Patent Application
20230322576
The invention generally relates to chalcogenide perovskites and methods for synthesizing chalcogenide perovskites. More specifically, the invention relates to formation of a chalcogenide perovskite with a solution-based method.
Chalcogenide perovskites are a class of materials that have recently gained great interest for photovoltaic applications due to their high stabilities and excellent predicted optoelectronic properties, including a direct band gap, high near-band-edge absorption coefficients, and good carrier transport. However, device-compatible synthesis remains a challenge for chalcogenide perovskites. In the literature, materials in this class have been synthesized through solid-state reactions of binary sulfides or the sulfurization of oxide perovskites, and through vacuum-based deposition. However, both synthesis procedures often require temperatures greater than 800° C., making these procedures incompatible with the contact layers needed to complete a semiconductor device. Such high temperatures have been required due to slow interdiffusion of constituent metals in chalcogenide perovskites (primarily a combination of calcium, strontium, or barium with zirconium or hafnium) in the case of solid-state reactions, or due to the highly oxyphilic nature of constituent metals in the case of sulfurization of oxide films. While there are many approaches to create oxide perovskite films through solution-based deposition, high temperatures are still required to synthesize chalcogenide perovskites from oxide perovskite films. Although attempts have been made to apply direct solution-based deposition to chalcogenide perovskites, these have relied on simple metal precursors like metal halides and none have been successful to date.
In view of the above, there is an ongoing desire for methods that are capable of synthesizing chalcogenide perovskites without requiring the use of processing temperatures exceeding 800° C.
The intent of this section of the specification is to briefly indicate the nature and substance of the invention, as opposed to an exhaustive statement of all subject matter and aspects of the invention. Therefore, while this section [identifies/is intended to be directed to and consistent with] subject matter recited in the claims, additional subject matter and aspects relating to the invention are set forth in other sections of the specification, particularly the detailed description, as well as any drawings.
The present invention provides, but is not limited to, chalcogenide perovskites and methods for synthesizing chalcogenide perovskites, including a solution-based deposition approach for oxygen-free synthesis of chalcogenide perovskites.
According to one nonlimiting aspect, a method for synthesizing a chalcogenide perovskite includes providing a precursor solution containing a metal precursor wherein the precursor solution is oxygen-free, depositing the precursor solution onto a substrate to form a precursor film, and heating the precursor film in the presence of a chalcogen source to form a chalcogenide perovskite. The steps of depositing and heating are conducted in an inert atmosphere.
Technical aspects of methods as described above preferably include the ability to form chalcogenide perovskites at temperatures below 800° C., which in turn provides the capability of fabricating semiconductor devices that contain chalcogenide perovskites.
These and other aspects, arrangements, features, and/or technical effects will become apparent upon detailed inspection of the figures and the following description.
The intended purpose of the following detailed description of the invention and the phraseology and terminology employed therein is to describe what is shown in the drawings, which include the depiction of and/or relate to one or more nonlimiting embodiments of the invention, and to describe certain but not all aspects of the embodiment(s) to which the drawings relate. The following detailed description also describes certain investigations relating to the embodiment(s), and identifies certain but not all alternatives of the embodiment(s). As nonlimiting examples, the invention encompasses additional or alternative embodiments in which one or more features or aspects described as part of a particular embodiment could be eliminated, and also encompasses additional or alternative embodiments that combine two or more features or aspects described as part of different embodiments. Therefore, the appended claims, and not the detailed description, are intended to particularly point out subject matter regarded to be aspects of the invention, including certain but not necessarily all of the aspects and alternatives described in the detailed description.
The following describes various aspects of methods capable of synthesizing chalcogenide perovskites utilizing a metal precursor-containing solution. As used herein, the term “chalcogenides” refers to sulfur and/or selenium anions. Examples of chalcogenide perovskites include, but are not limited to, BaZrS3, BaHfS3, CaZrS3, SrZrS3, CaHfS3, SrHfS3, BaZrSe3, CaHfSe3, CaZrSe3, Ba3Zr2S7, Ba4Zr3S10, and Ba2HfS4. As described below, such methods preferably entail at least one constituent metal of a chalcogenide perovskite being delivered from a solution (liquid) phase containing the metal precursor(s), in which the metal precursor(s) do(es) not contain oxygen, i.e., preferred metal precursors are not oxygen-containing precursors. Once the metal precursor is supplied, heat treatment and the presence of the chalcogen produce a chalcogenide perovskite material.
