Metal halide perovskites have recently emerged as promising materials for the next generation of optoelectronic devices owing to their remarkable intrinsic properties. In the growth of perovskite crystals, the substrates are essential and play a vital role. Herein, substrate engineering in the growth of perovskite crystals have been reviewed. Particularly, various modified strategies and corresponding mechanism based on the substrate engineering applied to the optimization of thickness, nucleation and growth rate are highlighted. Then the alterable adhesion to substrates will also be discussed. Furthermore, applying the structural coherence of epitaxial crystals with substrate, scalable perovskite single-crystalline thin films have been obtained and can be transferred onto arbitrary substrates. Substrate engineering also can stabilize the desired perovskite phases by modulating the strain between crystals and substrates. Finally, several key challenges and related solutions in the growth of perovskite crystals based on substrate engineering are proposed. This review aims to guide the future of substrate engineering in perovskite crystals for various optoelectronic applications.
We perform first-principles density functional calculations to explore the role of substrate proximity effects on the octahedral rotation patterns in perovskite oxide superlattices. With cubic perovskite SrFeO$_3$ as our model film and tetragonal SrTiO$_3$ as the substrate, we show that in most cases the substrate octahedral rotation patterns propagate into the film across the heterointerface. We also identify elastic boundary conditions for which the enforced structural coherence induces atomic displacement patterns that are not found in the bulk phase diagram of either individual constituent…
Oxide electronics relies on the availability of epitaxial oxide thin films. The extreme flexibility of the chemical composition of ABO3 perovskites and the broad spectrum of properties they cover, inspire the creativity of scientists and place perovskites in the lead of functional materials for advanced technologies. Moreover, emerging properties are being discovered at interfaces between distinct perovskites that could not be anticipated on the basis of those of the adjacent epitaxial layers. All dreamed new prospects require the use of suitable substrates for epitaxial growth. Perovskite sin…
Perovskite transition-metal oxides are networks of corner-sharing octahedra whose tilts and distortions are known to affect their electronic and magnetic properties. We report calculations on a model interfacial structure to avoid chemical influences and show that the symmetry mismatch imposes an interfacial layer with distortion modes that do not exist in either bulk material, creating new interface properties driven by symmetry alone. Depending on the resistance of the octahedra to deformation, the interface layer can be as small as one unit cell or extend deep into the thin film.
Strain engineering with different substrate facets is promising for tuning functional properties of thin film perovskite oxides. By choice of facet, different surface symmetries and chemical bond directions for epitaxial interfaces can be tailored. Here, preparation of well-defined pseudo-cubic (111)-oriented orthorhombic substrates of DyScO3 , GdScO3 , and NdGaO3 is reported. The choice of orthorhombic facet, (011)o or (101)o , both corresponding to pseudo-cubic (111)pc , gives vicinal surfaces with single or double (111pc layer terrace step heights, respectively, impacting subsequent thin fi…
Single-atom catalysts (SACs) combine the best of two worlds by bridging heterogeneous and homogeneous catalysis. The superior catalytic properties of SACs, however, can hardly be exploited without a suitable substrate. Here, we explore the possibility of using hybrid organic-inorganic perovskites as supporting materials for single transition-metal atoms. By means of first-principles calculations, we predict that single Pt atoms can be incorporated into methylammonium lead iodide surfaces by replacing the methylammonium groups at the outermost layer. The iodide anions at the surface provide pot…
Metal halide perovskites single-crystalline thin films (SCTFs) have recently emerged as promising materials for the next generation of optoelectronic devices due to their superior intrinsic properties. However, it is still challenging to transfer and integrate them with other functional materials for hybrid multilayer devices because of their substrate-dependent growth. Herein, a method that allows the SCTFs to be transferred with high quality onto arbitrary substrates has been reported. By introducing hydrophobic treatment to the growth substrates, the adhesion between SCTFs and growth substr…
Perovskite solar cells employing self assembled monolayers such as Me-4PACz as hole transport layer has been reported to demonstrate high device efficiency. However, the poor perovskite wetting on the Me-4PACz caused by poor perovskite ink interaction with the underlying Me-4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co-solvent system comprising of dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and N-methyl-2-pyrrolidone (NMP) is employed to improve the perovskite ink-substrate interaction and obtain a uniform perovskite layer. In comparison…
We report on the synthesis of perovskite SrIrO3 thin films using sputtering technique. Single phase (110) oriented SrIrO$_3$ thin films were epitaxially grown on SrTiO3 (001) substrate. Using off-axis XRD $θ-2θ$ scans, we demonstrate that these films exhibit (110) out-of-plane orientation with (001) and (1-10) lying in-plane. The sputtering grown thin films have a smooth, homogeneous surface, and excellent coherent interface with the substrate.
