Compounds comprising perovskite nanocrystals and zwitterionic ligands

Abstract

The present invention relates to a compound comprising a Yb-doped lead-halide perovskite nanocrystal and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, wherein the zwitterionic ligands are selected from the group consisting of 3-(N,N- dimethylpalmitylammonio)propanesulfonate, lecithin, n-hexadecylphosphocholine, and combinations thereof.

Description

[0001] Compounds Comprising Perovskite Nanocrystals and Zwitterionic Ligands

[0002] Cross-Reference to Related Applications

[0003] This application claims priority to Singapore application no. 10202401116Y filed with the Intellectual Property Office of Singapore on 16 April 2024, the contents of which is hereby incorporated by reference in its entirety for all purposes.

[0004] Technical Field

[0005] The present disclosure generally relates to compounds comprising perovskite nanocrystals and zwitterionic ligands, and more particularly relates to ytterbium (Yb) -doped perovskite nanocrystals coordinated with zwitterionic ligands. The present disclosure also relates to methods of producing said compounds.

[0006] Background Art

[0007] Quantum cutting (QC) is an appealing energy conversion process wherein a single high- energy photon is transformed into two lower-energy photons. This process holds promise for improving the power conversion efficiency (PCE) of photovoltaic (PV) devices, as well as enabling applications in low-cncrgy illumination and communications. For example, QC may be employed in perovskite compounds to improve their PCE. However, perovskite compounds may not be able to achieve QC due to lack of an electronic transition at the appropriate wavelength to align with materials used in common photovoltaic devices such as silicon (-1.1 eV).

[0008] To circumvent this problem, perovskite compound may be doped with Yb. The sensitized f-f transition of Yb3+in perovskite host located at near-infrared region (~980nm) aligns well with the bandgap of silicon. This is due to the favored Yb3+octahedral cooperation and the soft nature of perovskites. NIR light-emitting diodes with emission wavelength over 800nm may also be achieved through Yb doped perovskite NCs, extending the application of perovskite nanocrystals (NCs) to optical communication, night-vision devices, and biomedical imaging.

[0009] Common ligands such as oleylamine (OAm) and oleic acid (OA) may be utilized to ensure uniform growth of Yb-doped nanocrystals, and improve the colloidal stability and luminescence of the perovskite nanocrystals. However, such conventional ligands come with stability issues. The proton exchange process between OA and OAm molecules and thus the formation of neutral complex leads to the rapid detachment of ligands from the nanocrystal's surface during purification and storage, resulting in poorer stability and deteriorated emission performance. Additionally, the ligand binding of OA and OAm pairs also brings about the loss of structural integrity, such as the sintering between perovskite NCs, creating more trap states and hindering its further applications.

[0010] Thus, there is a need to provide perovskite compounds that overcome, or at least ameliorate one or more of the disadvantages described above.

[0011] Summary

[0012] In an aspect of the present disclosure, there is provided a compound comprising: a Yb-doped lead-halide perovskite nanocrystal; and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, wherein the zwitterionic ligands are selected from the group consisting of 3-(N,N- dimethylpalniitylammonio)propanesulfonate, lecithin, n-hexadecylphosphocholine, and combinations thereof.

[0013] In another aspect of the present disclosure, there is provided a compound comprising: a Yb-doped lead-halide perovskite nanocrystal; and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, wherein the zwitterionic ligands are selected from the group consisting of 3-(N,N- dimethylpalmitylammonio) propanesulfonate, lecithin, n-hexadecylphosphocholine, and combinations thereof, wherein the perovskite nanocrystal has a molar concentration of Yb / (Pb+Yb) at about 0.5% to about 10%, and wherein about 80% to about 100% of the Yb is incorporated into the perovskite nanocrystal.

[0014] In a further aspect of the present disclosure, there is provided a method of producing a compound comprising Yb-doped lead-halide perovskite nanocrystal and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, the method comprising:

[0015] (a) preparing a mixture comprising Pb(OAc)2, YbX3, phosphine oxide, and one or more zwitterionic ligands, wherein X is Cl, Br, I, or combinations thereof; and

[0016] (b) adding caesium oleate to the mixture.

[0017] In another aspect of the present disclosure, there is provided a compound comprising Yb- doped lead-halide perovskite nanocrystal and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, said compound produced by the method as disclosed herein.

[0018] Advantageously, the compounds of the present disclosure may exhibit high near -infrared photoluminescence quantum yield (PLQY) close to the quantum cutting limit, while exhibiting long- term colloidal storage stability. The compounds of the present disclosure may also advantageously exhibit high photostability when exposed to high UV irradiation flux, and maintain a single exponential decay. Further advantageously, the zwitterions coordinated to the compound of the present disclosure may be readily available and may not require a complicated synthesis.

[0019] Further advantageously, the methods of the present disclosure may be one-pot reactions that produce the disclosed compounds in situ. Further advantageously, the method of the present disclosure may also produce Yb-doped perovskite nanocrystals that exhibit sufficient and effective Yb-doping in the perovskite nanocrystal.

