APPLICATIONS

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 62/586,837, filed November 15, 2017 and entitled“LIGHT-EMITTING DEVICE

STRUCTURES FOR BLUE LIGHT AND OTHER APPLICATIONS,” which is incorporated herein by reference in its entirety for all purposes.

FIELD

The present invention generally relates to materials for use in applications such as light- emitting devices, such as perovskite structures.

BACKGROUND

Light-emitting devices are useful for a variety of applications, including automobiles and traffic signals, aviation, cameras, home use, and personal electronics. One common example is the light-emitting diode, or LED. LEDs may include a hole transport region, an electron transport region, and a light-emitting region. Typically, extra electrons from the electron transport region and“holes” from the hole transport region combine together within the light- emitting region to produce light. (A hole is more accurately described as the lack of an electron in a position where one could exist, although those of ordinary skill in the art will often refer to a hole as if it were an actual particle, rather than the absence of a particle.) The efficiency of currently available LEDs, for example based on perovskite structures, has faced limitations. Therefore, improvements are needed.

SUMMARY

The present invention generally relates to materials for use in applications such as light- emitting devices, such as perovskite structures. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles.

In one aspect, the present invention is generally directed to a composition. In one set of embodiments, the composition comprises poly((9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N-(4- sec-butylphenyl)diphenylamine))) (TFB) and a perfluorinated ionomer (PFI). In some cases, the composition is present within an electrical device, such as a light-emitting device. Another aspect is generally directed to a light-emitting device, such as a light-emitting diode. In accordance with one set of embodiments, the light-emitting device comprises an electron transport region, a hole transport region comprising poly((9,9-dioctylfluorenyl-2,7- diyl)-co-(4,4’-(N-(4-sec-butylphenyl)diphenylamine))) (TFB) and a perfluorinated ionomer (PFI), and a light-emitting region in electrical contact with each of the electron transport region and the hole transport region.

Still another aspect is generally directed to a method of fabricating a light-emitting device, such as a light-emitting diode. In some embodiments, the method includes acts of depositing a hole transport region, depositing a light-emitting region, and depositing an electron transport region to form a light-emitting device. The hole transport region may comprise poly((9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N-(4-sec-bu tylphenyl)diphenylamine))) (TFB) and a perfluorinated ionomer (PFI).

Yet another aspect is generally directed to a method of operating a light-emitting device, such as a light-emitting diode. The method includes, in certain embodiments, an act of applying a voltage across the light-emitting device. In some cases, the light-emitting device includes a hole transport region, a light-emitting region, and an electron transport region. In certain instances, the hole transport region comprises poly((9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N- (4-sec-butylphenyl)diphenylamine))) (TFB) and a perfluorinated ionomer (PFI). In one set of embodiments, the voltage is applied between the electron transport region and the hole transport region of the light-emitting device.

In another aspect, the present invention encompasses methods of making one or more of the embodiments described herein. In still another aspect, the present invention encompasses methods of using one or more of the embodiments described herein.

Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures.

BRIEF DESCRIPTION OF DRAWINGS

Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures:

FIG. 1 illustrates a chemical structure of poly((9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’- (N-(4-sec-butylphenyl)diphenylamine))) (TFB), in accordance with some embodiments of the invention;

FIG. 2 illustrates a chemical structure of a perfluorinated ionomer (PFI), in accordance with some embodiments of the invention;

FIG. 3 illustrates a chemical structure of poly(3,4-ethylenedioxythiophene) (PEDOT), in accordance with some embodiments of the invention;

FIG. 4 illustrates a chemical structure of polystyrene sulfonate (PSS), in accordance with some embodiments of the invention;

FIG. 5 illustrates a chemical structure of 2,2’,2”-(l,3,5-benzinetriyl)-tris(l-phenyl-l-H- benzimidazole) (TPBi), in accordance with some embodiments of the invention;

FIG. 6 illustrates a CsPbBr _x Cl;v _x perovskite nanocrystal structure, in accordance with some embodiments of the invention;

FIG. 7 illustrates a transmission electron microscopy (TEM) image of synthesized CsPbBi _x Cl v _x perovskite nanocrystals, in accordance with one embodiment of the invention as a non-limiting example of FIG. 6;