Organic-inorganic halide perovskite solar cells have recently attracted much attention due to their low-cost fabrication, flexibility, and high-power conversion efficiency. The reduction from three- to two-dimension (2D) promises an exciting opportunity to tune the electronic properties of organic-inorganic halide perovskites. Here, we propose first-principles density-functional theory based route to study the effect of reduced dimensionality, impurity doping, and heterostructure engineering on energy stability, band-gap and transport properties of 2D hybrid organic-inorganic halide perovskite…
Perovskite stability is of the core importance and difficulty in current research and application of perovskite solar cells. Nevertheless, over the past century, the formability and stability of perovskite still relied on simplified factor based on human knowledge, such as the commonly used tolerance factor t. Combining machine learning (ML) with first-principles density functional calculations, we proposed a strategy to firstly calculate the decomposition energies, considered to be closely related to thermodynamic stability, of 354 kinds halide perovskites, establish the machine learning rela…
Organic-inorganic halide perovskite solar cells have attracted much attention due to their low-cost fabrication, flexibility, and high-power conversion efficiency. More recent efforts show that the reduction from three- to two-dimensions (2D) of organic-inorganic halide perovskites promises an exciting opportunity to tune their electronic properties. Here, we explore the effect of reduced dimensionality and heterostructure engineering on the intrinsic material properties, such as energy stability, bandgap and transport properties of 2D hybrid organic-inorganic halide perovskites using first-pr…
Using a CO$_2$ laser to directly heat the crystals from the back side, SrTiO$_3$ substrates may be thermally prepared in situ for epitaxy without the need for ex-situ etching and annealing. We find that the formation of large terraces with straight steps at 900-1100 °C is independent from the formation of the ideal surface reconstruction for epitaxy, which requires temperatures in excess of 1200 °C to complete. The process may be universal, at least for perovskite oxide surfaces, as it also works, at different temperatures, for LaAlO$_3$ and NdGaO$_3$, two other widely used oxide substrate mat…
Materials with low work functions are critical for an array of applications requiring the facile removal or efficient transport of electrons through a device. Perovskite oxides are a promising class of materials for finding low work functions, and here we target applications in thermionic and field electron emission. Perovskites have highly malleable compositions which enable tunable work function values over a wide range, robust stability at high temperatures, and high electronic conductivities. In this work, we screened over 2900 perovskite oxides in search of stable, conductive, low-work-fu…
A topological insulating phase has theoretically been predicted for the thermodynamically unstable perovskite phase of YBiO$_{3}$. Here, it is shown that the crystal structure of the Y-Bi-O system can be controlled by using a BaBiO$_{3}$ buffer layer. The BaBiO$_{3}$ film overcomes the large lattice mismatch of 12% with the SrTiO$_{3}$ substrate by forming a rocksalt structure in between the two perovskite structures. Depositing an YBiO$_{3}$ film directly on a SrTiO$_{3}$ substrate gives a fluorite structure. However, when the Y-Bi-O system is deposited on top of the buffer layer with the cor…
The use of water-soluble sacrificial layer of Sr$_3$Al$_2$O$_6$ has tremendously boosted the research on freestanding functional oxide thin films, especially thanks to its ultimate capability to produce high-quality epitaxial perovskite thin films. However, the costly single-crystalline substrates, e.g. SrTiO$_3$, were generally discarded after obtaining the freestanding thin films. Here, we demonstrate that the SrTiO$_3$ substrates can be recycled to fabricate La$_{0.7}$Sr$_{0.3}$MnO$_3$ films with nearly identical structural and electrical properties. After attaining freestanding thin films,…
The discovery of double perovskites A2B(I)B(III)X6 (A=monovalent cation; B(I)/B(III) = metal cation; X = halogen) as Pb(II)-free alternatives has attracted widespread attention, making it possible to introduce d-block metal cations (e.g., d0 and d10) into halide perovskites. However, at present, there are quite limited insights into the underlying bonding orbitals for d-block metal cation-based halide perovskites. Here, we present an orbital engineering strategy to construct two-dimensional (2D) electronic structures in three-dimensional (3D) halide perovskites by rationally controlling the d …