[0020] Definitions

[0021] Unless otherwise defined herein, scientific and technical terms used in this application shall have the meanings that are commonly understood by those of ordinary skill in the art. Generally, nomenclature used in connection with, and techniques of, chemistry described herein, are those well- known and commonly used in the art.

[0022] Unless the context requires otherwise or specifically stated to the contrary, integers, steps, or elements of the invention recited herein as singular integers, steps or elements clearly encompass both singular and plural forms of the recited integers, steps or elements. The word “substantially” does not exclude “completely” e.g. a composition which is “substantially free” from Y may be completely free from Y. Where necessary, the word “substantially” may be omitted from the definition of the invention.

[0023] As used herein in the specification and in the claims, the phrase "at least," in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase "at least one" refers, whether related or unrelated to those elements specifically identified. Thus, as a nonlimiting example, "at least one of A and B" (or, equivalently, "at least one of A or B," or, equivalently "at least one of A and / or B") can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0024] Unless specified otherwise, the terms "comprising" and "comprise", and grammatical variants thereof, are intended to represent "open" or "inclusive" language such that they include recited elements but also permit inclusion of additional, unrecited elements.

[0025] As used herein, the term "about", in the context of concentrations of components of the formulations, typically means + / - 5% of the stated value, more typically + / - 4% of the stated value, more typically + / - 3% of the stated value, more typically, + / - 2% of the stated value, even more typically + / - 1 % of the stated value, and even more typically + / - 0.5% of the stated value.

[0026] Throughout this disclosure, certain embodiments may be disclosed in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the disclosed ranges. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed sub -ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

[0027] Certain embodiments may also be described broadly and generically herein. Each of the narrower species and subgeneric groupings falling within the generic disclosure also form part of the disclosure. This includes the generic description of the embodiments with a proviso or negative limitation removing any subject matter from the genus, regardless of whether or not the excised material is specifically recited herein. Brief Description of Drawings

[0028] The accompanying drawings illustrate disclosed embodiments and serve to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0029] Fig. la

[0030] Fig. la is a diagram showing the synthesis of a comparative embodiment.

[0031] Fig. lb

[0032] Fig. lb is a diagram showing the synthesis of an embodiment of the present invention.

[0033] Fig. 1c

[0034] Fig. 1c is a graph showing the Yb-photoluminescence quantum yield (PLQY) of a comparative embodiment.

[0035] Fig. Id

[0036] Fig. Id is a graph showing the Yb-PLQY of an embodiment of the present invention.

[0037] Fig. le

[0038] Fig. 1c is a graph showing the Yb emission lifetime as the function of Yb precursor amount during synthesis of a comparative embodiment.

[0039] Fig. If

[0040] Fig. If is a graph showing the Yb emission lifetime as the function of Yb precursor amount during synthesis of an embodiment of the present invention.

[0041] Fig. 2a

[0042] Fig. 2a is a graph showing the photostability of a comparative embodiment (Yb doped CsPbCl3perovskite nanocrystals with traditional OA / OAm ligands) and an embodiment of the present invention (Yb doped CsPbCl3perovskite nanocrystals with ASC-16 ligands).

[0043] Fig. 2b

[0044] Fig. 2b is a graph showing the time resolved photoluminescence (TRPL) spectra of a comparative embodiment (Yb doped CsPbCl3perovskite nanocrystals with traditional OA / OAm ligands) before and after degradation.

[0045] Fig. 2c

[0046] Fig. 2c is a graph showing tire time resolved photoluminescence (TRPL) spectra of an embodiment of the present invention (Yb doped CsPbCl3perovskite nanocrystals with ASC-16 ligands) before and after degradation.

[0047] Detailed Disclosure of Embodiments

[0048] The present invention provides a compound comprising: a Yb-dopcd lead-halidc perovskite nanocrystal; and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, wherein the zwitterionic ligands are selected from the group consisting of 3-(N,N- dimethylpalmitylammonio)propanesulfonate, lecithin, n-hexadecylphosphocholine, and combinations thereof. Advantageously, the compound may exhibit high near-infrared photoluminescence quantum yield (PLQY) close to the quantum cutting limit, while exhibiting long-term colloidal storage stability. The compounds may also advantageously exhibit high photostability when exposed to high UV irradiation flux, and maintains a single exponential decay.

[0049] Still advantageously, the zwitterionic ligands may not involve the formation of a neutral complex, which could lead to greater stability of the compound. Further advantageously, the zwitterionic ligands chosen may be commercially available and therefore may not require complex synthesis methods before use.