FIG. 8 illustrates an absorption spectrum and an emission spectrum of 469 nm

CsPbBi _x Cl v _x perovskite nanocrystals, in accordance with some embodiments of the invention as non-limiting examples of FIG. 6;

FIG. 9 and FIG. 10 are energy level diagrams of fabricated light-emitting diodes (LEDs), in accordance with other embodiments of the invention;

FIG. 11 illustrates time-resolved photoluminescence data for nanocrystals spun-cast (e.g., spin coated) on top of glass, PEDOT:PSS/TFB/PFI, and NiO _x in the first nanosecond after excitation, in accordance with some embodiments of the invention;

FIG. 12 illustrates electroluminescence spectra for NiO _x and PEDOT:PSS/TFB/PFI, in other embodiments of the invention;

FIG. 13 illustrates current density-voltage-luminance (J-V-L) curves for light-emitting diodes (LEDs) fabricated using 469 nm perovskite nanocrystals and either NiO _x or

PEDOT:PSS/TFB/PFI as the hole transport layer, in still other embodiments of the invention; FIG. 14 illustrates external quantum efficiency (EQE) curves for LEDs fabricated using 469 nm perovskite nanocrystals and either NiO _x or PEDOT:PSS/TFB/PFI as the hole transport layer, in other embodiments of the invention;

FIG. 15 illustrates the electroluminescence spectra of devices with electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm, in still other embodiments of the invention;

FIG. 16 illustrates the J-V-L curves of devices with electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm, in yet other embodiments of the invention;

FIG. 17 illustrates EQE of devices with electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm, in other embodiments of the invention;

FIG. 18 illustrates photographs of devices with electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm, in accordance with other embodiments of the invention;

FIG. 19 illustrates electroluminescence spectra of light-emitting diodes with the same nanocrystals and a variety of hole transport layers, in accordance with some embodiments of the invention;

FIG. 20 illustrates subtracted TFB photoluminescence data, scaled to best fit the data in FIG. 11, in accordance with certain embodiments of the invention;

FIG. 21 illustrates photoluminescence spectra of perovskite nanocrystals spun atop a variety of hole transport layers (HTLs), in accordance with still other embodiments of the invention;

FIG. 22 illustrates electroluminescence of the PEDOT:PSS/TFB/PFEnanocrystal devices as a function of applied voltage, in accordance with other embodiments of the invention;

FIG. 23 illustrates electroluminescence (EL) spectra of PEDOT:PSS/TFB HTL devices with and without PFI, in accordance with some embodiments of the invention;

FIG. 24 illustrates electroluminescence and photoluminescence from a variety of perovskite nanocrystals, in accordance with certain embodiments of the invention;

FIG. 25 illustrates current efficiencies of the devices presented in FIG. 15, FIG. 16, FIG. 17, and FIG. 18, in accordance with some embodiments of the invention; and

FIG. 26 illustrates spin conditions for each of the devices presented in FIG. 15, FIG. 16, FIG. 17, and FIG. 18, in accordance with some embodiments of the invention. DETAILED DESCRIPTION

The present disclosure generally relates to materials for use in applications such as light- emitting devices. For example, certain aspects are generally directed to light-emitting diodes such as perovskite structure light-emitting diodes having high efficiency, and methods of making or using such devices. In some embodiments, the light-emitting device includes an electron transport region and a hole transport region. The hole transport region, in some cases, includes poly((9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N-(4-sec-bu tylphenyl)diphenylamine))) (TFB) and/or a perfluorinated ionomer (PFI). The light-emitting device may also include a light-emitting region that, in some cases, is in electrical contact with the electron transport region and the hole transport region.

In accordance with some embodiments of the disclosure, a light-emitting device is provided, e.g., a light-emitting diode. The light-emitting device may include a hole transport layer that includes poly(3,4-ethylenedioxythiophene): (poly styrene sulfonate) (PEDOT:PSS), TFB, and PFI layered directly on top of one another, e.g., in the listed order. Each of the PEDOT:PSS, the TFB, and the PFI can be deposited by spin coating onto an indium tin oxide (ITO) electrode, followed by annealing before depositing the next material layer. Other techniques are discussed in more detail below. The light-emitting device can also include a light-emitting layer of perovskite nanocrystals having a composition CsPbBr _x Cl;v _x, layered directly on top of the hole transport layer by spin coating. In some cases, the perovskite may be doped with manganese, e.g., as discussed in U.S. Provisional Application No. 62/586,846, filed November 15, 2017 and entitled“MANGANESE-DOPED PEROVSKITE STRUCTURES FOR LIGHT-EMITTING DEVICES AND OTHER APPLICATIONS,” incorporated herein by reference in its entirety. In some cases, the perovskite may be doped with a dopant (e.g., manganese, ytterbium, nickel), e.g., as discussed in a PCT application filed on even date herewith, entitled“DOPED PEROVSKITE STRUCTURES FOR LIGHT-EMITTING

DEVICES AND OTHER APPLICATIONS,” incorporated herein by reference in its entirety.

