Perovskite-based Heterostructures Research Articles

Unraveling the Transformation from Type-II to Z-Scheme in Perovskite-Based Heterostructures for Enhanced Photocatalytic CO2 Reduction.

The ability to create perovskite-based heterostructures with desirable charge transfer characteristics represents an important endeavor to render a set of perovskite materials and devices with tunable optoelectronic properties. However, due to similar material selection and band alignment in type-II and Z-scheme heterostructures, it remains challenging to obtain perovskite-based heterostructures with a favorable electron transfer pathway for photocatalysis. Herein, we report a robust tailoring of effective charge transfer pathway in perovskite-based heterostructures via a type-II to Z-scheme transformation for highly efficient and selective photocatalytic CO2 reduction. Specifically, CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 heterostructures are synthesized and then investigated by ultrafast spectroscopy. Moreover, taking CsPbBr3/TiO2 and CsPbBr3/Au/TiO2 as examples, operando experiments and theoretical calculations confirm that the type-II heterostructure could be readily transformed into a Z-scheme heterostructure through establishing a low-resistance Ohmic contact, which indicates that a fast electron transfer pathway is crucial in Z-scheme construction, as further demonstrated by CsPbBr3/Ag/TiO2 and CsPbBr3/MoS2 heterostructures. In contrast to pristine CsPbBr3 and CsPbBr3/TiO2, the CsPbBr3/Au/TiO2 heterostructure exhibits 5.4- and 3.0-fold enhancement of electron consumption rate in photocatalytic CO2 reduction. DFT calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy unveil that the superior CO selectivity is attributed to the lower energy of *CO desorption than that of hydrogenation to *HCO. This meticulous design sheds light on the modification of perovskite-based multifunctional materials and enlightens conscious optimization of semiconductor-based heterostructures with desirable charge transfer for catalysis and optoelectronic applications.

In-situ producing CsPbBr3 nanocrystals on (001)-faceted TiO2 nanosheets as S‑scheme heterostructure for bifunctional photocatalysis

Fabricating a cost-effective yet highly active photocatalyst to reduce CO2 to CO and oxidize benzyl alcohol to benzaldehyde simultaneously, is challenging. Herein, we construct an S-scheme 0D/2D CsPbBr3/TiO2 heterostructure for bifunctional photocatalysis. An in-situ synthetic route is used, which enables the precise integration between CsPbBr3 nanocrystals and ultrathin TiO2 nanosheets exposed with (001) facets (termed as TiO2-001), resulting in a tightly coupled heterointerface and desirable band offsets. The as-prepared CsPbBr3/TiO2-001heterojunctions exhibit boosted charge carrier kinetics, particularly, quick carrier separation/transfer and efficient utilization. Experimental results and theoretical calculations validate the S-scheme route in CsPbBr3/TiO2-001, which allows the enrichment of strongly conserved electrons-holes at conduction and valence bands of CsPbBr3 and TiO2-001, respectively. Consequently, compared to its counterparts, an excellent bifunctional activity (with 24 h reusability) is realized over CsPbBr3/TiO2-001, where the production rate of CO and benzaldehyde reach up to 78.06 μmol g-1h−1 and 1.77 mmol g-1h−1 respectively, without employing any sacrificial agents. This work highlights the development of perovskite-based heterostructures and describes the efficient harnessing of redox potentials and charge carriers towards combined photocatalytic systems.

In Situ Growth of Lead-Free Cs2CuBr4 Perovskite Quantum Dots in KIT-6 Mesoporous Molecular Sieve for CO2 Adsorption, Activation, and Reduction.

Metal halide perovskites (MHPs) are emerging as promising candidates for photocatalytic CO2 conversion. However, their practical application is still restricted by the poor intrinsic stability and weak adsorption/activation toward CO2 molecules. The rational design of MHPs-based heterostructures with high stability and abundant active sites is a potential solution to this obstacle. Herein, we report the in situ growth of lead-free Cs2CuBr4 perovskite quantum dots (PQDs) in KIT-6 mesoporous molecular sieve, obtaining remarkable photocatalytic CO2 reduction activity and durable stability. The optimized Cs2CuBr4@KIT-6 heterostructure exhibits the photocatalytic CO and CH4 evolution rates of 51.6 and 17.2 μmol g-1 h-1, respectively, far exceeding those of pristine Cs2CuBr4. On the basis of in situ diffuse reflectance infrared Fourier transform spectra and theoretical investigations, the detailed CO2 photoreduction pathway is systematically revealed. This work provides a new route for the rational construction of perovskite-based heterostructures with strong CO2 adsorption/activation and good stability for photocatalytic CO2 reduction.