[0050] In some embodiments, the perovskite nanocrystal may have a molar concentration of Yb / (Pb+Yb) in a range of about 0.50% to about 10.00%, from about 0.50% to about 9.50%, from about 0.50% to about 9.00%, from about 0.50% to about 8.50%, from about 0.50% to about 8.00%, from about 0.50% to about 7.50%, from about 0.50% to about 7.00%, from about 0.50% to about 6.50%, from about 0.50% to about 6.19%, from about 0.50% to about 6.00%, from about 0.50% to about 5.50%, from about 0.50% to about 5.02%, from about 0.50% to about 5.00%, from about 0.50% to about 4.50%, from about 0.50% to about 4.21%, from about 0.50% to about 4.00%, from about 0.50% to about 3.50%, from about 0.50% to about 3.00%, from about 0.50% to about 2.50%, from about 0.50% to about 2.46%, from about 0.50% to about 2.00%, from about 0.50% to about 1.50%, from about 0.50% to about 1.00%, from about 0.50% to about 0.70%, or from 0.70% to about 10.00%, from about 1.00% to about 10.00%, from about 1.50% to about 10.00%, from about 2.00% to about 10.00%, from about 2.46% to about 10.00%, from about 2.50% to about 10.00%, from about 3.00% to about 10.00%, from about 3.50% to about 10.00%, from about 4.00% to about 10.00%, from about 4.21% to about 10.00%, from about 4.50% to about 10.00%, from about 5.00% to about 10.00%, from about 5.02% to about 10.00%, from about 5.50% to about 10.00%, from about 6.00% to about 10.00%, from about 6.19% to about 10.00%, from about 6.50% to about 10.00%, from about 7.00% to about 10.00%, from about 7.50% to about 10.00%, from about 8.00% to about 10.00%, from about 8.50% to about 10.00%, from about 9.00% to about 10.00%, from about 9.50% to about 10.00%, or about 0.50%, about 0.70%, about 1.00%, about 1.50%, about 2.00%, about 2.46%, about 2.50%, about 3.00%, about 3.50%, about 4.00%, about 4.21%, about 4.50%, about 5.00%, about 5.02%, about 5.50%, about 6.00%, about 6.19%, about 6.50%, about 7.00%, about 7.50%, about 8.00%, about 8.50%, about 9.00%, about 9.50%, about 10.00%, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub -ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0051] A common problem associated with Yb-doping in perovskite nanocrystal is that the doped Yb are not fully incorporated into the structure of the perovskite nanocrystals. Instead, it is commonly found that Yb may simply replace surface ions which results in a lower Yb3+ion lifetime. This is because surface organic molecules have high-energy vibrations arising from C— H, N— H, or O-H bonds. However, the inventors have unexpectedly found that the compounds of the present invention may advantageously show that a substantial amount of Yb is incorporated into the perovskite nanocrystal. Sufficient Yb doping is realized when Yb is incorporated into the crystal as compared to simply replacing surface ions.

[0052] In some embodiments, a percentage of the doped Yb may be incorporated into the perovskite nanocrystal. The percentage of doped Yb may be in a range of about 80 % to about 100 %, from about 80 % to about 95 %, from about 80 % to about 90 %, from about 80 % to about 85 %, or from about 85 % to about 100 %, from about 90 % to about 100 %, from about 95 % to about 100 %, or about 80 %, about 85 %, about 90 %, about 95 %, about 100 %, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub -ranges or discrete values (which may or may not be a whole number) that are within the stated range(s). In some embodiments, essentially all of die doped Yb ( that is, 100% of the doped Yb) may be incorporated into the perovskite nanocrystal. Advantageously, when the perovskite nanocrystal comprises incorporation of the doped Yb at the above ranges or incorporation of all the doped Yb, the compound may exhibit stable emission lifetime.

[0053] In some embodiments, the lead-halide perovskite nanocrystal may be a C3PbX3nanocrystal or a CH3N H3PbX3nanocrystal, wherein X is Cl, Br, I, or combinations thereof.

[0054] In addition, the inventors have surprisingly found that the compounds of the present invention may exhibit high near-infrared photoluminescence quantum yield (NIR PLQY), which is close to the quantum cutting limit of about 192+5%. Tn some embodiments, the compound may exhibit a photoluminescence quantum yield in a range of about 150% to about 195%, from about 150% to about 192%, from about 150% to about 190%, from about 150% to about 185%, from about 150% to about 180%, from about 150% to about 175%, from about 150% to about 173%, from about 150% to about 170%, from about 150% to about 165%, from about 150% to about 160%, from about 150% to about 155%, or from about 155% to about 195%, from about 160% to about 195%, from about 165% to about 195%, from about 170% to about 195%, from about 173% to about 195%, from about 175% to about 195%, from about 180% to about 195%, from about 185% to about 195%, from about 190% to about 195%, from about 192% to about 195%, or about 150%, about 155%, about 160%, about 165%, about 170%, about 173%, about 175%, about 180%, about 185%, about 190%, about 192%, about 195%, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s).