In some embodiments, the light-emitting device includes an electron transport layer that includes 2,2’,2”-(l,3,5-benzinetriyl)-tris(l-phenyl-l-H-benzimida zole) (TPBi) and lithium fluoride (LiF) layered directly on top of the layer of perovskite nanocrystals and directly on top of one another in the listed order. This can be formed using deposition in an evaporation chamber. In one embodiment, the light-emitting device includes an aluminum (Al) electrode that is deposited directly onto the LiF layer in an evaporation chamber. The light-emitting device may emit blue light, or other wavelengths, e.g., as discussed herein.

Without wishing to be bound by theory, it is believed that the combination of the TFB and the PFI results in an increase in external quantum efficiency (EQE). In some embodiments, the light-emitting device has an EQE of greater than or equal to 0.1%. In some embodiments, the light-emitting device has a brightness of at least 111 cd/m ² at an emission wavelength of 469 nm, or other brightnesses such as those discussed herein.

The embodiments described above are examples of the present disclosure. However, the light-emitting device need not have any and/or all of the above-described features in all embodiments. More generally, other embodiments of light-emitting devices are described below.

In some embodiments, for example, a light-emitting device is provided. The light- emitting device may comprise a hole transport region, an electron transport region, and a light- emitting region. In some embodiments, the light-emitting region is in contact with the electron transport region and/or the hole transport region. The contact may be physical, i.e., the regions may be in direct physical contact with each other, or there may be an intervening region.

Without wishing to be bound by any theory, it is believed that holes (from the hole transport region) and electrons (from the electron transport region) may be able to recombine to produce light within the light-emitting region. One of more of these regions may each independently be substantially planar, e.g., forming a layer of material within the device, and/or the regions may be nonplanar in some cases. Thus, in one embodiment, the device may comprise three layers of material, e.g., a hole transport layer, an electron transport layer, and a light-emitting layer.

The hole transport region may be formed out of any material able to transport“holes” (lack of electrons) from one location to another, e.g., to a light-emitting region. The hole transport region may have any shape and/or size, e.g., as discussed herein. In some

embodiments, the hole transport region may comprise poly((9,9-dioctylfluorenyl-2,7-diyl)-co- (4,4’-(N-(4-sec-butylphenyl)diphenylamine) (TFB) and/or a perfluorinated ionomer (PFI). It is believed that the combination of TFB and PFI within the hole transport region may present surprisingly large quantum efficiencies or photoluminescence quantum yields, e.g., as discussed herein, even as compared to other materials, or to separate uses of TFB and PFI. Without wishing to be bound by any theory, it is believed that the combination of TFB and PFI within a hole transport region surprisingly prevents or limits non-radiative decay from the nanocrystals, thus promoting a higher efficiency of hole transport, and accordingly, more light production due to the recombination of holes and electrons within the light-emitting region.

TFB is also known as poly((9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N-(4-sec- butylphenyl)diphenylamine))) and its structure can be seen in Fig. 1. It can be readily obtained commercially. The TFB may have any distribution of sizes, molecular weights, or

polydispersities. For example, the TFB, in some embodiments, has a weight- average molecular weight of at least 500 Daltons (Da), at least 1 kilodaltons (kDa), at least 2 kDa, at least 5 kDa, at least 10 kDa, at least 20 kDa, at least 30 kDa, at least 35 kDa, at least 40 kDa, at least 45 kDa, at least 50 kDa, at least 60 kDa, at least 70 kDa, at least 80 kDa, at least 90 kDa, at least 100 kDa, or at least 500 kDa. The TFB, in some embodiments, has a weight-average molecular weight of at most 1000 kDa, at most 500 kDa, at most 100 kDa, at most 90 kDa, at most 80 kDa, at most 70 kDa, at most 60 kDa, at most 50 kDa, at most 45 kDa, at most 40 kDa, at most 35 kDa, at most 30 kDa, at most 20 kDa, at most 10 kDa, at most 5 kDa, at most 2 kDa, at most 1 kDa, or at most 500 Da. Combinations of the above-reference ranges are also possible (e.g., from 500 Da to 1000 kDa, from 2 kDa to 1000 kDa, from 500 Da to 2 kDa, from 30 kDa to 50 kDa, from 35 kDa to 45 kDa).