Chalcogenide perovskites are a family of materials that are defined by their corner-sharing octahedra in the crystal structure. One common crystal structure for chalcogenide perovskites is the distorted perovskite structure, which as known in the art is a structure that generally takes the ABX3 composition where A and B refer to the cations and X is the chalcogen anion (S2− or Se2+ or a combination of the two). To maintain charge balance with the chalcogen anions, there are several combinations for the charges of the cations that are viable. This includes A2+ with B4+ (II-IV) and A3+ with B3+ (III-III). Potential examples of A2+ include but are not limited to Ba2+, sr2+, ca2+, pb2+, sn2+, and Eu2+. Potential examples of A3+ or B3+ include but are not limited to Y3+, Sc3+, and La3+. Potential examples of B4+ include but are not limited to Ti4+, Zr4+, Hf4+, Sn4+. A second form of chalcogenide perovskite is the layered Ruddlesden-Popper crystal structure which has the chemical composition An+1BnX3n+1. These two-dimensional (2D) perovskite chalcogenides are formed by alternating a number (n) layers of ABX3 perovskite with a layer of a rock salt AX. The cations in the ABX3 layer may be different from the cations in the rock salt AX layer. To maintain charge balance in the Ruddlesden-Popper perovskites the A2+ and B4+ (II-IV) combination of cations is needed. In addition to the materials synthesized with a single element at the A, B, and X positions of the crystal structures, alloying at these sites can also be used to adjust the properties of the material. To date, the II-IV distorted chalcogenide perovskites have received significant attention, especially BaZrS3. However, the methods exemplifying nonlimiting aspects of the present invention presented here are not intended to be limited to BaZrS3 only and could be applied to other chalcogenide perovskites by changing the organometallic, metal organic, or nanoparticulate precursors to include the respective cations and anions or by changing the relative ratios of the precursors that are used.
Once the precursor solution is obtained, at a step 24 the precursor solution optionally may be heated to induce one or more chemical changes in the precursor metals and/or the precursor solution. However, this heating step 24 may be omitted in some embodiments.
Next at a step 26, the precursor solution is used to deliver the precursors to a substrate. Depositing the precursor solution onto the substrate forms a precursor film on the substrate. The precursor solution may be deposited onto the substrate in any suitable manner to form the precursor film, some non-limiting examples of which include casting, blade-coating, and drop-casting. However, other methods of depositing the liquid precursor solution onto the substrate to form the precursor film may also be used. As with the formation of the precursor solution, the deposition in step 26 is typically performed in an inert (substantially oxygen-free) atmosphere to prevent oxygenation of the precursor solution and/or the precursor film.
At a step 28, an optional heat treatment can then be performed on the precursor film to remove solvent and/or alter the chemical composition. For example, the optional heat treatment may be used to at least partially anneal and/or solidify the precursor film on the substrate, if for example the precursor solution was in a highly viscous, liquid state when applied to the substrate. The optional heat treatment may be performed temperatures much lower than 800° C. In some nonlimiting examples, the optional heat treatment may be performed at about 200° C. to about 500° C. The optional heat treatment may last a period of time sufficient to form the precursor film in a preferred state, typically only a few minutes. In some nonlimiting examples, the optional heat treatment may last from about one minute to about five minutes and/or about one to about five minutes per layer of precursor film (if, for example, multiple layers of precursor solution are deposited so as to form a corresponding multiple layers of precursor film). It is possible that the heat treatment at step 28 could be omitted, for example if the precursor film is already in a sufficiently solid state for further processing and/or of longer drying/solidifying times are acceptable.
At a step 30, the precursor film is heated in the presence of a chalcogen source for a period of time sufficient to convert at least some of the metal precursors into the chalcogenide perovskite material. The precursor film is typically (although not always necessarily) heated for at least ten minutes. In some nonlimiting examples, the precursor film is heated for about one hour to about forty-eight hours; however other time periods may be appropriate to obtain partial or complete conversion of the metal precursors into the chalcogenide perovskite material. The chalcogen source may include, but is not limited to, sulfur powder, selenium powder, CS2, CSe2, H2S, and/or H2Se. The step 30 may include a sulfurization process. All of the synthesis steps 22, 24, 26, 28, and 30 are conducted in an inert atmosphere.
Example 1: A first nonlimiting experimental example of the method 20 began at step 22 in which organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(dimethylamido)zirconium(IV) were used as metal precursors in a carbon disulfide solution. A long-chain amine, such as oleylamine, was then added to the solution. At step 24, the solution was heated to 350° C. for 1 to 2 hours, thereby inducing a reaction that produces solids. The solids resulting from this reaction were washed by means of centrifugation using toluene as an antisolvent. The solids were then redispersed in a coating solvent, such as toluene, to create a precursor solution. At step 26, this precursor solution was then deposited on a glass substrate to form a precursor film and at step 28 heated in an inert atmosphere at temperatures of about 300° C. to about 400° C. Finally at step 30, a sulfurization process was employed by placing the sample produced in step 26 in an evacuated ampule containing excess elemental sulfur and heating it at 575° C. for twelve hours to produce the BaZrS3 chalcogenide perovskite.