Excessive Iodine Enabled Ultrathin Inorganic Perovskite Growth at the Liquid-Air Interface.

The liquid-air interface offers a platform for the in-plane growth of free-standing materials. However, it is rarely used for inorganic perovskites and ultrathin non-layered perovskites. Herein the liquid-air interfacial synthesis of inorganic perovskite nanosheets (Cs3 Bi2 I9 , Cs3 Sb2 I9 ) is achieved simply by drop-casting the precursor solution with only the addition of iodine. The products are inaccessible without iodine addition. The thickness and lateral size of these nanosheets can be adjusted through the iodine concentration. The high volatility of the iodine spontaneously drives precursors that normally stay in the liquid to the liquid-air interface. The iodine also repairs in situ iodine vacancies during perovskite growth, giving enhanced optical and optoelectronic properties. The liquid-air interfacial growth of ultrathin perovskites provides multi-degree-of-freedom for constructing perovskite-based heterostructures and devices at atomic scale.

Light‐Induced Mott‐Insulator‐to‐Metal Phase Transition in Ultrathin Intermediate‐Spin Ferromagnetic Perovskite Ruthenates (Adv. Mater. 12/2023)

Insulator–Metal Transition In article number 2211612, Zhicheng Zhong, Xuefeng Wang, and co-workers report that UV-light irradiation on perovskite-based heterostructures can drive the photocharge transfer from SrTiO3 substrates to intermediate-spin ferromagnetic SrRuO3 ultrathin films containing oxygen vacancies. As a consequence, a reversible Mott-insulator-to-metal phase transition occurs in the SrRuO3 layer, as revealed by systematic light-irradiation transport experiments and dynamical mean-field theory calculations.

Realization of multifunction in perovskite-based van der Waals heterostructure by interface engineering strategy: The case of CsPbBr3/Janus MoSSe

The flexibility and versatility is crucial for the perovskite-based heterostructure to realize multifunctional integration, while it is hard to be achieved in the conventional systems.Herein, we propose an interface engineering strategy, which utilizes the structural characteristics of perovskite and the mirror asymmetry of 2D Janus material to realize the multifunction of CsPbBr3/Janus MoSSe heterostructure. We demonstrate that type-Ⅰ and type-II band alignment can be achieved simultaneously in CsPbBr3/Janus MoSSe heterostructure by modulating the atomic terminal contacts. The underlying mechanism is that the band alignment can be shifted by the interface dipole and its induced interface potential step. The interface effect renders CsPbBr3/Janus MoSSe heterostructure an adjustable band gaps and band types, and an improved light absorption range and intensity in the visible and ultraviolet regions. More promisingly, we find that gate voltage regulation can also realize the transition of band alignment from intrinsic type-II to type-I or type-III for CsBr-T/SMoSe heterostructure. These findings enrich the functionality of perovskite-based heterostructures and provide more possibilities for realizing high-efficiency multifunctional nanodevices.

Lead-Free Cs3Bi2Br9 perovskite In-situ growth on 3D Flower-like g-C3N4 microspheres to improve photocatalytic performance

Nitrogen oxide (NOx) removal has long been a subject that has motivated researchers to develop a diverse range of techniques, including physical adsorption, biofiltration, low temperature plasma, selective catalytic reduction, and photocatalytic oxidation. In this work, Cs3Bi2Br9 lead-free perovskite was synthesized via in-situ growth on a 3D flower-like g-C3N4 microsphere, whichusesaseriesofCs3Bi2Br9/g-C3N4 (labeled as X% CBB/CN, where X = 5, 10, 20, 30, and 50) heterojunctions for the photocatalytic removal of NOx. The efficiency of NO removal was enhanced considerably, compared with that of the pristine elements, when irradiated with a 300 W Xe lamp with the concentration of NO at the ppb level. The results of photocurrent measurements and electrochemical impedance spectroscopy are consistent with the results of the NO removal test. Electron spin resonance results verified that ⋅OH and ⋅O2− are formed under visible light irradiation. We report the detailed mechanism for the photocatalytic process of NO removal by CBB/CN heterojunctions and provide insights into the potential applications of lead-free perovskite-based heterostructures in the field of photocatalysis.

