MIXED HALIDE PEROVSKITE, MEGALIBRARIES, HETEROSTRUCTURES AND SOLID SOLUTIONS AND METHODS OF FORMING THE SAME
20250154019 ยท 2025-05-15
Inventors
Cpc classification
B82Y40/00
PERFORMING OPERATIONS; TRANSPORTING
International classification
Abstract
A method of forming a combinatorial mixed halide perovskite library can include depositing an array of halide perovskite particles on a substrate. The method further includes exposing the array of halide perovskites to a laser to from defects in each of or a selected portion of the halide perovskite particles. The exposure conditions are modified across the array to generate a variation of defect concentration in the halide perovskite particles in the array. The defect containing halide perovskites are then exposed to an ion exchange solution and either anion exchanged or cation exchanged to thereby form a mixed halide perovskite particle.
Claims
1. A method of forming a combinatorial mixed halide perovskite library, comprising: depositing an array of halide perovskite particles on a substrate, wherein each halide perovskite particle is a compound of formula ABX.sup.1.sub.3, wherein A is a cation, B is a metal, and X.sup.1 is a first halogen; exposing the array of halide perovskite particles to a laser to form defects in at least a portion of the halide perovskite particles, wherein an exposure condition is modified across the array to generate a variation of defect concentration in the halide perovskite particles in the array; and exposing the array of halide perovskite particles having the defect concentration to an ion exchange solution comprising at least one halogen X.sup.2 to thereby exchange a portion of X.sup.1 with X.sup.2 and form mixed halide perovskite particles, each mixed halide perovskite particle being a compound of formula AB(X.sup.1.sub.(1-n)X.sup.2.sub.n).sub.3, wherein 0<n<1), and X.sup.2 is a second halogen different from X.sup.1.
2. The method of claim 1, wherein the array of halide perovskite particles is deposited using evaporation-crystallization polymer pen lithography.
3. The method of claim 1 or 2, wherein the array of halide perovskite particles has a gradient of crystal size of the halide perovskite particles across the array.
4. The method of any one of the preceding claims, wherein the halide perovskite particles have a crystal size of about 100 nm to about 400 nm before laser exposure.
5. The method of any one of the preceding claims, wherein the exposure condition of the laser is varied such that a gradient of defect concentration is generated across the array of halide perovskite particles.
6. The method of any one of the preceding claims, wherein ion exchange is performed at a temperature of about 20 C. to about 65 C.
7. The method of any one of the preceding claims, wherein ion exchange is performed by exposing the array of halide perovskite particles having the defect concentration to a solution comprising a perovskite precursor BX.sup.2.sub.2, cyclohexane, oleic acid, and oleylamine.
8. The method of any one of the preceding claims, wherein X.sup.1 and X.sup.2 are independently selected from Cl, Br, F, and I.
9. The method of any one of the preceding claims, wherein B is one or more of lead, tin, and/or germanium.
10. The method of any one of the preceding claims, wherein A is one or more of methylammonium, butylammonium, formamidinium, phenethylamine, cesium, and rubidium.
11. The method of any one of the preceding claims, wherein varying the exposure conditions comprises varying the exposure time.
12. The method of claim 11, wherein the exposure time is about 10 s to about 80 s.
13. The method of any one of the preceding claims, wherein varying the exposure conditions comprises varying the laser power.
14. The method of claim 13, wherein the laser power is about 0.2 mW to about 25 mW.
15. The method of any one of the preceding claims, wherein the exposure conditions comprise delivering an energy in a range of about 2.5 to about 2000 mJ.
16. The method of claim 15, wherein the delivered energy is varied as a gradient across the array of halide perovskite particles.
17. The method of any one of the preceding claims, wherein the laser has a wavelength from about 300 nm to about 700 nm.
18. The method of claim 17, wherein the wavelength is 473 nm.
19. A mixed halide perovskite crystal having a lateral heterostructure and being of formula I:
A.sub.1-xA.sub.xBX.sub.3, wherein A is a first cation, A is a second cation, wherein A and A are different cations, B is a metal, X is at least one halogen, 0<x<1, and the lateral heterostructure comprises an A rich phase in a central region of the crystal, surrounded partially by an A rich phase.
20. The mixed halide perovskite of claim 19, wherein A and A are independently selected from methylammonium, dimethylammonium, ethylammonium, butylammonium, formamidinium, phenethylamine, and cesium.
21. The mixed halide perovskite of claim 20, wherein A is cesium and A is formamidinium with a ratio A/A=1.
22. The mixed halide perovskite any one of claims 19 to 21, wherein X is one of Cl, Br, and I.
23. The mixed halide perovskite of any one of claims 19 to 21, wherein X is a combination of two or more anions selected from Cl, Br, and I.
24. The mixed halide of claim 23, comprising a first anion X and a second anion X present in a ration X:X=(1-y)/y, wherein 0<y<1.
25. The mixed halide perovskite of claim 23 or 24, wherein X is Br and I.
26. The mixed halide perovskite of claim 23 or 24, wherein X is Cl and Br.
27. The mixed halide perovskite of claim 23 or 24, wherein X is Cl, Br, and I.
28. The mixed halide perovskite of any one of claims 19 to 27, wherein B is selected from lead, tin, and/or germanium.
29. The mixed halide perovskite of any one of claims 19 to 28, wherein 0.25x0.75.
30. The mixed halide perovskite of any one of claims 19 to 29 comprising a crystal size of at least 60 nm.
31. The mixed halide perovskite of any one of claims 19 to 30, wherein the A rich phase surrounds a perimeter of the A rich phase, leaving at least a portion of the A rich phase exposed.
32. The mixed halide perovskite of any one of claims 19 to 31, wherein the X is Br and I, and the lateral heterostructure comprises an A-Br rich phase in the center surrounded partially by an A-I rich phase.
33. The mixed halide perovskite of any one of claims 19 to 32, wherein the mixed halide perovskite crystal is selected from Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3, Cs.sub.0.5FA.sub.0.5PbBr.sub.3, Cs.sub.0.5FA.sub.0.5Pb(C.sub.0.83Br.sub.0.17).sub.3, Cs.sub.0.5FA.sub.0.5Pb(C.sub.0.33Br.sub.0.66).sub.3, Cs.sub.0.5FA.sub.0.5Pb(Br.sub.0.9I.sub.0.1).sub.3, Cs.sub.0.5FA.sub.0.5Pb(Br.sub.0.8I.sub.0.2).sub.3, Cs.sub.0.5FA.sub.0.5Pb(Br.sub.0.66I.sub.0.33).sub.3, Cs.sub.0.5FA.sub.0.5Pb(Br.sub.0.33I.sub.0.66).sub.3, Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.67Br.sub.0.17I.sub.0.1).sub.3, Cs.sub.0.5FA.sub.0.5Pb(C.sub.0.42Br.sub.0.42I.sub.0.17).sub.3).
34. A solid-solution mixed halide perovskite having the formula A.sub.1-xA.sub.xBX.sub.3, wherein
A.sub.1-xA.sub.xBX.sub.3, wherein A is a first cation A is a second cation, wherein A and A are different cations, B is a metal X is at least one halogen, 0<x<1, and wherein the crystal size is less than 60 nm.