[0055] The present invention also provides a compound comprising: a Yb-doped lead-halide perovskite nanocrystal; and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, wherein the zwitterionic ligands are selected from the group consisting of 3-(N,N- dimcthylpalmitylammonio) propancsulfonatc, lecithin, n-hcxadccylphosphocholinc, and combinations thereof, wherein the perovskite nanocrystal has a molar concentration of Yb / (Pb+Yb) in a range of about 0.50% to about 10.00%, from about 0.50% to about 9.50%, from about 0.50% to about 9.00%, from about 0.50% to about 8.50%, from about 0.50% to about 8.00%, from about 0.50% to about 7.50%, from about 0.50% to about 7.00%, from about 0.50% to about 6.50%, from about 0.50% to about 6.19%, from about 0.50% to about 6.00%, from about 0.50% to about 5.50%, from about 0.50% to about 5.02%, from about 0.50% to about 5.00%, from about 0.50% to about 4.50%, from about 0.50% to about 4.21%, from about 0.50% to about 4.00%, from about 0.50% to about 3.50%, from about 0.50% to about 3.00%, from about 0.50% to about 2.50%, from about 0.50% to about 2.46%, from about 0.50% to about 2.00%, from about 0.50% to about 1.50%, from about 0.50% to about 1.00%, from about 0.50% to about 0.70%, or from 0.70% to about 10.00%, from about 1.00% to about 10.00%, from about 1.50% to about 10.00%, from about 2.00% to about 10.00%, from about 2.46% to about 10.00%, from about 2.50% to about 10.00%, from about 3.00% to about 10.00%, from about 3.50% to about 10.00%, from about 4.00% to about 10.00%, from about 4.21% to about 10.00%, from about 4.50% to about 10.00%, from about 5.00% to about 10.00%, from about 5.02% to about 10.00%, from about 5.50% to about 10.00%, from about 6.00% to about 10.00%, from about 6.19% to about 10.00%, from about 6.50% to about 10.00%, from about 7.00% to about 10.00%, from about 7.50% to about 10.00%, from about 8.00% to about 10.00%, from about 8.50% to about 10.00%, from about 9.00% to about 10.00%, from about 9.50% to about 10.00%, or about 0.50%, about 0.70%, about 1.00%, about 1.50%, about 2.00%, about 2.46%, about 2.50%, about 3.00%, about 3.50%, about 4.00%, about 4.21%, about 4.50%, about 5.00%, about 5.02%, about 5.50%, about 6.00%, about 6.19%, about 6.50%, about 7.00%, about 7.50%, about 8.00%, about 8.50%, about 9.00%, about 9.50%, about 10.00%, or any value or range therein, and wherein about 80% to about 100% of the doped Yb is incorporated into the perovskite nanocrystal.

[0056] The present invention further provides a method of producing a compound comprising Yb- doped lead-halide perovskite nanocrystal and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, the method comprising:

[0057] (a) preparing a mixture comprising Pb(OAc)2, YbX3. phosphine oxide, and one or more zwitterionic ligands, wherein X is Cl, Br, I, or combinations thereof; and

[0058] (b) adding caesium oleate to the mixture.

[0059] The inventors have surprisingly found that the use of a phosphine oxide may facilitate the dissolution of the YbCl3.6H2O precursor in the reaction mixture, playing a crucial role in achieving effective Yb doping. Advantageously, the method of the present invention may involve one-pot reactions that produce the disclosed compounds in situ. Further advantageously, the method of the present invention may also produce Yb-dopcd perovskite nanocrystals that exhibit sufficient and effective Yb-doping in the perovskite nanocrystal.

[0060] In some embodiments, step (a) may further comprise heating the mixture at a temperature in a range of about 100 °C to about 150 °C, from about 100 °C to about 145 °C, from about 100 °C to about 140 °C, from about 100 °C to about 135 °C, from about 100 °C to about 130 °C, from about 100 °C to about 125 °C, from about 100 °C to about 120 °C, from about 100 °C to about 115 °C, from about 100 °C to about 1 10 °C, from about 100 °C to about 105 °C, from about 105 °C to about 150 °C, or from about 105 °C to about 150 °C, from about 110 °C to about 150 °C, from about 115 °C to about 150 °C, from about 120 °C to about 150 °C, from about 125 °C to about 150 °C, from about 130 °C to about 150 °C, from about 135 °C to about 150 °C, from about 140 °C to about 150 °C, from about 145 °C to about 150 °C, or about 100 °C, about 105 °C, about 110 °C, about 115 °C, about 120 °C, about 125 °C, about 130 °C, about 135 °C, about 140 °C, about 145 °C, about 150 °C, or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated rangc(s). In some embodiments, step (a) may be performed under vacuum. In some embodiments, step (a) may be performed for about 30 minutes to about 2 hours, or about 1 hour.

