Patent Application
20240170591
The invention relates to a method of fabricating a halide perovskite. The invention also relates to a halide perovskite nanowire and a photoelectronic device with the halide perovskite nanowire.
Known methods for producing halide perovskites (HPs) include solution synthesis processes and chemical vapor deposition (CVD) processes. Compared with the solution synthesis processes, CVD processes are better for controlling the geometry of HP nanostructures, such as diameter, length, shape, and phase.
Crystalline HPs produced by CVD could serve as perfect platforms for exploring their fundamental physical properties and practical device implementations.
To date, the most used CVD-based growth technique for HP synthesis is the vapor-solid (VS) process, in which the vapor-phase precursor is converted into a solid product via surface adsorption. This way, the yielded VS-HP nanostructures are determined by the crystal surface energy and substrate feature. For instance, sapphire, mica, and SrTiO3 are used to grow all-inorganic HP nanostructures with specific crystallographic orientations. At the same time, high growth temperature, stringent substrate requirement, and elusive heteroepitaxial relationships are always involved in the VS process, and thus may impose constraints on the material synthesis and further utilization.
Another example of a CVD-based growth technique is the vapor-liquid-solid (VLS) process where nanostructures are precipitated from the supersaturated molten seeds. Compared to the VS process, the VLS process is more attractive for achieving controllable growth and bottom-up synthesis of integration-ready nanostructures. VLS-grown all-inorganic CsPbX3 (X═Cl, Br, or I) HPs nanowires (NWs) and core-shell perovskite NWs using Sn nanoparticles as catalytic seeds are known, due to the low melting temperature (232° C.) and good compatibility to Pb-based HPs of Sn. Such VLS-HP synthesis was achieved at the expense of the Sn impurity atom diffusion into HP host lattices, which could deteriorate the material homogeneities regarding phase purity, surface morphology, and electrical characteristics.
In a first aspect, there is provided a method of fabricating a halide perovskite having a general formula of ABX3, wherein A (e.g., Cs), B (e.g., Pb or Sn), and X (e.g., I, Br, or Cl) are inorganic elements and X is a halide, the method comprising a vapor-liquid-solid process triggered by a catalyst formed from a noble metal. Preferably, A is Cs and B is Pb.
Optionally, the vapor-liquid-solid process is enabled by a spontaneous exothermic nucleation process.
Optionally, the method is at least partly conducted at a temperature of about 250° C. to about 350° C., e.g., about 290° C.; for example, this temperature may be the growth temperature for the vapor-liquid solid process. Additionally, the method may be partly conducted at a temperature of about 400° C. to about 500° C., e.g., about 430° C.; for example, this temperature may be the heating temperature for a source evaporation process.
Preferably, the noble metal is Au and the catalyst is in the form of Au nanoparticles with a diameter of about 10 nm to about 200 nm, e.g., about 100 nm. The catalyst may be transformed into a Au—Pb or Au—Sn alloying catalyst.
Optionally, the method further comprises the step of preparing the catalyst by drop-casting a dispersion solution of Au nanoparticles onto a growth substrate. The growth substrate may be an amorphous SiO2/Si growth substrate with a SiO2 thickness of about 270 nm.
Optionally, the method further comprises the steps of mixing CsI and PbX2 or CsI and SnX2 with a molar ratio of 2:1 and heating the mixture in a first heating zone (upstream) to serve as a vapor-phase Cs, Pb or Sn, and X source. The heating temperature of the first heating zone may be about 400° C. to about 500° C., e.g., 430° C.
Optionally, the method further comprises the step of placing the growth substrate with the catalyst into a second heating zone (downstream) at a growth temperature of about 250° C. to about 350° C. to react with the vapor-phase Cs, Pb or Sn, and X source such that Au nanoparticles alloy with Pb or Sn and convert to a Au—Pb or Au—Sn alloying catalyst. The step may take 120 mins for the growth of CsPbX3 or CsSnX3 nanowire on the growth substrate.
Optionally, the second heating zone may have a growth temperature of about 290° C. The second heating zone may have a growth pressure of 0.8 Torr. The second heating zone may include a carrier gas flow comprises Ar at about 80 sccm.
Optionally, the Au—Pb or Au—Sn alloying catalyst comprises a eutectic alloying catalyst, e.g., having a melting temperature of about 212° C. for Au—Pb alloying catalyst.
Optionally, the CsPbX3 or CsSnX3 nanowire grows along a plane with a lower surface free energy than other planes, via a supersaturation process. For example, the CsPbX3 or CsSnX3 nanowire grows along the (100) plane of the CsPbX3 or CsSnX3 nanowire. The CsPbX3 or CsSnX3 nanowire may be selected from a group comprising CsPbI3, CsPbCl3, CsPbBr3, CsSnI3, CsSnCl3, and CsSnBr3 nanowires.
Optionally, the CsPbX3 or CsSnX3 nanowire is about 15 μm to about 20 μm in length and about 200 nm in diameter.