35. A method of forming mixed halide perovskite crystals having a lateral heterostructure, comprising: dissolving at least one first perovskite precursor having the formula AX, at least one second perovskite precursor having the formula AX and at least one third perovskite precursor having the formula BX.sub.2, and at least one fourth perovskite precursor having the formula BX.sub.2 in a solvent to form a precursor solution, wherein A and A are each cations and are different cations, B is a metal, and X and X are each a halogen and can each be the same or different; depositing the precursor solution onto a substrate; and evaporating the solvent, wherein the halide perovskite crystals form upon evaporation of the solvent, wherein the crystals form as two stages, the first stage being a A-X-rich perovskite phase and the second stage being a A-X-rich perovskite phase partially surrounding the A-X-rich perovskite phase to thereby form the mixed halide perovskite having a lateral heterostructure and being of formula I
A.sub.1-xA.sub.xBX.sub.3, wherein A is a first cation A is a second cation, wherein A and A are different cations, B is a metal X is at least one halogen, 0<x<1.
36. A method of forming mixed halide perovskite crystal array having a plurality of halide perovskite crystals arranged in a pattern, comprising: coating an array of pens with a precursor solution comprising at least one first perovskite precursor having the formula AX, at least one second perovskite precursor having the formula AX, at least one third perovskite precursor having the formula BX.sub.2 dissolved in a solvent, and at least one fourth perovskite precursor having the formula BX.sub.2 wherein A and A are each cations and are different cations, B is a metal, and X and X are each a halogen and can each be the same or different; contacting a substrate with the coated pen array to thereby deposit the precursor solution as a pattern of printed indicia on the substrate, wherein: the printed indicia form nanoreactors on the substrate and a mixed halide perovskite crystal nucleates and grows within each nanoreactor in two stages, the first stage being a A-X-rich perovskite phase and the second stage being a A-X-rich perovskite phase partially surrounding the A-X-rich perovskite phase to thereby form the mixed halide perovskite having a lateral heterostructure and being of formula I
A.sub.1-xA.sub.xBX.sub.3, wherein A is a first cation A is a second cation, wherein A and A are different cations, B is a metal X is at least one halogen defined by selection of X, X, and X, 0<x<1.
37. The method of claim 35 or 36, wherein X, X, and X are the same halogen.
38. The method of claim 35 or 36, wherein X. X, X are different halogens and the at least one third precursor comprises a precursor of formula BX, a precursor of formula BX and a precursor of formular BX.
39. The method of any one of claims 35 to 38, wherein the solvent comprises one or more of dimethyformamide (DMF), dimethyl sulfoxide (DMSO), y-butyrolactone (GBL), and sulfolane.
40. The method of claim 39, wherein the solvent comprises dimethyl sulfoxide (DMSO) and sulfolane.
41. A combinatorial library of mixed halide perovskite crystals, comprising a patterned array of a plurality of the mixed halide perovskite crystals of claim 19.
42. The combinatorial library of claim 41, wherein the single crystal halide perovskite heterostructure crystals have a crystal size of about 60 nm to about 5000 nm.
43. The combinatorial library of claim 41 or 42, wherein the plurality of mixed halide perovskite crystals has a gradient of crystal size, wherein the gradient is present in a defined gradient pattern across the patterned array.
44. The combinatorial library of any one of claims 41 to 43, wherein the plurality of mixed halide perovskite crystals comprises at least first and second mixed halide perovskite crystals, wherein the first and second halide perovskite crystals are arranged in a defined pattern with respect to one another.
45. The combinatorial library of claim 44, wherein the first and second mixed halide perovskite crystals differ in one or more of size, geometry, and composition.
46. The combinatorial library of any one of claims 41 to 44, wherein the plurality of mixed halide perovskite crystals comprises at least first, second, and third mixed halide perovskite crystals arranged in a defined pattern with respect to one another.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] While color is not shown in the drawings, the observed color of photoemissions and changes thereof are described throughout the description of the drawings and the detailed description.
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DETAILED DESCRIPTION
Mixed Halide Megalibraries
[0087] Methods of the disclosure can be utilized to form libraries of mixed halide perovskite particles with varying size and a laser excitation can be used to toggle the defect concentrations in the nanostructures. The defect concentration of individual particles is dependent on the laser exposure conditions owing to a vacancy formation mechanism induced by strong photocarrier-lattice interactions. The method can further include performing anion exchange in a parallelized manner because the degree of ion exchange of each particle is dependent on its defect concentration and size. The method can enable creation of combinatorial libraries that can be screened for various properties, such as optoelectronic properties.
[0088] Methods of making libraries of mixed halide perovskite particles can include depositing an array of halide perovskite particles on a substrate. The halide perovskite particles can be a compound of formula A.sup.1BX.sup.1.sub.3, where A.sup.1 is a first cation, B is a metal, and X.sup.1 is a first halogen. The array can have a variation of size of the halide perovskite particles and/or can have a uniform crystal size. The array can have a variation of composition of halide perovskite particles or particles can each have a uniform composition. For example, the array can include halide perovskite particles of uniform composition but varying crystal size. The crystal size can vary, for example, as a gradient across the array.
[0089] The defects are then introduced into the halide perovskite particles using laser excitation. The array is exposed to the laser, for example, a confocal laser, with variation of the exposure conditions to change the defect concentration in at least a portion of the particles in the array based on the changes in exposure conditions. For example, the exposure conditions can be varied in a gradient such that a gradient of defect concentrations is generated. The exposure conditions can be varied selectively such that selected ones of the particles have more or less defect concentration. Additionally, or alternatively, selective ones of the particles can be exposed to the laser while others remain unexposed. As a result, only those selected particles exposed to the laser will ion exchange and form the mixed halide perovskites, thereby resulting in a variation of composition between single anion or cation halide perovskites and mixed anion or cation halide perovskites in the array.
[0090] Variation of the laser exposure can include varying one or both of the exposure time and the power of the laser. For example, the exposure time can be about 10 s to about 80 s, about 20 s to about 60 s, about 50 s to about 80 s, about 10 s to about 40 s. Other suitable times can include about 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, and any values therebetween or ranges defined by these values. For example, the power can be about 0.25 mW to about 25 mW, about, about 1 mw to about 10 mW, about 0.25 mW to about 5 mW, or about 15 mW to about 25 mW. Other suitable powers include about 0.25, 0.5, 0.75, 1, 5, 10, 15, 20, 25 mW or any values therebetween or ranges defined by these values.
[0091] The variation of the exposure conditions of time and power varies the amount of energy delivered to the particles in the array. The energy can range from about 2.5 mJ to about 2000 mJ. The energy delivered to the particles can be varied across the array. For example, the energy can be varied as a gradient. For example, selected particles can have different energies delivered through the laser exposure. It is also contemplated herein that a uniform exposure can be used to deliver the same amount of energy to each of the particles.
[0092] The laser can have a wavelength, for example, in the range of UV to IR wavelength. For example, the laser can have a wavelength of about 300 nm to about 700 nm. For example, the laser can have a wavelength of 473 nm.