Stabilizing Solution-Substrate Interaction of Perovskite Ink on PEDOT:PSS for Scalable Blade Coated Narrow Bandgap Perovskite Solar Modules by Gas Quenching
Owing to their high energy-conversion efficiency and inexpensive fabrication routes, solar cells based on metal-organic halide perovskites have rapidly gained prominence as a disruptive technology. An attractive feature of perovskite absorbers is the possibility of tailoring their properties by changing the elemental composition through the chemical precursors. In this context, rational in silico design represents a powerful tool for mapping the vast materials landscape and accelerating discovery. Here we show that the optical band gap of metal-halide perovskites, a key design parameter for so…
Lead (Pb) halide perovskites have achieved great success in recent years due to their excellent optoelectronic properties, which is largely attributed to the lone-pair s orbital-derived antibonding states at the valence band edge. Guided by the key band-edge orbital character, a series of ns2-containing (i.e., Sn2+, Sb3+, Bi3+) Pb-free perovskite alternatives have been explored as potential photovoltaic candidates. On the other hand, based on the band-edge orbital components (i.e., M2+ s and p/X- p orbitals), a series of strategies have been proposed to optimize their optoelectronic properties…
Our first-principles results show that geometric frustration can be induced in thin films of multiferroic BiFeO3. We find that competing magnetic interactions occur in the so-called super-tetragonal phase of this material, which can be grown on strongly-compressive substrates. We show that the frustration level can be tuned by appropriately choosing the substrate; in fact, the three-dimensional spin order gets totally annihilated in a narrow range of epitaxial strains. We argue that the effects revealed here are not exclusive to BiFeO3, and predict that they also occur in multiferroic BiCoO3.
Large single crystals of the double-perovskite Ba$_2$ScNbO$_6$ were grown from the melt for the first time. With a lattice parameter at room temperature of 4.11672(1) Å, this cubic double-perovskite has an excellent lattice match to BaSnO$_3$, PbZr$_{0.9}$Ti$_{0.1}$O$_3$, LaInO$_3$, BiScO$_3$, and other perovskites of contemporary interest. Differential thermal analysis showed that Ba$_2$ScNbO$_6$ melts at 2165$\pm$30°C in an inert atmosphere. Competitive grain growth was visualized by energy dispersive Laue mapping. X-ray diffraction rocking curve measurements revealed full width at half maxi…
The influence of the deposition pressure PO2 and substrate temperature TS during the growth of Bi2FeCrO6 thin films grown by pulsed laser deposition has been investigated. It is found that the high volatility of Bi makes the deposition very difficult and that the growth of pure Bi2FeCrO6 thin films on SrTiO3 substrates is possible only in a narrow deposition parameter window. We find that the pure Bi2FeCrO6 phase is formed within a narrow window around an oxygen pressure PO2 =1.210-2 mbar and around a substrate temperature TS=680 degC. At lower temperature or higher pressure, Bi7.38Cr0.62O12+x…
Molecular ferroelectrics have attracted increasing interests over the past decade due to mechanical flexibility, chemical diversity, environmental friendliness, easy-processing, and lightness. The performance of molecular ferroelectrics is approaching more and more competitive to their inorganic counterparts. Despite the chemical diversity and tunability of the molecular cations or anions, molecular ferroelectrics are not abundant. In particular, physical directed design principles for new discovery or performance optimization are still lacking. Here, through first-principles calculations, we …
Polar heterogeneous photocatalysts were shown to lead to enhanced charge-carrier separation that results in superior activity for example for photocatalytic water splitting. Promising photocatalyst materials such as oxynitrides can be rendered polar by epitaxial strain, which however also increases their band gap, making them unsuitable for visible light absorption. This suggests a trade-off between small band gaps and polar distortions - both being crucial for the catalyst's efficiency. In this paper we investigate, using density functional theory calculations, the suitability of strained AB(…