Rashba spin splitting in two-dimensional electron gas in polar-polar perovskite oxide heterostructure LaVO3/KTaO3: A DFT investigation

Perovskite oxide surfaces and their interfaces host two-dimensional electron gas (2DEG) and many other emergent properties. Polar-polar perovskite oxide heterostructure LaVO3/KTaO3 with the n-type interface is studied using comprehensive first principle calculations. Our calculations involve crystal orientation-dependent investigation of 2DEG for two types of terminations of KTO surface slab namely asymmetric and symmetric terminations in [001] and [111] orientations. Electronic structure calculations show n-type conducting interface and the Rashba spin splitting in the bands with αR in the range 0.37−0.9eVÅ and ER in the range of 0.6−4.5eV owing to the high spin–orbit coupling of Ta and symmetry breaking electric field present in the heterostructure. The occupation of heavy bands dyz/dxz and the additional occupation of dz2 bands in [111] orientation give rise to orbital-dependent Rashba splitting. The charge density difference plots corroborate the transfer of charge from the surface to the interfacial region. Constant energy contour plots of spin texture confirm the 2D Rashba spin splitting of 2DEG in [001] orientation, while a complex spin structure is observed in [111] orientation. Thus, our findings extend the scope of perovskite-based heterostructures for future spintronic applications maneuvering the Rashba effect with a fascinating spin structure.

Effect of vertical strain and in-plane biaxial strain on type-II MoSi2N4/Cs3Bi2I9 van der Waals heterostructure

Construction of van der Waals heterostructures (vdWHs) from layered materials may form new types of optoelectronic devices with better performance compared to individual layers. Here, we investigate theoretically the structural stability, electronic properties, charge-transport mechanisms, and optical properties of two-dimensional (2D) MoSi2N4/Cs3Bi2I9 vdWHs by using the first-principles calculations. Our results demonstrate that the 2D MoSi2N4/Cs3Bi2I9 vdWHs possess a direct bandgap and type-II band alignment due to the built-in electric field induced by the electron transfer from MoSi2N4 to Cs3Bi2I9 layer, which can prevent photoinduced electrons and holes from recombination and thus enhance the carrier lifetime. Furthermore, the optical absorption of the heterostructure is enhanced in the visible and ultraviolet region, and its electronic property is tunable under in-plane strains with a clear metal–semiconductor transition. Finally, we explore more A3B2X9/MA2Z4 vdWHs with A = Cs; B = In, Sb, Bi; and X = Cl, Br, I in A3B2X9 and M = Cr, Mo, Ti; A = Si; and Z = N, P in MA2Z4, and we find all three types of band alignments (type-I, type-II, and type-III). Our study provides a comprehensive theoretical understanding of the electronic and optical properties of perovskite-based heterostructures and indicates its potential applications in optoelectronic devices.

Stable CsPbBr3 Nanoclusters Feature a Disk-like Shape and a Distorted Orthorhombic Structure.

CsPbBr3 nanoclusters have been synthesized by several groups and mostly employed as single-source precursors for the synthesis of anisotropic perovskite nanostructures or perovskite-based heterostructures. Yet, a detailed characterization of such clusters is still lacking due to their high instability. In this work, we were able to stabilize CsPbBr3 nanoclusters by carefully selecting ad hoc ligands (benzoic acid together with oleylamine) to passivate their surface. The clusters have a narrow absorption peak at 400 nm, a band-edge emission peaked at 410 nm at room temperature, and their composition is identified as CsPbBr2.3. Synchrotron X-ray pair distribution function measurements indicate that the clusters exhibit a disk-like shape with a thickness smaller than 2 nm and a diameter of 13 nm, and their crystal structure is a highly distorted orthorhombic CsPbBr3. Based on small- and wide-angle X-ray scattering analyses, the clusters tend to form a two-dimensional (2D) hexagonal packing with a short-range order and a lamellar packing with a long-range order.