A variety of PFIs or perfluorinated ionomers may also be used in accordance with certain embodiments. A non-limiting example of a PFI is shown in Fig. 2 (e.g., Nafion®, which is a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer ionomer). However, in other embodiments, other PFIs may be used. Non-limiting examples include Aciplex® or Flemion®. More than one PFI may also be used within in hole transport region in certain cases. Many such PFIs can be obtained commercially.

The PFI, in some embodiments, has a weight-average molecular weight of at least 500 Da, at least 1 kDa, at least 2 kDa, at least 5 kDa, at least 10 kDa, at least 20 kDa, at least 30 kDa, at least 35 kDa, at least 40 kDa, at least 45 kDa, at least 50 kDa, at least 60 kDa, at least 70 kDa, at least 80 kDa, at least 90 kDa, at least 100 kDa, at least 110 kDa, at least 120 kDa, at least 200 kDa, at least 300 kDa, or at least 500 kDa. The PFI, in some embodiments, has a weight- average molecular weight of at most 1000 kDa, at most 500 kDa, at most 300 kDa, at most 200 kDa, at most 120 kDa, at most 110 kDa, at most 100 kDa, at most 90 kDa, at most 80 kDa, at most 70 kDa, at most 60 kDa, at most 50 kDa, at most 45 kDa, at most 40 kDa, at most 35 kDa, at most 30 kDa, at most 20 kDa, at most 10 kDa, at most 5 kDa, at most 2 kDa, at most 1 kDa, or at most 500 Da. Combinations of the above-reference ranges are also possible (e.g., from 500 Da to 1000 kDa, from 2 kDa to 1000 kDa, from 500 Da to 2 kDa, from 80 kDa to 120 kDa). The PFI, in some embodiments, has a weight-average molecular weight of 100 kDa.

In one set of embodiments, the hole transport region comprises one or more sublayers or subregions. For instance, in some embodiments, other subregions or sublayers may be present within a hole transport region. For instance, the hole transport region may comprise 4, 5, 6, 7, 8, 9, 10, or more sublayers the regions within the hole transport region may be distributed in any suitable arrangement. For example, in one set of embodiments, the subregions are present as one or more layers, which are generally planarly arranged within the hole transport region. For example, the layers may have one dimension (i.e., a cross-sectional thickness) that is

substantially less than the other two orthogonal dimensions. In some cases, the layers are rectangularly- shaped, although other geometries are also possible in other cases. In some cases, the cross-sectional thickness may be determined as the minimum dimension of the layer or region. The cross-sectional thickness may be measured for example by ellipsometry,

profilometry, transmission electron microscopy, or another suitable method.

For example, the first sublayer may comprise TFB while a second sublayer may comprise PFI. Thus, in some cases, the TFB and the PFI may be present in separate regions within the hole transport region. However, in other embodiments, the TFB and PFI may have other distributions, e.g., intermingled, within the hole transport region.

In some cases, the hole transport may also contain one or more materials to facilitate transport of holes across the hole transport layer. Such materials may be interspersed with one or more of the TFB and/or PFI (which may also, be combined together and/or present in different regions), or present as a separate layer or region. For example, in one set of embodiments, the hole transport region may contain PEDOT:PSS, which is poly(3,4- ethylenedioxythiophene) polystyrene sulfonate. PEDOT:PSS can be commercially obtained.

As another example, the hole transport region may contain one or more conductive polymers, such as poly thiophene. In some embodiments, the hole transport region may include such materials as a sublayer or subregion (for example, as a third sublayer or subregion in addition to one or more sublayers or subregions for TFB and/or PFI). For example, the TFB, PFI, and PEDOT:PSS may be present as 3 separate layers.