[0061] In some embodiments, prior to step (b), the mixture may be further heated at a temperature in a range of about 200 °C to about 300 °C, from about 200 °C to about 295 °C, from about 200 °C to about 290 °C, from about 200 °C to about 285 °C, from about 200 °C to about 280 °C, from about 200 °C to about 275 °C, from about 200 °C to about 270 °C, from about 200 °C to about 265 °C, from about 200 °C to about 260 °C, from about 200 °C to about 255 °C, from about 200 °C to about 250 °C, from about 200 °C to about 245 °C, from about 200 °C to about 240 °C, from about 200 °C to about 235 °C, from about 200 °C to about 230 °C, from about 200 °C to about 225 °C, from about 200 °C to about 220 °C, from about 200 °C to about 215 °C, from about 200 °C to about 210 °C, from about 200 °C to about 205 °C, or from about 205 °C to about 300 °C, from about 210 °C to about 300 °C, from about 215 °C to about 300 °C, from about 220 °C to about 300 °C, from about 225 °C to about 300 °C, from about 230 °C to about 300 °C, from about 235 °C to about 300 °C, from about 240 °C to about 300 °C, from about 245 °C to about 300 °C, from about 250 °C to about 300 °C, from about 255 °C to about 300 °C, from about 260 °C to about 300 °C, from about 265 °C to about 300 °C, from about 270 °C to about 300 °C, from about 275 °C to about 300 °C, from about 280 °C to about 300 °C, from about 285 °C to about 300 °C, from about 290 °C to about 300 °C, from about 295 °C to about 300 °C, or about 200 °C, about 205 °C, about 210 °C, about 215 °C, about 220 °C, about 225 °C, about 230 °C, about 235 °C, about 240 °C, about 245 °C, about 250 °C, about 255 °C, about 260 °C, about 265 °C, about 270 °C, about 275 °C, about 280 °C, about 285 °C, about 290 °C, about 295 °C, about 300 °C, or any value or range therein. Tt is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s). In some embodiments, the further heating of the mixture may be performed in an inert gas environment, such as argon or nitrogen.

[0062] In some embodiments, the molar ratio of Yb : Pb in the mixture of step (a) may in a range of about 1.2 : 1 to about 4.0 : 1 , from about 1 .2 : 1 to about 3.8 : 1 , from about 1.2 : 1 to about 3.6 : 1 , from about 1.2 : 1 to about 3.4 : 1, from about 1.2 : 1 to about 3.2 : 1, from about 1.2 : 1 to about 3.0 : 1, from about 1.2 : 1 to about 2.8 : 1, from about 1.2 : 1 to about 2.6 : 1, from about 1.2 : 1 to about 2.4 : 1, from about 1.2 : 1 to about 2.2 : 1, from about 1.2 : 1 to about 2.0 : 1, from about 1.2 : 1 to about 1.8 : 1, from about 1.2 : 1 to about 1.6 : 1, from about 1.2 : 1 to about 1.4 : 1, or from about 1.4 : 1 to about 4.0 : 1, from about 1.6 : 1 to about 4.0 : 1, from about 1.8 : 1 to about 4.0 : 1, from about 2.0 : 1 to about 4.0 : 1, from about 2.2 : 1 to about 4.0 : 1, from about 2.4 : 1 to about 4.0 : 1, from about 2.6 : 1 to about 4.0 : 1, from about 2.8 : 1 to about 4.0 : 1, from about 3.0 : 1 to about 4.0 : 1, from about 3.2 : 1 to about 4.0 : 1, from about 3.4 : 1 to about 4.0 : 1, from about 3.6 : 1 to about 4.0 : 1, from about 3.8 : 1 to about 4.0 : 1, or about 1.2 : 1, about 1.4 : 1, about 1.6 : 1, about 1.8 : 1 , about 2.0 : 1 , about 2.2 : 1 , about 2.4 : 1 , about 2.6 : 1 , about 2.8 : 1 , about 3.0 : 1 , about 3.2 : 1, about 3.4 : 1, about 3.6 : 1, about 3.8 : 1, about 4.0 : 1 , or any value or range therein. It is to be appreciated that the above ranges should be interpreted as including and supporting any sub-ranges or discrete values (which may or may not be a whole number) that are within the stated range(s) .

[0063] In some embodiments, the mixture of step (a) may further comprise oleic acid.

[0064] In some embodiments, the zwitterionic ligands may be selected from the group consisting of 3-(N,N-dimcthylpalmitylammonio)propancsulfonatc, lecithin, n-hcxadccylphosphocholinc, and combinations thereof. Advantageously, the zwitterionic ligands may be readily available instead of requiring a complicated synthesis before use.

[0065] In some embodiments, the phosphine oxide may be selected from the group consisting of tri- n-octylphosphinc oxide, tributylphosphinc oxide, and diphcnyl(2,4,6-trimcthylbcnzoyl)phosphinc oxide. Advantageously, the use of a phosphine oxide may facilitate the dissolution of the YbCl3.6H2O precursor in the reaction mixture.

[0066] In some embodiments, wherein the lead-halide perovskite nanocrystal may be a CsPbX3nanocrystal or a CH3NH3PbX3nanocrystal.

[0067] In some embodiments, the method may further one or more post-treatment step(s). The post- treatment step may he step (c): cooling the mixture to about 0 °C. In some embodiments, the cooling may be performed by using an ice bath.