Band alignment engineering of a Ruddlesden–Popper perovskite-based heterostructure constructed using Cs2SnI2Cl2 and α-In2Se3: The effects of ferroelectric polarization switching and electric fields

Ferroelectricity is an important source of the fascinating optoelectronic properties of heterostructures. Interfaces formed between ferroelectrics and oxides or transition metal dichalcogenides have undergone rapid development. However, the integration of ferroelectrics and two-dimensional Ruddlesden–Popper (RP) perovskites has rarely been studied so far. Herein, we use first-principle calculations to investigate ferroelectric polarization and electric field control of band alignments within the RP perovskite-based heterostructure α-In2Se3/Cs2SnI2Cl2. Our calculations demonstrate that the band alignment of heterostructure can be changed from type-II to type-III by switching the ferroelectric polarization direction in the α-In2Se3 layer. Furthermore, application of an external electric field can modulate the band structure of the α-In2Se3/Cs2SnI2Cl2 heterostructure and induce the band alignment transition. These findings highlight the importance of ferroelectric polarization switching in band alignment engineering and suggest the possibility of electric field-tunable multi-band alignment in Ruddlesden–Popper perovskite-based heterostructures.

Atomic origin of room-temperature two-dimensional itinerant ferromagnetism in an oxide-monolayer heterostructure

Materials with room-temperature two-dimensional itinerant ferromagnetism enable ultracompact device density and quantum computing in next-generation nano-spintronics. Among numerous candidates, perovskite-based heterostructures have offered an excellent platform to manipulate spin-orbital-charge coupling, unveiling a series of emergent spin-dependent phenomena. In this work, we have fulfilled a robust room-temperature soft ferromagnetism together with a metallic characteristic based on a high quality SrRuO3-monolayer-based superlattice. Further examination on this short-range ferromagnetism has been carried out by synchrotron-related spectroscopy, where charge-transfer-induced antiferromagnetic coupling between partial Ru and Ti ions have been found. Although such local antiferromagnetic coupling would break long range ferromagnetic order, it simultaneously stabilize the localized intralayer ferromagnetic order in the SrRuO3 monolayers, which is confirmed by theoretical calculations. Our study not only represents a methodological advance of achieving fantastic magnetic properties in functional oxide monolayer, but is promising to unlock new opportunities for oxide-based spintronic devices toward room-temperature applications.

Modulating Polarization of Perovskite-Based Heterostructures via In Situ Semiconductor Generation and Enzyme Catalysis for Signal-Switchable Photoelectrochemical Biosensing.

Polarization of photoactive materials in current photoelectric (PE) systems is difficult to be adjusted, and thus electron-transfer routes of these systems are unchangeable, which limits their performance in photoelectrochemical (PEC) analysis. Herein, we attempted to modulate the polarization of perovskite-based heterostructures by both in situ semiconductor generation and enzyme catalysis. Owing to their band alignments, Cs3Bi2Br9 quantum dots (QDs) and BiOBr are confirmed to construct a Z-scheme structure, leading to a large anodic photocurrent. In the presence of ascorbic acid 2-phosphate (AAP), BiPO4 is generated on the surface of the Cs3Bi2Br9 QDs/BiOBr heterostructure, reassigning energy bands of BiOBr. Accordingly, polarization of the photoactive materials is converted, and a new Z-scheme structure with a reversed electron-transfer route is constructed, which leads to an evident cathodic photocurrent. Furthermore, abundant electron donors can be obtained by catalyzing AAP with alkaline phosphatase (ALP). In this case, photogenerated holes in BiOBr are preferentially annihilated by electron donors, thereby blocking transfer of photogenerated electrons in the Cs3Bi2Br9 QDs/BiOBr/BiPO4 heterostructure. Consequently, a second polarization conversion is triggered by enzyme catalysis, resulting in the recovery of an anodic photocurrent. Benefited from the polarization conversion, a PEC biosensor with a feature of two-wing signal switch is designed, which remarkably enlarges the range of the signal response and subsequently improves the analytical performance. As a result, ALP in small volume of human serum can be quantified with this method. In this work, polarization of perovskite-based photoactive materials is tuned, proposing an alternative perspective on the design of advanced PE systems.