The PEDOT, in some embodiments, has a weight- average molecular weight of at least 500 Da, at least 1 kDa, at least 2 kDa, at least 5 kDa, at least 10 kDa, at least 20 kDa, at least 30 kDa, at least 40 kDa, at least 50 kDa, at least 60 kDa, at least 70 kDa, at least 80 kDa, at least 90 kDa, at least 100 kDa, at least 200 kDa, at least 300 kDa, or at least 500 kDa. The PEDOT, in some embodiments, has a weight-average molecular weight of at most 1000 kDa, at most 500 kDa, at most 300 kDa, at most 200 kDa, at most 100 kDa, at most 90 kDa, at most 80 kDa, at most 70 kDa, at most 60 kDa, at most 50 kDa, at most 40 kDa, at most 30 kDa, at most 20 kDa, at most 10 kDa, at most 5 kDa, at most 2 kDa, at most 1 kDa, or at most 500 Da. Combinations of the above-reference ranges are also possible (e.g., from 500 Da to 1000 kDa, from 2 kDa to 1000 kDa, from 500 Da to 2 kDa).

The PSS, in some embodiments, has a weight-average molecular weight of at least 500 Da, at least 1 kDa, at least 2 kDa, at least 5 kDa, at least 10 kDa, at least 20 kDa, at least 30 kDa, at least 40 kDa, at least 50 kDa, at least 60 kDa, at least 70 kDa, at least 80 kDa, at least 90 kDa, at least 100 kDa, at least 200 kDa, at least 300 kDa, or at least 500 kDa. The PSS, in some embodiments, has a weight- average molecular weight of at most 1000 kDa, at most 500 kDa, at most 300 kDa, at most 200 kDa, at most 100 kDa, at most 90 kDa, at most 80 kDa, at most 70 kDa, at most 60 kDa, at most 50 kDa, at most 40 kDa, at most 30 kDa, at most 20 kDa, at most 10 kDa, at most 5 kDa, at most 2 kDa, at most 1 kDa, or at most 500 Da. Combinations of the above-reference ranges are also possible (e.g., from 500 Da to 1000 kDa, from 2 kDa to 1000 kDa, from 500 Da to 2 kDa).

In some embodiments, a sublayer has a minimum cross-sectional thickness of at least 1 nm, at least 2 nm, at least 5 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 35 nm, at least 40 nm, at least 45 nm, at least 50 nm, at least 55 nm, at least 60 nm, at least 65 nm, at least 70 nm, at least 75 nm, at least 80 nm, at least 85 nm, at least 90 nm, at least 95 nm, at least 100 nm, at least 200 nm, at least 300 nm, at least 500 nm, or at least 900 nm. In some embodiments, the sublayer has a minimum cross-sectional thickness of at most 1000 nm, at most 900 nm, at most 500 nm, at most 300 nm, at most 200 nm, at most 100 nm, at most 95 nm, at most 90 nm, at most 85 nm, at most 80 nm, at most 75 nm, at most 70 nm, at most 65 nm, at most 60 nm, at most 55 nm, at most 50 nm, at most 45 nm, at most 40 nm, at most 35 nm, at most 30 nm, at most 20 nm, at most 10 nm, at most 5 nm, or at most 2 nm. Combinations of the above- referenced ranges are also possible (e.g., from 1 nm to 1000 nm, from 20 nm to 80 nm, from 35 nm to 45 nm, from 40 nm to 60 nm). The sublayer in some embodiments has a cross-sectional thickness of 40 nm.

In some embodiments, a ratio of a first cross-sectional thickness of a first layer to a second cross-sectional thickness of a second layer is at least 1:0.01, at least 1:0.02, at least 1:0.05, at least 1:0.08, at least 1:0.1, at least 1:0.15, at least 1:0.2, at least 1:0.3, at least 1:0.4, at least 1:0.5, at least 1:0.6, at least 1:0.7, at least 1:0.8, at least 1:0.9, or at least 1:0.95. In some embodiments, a ratio of the first cross-sectional thickness to the second cross-sectional thickness is at most 1:99, at most 1:90, at most 1:80, at most 1:70, at most 1:60, at most 1:50, at most 1:40, at most 1:30, at most 1:20, at most 1:10, at most 1:5, at most 1:2, at most 1:1, at most 1:0.99, at most 1:0.15, at most 1:0.1, or at most 1:0.08. Combinations of the above-referenced ranges are also possible (e.g., from 1:0.01 to 1:99, from 1:0.01 to 1:0.99, from 1:0.05 to 1:0.15, from 1:0.02 to 1:0.08). The ratio of the first cross-sectional thickness to the second cross-sectional thickness in some embodiments is 1:0.05.