[0068] In some embodiments, the post-treatment step may further comprise step (d): centrifuging the mixture of step (c) at about 10000 rpm to about 14000 rpm, and collecting the precipitate thereafter. The centrifuging may be performed for an appropriate duration to obtain the precipitate, such as for about 10 minutes. In some embodiments, the centrifuging may be performed at room temperature. In some embodiments, the post-treatment step may further comprise step (e): collecting the precipitate of step (d), dispersing it in a solvent, and centrifuging the resulting solution at about 2000 rpm to about 6000 rpm, and collecting the supernatant thereafter.

[0069] In some embodiments, steps (d) and (e) may be repeated at least once.

[0070] The present invention also provides a compound comprising Yb-doped lead-halide perovskite nanocrystal and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, said compound produced by the method as disclosed herein.

[0071] Examples

[0072] Non-limiting examples of the invention and comparative examples will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

[0073] Materials and Methods

[0074] Cs2CO3, 1-octadecene (ODE), oleic acid (OA), Pb(OAc)2-3H2O, Yb(NO3)35H2O, potassium oleate (KOA), YbCl3.6H2O, 3-(N,N-Dimcthylpalmitylammonio)propancsulfonatc, and tri-n- octylphosphine oxide were purchased from Sigma- Aldrich.

[0075] General synthetic procedure: The Yb-doped perovskite nanocrystals were synthesized using the hot-injection method, involving degassing, inert gas filling, and injection procedures. The degassing step aimed to eliminate water and oxygen from the precursor solution, while inert gas was introduced to prevent the oxidation of organic ligands. Simultaneously, the temperature was raised to the specified reaction temperature. Once the desired temperature was reached, a second precursor solution was injected to initiate nanocrystal formation. Throughout the synthesis, a pump was employed for degassing, and a Schlenk line was utilized to switch between vacuum and inert gas. The overall synthesis process encompassed several distinct stages.

[0076] Preparation of cesium oleate: 2.5 mmol Cs2CO3, 15 mL 1 -octadecene (ODE) and 1.25 mL oleic acid (OA) were loaded into a 50 mL three-neck flask and then degassed at 120 °C until bubbling stopped. Subsequently, filled the flask with argon and heated it to 150 °C until all precursors dissolved completely and get a clear solution. This solution was pre-heated at 100 °C before use.

[0077] Preparation of lead oleate (Pb(OA)2): 6 mmol Pb(OAc)2-3H2O (2.3033 g), 3.8 mL OA and 8.2 mL ODE were loaded in a 25 mL three -necks flask and then degassed at 120 °C until bubbling stopped. The precursor solution is solid at room temperature and requires preheating at 100 °C before use.

[0078] Preparation of ytterbium oleate (Yb(OA)3): 4 mmol Yb(NO3)35H2O (1.797 mg) was dissolved in 20 mL deionized water. 4 g KOA was dissolved in 20 mL deionized water and 25 mL ethanol mixture to get a clear solution. Then, these two solutions were mixed and 50 mL cyclohexane was added to extract the Yb(OA)3by continuous stirring for 20 minutes. Subsequently, the upper cyclohexane layer containing Yb(OA)3was separated from the lower layer by a separatory funnel. 10 mL deionized water and 10 mL ethanol were added to wash the upper layer and subsequently separated by a separatory funnel. This washing procedure was repeated at least three times to remove the excess KOA. Finally, the cyclohexane in the upper organic layer was evaporated under vacuum at 80 °C and the Yb(OA)3was obtained.

[0079] Photostability: In situ photoluniinescence (PL) measurement was carried out by irradiating the colloidal solution with a UV laser at room temperature, and recording the PL intensity as the function of irradiation time.

[0080] Lifetime: The lifetime of Yb emission was obtained by irradiating the colloidal nanocrystals solution with a 375 nm continuous -wave (CW) laser using 30 Hz square-wave pulses, and the NIR luminescence was detected using a silicon photodiode and recorded with a digital oscilloscope.

[0081] Photoluminescence quantum yield (PLQY) measurements: The absolute PLQY was obtained using diluted Yb-doped perovskite nanocrystals dispersed in toluene (OD<0.1 at excitation wavelengdi) placed in a 10 mm path length quartz cuvette and fixed in a 10 cm integrating sphere (Gooch & Housego). A 375 nm continuous-wave laser was used as the excitation light to excite the samples and a neutral-density fiber was used to adjust the excitation power. The PLQY is defined as emitted photon number divided by the absorbed photon number.