Spectroscopic Evidence of a Dimensionality-Induced Metal-to-Insulator Transition in the Ruddlesden–Popper Lan+1NinO3n+1 Series

Perovskite-based heterostructures have recently gained remarkable interest, thanks to atomic-scale precision engineering. These systems are very susceptible to small variations of control parameters, such as two-dimensionality, strain, lattice polarizability, and doping. Focusing on the rare-earth nickelate diagram, LaNiO3 (LNO) catches the eye, being the only nickelate that does not undergo a metal-to-insulator transition (MIT). Therefore, the ground state of LNO has been studied in several theoretical and experimental papers. Here, we show by means of infrared spectroscopy that an MIT can be driven by dimensionality control in ultrathin LNO films when the number of unit cells drops to 2. Such a dimensionality tuning can eventually be tailored when a physically implemented monolayer in the ultrathin films is replaced by a digital single layer embedded in the Ruddlesden–Popper Lan+1NinO3n+1 series. We provide spectroscopic evidence that the dimensionality-induced MIT in Ruddlesden–Popper nickelates strongly resembles that of ultrathin LNO films. Our results can pave the way to the employment of Ruddlesden–Popper Lan+1NinO3n+1 to tune the electronic properties of LNO through dimensional transition without the need of physically changing the number of unit cells in thin films.

Molecular engineer halide perovskite/lead chalcogenide heterostructure toward optoelectronic applications: A case study on CsPbBr3/PbS interface

Perovskite/PbS heterostructures have been synthesized to improve the performance of halide perovskite-based optoelectronic devices. The preparation of halide perovskites and PbS is often accompanied with molecular ligand coordination and molecular passivation methods. In this manuscript, we build novel CsPbBr3/PbS heterostructures based on interfacial molecular engineering approach, employing first-principles calculations. The interfacial organic molecules simultaneously interact with the CsPbBr3 surface and the PbS surfaces, modifying the nanoscopic structures of the heterostructure. The electronic and optical properties of the CsPbBr3/PbS heterostructures are effectively manipulated via the molecular engineering method. This theoretical study facilitates the understanding and the molecular engineering aspects of halide perovskite-based heterostructures toward optoelectronic applications.

Recent progress of the optoelectronic properties of 2D Ruddlesden-Popper perovskites

Two-dimensional (2D) hybrid organic-inorganic perovskites have recently attracted attention due to their layered nature, naturally formed quantum well structure, large exciton binding energy and especially better long-term environmental stability compared with their three-dimensional (3D) counterparts. In this report, we present a brief overview of the recent progress of the optoelectronic applications in 2D perovskites. The layer number dependent physical properties of 2D perovskites will first be introduced and then the different synthetic approaches to achieve 2D perovskites with different morphologies will be discussed. The optical, optoelectronic properties and self-trapped states in 2D perovskites will be described, which are indispensable for designing the new device structures with novel functionalities and improving the device performance. Subsequently, a brief summary of the advantages and the current research status of the 2D perovskite-based heterostructures will be illustrated. Finally, a perspective of 2D perovskite materials is given toward their material synthesis and novel device applications.

Interfacial Interactions in Monolayer and Few-Layer SnS/CH3 NH3 PbI3 Perovskite van der Waals Heterostructures and Their Effects on Electronic and Optical Properties.