In some embodiments, the hole transport region comprises a crystalline grain or a plurality of crystalline grains. For example, the TFB, PFI, and/or PEDOT:PSS may have a crystalline grain or a plurality of crystalline grains. However, in some embodiments, one or more of these may be free of crystalline grains. In some embodiments, the presence or absence of a crystalline grain or a plurality of crystalline grains can be determined by methods known to those of skill in the art, including but not limited to x-ray diffraction and transmission electron microscopy.

As mentioned, the device can also include an electron transport region, which may be present as a layer in some cases. In some embodiments, the electron transport region comprises 2,2’,2”-(l,3,5-benzinetriyl)-tris(l-phenyl-l-H-benzimida zole) (TPBi) and/or lithium fluoride (LiF). As mentioned, the electron transport region may facilitate the transport of electrons to the light-emitting region, where they can combine with“holes” from the hole transport region.

The electron transport region or layer may have any of the dimensions described above with respect to the hole transport region. For example, in some embodiments, the electron transport region may have a minimum cross-sectional dimension of at least 1 nm, at least 5 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, at least 100 nm, at least 500 nm, or at least 900 nm. In some embodiments, the electron transport region has a minimum cross-sectional dimension of at most 1000 nm, at most 900 nm, at most 500 nm, at most 100 nm, at most 50 nm, at most 40 nm, at most 30 nm, at most 20 nm, at most 10 nm, or at most 5 nm. Combinations of the above-referenced ranges are also possible (e.g., from 1 nm to 1000 nm, from 30 nm to 50 nm).

The TPBi may be present as a region, e.g., as a layer in some cases. The TPBi region or layer may have any of the dimensions described above with respect to the electron transport region. For example, in some embodiments, the TPBi region may have a minimum cross- sectional dimension of at least 1 nm, at least 5 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, at least 100 nm, at least 500 nm, or at least 900 nm. In some embodiments, the TPBi region has a minimum cross-sectional dimension of at most 1000 nm, at most 900 nm, at most 500 nm, at most 100 nm, at most 50 nm, at most 40 nm, at most 30 nm, at most 20 nm, at most 10 nm, or at most 5 nm. Combinations of the above-referenced ranges are also possible (e.g., from 1 nm to 1000 nm, from 10 nm to 100 nm, from 20 nm to 50 nm).

The LiF may be present as a region, e.g., as a layer in some cases. The LiF region or layer may have any of the dimensions described above with respect to the electron transport region. In some embodiments, the LiF region may have a minimum cross-sectional dimension of at least 0.1 nm, at least 0.2 nm, at least 0.3 nm, at least 0.4 nm, at least 0.5 nm, at least 0.6 nm, at least 0.7 nm, at least 0.8 nm, at least 0.9 nm, at least 1 nm, at least 2 nm, at least 3 nm, at least 4 nm, at least 5 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 40 nm, at least 50 nm, at least 100 nm, at least 500 nm, or at least 900 nm. In some embodiments, the LiF region has a minimum cross-sectional dimension of at most 1000 nm, at most 900 nm, at most 500 nm, at most 100 nm, at most 50 nm, at most 40 nm, at most 30 nm, at most 20 nm, at most 10 nm, at most 5 nm, at most 4 nm, at most 3 nm, at most 2 nm, at most 1 nm, at most 0.9 nm, at most 0.8 nm, at most 0.7 nm, at most 0.6 nm, at most 0.5 nm, at most 0.4 nm, at most 0.3 nm, or at most 0.2 nm. Combinations of the above-referenced ranges are also possible (e.g., from 0.1 nm to 1000 nm, from 0.1 nm to 5 nm, from 0.5 nm to 2 nm).

The device may also include a light-emitting region or layer, which is able to emit light through the combination of holes with electrons. The light-emitting region or layer may have any of the dimensions described above with respect to the hole transport region.

In some embodiments, the light-emitting region comprises particles, such as a nanoparticles. The nanoparticle, in certain embodiments, comprises a nanocrystal.