Engineering oxygen octahedra rotation patterns in $ABO_3$ perovskites is a powerful route to design functional materials. Here we propose a strategy that exploits point defects that create local electric dipoles and couple to the oxygen sublattice, enabling direct actuation on the rotational degrees of freedom. This approach, which relies on substituting an $A$ site with a smaller ion, paves a way to couple dynamically octahedra rotations to external electric fields. A common antisite defect, $\mathrm{Al_{La}}$ in rhombohedral LaAlO$_3$ is taken as a prototype to validate the idea, with atomis…
Halide perovskites are a promising class of materials for optoelectronic applications, due to their excellent optoelectronic performance. However, they suffer several dynamical degradation problems, the characterization of which is challenging in experiments. Atomic scale simulations can provide valuable insights, however, the high computational cost of traditional quantum mechanical methods such as DFT makes it difficult to model dynamical processes in large perovskite systems. In this work, we present a re-parameterized GFN1-xTB method for the accurate description of structural and dynamical…
Antiferromagnetic thin films typically exhibit a multi-domain state, and control of the antiferromagnetic Néel vector is challenging as antiferromagnetic materials are robust to magnetic perturbations. By relying on anisotropic in-plane strain engineering of epitaxial thin films of the prototypical antiferromagnetic material LaFeO3, uniaxial Néel vector control is demonstrated. Orthorhombic (011)- and (101)-oriented DyScO3, GdScO3 and NdGaO3 substrates are used to engineer different anisotropic in-plane strain states. The anisotropic in-plane strain stabilises structurally monodomain monoclini…
We performed ab initio simulations aimed at identifying the atomistic and electronic structure origin of the high valence and conduction band, and band gap tunability of halide perovskites. We found that the two key ingredients are the overlap between bivalent cation and halide atomic orbitals, and the electronic charge of the bottom of the conduction band (CBM) state on the Sn or Pb atoms. In particular, we found that lower gaps are associated to higher negative antibonding overlap, and higher CBM charge on the bivalent cation. Both overlap and CBM charge on Sn/Pb can be tuned by the chemical…
The scalability of highly efficient organic-inorganic perovskite solar cells (PSCs) is one of the remaining challenges of solar module manufacturing. Various scalable methods have been explored to strive for uniform perovskite films of high crystal quality on large-area substrates. However, each of these methods have individual drawbacks, limiting the successful commercialization of perovskite photovoltaics. Here, we report a fully scalable hybrid process, which combines vapor- and solution-based techniques to deposit high quality uniform perovskite films on large-area substrates. This two-ste…
The exploration of emerging materials physics and prospective applications of two-dimensional materials greatly relies on the growth control of their thickness, phases, morphologies and film-substrate interactions. Though substantial progresses have been made for the development of two-dimensional films from conventional layered bulky materials, particular challenges remain on obtaining ultrathin, single crystalline, dislocation-free films from intrinsically non-Van der Waals-type three-dimensional materials. In this report, with the successful demonstration of single crystalline ultrathin lar…
Reflection high-energy electron diffraction (RHEED) is a ubiquitous in situ molecular beam epitaxial (MBE) characterization tool. Although RHEED can be a powerful means for crystal surface structure determination, it is often used as a static qualitative surface characterization method at discrete intervals during a growth. A full analysis of RHEED data collected during the entirety of MBE growths is made possible using principle component analysis (PCA) and k-means clustering to examine significant boundaries that occur in the temporal clusters grouped from RHEED data and identify statistical…
Paper offers a low-cost and widely available substrate for electronics. It posses alternative characteristics to silicon, as it shows low density and high-flexibility, together with biodegradability. Solution processable materials, such as hybrid perovskites, also present light and flexible features, together with a huge tunability of the material composition with varying optical properties. In this study, we combine paper substrates with halide-mixed perovskites for the creation of low-cost and easy-to-fabricate perovskite-on-paper photodetectors with a broadband-tunable spectral response. Fr…