Example 2: A second nonlimiting example of the method 20 began by forming a precursor solution at step 22 by utilizing organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(dimethylamido)zirconium(IV) as metal precursors in a carbon disulfide solution. The suspension was stirred at ambient temperatures for at least 1 hour before being cast on a glass substrate to form a film at step 26 and annealed at 300° C. in an inert atmosphere for five minutes at step 28. Finally at step 30, the sulfurization process was employed by sealing the sample in an evacuated ampule containing excess elemental sulfur and heating it at 575° C. for at least ten minutes to produce the BaZrS3 chalcogenide perovskite.
Example 3: A third nonlimiting example of the method 20 began by forming a precursor solution at step 22 by utilizing organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(diethylamido)zirconium(IV) as metal precursors in a carbon disulfide solution. At step 24, the solution was heated to 100° C. for 1 hour in a pressurized microwave reactor. At step 26, the resulting precursor solution was then cast onto a glass substrate and at step 28 heated to 300° C. in an inert atmosphere for five minutes. At step 30, the sulfurization process was employed by sealing the sample in an evacuated ampule containing excess elemental sulfur and heating the sample at 575° C. for at least ten minutes to produce the BaZrS3 chalcogenide perovskite.
Example 4: A fourth nonlimiting example of the method 20 began by forming a precursor solution at step 22 by utilizing organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(ethylmethylamido)zirconium(IV) as metal precursors in a carbon disulfide solution. After stirring for at least one hour, excess CS2 was removed in-vacuo and the resulting solids were redissolved in pyridine to create a single-phase precursor solution. At step 26, the precursor solution was blade-coated onto a glass substrate, and at step 28 the sample was heated to 200° C. for 3 minutes per layer for a total of six layers to form a precursor film. The precursor film was then sealed in an evacuated ampule containing excess elemental sulfur and HfH2 as an oxygen trap, and at step 30 the sulfurization process was employed by heating the ampule at 575° C. for at least ten minutes to produce the BaZrS3 chalcogenide perovskite with the sulfurization process.
Example 5: A fifth nonlimiting example of the method 20 began by forming a precursor solution at step 22 by utilizing organometallic bis(pentamethylcyclopentadienyl) barium and organometallic tetrabenzylzirconium as metal precursors in a carbon disulfide solution and then stirring the precursor solution for at least one hour. At step 26, the precursor solution was then deposited on a glass substrate to form a precursor film, and at step 28, the sample was heated in an inert atmosphere at temperatures of about 300° C. to about 400° C. Finally at step 30, the sulfurization process was employed by placing the sample in an evacuated ampule containing excess elemental sulfur and heating it at 575° C. for at least ten minutes to produce the BaZrS3 chalcogenide perovskite.
Example 6: A sixth nonlimiting example of the method 20 began by forming a precursor solution at step 22 by utilizing the organometallic bis(pentamethylcyclopentadienyl) barium and zirconium hydride nanoparticles as metal precursors in a butylamine solution. Additionally, 2-methyl-2-propanethiol was added to the ink (precursor solution) as a sulfur source. At step 26, the precursor solution was then deposited on a glass substrate to form a precursor film, and at step 28 the sample was heated in an inert atmosphere at temperatures of about 300° C. to about 420° C. Finally at step 30, the sulfurization process was employed by placing the sample in an evacuated ampule containing excess elemental sulfur and heating it at 575° C. for at least ten minutes to produce the BaZrS3 chalcogenide perovskite.
Example 7: A seventh nonlimiting example demonstrated that the method 20 is extendable to the Ruddlesden-Popper perovskite phase. At step 22, a precursor solution was formed by mixing organometallic tetrabenzylzirconium and a stochiometric excess (2 Ba: 1 Zr) of organometallic bis(pentamethylcyclopentadienyl) barium, which were used as metal precursors, in a carbon disulfide solution. At step 26, this precursor solution was then deposited on a glass substrate to form a precursor film, and at step 28, the resulting sample was heated in an inert atmosphere at temperatures of about 300° C. to about 400° C. Finally at step 30, the sulfurization process was employed by heating the sample at 575° C. in an ampule containing sulfur to produce the Ba3Zr2S7 Ruddlesden-Popper perovskite phase.
