategy for designing low-cost and high-performance filter-free NPDs with a tunable spectral response.

Chiral Lead-Free Double Perovskite Single-Crystalline Microwire Arrays for Anisotropic Second-Harmonic Generation.

Halide double perovskites present a new branch for versatile optoelectronic devices because of their huge structural compatibility and environmental friendliness, whereas nonlinear optics (NLO) devices remain blank for this fascinating family. Simultaneously, the precise patterning of single-crystalline perovskite microwire arrays remains a challenge for the integration of NLO devices. Herein, we designed lead-free chiral 2D double perovskites with the nonsymmetrical structure presenting second-harmonic generation (SHG). Furthermore, perovskite single-crystalline arrays with regulated geometry, pure orientation, and high crystallinity are prepared using the capillary-bridge confined assembly technique. The efficient SHG originates from the asymmetric crystal structure and high crystallinity of the microwire arrays. Compared with their polycrystalline thin-film counterparts, linearly polarized SHG and a higher SHG conversion efficiency are demonstrated based on microwire arrays. The results not only expand the applications of lead-free double perovskites in the NLO-integrated fields but also provide a viable way for lead-free optoelectronic devices.

Temperature-activated dielectric relaxation in lead-free halide perovskite single crystals

Lead-free metal-halide perovskites have recently appeared as a promising candidate in optoelectronics and photovoltaics because of their non-toxicity, stability, and unique photophysical properties. Much scientific research has been done on optoelectronic characteristics and photovoltaic applications of lead-free perovskites, but the dielectric characteristics and insight into the relaxation phenomenon remain elusive. Here, we study the dielectric relaxation and conduction mechanism in the single crystalline (SC) A3Bi2X9 (A = MA+/FA+) perovskite using temperature-dependent electrochemical impedance spectroscopy in correlation with the modulus spectroscopy. With increasing temperature, the peak of −Z″(ω) shifts toward a high-frequency regime which specifies the thermally dependent relaxation mechanism in both crystals. The activation energy was estimated as 381 meV for MA3Bi2I9 (MBI) crystal and 410 meV for the FA3Bi2I9 (FBI) crystal suggesting hopping of mobile ions between lattice sites. The connected orientational polarization with the thermal motion of molecules leads to the enhancement in the dielectric constant (ϵ′) with temperature. The ϵ″(ω) in these crystals shows the significant ionic conductivity with a typical 1/fγ type characteristics (in the low-frequency regime) where γ is found to be in the range of 0.93–1.0 for MBI crystal and 0.88–0.98 for FBI crystal. The correlated imaginary part of impedance (−Z″) and modulus (M″) demonstrate the temperature-activated delocalized relaxation (non-Debye toward the Debye type) in these crystals. Stevels model suggests that the contribution of traps reduces with temperature rise and therefore conductivity enhances. Our study provides a comprehensive analysis and in-depth knowledge about the dielectric and conductivity relaxation mechanism in these lead-free perovskite SCs, which will help to implement efficient energy storage devices using these materials.

Single-Crystalline Perovskite p-n Junction Nanowire Arrays for Ultrasensitive Photodetection.

Highly sensitive photodetectors play significant roles in modern optoelectronic integrated circuits. Constructing p-n junctions has been proven to be a particularly powerful approach to realizing sensitive photodetection due to their efficient carrier separation. Recently, p-n-junction photodetectors based on organic-inorganic hybrid perovskites, which combine favorable optoelectronic performance with facile processability, hold great potential in practical applications. So far, these devices have generally been made of polycrystalline films, which exhibit poor carrier-transport efficiency, impeding the further improvement of their photoresponsivities. Here, a type of ultrasensitive photodetector based on single-crystalline perovskite p-n-junction nanowire arrays is demonstrated. The single-crystalline perovskite p-n-junction nanowire arrays not only possess high crystallinity that enables efficient carrier transport but also form a built-in electric field facilitating effective carrier separation. As a result, the devices show excellent photosensitivity over a wide spectral range from 405 to 635nm with an outstanding responsivity of 2.65×102 AW-1 at 532nm. These results will provide new insights into the design and construction of high-performance photodetectors for practical optoelectronic applications.