[0093] The array of halide perovskite particles is then ion exchanged either cation or anion exchanged to form the mixed halide perovskite structure. For example, for anion exchange, the array of halide perovskite particles having the laser-induced defects can be exposed to an exchange solution comprising a second halogen X.sup.2 that is different than the first halogen X.sup.1. The anion exchange results in a mixed halide perovskite being formed having the formula AB(X.sup.1.sub.(1-n)X.sup.2.sub.n).sub.3, where A is the cation, B is the metal, X.sup.1 is a first halogen and X.sup.2 is a second halogen different from the first halogen. For example, the halogen can be provided as a precursor of formula BX.sup.2.sub.y for anion exchange. For example, for cation exchange, the array of halide perovskite particles having the laser-induced defects can be exposed to an exchange solution comprising a cation A.sup.2. The cation exchanges results in a mixed-halide perovskite of formula (A.sup.1.sub.(1-n)A.sup.2.sub.n)BX.sub.3, wherein 0<n<1) where A.sup.1 is the first cation, A.sup.2 is a second cation different from the first cation, B is the metal, X is a halogen. For example, mixed cation halide perovskites can include Cs.sup.+-MA.sup.+, Cs.sup.+-FA.sup.+, Pb.sup.2+Sn.sup.2+ as the cations.
[0094] The degree of ion exchange is dependent on the defect concentration and the crystal size. Thus, by varying the crystal size and the defect concentration, the composition of the resulting mixed halide perovskite formed after ion exchange can be controlled. To avoid complete ion exchange, the ion exchange process can be performed at a reduced temperature, for example, about 20 C. to 65 C. to slow the reaction kinetics and thereby allow for partial ion exchange such that a mixed ion halide perovskite composition can be formed.
[0095] CsPbBr.sub.3 halide perovskites and resulting mixed anion halide perovskites are discussed herein by way of example only. It should be understood that the example methods described with respect to the CsPbBr system can be extended to any halide perovskites structure. Generally, the halide perovskite structures used in the methods herein and resulting mixed halide perovskites can have a composition in which A.sup.1 and A.sup.2 (if present) can be an organic or inorganic cation and are different cations, B is a metal cation, and X.sup.1 and X.sup.2 (if present) are different halogens. For example, A.sup.1 and A.sup.2 can be independently selected from one or more of methylammonium, butylammonium, formamidinium, phenethylamine, 3-(aminomethyl)piperidinium, 4-(aminomethyl)piperidinium, cesium, and rubidium. For example, B can be one or more of lead, tin, europium, and/or germanium. For example, X.sup.1 and X.sup.2 can be independently selected from Cl, Br, F, and I.
[0096] In a typical experiment, halide perovskite CsPbBr.sub.3 arrays for preparing combinatorial libraries of MHP particles were synthesized using a previously reported EC-PPL method, which enables the formation of an array of particles of uniform composition and a gradient of sizes (approximately 100 to 400 nm) (
[0097] The sizes and compositions of the particles were characterized using scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy, respectively. The PL peak locations of the CsPb(Br.sub.1-xCl.sub.x).sub.3a compositions are related to the value of x (
[0098] In order to access intermediate CsPb(Br.sub.xCl.sub.1-x).sub.3 compositions and avoid complete exchange from CsPbBr.sub.3 to CsPbCl.sub.3, a low reaction solution temperature (20-65 C.), which can allow for slow anion exchange kinetics, was used. Defects in this regime are likely in the form of halide vacancies (V.sub.X.sup.+) because they have the lowest formation energy compared to other defects and promote diffusion. Previously, researchers examined the relationship between vacancy concentration and diffusion in solids, and the vacancy-dependent modification to the diffusion coefficient (D) can be obtained based on the equation: D=a.sup.2N.sub.V; where N.sub.V is the vacancy concentration in the solid, is a geometric constant, a is the elementary jump distance, and is the jump frequency. Laser exposure introduces additional vacancies that proportionally increase with increasing diffusion coefficient (D), which promotes anion exchange. Thus, a significant blue-shift in the PL peak position of laser-exposed particles compared to their unexposed counterparts was observed (400 nm particles: 490 nm vs. 460 nm; 300 nm particles: 481 nm vs. 436 nm) (
[0099] Next, the V.sub.X.sup.+ concentration, and ultimately halide composition, of the particles in the CsPbBr.sub.3 arrays was tuned by adjusting the confocal laser exposure conditions. First, pre-patterned arrays of CsPbBr.sub.3 particles (396 nm25 nm) were prepared using EC-PPL with an identical 8-m extension length (
[0100] The increased sensitivity of V.sub.X.sup.+ concentration to laser power can be understood by considering the postulated process for laser-induced vacancy formation and its role in the synthetic method described herein. Light-matter interactions that occur during the laser-exposure of CsPbBr.sub.3 include: a local temperature increase due to laser heating and the generation and subsequent interaction of photocarriers with the crystal lattice. Of these, it was hypothesized that laser-induced V.sub.X.sup.+ formation is mainly attributed to strong photocarrier-phonon interactions. Laser-induced heating is unlikely to be relevant here because enhanced anion exchange was not observed in unexposed particles even after annealing at 200 C. for more than 20 min (
[0101] Interestingly though, with intermediate sub-bandgap 532 and 633-nm laser exposure (approximately 20 mW200 s), the PL peak positions moved to lower wavelengths (
[0102] Anion exchange is particle size-dependent (in the 100 to 400 nm range) in addition to being dependent on laser-induced effects (
[0103] Next, the ability to selectively modify the composition of single particles in a high-density particle array via selective laser exposure was demonstrated (
[0104] These single-particle MHP combinatorial libraries that encode both composition and size at high spatial resolution are an ideal platform for the rapid screening of particular properties for fundamental studies or applications. The discovery of efficient blue-emitting halide perovskites is a bottleneck to developing all-perovskite full-color displays, and much effort has been devoted to synthesizing blue-emitting MHPs of different compositions, sizes, and structures. However, each new composition is typically discovered via repetitive, synthetic trial-and-error, rather than through single, high-throughput screening experiments. As a proof-of-concept, a CsPb(Br.sub.xCl.sub.1-x).sub.3 library was screened for high-efficiency blue photoemission. First, a library of approximately 400-nm CsPbBr.sub.3 particles was generated with 8-m extension length during the EC-PPL process. Next, these CsPbBr.sub.3 particles were rapidly exposed to a continuous-wave 405-nm laser using scanning confocal microscopy. Vacancy generation was evidenced by the observed decrease in PL intensity (
[0105] Finally, to investigate whether these results are generalizable, thin-films with compositions of CsPb(Br.sub.xCl.sub.1-x).sub.3 (x=0.4, 0.5, 0.6, 0.75) were prepared via spin coating. The emission from the CsPb(Br.sub.0.60Cl.sub.0.40).sub.3 system showed the most intense PL emission (
[0106] Methods of the disclosure provide a high-throughput combinatorial approach to spatially program the compositions of individual single crystal particles in MHP megalibraries. The halide vacancy concentration can be tuned via laser exposure, due to strong photocarrier-lattice interactions, and along with particle size, can be used to dictate final particle composition after subsequent anion exchange. This new high-throughput screening platform is materialsgeneral, and therefore can be extended to many more unique compositions, sizes, and structures. For example, this technique is amenable to the exploration of new compositions formed by incorporating multiple cations in the A or B site in the ABX.sub.3 structure (such as Cs.sup.+-MA.sup.+, Cs.sup.+-FA.sup.+, Pb.sup.2+Sn.sup.2+) via cation exchange reactions; other heterostructures and ionic semiconductors also can be formed. This platform is integral to realizing a big-data approach to materials discovery and investigating the vast composition-structure landscape where fundamental insight is currently lacking. And yet, given the high-resolution and high-throughput nature of this technique, and its ability to encode composition with position in an array, this process may indeed be valuable in the creation of practical devices, such as ultrahigh pixel density displays, sensors, and data storage components. As a result, the platform reported here will substantively impact the fundamental study of halide perovskites and their utilization in next-generation optoelectronic devices.