Design of novel artificial materials based on ferroelectric perovskites relies on the basic principles of electrostatic coupling and in-plane lattice matching. These rules state that the out-of-plane component of the electric displacement field and the in-plane components of the strain are preserved across a layered superlattice, provided that certain growth conditions are respected. Intense research is currently directed at optimizing materials functionalities based on these guidelines, often with remarkable success. Such principles, however, are of limited practical use unless one disposes o…
Chalcogenide perovskites have emerged as a new class of electronic materials, but fundamental properties and applications of chalcogenide perovskites remain limited by the lack of high quality epitaxial thin films. We report epitaxial thin film growth of BaZrS3, a prototypical chalcogenide, by pulsed laser deposition. X-ray diffraction studies show that the films are strongly textured out of plane and have a clear in-plane epitaxial relationship with the substrate. Electron microscopy studies confirm the presence of epitaxy for the first few layers of the film at the interface, even though awa…
Halide perovskites have recently gained widespread attention for their exceptional optoelectronic properties which have been illuminated by extensive spectroscopic investigations. In this article, nanophotonic surface-engineering using soft-lithography has been used to reproduce nanostructures with enhanced functionalities. A non-invasive optical technique based on Raman and photolumines-cence (PL) spectroscopy is employed to investigate the interactive effect of the thermal and optical behaviour in surface-patterned hybrid organic-inorganic halide perovskite thin films. The thermophys-ical pr…
Films of (FA$_{0.79}$MA$_{0.16}$Cs$_{0.05}$)$_{0.97}$Pb(I$_{0.84}$Br$_{0.16}$)$_{2.97}$ were grown over TiO$_{2}$, SnO$_{2}$, ITO, and NiO. Film conductivity was interrogated by measuring the in-phase and out-of-phase forces acting between the film and a charged microcantilever. We followed the films' conductivity vs. time, frequency, light intensity, and temperature (233 to 312 K). Perovskite conductivity was high and light-independent over ITO and NiO. Over TiO$_{2}$ and SnO$_{2}$, the conductivity was low in the dark, increased with light intensity, and persisted for 10's of seconds after t…
Materials Science Institute of Seville. Consejo Superior de Investigaciones Científicas (CSIC)- Univ. Sevilla（塞维利亚材料科学研究所。西班牙国家研究委员会-塞维利亚大学）；Departamento de Física Aplicada I, Universidad de Sevilla（塞维利亚大学应用物理系）；Departamento de Química Física, Facultad de Química. Universidad de Sevilla（塞维利亚大学化学学院物理化学系）
Perovskite solar cells have achieved a substantial breakthrough via advanced interface engineerings. Reports have emphasized that combining the hybrid perovskites with Lewis base and graphene improve the performance; the underlying mechanisms are not yet fully understood. Here, using density functional theory, we show that upon the formation of CH3NH3PbI3 interfaces with three different Lewis base molecules and graphene, the binding strength with S-donors thiocarbamide and thioacetamide is higher than with O-donor dimethyl sulfoxide, while the interface dipole and work function reduction tend …
Hybrid organic-inorganic perovskites are exceedingly interesting candidates for new solar energy technologies, for both ground-based and space applications. However, their large-scale production is hampered by the lack of long-term stability, mostly associated to ion migration. The specific role of non-covalent bonds in contributing to the stability remains elusive, and in certain cases controversial. Here, we perform an investigation on a large perovskite chemical space via a combination of first-principles calculations for the bond strengths and the recently developed Sure Independent Screen…
We used first-principles calculations to investigate the existence and origin of the ferroelectric in- stability in the ABF3 fluoro-perovskites. We find that many fluoro-perovskites have a ferroelectric instability in their high symmetry cubic structure, which is of similar amplitude to that commonly found in oxide perovskites. In contrast to the oxides, however, the fluorides have nominal Born effective charges, indicating a different mechanism for the instability. We show that the instability originates from ionic size effects, and is therefore in most cases largely insensitive to pressure a…