In a second aspect, there is provided a ABX3 nanowire formed by a method with a vapor-liquid-solid process triggered by a noble metal catalyst, where the ABX3 nanowire is vertically formed on a growth substrate, and A is Cs, B is Pb or Sn, and X is a halide.
Optionally, X is selected from Cl, Br and I.
Optionally, the ABX3 nanowire is terminated with a spherical catalytic tip.
Optionally, when B is Pb and X is I, resulting CsPbI3 nanowire comprises an orthorhombic perovskite phase, e.g., at room temperature. When B is Pb and X is Cl or Br, resulting CsPbCl3 or CsPbBr3 may comprise a cubic perovskite phase, e.g., at room temperature.
Optionally, the CsPbI3 nanowire emits red light across its entire length. The CsPbI3 nanowire may comprise an optically active orthorhombic black phase, e.g., a pseudo cubic Pm-3m phase.
Optionally, the spherical catalytic tip comprises a Au—Pb or Au—Sn seed. The Au—Pb or Au—Sn seed may comprise a eutectic alloying catalyst
In a third aspect, there is provided a photoelectronic device comprising a ABX3 nanowire where A is Cs, B is Pb or Sn, and X is a halide. The ABX3 nanowire may be formed by a method with a vapor-liquid-solid process triggered by a catalyst formed from a noble metal.
Optionally, the photoelectronic device comprises a visible light photodetector.
Optionally, the ABX3 nanowire is dry transferred onto a Au electrode.
Optionally, the Au electrode is fabricated with a 2 μm channel length and is fabricated on a SiO2/Si substrate.
When the ABX3 nanowire is a CsPbX3 nanowire, the visible light photodetector may have a dark current of below about 0.1 pA, a light current of about 28 nA, a specific detectivity of about 1.1×1015 Jones, a responsivity of about 1400 A·W−1 with an incident light intensity of about 5 mW/cm2, or a photo-response time of about 120 s.
Other features and aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. Any feature(s) described herein in relation to one aspect or embodiment may be combined with any other feature(s) described herein in relation to any other aspect or embodiment as appropriate and applicable.
Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the described embodiments set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. Terms of degree, such as “about”, are understood by those of ordinary skill to refer to reasonable ranges outside of the given value, for example, general tolerances associated with manufacturing, assembly, testing, and use of the described embodiments.
To eliminate the above-mentioned impurity doping in VLS-grown HPs with the use of Sn nanoparticles, the inventors have derived, through trials and experiments, that utilizing typical noble metals (e.g., Au, Pd, and Pt) to seed the VLS growth of HPs is a feasible route due to the minimal lattice diffusion offered by them.
In one embodiment, there is provided a method of fabricating a perovskite material, commonly known as having a general formula of ABX3. The method includes a vapor-liquid-solid (VLS) process that is triggered by a catalyst formed from a noble metal. Preferably, the perovskite material is an all-inorganic perovskite (i.e., A, B, and X are inorganic elements), e.g., an all-inorganic halide perovskite. A may be Cs and B may be Pb or Sn, while X may be a halide such as Cl, Br, and I.
In one embodiment, ABX3 is selected from a group comprising CsPbI3, CsPbCl3, CsPbBr3, CsSnI3, CsSnCl3, CsSnBr3 nanowires. These nanowires may be about 10 μm to about 25 μm in length and about 10 nm to about 200 nm in diameter. As a result of the VLS process, the nanowire may be terminated with a spherical catalytic tip, e.g., containing a catalyst-Pb or -Sn seed.
The CsPbI3, CsPbCl3, CsPbBr3, CsSnI3, CsSnCl3, CsSnBr3 nanowires, which have excellent material stability, high optical absorption, and long carrier diffusion length, may be used for photoelectronic devices (e.g., visible light photodetectors) and field-effect transistors. For example, the nanowires may be used as the photosensitive channels of the photoelectronic device.
Before the VLS process, the method may include the step of preparing the catalyst seeds, e.g., by depositing Au nanoparticles with a diameter of about 10 nm to 200 nm onto the growth substrate through a drop casting method. The method may also include the step of preparing the vapor-phase Cs, Pb or Sn, and X source, e.g., by mixing CsX and PbX powders or CsX and SnX powders with a molar ratio of 2:1.
The growth of HP is typically determined by the supply of vapor source, which is controlled by the growth temperature or the growth pressure during the VLS process. When the growth temperature is too low, problems such as increased precursor decomposition, lower kinetic barrier for nucleation and decreased adatom diffusion length may exist, and thus it may not be able to achieve the desired nanowire morphology of the HP. However, if the growth temperature is too high, shorter nanowires may be grown due to the unlikely nucleation of the HP. On the other hand, when the growth pressure is too low, both HP and the catalyst may be found to coexist on the growth substrate. Increasing the growth pressure may facilitate evaporation of source material and increase the amount of source vapor, thus increasing the density of HP and length of the nanowire. However, if the growth pressure is too high, shorter nanowires may be grown due to the limited supply of the vapor.