A high light-absorption coefficient and long-range hot-carrier transport of hybrid organic-inorganic perovskites give huge potential to their composites in solar energy conversion and environmental protection. Understanding interfacial interactions and their effects are paramount for designing perovskite-based heterostructures with desirable properties. Herein, we systematically investigated the interfacial interactions in monolayer and few-layer SnS/CH3 NH3 PbI3 heterostructures and their effects on the electronic and optical properties of these structures by density functional theory. It was found that the interfacial interactions in SnS/CH3 NH3 PbI3 heterostructures were van der Waals (vdW) interactions, and they were found to be insensitive to the layer number of 2D SnS sheets. Interestingly, although their band gap decreased upon increasing the layer number of SnS, the near-gap electronic states and optical absorption spectra of these heterostructures were found to be strikingly similar. This feature was determined to be critical for the design of 2D layered SnS-based heterostructures. Strong absorption in the ultraviolet and visible-light regions, type II staggered band alignment at the interface, and few-layer SnS as an active co-catalyst make 2D SnS/CH3 NH3 PbI3 heterostructures promising candidates for photocatalysis, photodetectors, and solar energy harvesting and conversion. These results provide first insight into the nature of interfacial interactions and are useful for designing hybrid organic-inorganic perovskite-based devices with novel properties.

Controllable Synthesis of Two-Dimensional Ruddlesden-Popper-Type Perovskite Heterostructures.

Two-dimensional Ruddlesden-Popper type perovskites (2D perovskites) have recently attracted increasing attention. It is expected that 2D perovskite-based heterostructures can significantly improve the efficiency of the optoelectronic devices and extend the material functionalities; however, rational synthesis of such heterostructures has not been realized to date. We report on a general low-temperature synthetic strategy for the synthesis of 2D perovskite-based lateral and vertical (n-CH3(CH2)3NH3)2PbI4/(n-CH3(CH2)3NH3)2(CH3NH3)Pb2I7 heterostructures for the first time. A combination of solution synthesis and gas-solid phase intercalation approach allows us to efficiently synthesize both lateral and vertical heterostructures with great flexibility. X-ray diffraction, photoluminescence, and photoluminescence excitation mapping and electrical transport measurement studies reveal the successful synthesis of lateral and vertical heterostructures with precisely spatial-modulation control and distinguishable interfaces. Our studies not only provide an efficient synthetic strategy with great flexibility, enabling us to create 2D perovskite-based heterostructures, but also offer a platform to investigate the physical processes in those heterostructures.

Probing charge transfer in a novel class of luminescent perovskite-based heterostructures composed of quantum dots bound to RE-activated CaTiO3 phosphors.

We report on the synthesis and structural characterization of novel semiconducting heterostructures composed of cadmium selenide (CdSe) quantum dots (QDs) attached onto the surfaces of novel high-surface area, porous rare-earth-ion doped alkaline earth titanate micron-scale spherical motifs, i.e. both Eu-doped and Pr-doped CaTiO3, composed of constituent, component nanoparticles. These unique metal oxide perovskite building blocks were created by a multi-pronged synthetic strategy involving molten salt and hydrothermal protocols. Subsequently, optical characterization of these heterostructures indicated a clear behavioral dependence of charge transfer in these systems upon a number of parameters such as the nature of the dopant, the reaction temperature, and particle size. Specifically, 2.7 nm diameter ligand-functionalized CdSe QDs were anchored onto sub-micron sized CaTiO3-based spherical assemblies, prepared by molten salt protocols. We found that both the Pr- and Eu-doped CaTiO3 displayed pronounced PL emissions, with maximum intensities observed using optimized lanthanide concentrations of 0.2 mol% and 6 mol%, respectively. Analogous experiments were performed on Eu-doped BaTiO3 and SrTiO3 motifs, but CaTiO3 still performed as the most effective host material amongst the three perovskite systems tested. Moreover, the ligand-capped CdSe QD-doped CaTiO3 heterostructures exhibited effective charge transfer between the two individual constituent nanoscale components, an assertion corroborated by the corresponding quenching of their measured PL signals.

Control of strain relaxation in tensile and compressive oxide thin films

Tensile and compressive solid-solution thin films based on LaAlO 3 and CaZrO 3 compositions were grown on perovskite oxide substrates using pulsed laser deposition to study growth mode transitions and strain relaxation. A buried layer of SrRuO 3 between the thin film and the SrTiO 3 substrate was also introduced to provide an auxiliary embedded strain gauge, which helps identify the critical conditions for the onset of catastrophic strain relaxation events – cracking and dislocation cascades. The results are compared with theoretical predictions to provide guidelines on some general deposition conditions that may be used to obtain smooth, crystalline and defect-free thin films of interest to perovskite-based heterostructures.