[0082] Example 1: Synthesis of Yb doped CsPbCl3perovskite nanocrystals with ASC-16 ligands

[0083] Pb(OAc)2- 3H2O (0.123 mmol) and YbCl3.6H2O (0.492 mmol) were first dissolved in ImL methanol, before loading 2 ml OA, 30mg 3-(N,N-Dimethylpalmitylammonio)propanesulfonate (ASC-16), 4g Tri-n-octylphosphine oxide (TOPO) and 5ml ODE into a 25 mL quartz flask. This mixture was degassed at room temperature for 5 minutes and then heated to 120 °C under vacuum for 1 hour. Then, the flask was filled with argon and heated to 260 °C quickly. 0.5 ml cesium oleate was injected swiftly and the flask was transferred to the ice bath to stop the reaction immediately. After the solution was cooled down to room temperature, the crude solution was centrifuged at 12000 rpm for 10 minutes and the precipitate was collected. The precipitate was then dispersed in 3 mL toluene and cent'ifuged again at 4000 rpm for 1 minute to remove the large particles and the supernatant was used as the final colloidal solution (Fig. lb).

[0084] Example 2: Characterization of Yb doped CsPbCl3perovskite nanocrystals with ASC-16 ligands

[0085] The method of Example 1 was used here, with varying amounts of YbCl3.6H2O according to the Yb:Pb ratio of the precursors added, and resulting in the various Yb molar concentrations (as shown in Table 1). As seen, by increasing the YbCl3.6H2O amount during synthesis, the Yb PLQY increases accordingly (Fig. Id). The highest PLQY can approach quantum cutting limit (-195%).

[0086] Table 1. Yb real molar concentration for Yb-doped samples with different nominal Yb / Pb ratio during synthesis (ASC-16 ligands, YbCl3.6H2O / TOPO synthetic route). To confirm whether Yb was incorporated into the crystal, time -resolved photoluminescence lifetime (TRPL) measurements of Yb emission were conducted. The samples with different Yb concentration made in the Examples all exhibited single exponential decay, confirming more effective Yb doping into crystal (Figs. 1c and If).

[0087] The above synthetic strategy was also developed to utilize a more robust binding zwitterionic ligand, 3-(N,N-Dimethylpalmitylammonio)propanesulfonate (ASC-16), to replace the conventional OA / OAm ligand pair in doped QDs. Aside from achieving a high photoluminescence quantum yield (PLQY) (Figs. 1c and Id), the Yb-doped CsPbCl3perovskite nanocrystals also demonstrated enhanced photostability when exposed to high UV laser irradiation flux (Figs, le and If). In addition, the degraded Yb-doped CsPbC13 nanocrystals with ASC-16 ligands maintained a single exponential decay. This suggests the preservation of structural integrity, highlighting the superiority of ASC-16 ligands in preventing adverse effects on the nanocrystal structure during degradation.

[0088] Comparative Examples

[0089] Comparative Example 1: Synthesis of Yb doped CsPbCl3perovskite nanocrystals with ASC- 16 ligands (oleate precursors)

[0090] The same Yb-doped CsPbCl3was prepared with oleate precursors (Fig. la) instead of YbCl3. 0.25 mmol Pb(OA)2(500 μL), different amounts of Yb(OA)3(0.02, 0.04, 0.08, 0.16, 0.3 mmol), 5 mL ODE, ASC-16 (30mg) and 0.2 mol cesium oleate (1.3 mL) were loaded in a 25 mL quartz flask. This mixture was degassed at room temperature for 5 minutes and then heated to 110 °C under vacuum for 1 hour. Then, the flask was filled with argon and heated to 260 °C quickly. 0.2 mL TMS-C1 in 0.5 mL ODE was injected swiftly and after 5 seconds, the flask was transferred to the ice bath to stop the reaction. The solution was then cooled down to room temperature. The crude solution was centrifuged at 12000 rpm for 10 minutes and the supernatant was collected. 12 ml ethyl acetate was added into the supernatant and the mixture was centrifuged again at 12000 rpm for 10 minutes. The supernatant was then discarded, and the final product was dispersed in 10 mL toluene.

[0091] The Yb PLQY of the synthesized Yb-doped perovskite nanocrystals did not exhibit continuous incrcascmcnt, indicating an insufficient Yb doping. Additionally, the Yb PL decay evolved from a single exponential curve to a biexponential curve as the amount of Yb oleate added during the synthesis was increased. The reduced emission lifetime suggested that some of the Yb3+ions replaced some of the surface ions rather than being incorporated into the crystal since the surface organic molecules that have high- energy vibrations arising from C-H, N-H, or O-H bonds would reduce the Yb3+ions lifetime (Figs, la- If).

[0092] Based on the experimental results above, it is clear that although both the method of the present invention and the method of the above comparative example may result in Yb-doped CsPbCl3, the resulting structure of the Yb-doped CsPbCl3differs based on the method of synthesis. Hence, the usage of YbCl3as a precursor is advantageous to the synthesis of the Yb-doped CsPbCl3.