[0107] In
[0108] where X.sub.X is the halide anion in its own crystal site, X.sub.i.sup. is the halide anion in the interstitial space, and V.sub.X.sup.+ is the halide vacancy. According to this mechanism, Raman excitation enhances the magnitude of the displacement fluctuations of X.sub.X, which promotes the vacancy formation reaction (Eq. 1). This process results in a relatively small V.sub.X.sup.+ concentration because the charged X.sub.i.sup. has a high formation energy and the accumulated X.sub.i.sup. significantly hinders the formation of more V.sub.X.sup.+. This mechanism is further supported by the observation of an increase in vacancy formation with phonon mode intensity (
[0109] Notably, the use of the phonon excitation alone to modify the halide vacancy concentration in CsPbBr.sub.3 has not been demonstrated yet; however, it alone cannot explain the significantly higher vacancy concentrations observed under higher-energy laser illumination.
[0110] Without intending to be bound by theory, it is believed that the presence of photocarriers promotes vacancy formation by neutralizing the charged anion, forming X.sub.i.sup.0 via the combination of photo-generated holes h.sup.+ with charged interstitial halide ions X.sub.i.sup., in the defect reaction:
[0111] Per this reaction, a high-density of photo-generated holes favors V.sub.X.sup.+ formation (Eq. 2). In addition, since the maximum stable concentration of uncharged X.sub.i.sup.0 in the lattice is higher than the concentration of charged X.sub.i.sup. ions, this reaction represents a significant route for accommodating excess vacancies. Further, the potential to form diatomic gas molecules X.sub.2.sup.0 from neutralized X.sub.i.sup.0 also promotes V.sub.X.sup.+ formation when the lattice is saturated with X.sub.i.sup.0 per the following reaction:
[0112] The possible escape of gaseous X.sub.2.sup.0 from the lattice promotes the forward direction of this reaction, and therefore it prevents an excessive build-up of X.sub.i.sup.0, which in turn favors the forward direction of the preceding reaction (Eq. 2). The strong photocarrier-lattice interactions (Eq. 2 and Eq. 3), and the vacancy formation that is promoted as a result, accurately predict a significant increase in V.sub.X.sup.+ concentration compared to the case where pure phonon excitation was achieved or laser exposure did not occur (
[0113] A decrease in PL efficiency was observed in MAPbX.sub.3, which was attributed to an increase in the iodide vacancy concentration,.sup.5 analogous to our observations. However, high-intensity light induced (partial) decomposition to MAX and PbX.sub.2. The intrinsic instability of organic-inorganic hybrid perovskites makes it challenging to control vacancy concentration without laser-induced decomposition as demonstrated with all-inorganic CsPbBr.sub.3.
[0114] Without intending to be bound by theory, it is believed that the presence of photocarriers promotes vacancy formation by neutralizing the charged anion, forming X.sub.i.sup.0 via the combination of photo-generated holes h.sup.+ with charged interstitial halide ions X.sub.i.sup., in the defect reaction:
[0115] Per this reaction, a high-density of photo-generated holes favors V.sub.X.sup.+ formation (Eq. 2). In addition, since the maximum stable concentration of uncharged X.sub.i.sup.0 in the lattice is higher than the concentration of charged X.sub.i.sup. ions, this reaction represents a significant route for accommodating excess vacancies. Further, the potential to form diatomic gas molecules X.sub.2.sup.0 from neutralized X.sub.i.sup.0 also promotes V.sub.X.sup.+ formation when the lattice is saturated with X.sub.i.sup.0 per the following reaction:
[0116] The possible escape of gaseous X.sub.2.sup.0 from the lattice promotes the forward direction of this reaction, and therefore it prevents an excessive build-up of X.sub.i.sup.0, which in turn favors the forward direction of the preceding reaction (Eq. 2). The strong photocarrier-lattice interactions (Eq. 2 and Eq. 3), and the vacancy formation that is promoted as a result, accurately predict a significant increase in V.sub.X.sup.+ concentration compared to the case where pure phonon excitation was achieved or laser exposure did not occur (
[0117] A decrease in PL efficiency was observed in MAPbX.sub.3, which was attributed to an increase in the iodide vacancy concentration,.sup.5 analogous to our observations. However, high-intensity light induced (partial) decomposition to MAX and PbX.sub.2. The intrinsic instability of organic-inorganic hybrid perovskites makes it challenging to control vacancy concentration without laser-induced decomposition as demonstrated with all-inorganic CsPbBr.sub.3.
[0118] Based on the aforementioned defect reactions for vacancy formation:
[0119] Applying a quasi-steady state equilibrium assumption for the reactions during illumination gives the equilibrium constants:
[0120] [X.sub.X] can be considered to be constant throughout the process. If a constant concentration of X.sub.i.sup.0 in the solid lattice is considered because of reaction 3, the concentration [V.sub.X.sup.+] is determined by [h.sup.+].
[0121] The photo-generated hole concentration [h.sup.+] is directly determined by: the input light power, crystal size L (approximately 400 nm), CsPbBr.sub.3 absorption coefficient (a) at the excitation laser wavelength.sup.7 (110.sup.5 cm.sup.1 at 473 nm in the experiment), and the incident light intensity I.sub.0. According to the Beer-Lambert law, the absorbed photon energy is =I.sub.0(1exp(L)).
[0122] Therefore, the photo-carrier generation rate is:
[0123] Next, the steady state carrier density n=[h.sup.+] when
was considered, because the bimolecular charge recombination and Auger recombination lifetimes are much shorter than the laser exposure time scale in our experiments,.sup.9.
[0124] where k.sub.1 and k.sub.2 are the monomolecular and bimolecular charge recombination rate constants, respectively, and k.sub.3 is the Auger recombination rate constant.sup.10. Therefore,
[0125] Thus, I.sub.0 determines [h.sup.+] and is directly correlated with [V.sub.X.sup.+] induced from laser excitation.
[0126] The solution Cl.sup. exchange process of CsPbBr.sub.3 arrays involves two steps: (1) solution-surface exchange: Cl.sup. in solution diffuses and reacts on the surface of the particles; (2) solid-solid interdiffusion: Cl.sup. interdiffuses with Br in the solid lattice. Solution-surface exchange is mainly related to Cl.sup. concentration in solution and temperature for mesoscale nanoparticles, and the Cl.sup. concentration in solution and temperature are the same for the entire array during exchange. In addition, solution-surface exchange is much faster than solid-solid interdiffusion. Therefore, without intending to bound by theory, it is believed that that solid-solid interdiffusion dictates anion exchange kinetics. The diffusion coefficient D(x) is dynamic and inversely related to x. The Cl.sup. concentration in solution can be considered constant with x=1. When the Cl concentration in the solid crystal is low, the large concentration gradient offers a high D(x). As the x increased in the solid crystal, D(x) decreased.sup.11,12 For example, net Cl.sup. diffusion is not expected between the solution and solid when x=1. So, D(1)=0. Here, a diffusion model of Cl.sup. exchange with a certain perovskite cube-shaped crystal (size of L) isotropically from all directions with a semi-infinite model: l2{square root over (D(x)t)} was considered. As shown in time space, the concertation change speed (the slope in
[0127] It was observed large (>2 m) feature dimensions under laser exposure of bulk CsPbBr.sub.3 microcrystals (much larger than the laser spot) based on SEM and PL imaging (
[0128] First, photo-carriers in CsPbBr.sub.3 have a remarkably long diffusion length (>2 m) and high mobility in the crystal lattice. According to the laser-induced vacancy formation mechanism, diffusive photo-carriers induce vacancy formation, resulting in a larger defect area in these bulk crystals. Second, halide vacancies also have fast diffusion kinetics in the lattice, further increasing the region of high vacancy concentration. Therefore, even with high-resolution multi-halide compositions formed in bulk crystals, the fast anion interdiffusion would lead to well-mixed structures as reported for heterostructures previously.