We report charge-transfer up to a single electron per interfacial unit cell across non-polar heterointerfaces from the Mott insulator LaTiO3 to the charge transfer insulator LaCoO3. In high-quality bi- and tri-layer systems grown using pulsed laser deposition, soft X-ray absorption, dichroism and STEM-EELS are used to probe the cobalt 3d-electron count and provide an element-specific investigation of the magnetic properties. The experiments prove a deterministically-tunable charge transfer process acting in the LaCoO3 within three unit cells of the heterointerface, able to generate full conver…
Switchable Polarization in an A-site Deficient Perovskite through Vacancy and Cation Engineering
Kyoto University（京都大学）；Nantes Université（南特大学）；The University of Tokyo（东京大学）；Japan Fine Ceramics Center（日本先进陶瓷中心）；Kyushu University（九州大学）；Pennsylvania State University（宾夕法尼亚州立大学）
Organohalide perovskite with a variety of surface structures and morphologies have shown promising potential owing to the choice of the type of heterostructure dependent stability. We systematically investigate and discuss the impact of 2-dimensional molybdenum-disulphide (MoS2), molybdenum-diselenide (MoSe2), tungsten-disulphide (WS2), tungsten-diselenide (WSe2), boron- nitiride (BN) and graphene monolayers on band-gap and energy stability of organic-inorganic halide perovskites. We found that MAPbI3ML deposited on BN-ML shows room temperature stability (-25 meV~300K) with an optimal bandgap …
To realize a thermoelectric power generator, typically a junction between two materials with different Seebeck coefficient needs to be fabricated. Such difference in Seebeck coefficients can be induced by doping, which renders difficult when working with two-dimensional (2d) materials. Here, we employ substrate effects to form a thermoelectric junction in ultra-thin few-layer MoS2 films. We investigated the junctions with a combination of scanning photocurrent microscopy and scanning thermal microscopy. This allows us to reveal that thermoelectric junctions form across the substrate-engineered…
Intrinsic electrical and excitonic properties of monolayer transition metal dichalcogenides are studied on CYTOP fluoropolymer substrates with greatly suppressed unintentional doping and dielectric screening. Ambipolar transport behavior is observed in monolayer WS2 by applying solid states backdates. The excitonic properties of monolayer MoS2 and WS2 are determined by intricate interplays between the bandage renormalization, Pauli blocking and carrier screening against carrier doping.
We report the first single crystal growth of the correlated metal LaNiO3 using a high-pressure optical-image floating zone furnace. The crystals were studied using single crystal/powder x-ray diffraction, resistivity, specific heat, and magnetic susceptibility. The availability of bulk LaNiO3 crystals will (i) promote deep understanding in this correlated material, including the mechanism of enhanced paramagnetic susceptibility, and (ii) provide rich opportunities as a substrate for thin film growth such as important ferroelectric and/or multiferroic materials. This study demonstrates the powe…
The first examples of single crystal epitaxial thin films of a high entropy perovskite oxide are synthesized. Pulsed laser deposition is used to grow the configurationally disordered ABO3 perovskite, Ba(Zr0.2Sn0.2Ti0.2Hf0.2Nb0.2)O3, epitaxially on SrTiO3 and MgO substrates. X-ray diffraction and scanning transmission electron microscopy demonstrate that the films are single phase with excellent crystallinity and atomically abrupt interfaces to the underlying substrates. Atomically-resolved electron energy loss spectroscopy mapping shows a uniform and random distribution of all B-site cations. …
This study introduces a new chemical method for controlling the strain in methylammonium lead iodide (MAPbI3) perovskite crystals by varying the ratio of Pb(Ac)2 and PbCl2 in the precursor solution. To observe the effect on crystal strain, a combination of piezoresponse force microscopy (PFM) and X-ray diffraction (XRD) is used. The PFM images show an increase in the average size of ferroelastic twin domains upon increasing the PbCl2 content, indicating an increase in crystal strain. The XRD spectra support this observation with strong crystal twinning features that appear in the spectra. This…