Example 8: An eighth nonlimiting example showed that the method 20 can be used to synthesize the perovskite phase of BaHfS3. At step 22, a precursor solution was formed by mixing organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(ethylmethylamido)hafnium(IV), which were utilized as metal precursors, in a carbon disulfide solution. After stirring for at least one hour, excess CS2 was removed in-vacuo and the resulting solids were redissolved in pyridine to create a single-phase precursor solution. At step 26, the single-phase precursor solution was blade-coated onto a glass substrate, and at step 28, the resulting sample was heated to 200° C. for three minutes per layer for a total of six layers to form a precursor film. The precursor film was then sealed in an evacuated ampule containing excess elemental sulfur and HfH2 as an oxygen trap, and at step 30 the sulfurization process was employed by heating the ampule at 575° C. for at least ten minutes to produce the BaHfS3 chalcogenide perovskite.
Example 9: A ninth nonlimiting example demonstrated that the method 20 can be used to synthesize the Ruddlesden-Popper phase, Ba2HfS4. At step 22, a precursor solution was formed by mixing organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(dimethylamido)hafnium(IV), which were utilized as metal precursors, in a carbon disulfide solution. After stirring for at least one hour, at step 26 the precursor solution was dropcast onto a glass substrate and at step 28 heated to 300° C. for five minutes to form a precursor film. The precursor film was then sealed in an evacuated ampule containing excess elemental sulfur, and at step 30 the sulfurization process was employed by heating the ampule at 575° C. for 24 hours to produce the Ba2HfS4 chalcogenide perovskite.
Example 10: A tenth nonlimiting example showed that, in addition to CS2 and thiols, isothiocyanates can be utilized as chalcogen sources using the method 20 to synthesize chalcogenide perovskites. In this example, at step 22 BaZrS3 was synthesized by combining organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(ethylmethylamido)zirconium(IV) as metal precursors with ethyl isothiocyanate in a pyridine solution to form a precursor solution. After stirring for at least 1 hour, at step 24 the precursor solution was cast onto a glass substrate and heated to 200° C. for three minutes to form a precursor film. The precursor film was then sealed in an evacuated ampule containing excess elemental sulfur and HfH2 as an oxygen trap, and at step 30, the sulfurization process was employed by heating the ampule at 575° C. for one hour to produce the BaZrS3 chalcogenide perovskite.
Example 11: An eleventh nonlimiting example of the method 20 began at step 22 by utilizing the organometallic bis(pentamethylcyclopentadienyl) barium and metal organic tetrakis(ethylmethylamido)zirconium(IV) as metal precursors in a butylamine solution to form a precursor solution. Additionally, 2-methyl-2-propanethiol was added to the ink as a sulfur source. At step 26, the precursor solution was then deposited on a molybdenum-coated glass substrate to form a precursor film, and at step 28 the sample was heated in an inert atmosphere at temperatures of about 300° C. to about 420° C. Finally, at step 30 the sulfurization process was employed by placing the precursor film in an evacuated ampule containing excess elemental sulfur and ZrH2 as an oxygen trap and then heating the ampule at 575° C. for two hours to produce the BaZrS3 chalcogenide perovskite.
In the course of conducting the above experiments, it was concluded that the method 20 cannot be used to synthesize chalcogenide perovskites if metal halides or metal oxides were utilized to supply the A and B cations. Furthermore, it was concluded that the method 20 will not be successful in creating chalcogenide perovskites if the solvent or the precursor solution is exposed to oxygen or water before the formation of crystalline chalcogenide perovskites at step 30.
From the examples described herein, it can be seen that in some nonlimiting examples, methods in accordance with the present invention generally include at least one of the constituent metals being delivered onto the substrate in the (liquid) solution phase. A chalcogenide perovskite may refer to the distorted perovskite or Ruddlesden-Popper perovskite crystal structures. Chalcogenide may refer to the inclusion of sulfide or selenide anions in the crystal structure of the chalcogenide perovskite. The sulfide or selenide anions may be supplied by CS2, CSe2, isothiocyanates, isoselenocyanates, thiolates, selenolates, thioureides, selenoureides, dichalcogenocarbamates, or dichalcogenocarboxylates. The metal precursor(s) are preferably free of oxygen and may take the form of an organometallic, a metal organic, and/or metal-containing nanoparticles. However, other configurations of the methods of the present invention are also contemplated.
As previously noted above, though the foregoing detailed description describes certain aspects of one or more particular embodiments of the invention, alternatives could be adopted by one skilled in the art. For example, functions of certain components of the methods could be performed by components of different construction but capable of a similar (though not necessarily equivalent) function, and various materials could be used in the implementation of the methods. As such, and again as was previously noted, it should be understood that the invention is not necessarily limited to any particular embodiment described herein or illustrated in the drawings.
This application claims the benefit of U.S. Provisional Patent Application No. 63/329,772, filed Apr. 11, 2022, the contents of which are incorporated herein by reference.
This invention was made with government support under award numbers 1735282 and 1855882 awarded by the National Science Foundation. The government has certain rights in the invention.
| Number | Date | Country | |
|---|---|---|---|
| 63329772 | Apr 2022 | US |