[0129] In contrast, the isolated single-particle arrays produced in accordance with the disclosure overcome the resolution limit observed in the bulk system. Photo-carriers and halide vacancies cannot migrate between individual particles due to their spatial confinement. As a result, this process enables submicron composition resolution within the patterned arrays.
Mixed Halide Solid Solutions
[0130] Certain mixed halide perovskites composition, such as mixed Cs-FA based systems have been reported to either mix or phase-segregate without consensus as to the contributing factors for this behavior. Without intending to be bound by theory, it is believed that the behavior may be attributed to the balance between the soft lattice, which accommodates strain and facilitates mixing, and the fact that the large size mismatch between the two cations (R.sub.Cs=1.74 , R.sub.FA=2.77 , or (R.sub.FAR.sub.Cs)/R.sub.Cs=59%) creates substitutional strain and free energy penalty for mixing. As detailed herein, it has been observed that varying the synthetic conditions enables modulation of the magnitude of this energy barrier, allowing methods of the disclosure to provide a robust strategy for controlling the resultant degree of ion mixing.
[0131] Mixed halide perovskites in accordance with this embodiment of the disclosure are compounds of formula I: A.sub.1-xA.sub.1-xBX.sub.3, wherein A is a first cation; A is a second cation, wherein A and A are different cations, B is a metal, X is at least one halogen, and 0<x<1. The lateral heterostructure comprises an A rich phase in a central region of the crystal, surrounded partially by a rich phase.
[0132] For example, the mixed halide perovskite of the disclosure can be Cs.sub.1-xFA.sub.xPbX.sub.3, wherein X is one or more of Cl, Br, and I, and 0<X<1. The mixed halide perovskites heterostructures of the disclosure have a lateral structure morphology wherein an A phase is concentrated in the center and a phase is arranged in the edge regions of the crystal structure. In systems further including a mixed anion, anion segregation was also observed. Mixed halides perovskite heterostructures in accordance with the disclosure can have distinct photoluminescence (PL) signals attributed to the segregation, with a first PL peak in a central region of the crystal and a second PL peak on an edge region. In heterostructures of the disclosure, the central peak can be entirely attributable to the A cation perovskite, indicating that no A phase is covering the central region. That is, the A phase borders and surrounds only a portion of the A phase, such as boarding a perimeter portion, but leaving the top portion uncovered.
[0133] A and A can be either organic or inorganic. For example, A and A can be independently selected from methylammonium, butylammonium, formamidinium, phenethylamine, 3-(aminomethyl)piperidinium, 4-(aminomethyl)piperidinium, cesium, and rubidium.
[0134] B can be a metal cation. For example, B can be one or more of lead, tin, europium, and germanium.
[0135] In embodiments, X can halogen, including any one or more of F, Cl, Br, and I. The halogen in the precursors can be the same or different depending on the halide structure desired. In mixed halide perovskites having multiple anions, the anions are present in an atomic ratio adding 1. For example, in a two-anion system, for example, the composition can be A.sub.1-xA.sub.1-xB(X.sub.1-yX.sub.y).sub.3, where 0<y<1.
[0136] Lateral heterostructure of the disclosure can be produced using a two-step solution growth method, which includes depositing the constituent perovskite ions dissolved in a solvent onto a substrate followed by unconfined microcrystal growth during solvent evaporation. For example, a method of forming mixed halide perovskite crystals having a lateral heterostructure in accordance with the disclosure can include dissolving at least one first one first perovskite precursor having the formula AX, at least one second perovskite precursor having the formula AX and at least one third perovskite precursor having the formula BX.sub.2 in a solvent to form a precursor solution, wherein A and A are each cations and are different cations, B is a metal, and X, X, X are each a halogen and can each be the same or different. The precursor solution is then deposited onto a substrate. EC-PPL can be used for depositing the precursor solution on a substrate. This can be particularly advantageous when forming combinatorial libraries or arrays of the mixed halide perovskites. EC-PPL for forming single cation halide perovskite is described in International Patent Application Publication NO. WO 2021/188168, the disclosure of which is incorporated herein by reference, for single A-site cation perovskites. Conditions and alternatives described therein can be adapted to the methods of the disclosure using the precursor solution described herein. The method then further include evaporating the solvent, wherein the mixed halide perovskites nanocrystal form upon evaporation of the solvent. The crystals form in two stages, the first stage being a A-X-rich perovskite phase and the second stage being a A-X-rich perovskite phase partially surrounding the A-X-rich perovskite phase
[0137] When EC-PPL is used, the deposited pattern of indicia form nanoreactors on the substrate and the mixed halide perovskite crystals nucleate and grow within the nanoreactors. Depositing the printed indicial using EC-PPL generally includes contacting a substrate with the coated pen array to thereby deposit the precursor solution as a pattern of printed indicia on the substrate.
[0138] In the precursor solution, X, X, and X are the same halogen when a single anion mixed halide perovskite is being formed. When a multiple-anion mixed halide perovskite is being formed, the halogens are different and include each of the anions to be included in the final crystal. Each of the different halogens is included in each of the third precursors with the metal (B). For example, in a two-anion system, X and X are different halogens and the at least one third precursor can include both a precursor of formula BX and a precursor of formula BX.
[0139] The solvent can be one or more of one or more of dimethyformamide (DMF), dimethyl sulfoxide (DMSO), y-butyrolactone (GBL), and sulfolane. A combination of solvents can be used, for example, sulfolane and DMSO. For example, the sulfolane and DMSO can be combined in a solvent ratio of about 7:3. The solvent or combination of solvents is selected such that the halide perovskite precursor can be dissolved in the solvent. In embodiments, the solvent or solvent combination is further selected to have a low vapor pressure. Without intending to be bound by theory, it is believed that using solvents with low vapor pressure can improve the crystal quality.
[0140] The solvent can have a vapor pressure at 25 C. of 400 Pa or less, 380 Pa or less, or 360 Pa or less. For example, the vapor pressure at 25 C. can be about 50 Pa to about 400 Pa, about 56 Pa to about 380 Pa, about 100 Pa to about 300 Pa, about 50 Pa to about 100 Pa, or about 60 Pa to about 200 Pa. Other suitable vapor pressures at 25 C. can be about 50, 52, 54, 56, 58, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130,140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 280, 300, 310, 320, 330, 340, 350, 360, 370, 380, 390, or 400 Pa.