[0093] Comparative Example 2: Synthesis of Yb doped CsPbCl3, perovskite nanocrystals with traditional OA / OAm ligands

[0094] 0.123 mol Pb(OAc)2- 3H2O, 10 mL ODE, 2 mL OA, 2 mL OAm and different amounts of YbCl3.6H2O (Yb: Pb=1.5, 2, 2.5, 3, 3.5) in 1 mL methanol were loaded in a 25 mL quartz flask._This mixture was degassed at room temperature for 5 minutes and then heated to 120 °C under vacuum for 1 hour. Then, the flask was filled with argon and heated to 260 °C quickly. 0.8 mL cesium oleate was injected swiftly and after 8 seconds, the flask was transferred to the ice bath to stop the reaction. After the solution was cooled down to room temperature, the crude solution was centrifuged at 12000 rpm for 10 minutes and the precipitate was collected. The precipitate was dispersed in 3 mL toluene and centrifuged again at 10000 rpm for 8 minutes. The supernatant was discarded, and the final product was dispersed in 3 mL toluene.

[0095] The Yb-doped perovskite nanocrystals with traditional OA / OAm ligands exhibited a reduction in Yb emission lifetime after degradation, indicating Yb ion migration to the nanocrystals' surface due to crystal structure changes (Figs. 2a-2c).

[0096] Based on the above comparisons, it is clear that the choice of ligands plays an important role in determining the properties of the Yb-doped CsPbCl3nanocrystal.

[0097] Industrial Applicability

[0098] The present invention relates to Yb-doped perovskite nanocrystals for use in downconversion Si solar cell applications. The nanocrystals exhibit high quantum yield and stability and may he used in applications such as solar cells, solar concentrators, LEDs, optical communication, night-vision devices, biomedical imaging and / or quantum emitters. ft will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the ait after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.

Claims

CLAIMS1. A compound comprising: a Yb-dopcd Icad-halidc perovskitc nanocrystal; and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, wherein the zwitterionic ligands are selected from the group consisting of 3-(N,N- dimethylpalmitylammonio)propanesulfonate, lecithin. n-hexadecylphosphocholine, and combinations thereof.

2. The compound of claim 1, wherein the perovskite nanocrystal has a molar concentration of Yb / (Pb+Yb) at about 0.5% to about 10%.

3. The compound of claim 1 or 2, wherein about 80% to about 100% of the doped Yb is incorporated into the perovskite nanocrystal.

4. The compound of any one of claims 1 to 3, wherein the lead-halide perovskite nanocrystal is a CsPbX3nanocrystal or a CH3NH3PbX3nanocrystal, wherein X is Cl, Br, I, or combinations thereof.

5. The compound of any one of claims 1 to 4, wherein the compound exhibits a photoluminescence quantum yield of about 150% to about 195%.

6. A compound comprising: a Yb-doped lead-halide perovskite nanocrystal; and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, wherein the zwitterionic ligands are selected from the group consisting of 3-(N,N- dimcthylpalmitylammonio) propancsulfonatc, lecithin, n-hcxadccylphosphocholinc, and combinations thereof, wherein the perovskite nanocrystal has a molar concentration of Yb / (Pb+Yb) at about 0.5% to about 10%, and wherein about 80% to about 100% of the Yb is incorporated into the perovskite nanocrystal.

7. A method of producing a compound comprising Yb-doped lead-halide perovskite nanocrystal and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, the method comprising:(a) preparing a mixture comprising Pb(OAc)2, YbX3, phosphine oxide, and one or more zwitterionic ligands, wherein X is Cl, Br, I, or combinations thereof; and(b) adding caesium oleate to the mixture.

8. The method of claim 7, wherein step (a) further comprises heating the mixture at a temperature of about 100 °C to about 150 °C.

9. The method of claim 7 or 8, wherein prior to step (h), the mixture is further heated at a temperature of about 200 °C to about 300 °C.

10. The method of any one of claims 7 to 9, wherein the molar ratio of Yb : Pb in the mixture of step (a) is in the range of about 1.2 : 1 to about 4 : 1.

11. The method of any one of claims 7 to 10, wherein the mixture of step (a) further comprises oleic acid.

12. The method of any one of claims 7 to 11, wherein the zwitterionic ligands arc selected from the group consisting of 3-(N,N-dimethylpalmitylammonio)propanesulfonate, lecithin, n- hexadecylphosphocholine, and combinations thereof.

13. The method of any one of claims 7 to 12, wherein the phosphine oxide is selected from the group consisting of tri-n-octylphosphine oxide, tributylphosphine oxide, and diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide.

14. The method of any one of claims 7 to 13, wherein the lead-halide perovskite nanocrystal is a CsPbX3nanocrystal or a CH3NH3PbX3nanocrystal.

15. A compound comprising Yb-doped lead-halide perovskite nanocrystal and one or more zwitterionic ligands coordinated to the surface of the perovskite nanocrystal, said compound produced by the method of any one of claims 7 to 14.

16. The compound of claim 15, wherein about 80% to about 100% of the doped Yb is incorporated into the perovskite nanocrystal.

17. The compound of any one of claims 3, 6, or 16, wherein essentially 100% of the doped Yb is incorporated into the perovskite nanocrystal.

Images