In one embodiment, the VLS process may be conducted in a two-zone CVD system equipped with a furnace having a first heating region (upstream) with a higher temperature, and a second heating region (downstream) with a lower temperature. The prepared source materials may be placed in the first heating region with a set temperature of about 400° C. to about 500° C., and the substrate deposited with the Au nanoparticles may be placed in the second heating region with a set temperature of about 250° C. to about 350° C. The second heating region may also have a pressure of about 0.5 Torr to about 2 Torr, and include a carrier gas flow with Ar at about 70 sccm to about 90 sccm.
The Au catalyst has a high melting point of 1064° C. and thus it is difficult to exist in the liquid state. Nonetheless, with the introduction of Pb or Sn vapor, Au would react with Pb or Sn vapor to form Au—Pb or Au—Sn eutectic alloy as the catalytic liquid alloy phase which has a melting temperature of about 212° C. in the case of Au—Pb. As shown in
Hereinafter, the present invention is described more specifically by way of examples using a Au-seeded CsPbI3 NW, but the present invention is not limited thereto.
Unless otherwise specifically provided, all tests herein are conducted at standard conditions which include a room and testing temperature of 25° C., sea level (1 atm.) pressure, pH 7, and all measurements are made in metric units. Furthermore, all percentages, ratios, etc. herein are by weight, unless specifically indicated otherwise. It is understood that unless otherwise specifically noted, the materials compounds, chemicals, etc. described herein are typically commodity items and/or industry-standard items available from a variety of suppliers worldwide.
Synthesis of CsPbI3
Au catalyst seeds were prepared by drop-casting the dispersion solution of Au nanoparticles (with a diameter of 100 nm) on 270-nm-thick amorphous SiO2/Si growth substrates, as shown in
The growth substrates with the pre-deposited Au catalyst seeds were placed in the second heating zone with a set temperature of 290° C. With a growth pressure of 0.8 Torr and an Ar carrier gas flow of 80 sccm, the Au nanoparticles alloyed with Pb vapor and fully converted to Au—Pb eutectic alloying catalysts, which is responsible for the CsPbI3 NW growth. After about 120 mins, the reaction was terminated.
Characterization of CsPbI3
Surface morphologies of the NWs were examined using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). Crystal structures were determined by collecting the XRD pattern on a powder diffractometer and imaging with a high-resolution TEM. Elemental mappings and line scan were performed using an energy dispersive X-ray (EDS) detector.
As shown in
As shown in the TEM image in
To study the crystal structure, the XRD pattern was measured from Au-seeded CsPbI3 NWs (
From the PL mapping result shown in
The energy-dispersive X-ray spectroscopy (EDS) mapping shown in
As shown in
The orthorhombic perovskite structure of CsPbI3 NWs is thermally stable at room temperature because of the larger I-ionic radius than other halogens that would induce structural adaptation. Besides, as supported by the SAED pattern, since the (100) planes of CsPbI3 NWs have lower surface free energy than other planes, the Au-seeded CsPbI3 NWs is preferred to grow along [100] direction. Overall, the above structure and element analysis concludes that the CsPbI3 NWs are grown via a supersaturation process at the molten Au—Pb seeds, following the VLS mechanism.
Preparation of Visible Light Photodetectors
Individual CsPbI3 NWs were configured into visible light photodetectors (PDs) to demonstrate their optoelectronic applications. The single-NW photodetectors were prepared by dry transferring the CsPbI3 NWs from the growth substrates onto the pre-prepared Au paired electrodes. Such Au electrodes with a 2 μm channel length were fabricated by standard lithography and metallization on the 270-nm-thick SiO2/Si substrates.
Characterization of Visible Light Photodetectors
For photodetector measurements, Agilent 4155C semiconductor analyzer was employed to measure the I-V and I-T curves, while 532 nm laser diode was used as a light source.
As shown in
The transient response time is critical for PDs and highly depends on the efficient transport/collection of photo-generated carriers. A high-speed photoresponse measurement circuit, mainly composed of a current amplifier and digital oscilloscope, was used to record the dense photoresponse signals chopped at 800 Hz. As shown in
The above embodiments and examples provide an improved method of fabricating a HP that involves a VLS process. Enabled by a spontaneous exothermic nucleation process, the VLS growth temperature is lowered to 290° C., which is unachievable by conventional VS growth processes. Unlike other metal seeds, the enthalpy-mediated Au-seeded process would not lead to the impurity doping in HPs host lattice, thus eliminating the in-bandgap trap states and consequently avoids Shockley-Read-Hall recombination. This contributes to enhanced intrinsic material properties and photodetector performances, including a responsivity of 1400 A·W−1, a light/dark current ratio of ˜106, a detectivity of 1.1×1015 Jones, and a photoresponse time of 120 μs.
Overall, the Au-seeded VLS HP growth process bridges one of the most powerful growth techniques with the emerging HPs materials, facilitating their nanostructures with tailored material properties and promising for practical electronic and photoelectronic utilizations based on low-dimensional HPs.
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The described embodiments of the invention should therefore be considered in all respects as illustrative, not restrictive.