[0141] The solvent can have a viscosity of about 0.9 cP to about 10.1 cP, about 0.9 cP to about 5 cP, about 1 cP to about 8 cP, about 4 cP to about 10 cP. Other suitable amounts include about 0.9, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, 3.2, 3.4, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 5, 5.2, 5.4, 5.6, 5.8, 6, 6.2, 6.4, 6.6, 6.8, 7, 7.2, 7.4, 7.6, 7.8, 8, 8.2, 8.4, 8.6, 8.8, 9, 9.2, 9.4, 9.6, 9.8, 10, and 10.1 cP
[0142] The precursor solution can be printed on any suitable substrate. For example, the substrate can be glass, ITO-coated glass, silicon, silicon oxide thin films, quartz, silicon nitride, or carbon. The substrate can be surface treated in embodiments. For example, the substrate can be surface treated with hexamethyldisiliazne (HMDS), octadecyltrichlorsilane (OTS), or polyvinylcarbazole (PVK). In embodiments, the substrate can be treated with a fluoropolymer. For example, the substrate can be treated with a fluoropolymer by reactive ion etching from CHF.sub.3. The fluoropolymer surface treatment can have one or more repeating units selected from CF, CF.sub.2, and CF.sub.3.
[0143] Modifying the ratio of constituent ions can be used to tail the morphology and photoluminescence of the resulting mixed halide perovskite microcrystals. For example, in Cs.sub.1-xFA.sub.xPbBr.sub.3, as relative FA concentration was increased, the emission peak in the PL spectra of the resulting perovskite shifted towards higher wavelengths, which is expected given that FAPbBr.sub.3 has a smaller bandgap than CsPbBr.sub.3. Where segregation is most pronounced (x=0.5), two should were clearly observed in the PL spectrum (
[0144] The perovskites are referred to herein interchangeable as crystals or nanocrystals. In any of the foregoing embodiments, the heterostructures can have a size of greater than about 60 nm to about 1000 nm, about 100 nm to about 800 nm, or about 60 nm to about 100 nm. Other sizes of nanocrystals include about 60, 65, 70, 75, 80, 85, 90, 95, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000 nm. Larger crystal sizes than 1000 nm can be formed with the methods of the disclosure. However, the methods of the disclosure are particularly useful in forming small crystal sizes, which cannot be readily achieved with prior halide perovskite formation methods.
[0145] Crystal sizes below about 60 nm generally results in solid-solution mixed halide perovskites. For example, solid-solution mixed halide perovskites can have a crystal size of about 20 nm to about 60 nm, about 20 nm to about 50 nm, or about 30 nm to about 40 nm. Other sizes of nanocrystals include about 20, 25, 30, 35, 40, 45, 50, 55, 60 nm.
[0146] Anion segregation was also observed when a secondary anion was present. When an equal mixture of both cations and anions, Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3, were incorporated, unique PL emission peaks were observed in Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3 crystals (>5 mm) from both the center (450-nm) and edge (500-nm) respectively, as resolved via multi-channel confocal imaging (
[0147] Referring to
[0148] EC-PPL was used herein to generate heterostructure crystals ranging in size from micro- (up to microns) to nano down to tens of nanometers) (
[0149] Transmission electron microscopy (TEM) and selected-area electron diffraction (SAED) were used to determine whether structural differences arise between the heterostructure and the solid-solution phases by patterning crystals directly onto a TEM grid (
[0150] Without intending to be bound by theory, it is believed that physical confinement enabled by EC-PPL can be used for a generalized synthesis scheme for an array of precursor ions and rations. Control over particle size serves as a means of turning the particle morphology, degree of mixing and ultimately the PL. Referring to
[0151] The difference in formation enthalpy can be used as a proxy to understand the energetics of the various phases available and can be achieved by comparing the energy of the FA- and Csphases.
[0152] (FA)+(Cs) are common terms for different X, thus they can be ignored for relative comparison.
TABLE-US-00001 Relative X E(FAPbX.sub.3) E(CsPbX.sub.3) difference Cl 41.401 eV 0 meV Br 41.433 eV 28 meV I 41.461 eV 60 meV
[0153] Photo-induced anion segregation has proven to be a significant barrier to the practical use of mixed anion perovskite systems, because it results in device deterioration, especially in the APb(Br.sub.1-yI.sub.y).sub.3 (A=MA or FA) compositions where 0.2y0.7. Cs-FA heterostructures crystals of the disclosure exhibited the same anion migration effect reported to result in device deterioration during photoillumination. When the as-synthesized crystals with an anion composition of y=0.2 were exposed to laser excitation for several minutes, significant red-shifts in the PL peak positions were observed (
[0154] To investigate the effect of polaron-induced segregation at higher mixing fractions, small, alloyed particles with the same composition as the microcrystals, Cs.sub.0.5FA.sub.0.5Pb(Br.sub.0.8I.sub.0.2).sub.3, were synthesized. These alloyed particles showed substantially improved stabilities under illumination (3-min accumulation) (
Density Functional Theory Analysis
[0155] Density functional theory (DFT) calculations were employed to understand the thermodynamics governing the cation segregation observed in the Cs.sub.1-xFA.sub.xPbX.sub.3 (0x1, X=Cl, Br, I) perovskites. Positive formation energies were found among all surveyed cation arrangements on the A-site (
[0156] Post-synthetic annealing can promote the mixing of the two phases of the heterostructure, as the entropy of mixing increases. However, despite 12 h of continuous heating at 120 C. (to ensure the organic cation is stable), changes in the PL emission, peripheral layer thickness, and morphology were not observed for the large heterostructure microcrystals (>5 m, Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3),
[0157] In order to maximize the effect of surface energy, smaller heterostructure crystals were synthesized. Increasing the temperature increases the entropic contribution to the formation free energy (
[0158] The DFT results suggest that a large enthalpy barrier (H) leads to the stable cation segregation observed experimentally for larger Cs.sub.0.5FA.sub.0.5PbX.sub.3 crystals. However, as temperature increases (T>0 K) the entropic contribution (S) to the free energy of formation (G) increases (
[0159] As particle size decreases, the roles of surface and interfacial energies become more relevant to determining the thermodynamically preferred structure, and generally these contributions favor mixing. Thus, for the lateral heterostructures of the disclosure, it was believed that the immiscible region of the phase diagram would shrink with decreasing crystal size (
Combinatorial Libraries
[0160] Methods of the disclosure can be used to form combinatorial libraries of mixed halide perovskite crystals or nanocrystals. EC-PPL can be particularly useful in forming combinatorial libraries having array of nanocrystals. The array can have a defined pattern and can have nanocrystals of different size, crystal structure, and/or composition. Any combination of features can be used to generate the combinatorial arrays. The arrays can be used in various applications including for example in optoelectronic devices, such as optical displays, photovoltaic devices, such as solar cells, LEDs, lasers, transistors, batteries, in photocatalysis, piezoelectric energy generators, and in screening methods and sensors.
[0161] In embodiments, the combinatorial library has mixed halide perovskite nanocrystals having a substantially uniform size. In other embodiments, the combinatorial library has mixed halide perovskite nanocrystals having a gradient of sizes. In still further embodiments, the combinatorial library has halide perovskite nanocrystals having various sizes arranged in a defined pattern.
[0162] In embodiments, the combinatorial library has mixed halide perovskite nanocrystals having the same composition. In embodiments, the combinatorial library has two or more different compositions of mixed halide perovskite nanocrystals and/or single cation halide perovskite nanocrystals with mixed halide perovskite nanocrystals.
[0163] In any of the foregoing embodiments, combinations of features such as size difference, compositional differences, or patterning can be combined in the combinatorial library.