(Invited, Digital Presentation) Nanostructured Perovskite Resistive RAM for Next Generation Data Storage

Resistive RAMs (Re-RAMs) have emerged as a propitious candidate among next generation non volatile memories because of their strikingly fast speed, prolonged data retention ability and high storage density. Herein, we developed an electrochemical metallization (ECM) based Re-RAM with three-dimensionally integrated single-crystalline perovskite (methyl ammonium lead halide or MAPbX3 where X=I, Br and Cl) quantum wire (PQW)/ nanowire (PNW) array embedded in a nano-engineered porous alumina membrane (PAM) serving as the switching medium. The PQWs and PNWs were grown inside the PAM template by a vapor-solid-solid-reaction (VSSR) process and were clubbed between silver (Ag) and aluminum (Al) contacts. The nanostructured perovskite Re-RAM exhibited 100 ps switching speed which is a record for perovskite Re-RAMs and also among the fastest for all types of Re-RAMs reported. The fast switching was attributed to the increased ionic (Ag+) and electronic mobility and subsequent accelerated filament formation within the body of the monocrystalline PQWs/PNWs. The PAM scaffolding imparted material and electrical stability to the environmentally delicate perovskite. As a consequence, we were able to obtain a record long (among perovskite Re-RAMs) estimated retention time > 28 years and record-high (among perovskite Re-RAMs) uninhibited cyclic endurance of 6×106 cycles. Also, utilizing the ultra-high density (2×1011/cm2) of the PQWs, a 14 nm lateral dimension ultra-small memory cell was built. In conjunction with multi-bit switching, an effective device footprint of 76.5 nm2 was achieved for a single bit storage. Further, as a concept proof, an 8×8 Re-RAM crossbar array device was fabricated which demonstrated temporally robust alphabetic data storage, with a unique metal-semiconductor-insulator-metal (MSIM) architecture to alleviate the sneaky path problem. The MSIM scheme based on quasi-self-selecting elements, demonstrated a strong potential for unhindered scalability in the future, a problem often encountered with integrating external selecting diodes and transistors. The PQW/PNW Re-RAMs also responded to light stimuli, exhibiting optical programmability among the low resistance states. In summary, these intriguing results propel perovskite Re-RAMs to the state-of-the-art standard and demonstrate an attractive potency for PQW/PNW devices to be used as an alternative technology in future storage and computing modules.

Phase‐Control of Single‐Crystalline Inorganic Halide Perovskites via Molecular Coordination Engineering (Adv. Funct. Mater. 16/2022)

Molecular Coordination Engineering In article number 2109442, Asaph Widmer-Cooper, Wenxin Mao, Udo Bach, and co-workers demonstrate the precise control of crystallisation species for caesium inorganic halide perovskite materials by tuning the molecular coordination dynamics. The capability to reach phase-pure single-crystalline perovskite structures provides direct access to the fabrication of advanced optoelectronic devices that require specific crystal structures and morphologies.

Perovskite-Type 2D Materials for High-Performance Photodetectors.

Photodetectors are light sensors in widespread use in image sensing, optical communication, and consumer electronics. In current smart optoelectronic technology, conventional semiconductors have encountered a bottleneck caused by inflexibility and opacity. With the ever-increasing demands for versatile optoelectronic applications, perovskite-type 2D materials demonstrate great potential for advanced photodetectors inspired by molecularly thin 2D materials. Through the reduction of thickness to thin or molecularly thin levels, single-crystalline 2D perovskites can exhibit superior optoelectronic performance characteristics, such as tunable absorption property by chemical design, enhanced carrier separation by remarkable photosensing capability, and improved carrier extraction by versatile band engineering. More importantly, perovskite-type 2D materials exhibit great potential for large-scale monolithic integration to achieve all-in-one sensing-memory-computing optoelectronic devices. In this Perspective, recent progress in 2D perovskite-based photodetectors is presented in detail. The focus is on growth strategies for reducing thickness, thickness-dependent optical and electrical properties, device engineering, heterojunction fabrication, and device performance. Finally, the current challenges and future prospects in this field are presented.