EXAMPLES
Example 1: Synthesis of Mixed (Anion) Halide Perovskite Libraries
[0164] Synthesis of CsPbBr.sub.3 Arrays. CsPbBr.sub.3 arrays were synthesized by polymer pen lithography (PPL) based on our previous report. The pyramidal shaped-polymer pen arrays were fabricated based on a published protocol using h-polydimethylsiloxane (h-PDMS, Gelest).sup.33. The pen array was mounted onto the XYZ motorized piezo scanner of a desktop nanopatterning instrument (TERA-Fab M series, TERA-print, LLC). The pen array was finely leveled parallel to the substrate with two piezo actuators before patterning. The pen array was removed from the instrument, treated with O.sub.2 plasma, and then spin-coated with the ink at a spin speed of 3,000 rpm for 1 min or less depending on the type of ink precursor used. The ink was prepared by fully dissolving 1 mmol PbBr.sub.2 and 1 mmol CsBr in 5 mL of dimethyl sulfoxide (DMSO). The inked pen array in the instrument was brought in contact with the substrate for a few seconds, and then it was retracted from the substrate to deliver small nanoreactors of sample to the surface. The crystal size gradient was tuned by varying extension length with higher extension lengths resulting in larger particles (extension length: 0-8 m from a contact point against the substrate). Nanoreactors of the ink were formed on the substrate after retraction of the pen array, and these droplets were allowed to evaporate under ambient conditions to form individual halide perovskite nanocrystals.
[0165] Laser exposure. The laser exposure of individual crystals in CsPbBr.sub.3 arrays was performed with confocal Raman setup (LabRAM HR Evolution, Horiba) with an optical objective (100, NA=0.9, dry) at room temperature. The power was controlled by different neutral density filters built into the system. The excitation light source was typically a continuous wave laser (473 nm). To realize a larger area of laser exposure, scanning confocal microscopy (Leica SP8) was used to irradiate different CsPbBr.sub.3arrays at a fast scan speed (400 Hz) with an optical objective (10, NA=0.4, dry) under high-power 405-nm laser excitation. Laser wavelengths of 532 nm, 633 nm, 785 nm were used to conduct the wavelength-dependent study.
[0166] Anion exchange reaction. The anion exchange method was adapted from a previous report.sup.18. Anhydrous cyclohexane (5 mL), PbCl.sub.2 or PbI.sub.2 (0.188 mmol), oleic acid (OA, 90%, Aldrich) (0.5 mL), and oleylamine (OAm, Aldrich, 70%) (0.5 mL) were added to a 20-mL glass vial. The solution was stirred at 100 C. under ambient conditions with the glass vial well-capped. It took several hours for the PbCl.sub.2 to fully dissolve in the solution (solution A). The Clanion exchange solution (solution B) was prepared by diluting 0.2 mL solution A with 1.8 mL anhydrous cyclohexane. The substrates with CsPbBr.sub.3arrays were incubated in solution B for a controlled period of time to induce Clexchange, with the temperature elevated using a hot plate and monitored using temperature controller. After the Cl-exchange reaction, the substrate was rinsed with anhydrous cyclohexane. For I.sup. exchange, a corresponding PbI.sub.2 solution was used.
[0167] Structural characterizations. The morphologies and size distributions of the crystals were imaged by scanning electron microscopy (SEM) on a Hitachi SU8030. The energy-dispersive X-ray spectroscopy (EDS) was based on silicon drift detector (SDD) (X-Max.sup.N, Oxford Instruments) equipped on a Hitachi SU8030.
[0168] Optical characterization of halide perovskite arrays. Photoluminescence spectra of CsPbBr.sub.3 crystals before or after laser exposure at different wavelength were acquired from a LabRAM HR Evolution (Horiba). Raman scattered photons were dispersed by a 600 g/cm grating and collected by a spectrometer under 785-nm or 633-nm laser excitation at different powers. The spectrum of each particle in the CsPb(Br.sub.xC.sub.1-x).sub.3 arrays was acquired via the lambda scan mode in the confocal PL maps under 405-nm laser excitation. The spectral range is typically 420 nm to 550 nm with 3-nm intervals (512512 per frame, 400 Hz scanning speed). The total acquisition time was within 2 minutes. Multi-channel confocal imaging was used during confocal fluorescence microscopy on a Leica SP8 Confocal (Leica Microsystem). All confocal PL images were acquired with an objective (10/0.40 NA air; pinhole size=1 AU; 512512 per frame) with a high-resolution zoom at room temperature under a 405-nm laser diode. The gain of the different channels was adjusted to acquire a strong signal from each. Blue, green and red channels represent PL emission from 420 to 480 nm, from 480 nm to 550 nm and from 600 nm to 700 nm, respectively.
[0169] PL lifetime measurements. The PL lifetime measurements were performed using a 20, 0.55 NA air objective with the Leica DiveB Sp8 Multiphoton confocal laser scanning microscope. The excitation wavelength is 800 nm from a Physics Mai Tai tunable laser (690-1040 nm). The lifetime decay was collected and analyzed using the Leica X software.
[0170] Synthesis of bulk microcrystals. The synthesis of bulk CsPbBr.sub.3 microcrystals was adapted from a previous report.sup.4. A spin-coated PbI.sub.2 film on a glass substrate was mixed and reacted with CsBr in methanol under mild heating and ambient conditions. The CsPbBr.sub.3 microcrystals were then be transferred to a Si substrate for laser exposure treatment and anion exchange in the same manner as described above.
[0171] Spin-coated CsPb(Br.sub.xCl.sub.1-x).sub.3 thin films. The 0.05 M CsPb(Br.sub.xCl.sub.1-x).sub.3 (x=0.4, 0.5, 0.6, 0.75) solutions were prepared by dissolving corresponding combinations of precursors in DMSO. The CsPb(Br.sub.xCl.sub.1-x).sub.3 solution was spin-coated onto O.sub.2 plasma-treated Si substrates at 1,500 rpm for 120 s. These thin films were then annealed at 150 C. for 10 minutes. The confocal PL images and corresponding spectra of these thin films were acquired under the same laser scanning conditions with a Leica SP8.
Example 2: Synthesis of Complex Mixed Halide Perovskite Heterostructure Microcyrstals
[0172] All of the chemicals were purchased from Sigma-Aldrich unless otherwise stated. For the Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3 system, FABr (0.25 mmol), CsCl (0.25 mmol), PbBr (0.25 mmol), and PbCl.sub.2 (0.25 mmol) were dissolved in 10 mL of DMSO. Then the Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3 solution was drop-casted on O.sub.2 plasma-pre-treated Si substrates. The substrates were heated at approximately 120 C. for approximately 10 min on a hot plate in air. The square-shaped heterostructure microcrystals formed after the solvent fully evaporated.
[0173] The same process was used for the other mixed-composition perovskites (
[0174] The sizes and shapes of the crystal cores and the shells in the heterostructures were changed by toggling the solution evaporation rate. The overall crystal size was tuned by varying the concentration of precursors in solution and the ratio of solvents. A smaller size Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3 heterostructure microcrystal was obtained by diluting DMSO using DMF at a DMF:DMSO volume ration of 9:1 (0.5M) (
[0175] Nucleation and crystallization commence during solvent evaporation, which causes a CsPbCl-rich blue-emitting perovskite phase to grow. Without intending to be bound by theory, it is believed that this is attributable to its significantly lower solubility in the solvent (i.e., dimethyl sulfoxide (DMSO) or dimethylformamide (DMF)). The other precursors remain in solution (
Example 3: Synthesis of Complex Mixed-Halide Perovskite Arrays
[0176] Mixed-halide perovskite arrays were synthesized using EC-PPL. The pyramidal shaped-polymer pen arrays were fabricated following a published protocol using h-polydimethylsiloxane (h-PDMS, Gelest). Eichelsdoerfer et al., Larger-area molecular patterning with polymer pen lithography, 8 Nat. Protec. 2548-60 (2013). The pen arrays were mounted onto the XYZ-motorized piezo scanner of a desktop nanopatterning instrument (TERA-Fab M series, TERA-print, LLC). The pen array was finely leveled parallel to the substrate with two piezo actuators before patterning. The pen array was removed from the instrument, treated with O.sub.2 plasma, and then spin-coated with the ink at a spin speed of 3,000 rpm for 1 min or less depending on the type of ink precursor used. The precursor solutions used in Example 1 were used as the ink. The inked pen array in the instrument was brought into contact with the substrate for a few seconds, and then retracted from the substrate to make small nanoreactors (
[0177] The crystal size was tuned by modulating dwell time (pen to substrate for 1-10 s) and extension length (0-10 m from a contact point against the substrate). Nanoreactors of the ink were formed on the substrate after retraction of the pen array, and these droplets were allowed to evaporate under atmospheric conditions to form individual halide perovskite nanocrystals.
[0178] To achieve patterning at high-temperature, a micro-heater made of Pt-wires 0.2 mm in diameter was attached below the substrate. Consistent heat was applied to the substrate during patterning. The temperature on the surface of the substrate was measured using a source mete (Keithley-2400).
[0179] The time-transient nucleation of Cs.sub.0.5FA.sub.0.5Pb(Cl.sub.0.5Br.sub.0.5).sub.3 was imaged using an optical microscope (Zeiss Axio Imager M2) under the bright-field and fluorescence modes with a LED illuminator (X-Cite, Excelitas Tech). For the kinetic comparison between CsPbBr and FAPbBr.sub.3, similar amounts of solution were accumulated onto the pyramidal tips of the uniform pen array by controlling the spin-coating conditions. The nucleation kinetics of CsPbBr.sub.3 and FAPbBr.sub.3 were compared using a CMOS camera (objective 20) equipped on the TERA-Fab M series instrument.
[0180] The morphologies of all the crystals were imaged by scanning electron microscopy (SEM) on both a Hitachi SU8030 and a JEOL JSM-7900FLB equipped with a cold-field emission gun (cFEG) operated at 1 kV to 15 kV. Elemental distributions were confirmed using energy dispersive X-ray spectroscopy (EDS) silicon drift detector (SDD) (X-Max.sup.N, Oxford Instruments) equipped on the Hitachi SU8030.
[0181] Transmission electron microscopy (TEM) was performed on a JEOL ARM200CF equipped with a cFEG operated at 200 kV. Diffraction patterns were obtained from a Gatan OneView CMOS camera. All images were obtained within a few seconds after the focusing and alignment process to avoid extensive electron beam damage. Simulated electron diffraction data were generated using the SingleCrystal package (SingleCrystal and Crystal Maker Software Ltd.) based on the simulated crystal structures from the DFT results. The structural models were constructed using the VESTA software.
[0182] The heights of the heterostructures were defined using atomic force microscopy (AFM, Dimension Icon; Bruker) in tapping mode (probe k=42 N/m) at a scan rate between 0.1-0.2 Hz. The obtained images were analyzed using Gwyddion software).
[0183] Grazing incidence x-ray diffraction analysis was performed using a SmartLab Rigaku X-ray operating with Cu K.sub.a radiation at 40 kV and 30 mA at room temperature. The scan rate was 2 sec/step with a step size of 0.2.
[0184] Multi-channel crystals were imaged using confocal fluorescence microscopy on a Leica SP8 Confocal (Leica Microsystem). All optical sections were acquired with an objective (10/0.4NA air; pinhole size=1 AU) with a high-resolution zoom at room temperature. The fluorophores were excited using a solid-state diode laser at 405 nm.
[0185] For the resolution-sensitive heterostructure, high-resolution photoluminescence (HRPL) was performed on a modified confocal Raman spectrometer, LabRAM HR Evolution (Horiba), with an excitation wavelength of 473 nm at room temperature.
Example 4: DFT Simulation
[0186] The Vienna Ab-initio Simulation Package (VASP) was used to investigate the electronic structure and relative stability of the halide perovskites. The calculation utilized generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional (PBE). Projector-augmented wave (PAW) potentials were used to describe the core and valence electrons, and the plane-wave basis set employed a kinetic energy cutoff of 550 eV. The tetrahedron method was used along with a 545 Monkhorst-Pack grids for Brillouin zone integrations and k-space sampling of the Pnma unit cell with four formula units. Changes to the sampling were modified accordingly depending on the size of supercell. The cell volume and atomic positions were relaxed until the forces on each atom were less than 0.03 eV A-.sup.1.
[0187] Density functional theory (DFT) calculations were performed to understand the thermodynamics governing the cation-mixing behavior in Cs1-xFAxPbX3 (0x1, X=Cl, Br, I) perovskites at different Cs:FA ratios. Three possible arrangements for the A-site, with dispersed, columnar, and layered configurations, representative of cation-mixing, were calculated for x=0.5 composition and similar configurations for other compositions. For purposes of the calculation, core and valence electrons were treated with projector-augmented wave potentials using the following configurations: Cs (5s.sup.25p.sup.66s.sup.1), C (2s.sup.22p.sup.2), N (2s.sup.22p.sup.3), H(1 s.sup.1), Pb (6s.sup.25d.sup.106p.sup.2), Cl (3s.sup.23p.sup.5), Br (4s.sup.24p.sup.5), I (5s.sup.25p.sup.5). For structural models of intermediate compositions (x=0.25, 0.5, 0.75), modeling started from the CsPbX.sub.3 structure (Pnma; 4 Pb atoms in the structure) and substituted Pb with FA molecules. For x=0.5, the cation arrangements were made without constructing a supercell, and for x=0.25 and 0.75, a 221 supercell was prepared. For these Pnma structure and the supercell, k-mesh grids of 554 and 444 were used based on the Monkhorst-Pack grids.
[0188] Cation configurations are referred to layered, columnar, or dispersed based on the local cation arrangements of the x=0.5 compositions. Except for the 50% mixing of two cation types, these names do not reflect strictly homogenous cation layers or columns as the different number of cations make is difficult to define ordering wavevectors for each cation type. Given this difficulty, .sub.x, .sub.y, .sub.z axes for the FA cation were additionally defined as shown in
[0189] Positive enthalpy of mixing was found for the Cs1-xFAxPbX3 (X=Br, Cl, and I) as shown in
[0190] Another observed trend was from the formation energies of C.sub.S1-xFA.sub.xPbX.sub.3 was that two different layered-cation configurations exhibited the highest and lowest energy at x=0.25 and 0.75. Without intending to be bound by theory, it is believed that the trend suggests that the energetics in hybrid perovskites are governed by both cation order and secondary local structural distortions induced by the chemical order. Specifically, the layered configurations with dispersed FA molecules (layered (far);
[0191] As shown in
[0192] Three different molecule arrangements were calculated to examine the effect of the molecule orientations on the structure stability (
[0193] The molecular arrangement shown in
[0194] The use of a or an are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the description. This description should be read to include on or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.
[0195] The Figures depict embodiments for purposes of illustration only. One of ordinary skill in the art will readily recognize from the description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles described herein.
[0196] Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those skilled in the art, may be made in the arrangement, operation, and details of the methods and structures disclosed herein without departing from the spirt and scope defined in the appended claims.
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