In some embodiments, the light-emitting region comprises perovskite-type materials, e.g., materials having a perovskite structure, of which perovskite itself (CaTi0 ₃ ) is the prototypical example. However, as is understood by those of ordinary skill in the art, perovskite- type materials (or sometimes, just“perovskite”), such as those discussed herein, are not to be construed as being limited to only CaTi0 ₃ , but may include any material having the same crystal structure as the prototypical perovskite crystal structure. For example, a perovskite-type material, in some embodiments, may have a composition comprising CsPbX ₃ . X may include one or more than one halogen, e.g., one or more of F, Cl,

Br, I, etc. Thus, for example, in certain embodiments, the perovskite nanocrystal has a composition comprising CsPbBr _x Cl;v _x or CsPbBr _x Cl _y l3- _x-y . x and y may each range from 0 to 3, inclusively, including decimals. For instance, x may be at least 0.2, at least 0.4, at least 0.6, at least 0.8, at least 1, at least 1.2, at least 1.4, at least 1.6, at least 1.8, at least 2, at least 2.2, at least 2.4, at least 2.6, at least 2.8, and/or no more than 2.8, no more than 2.6, no more than 2.4, no more than 2.2, no more than 2, no more than 1.8, no more than 1.6, no more than 1.4, no more than 1.2, no more than 1, no more than 0.8, no more than 0.6, no more than 0.4, or no more than 0.2. Other examples of perovskite-type materials include, but are not limited to,

organic/inorganic hybrid halide perovskites (e.g., CH ₃ NH ₃ PbX ₃ , Cs _a (CH ₃ NH ₃ )i- _a PbX ₃ ), etc.“a” may be at least 0.2, at least 0.4, at least 0.6, at least 0.8, and/or no more than 0.8, no more than 0.6, no more than 0.4, no more than 0.2.

The perovskite material, in some embodiments, comprises a ligand. The ligand may comprise as non-limiting examples octadecene, oleylamine, and/or trioctylphosphine, or a combination thereof.

In addition, in one set of embodiments, the perovskite may be doped with one or more dopants. In some embodiments, a dopant comprises manganese, ytterbium, or nickel, or a combination thereof. In some embodiments, a dopant is manganese, ytterbium, or nickel. For example, certain aspects are generally directed to a composition such as a composition including a perovskite structure (e.g., a perovskite nanocrystal) having a formula ABX ₃ , and methods of making or using such compositions. In some embodiments, a perovskite structure comprises a nanocrystal, a film, a bulk structure, or a combination thereof. In some embodiments, a perovskite film has a thickness of from 5 nm to 1 microns (e.g., from 20 nm to 500 nm). For example, the thickness may be at least 5 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 50 nm, at least 100 nm, at least 200 nm, at least 300 nm, at least 500 nm, etc., and/or no more than 1000 nm, no more than 500 nm, no more than 300 nm, no more than 200 nm, no more than 100 nm, no more than 50 nm, no more than 30 nm, no more than 20 nm, no more than 10 nm, etc. In some embodiments, the film comprises crystalline grains having a size of from 20 nm and 10 microns (e.g., from 50 nm to 1 micron). For example, the size may be at least 20 nm, at least 30 nm, at least 50 nm, at least 100 nm, at least 200 nm, at least 300 nm, at least 500 nm, at least 1 micron, at least 2 microns, at least 3 microns, at least 5 microns, etc., and/or no more than 10 microns, no more than 5 microns, no more than 3 microns, no more than 2 microns, no more than 1 micron, no more than 500 nm, no more than 300 nm, no more than 200 nm, no more than 100 nm, no more than 50 nm, no more than 30 nm, etc. In some embodiments, a bulk structure has a minimum dimension of at least 50 nm, at least 100 nm, at least 300 nm, at least 1 micron, at least 10 microns, etc.

In some embodiments, A comprises one or more cations, e.g., methylammonium, formamidinium, and/or cesium. In some embodiments, B comprises one or more metals and/or one or more transition metals (e.g., lead) and/or one or more dopants (e.g., manganese). In some embodiments, B comprises one or more metals and/or one or more transition metals (e.g., lead) and/or one or more dopants (e.g., manganese, ytterbium, nickel). In some embodiments, a dopant is incorporated into a perovskite structure at a mole ratio, of the dopant to the one or more metals and/or one or more transition metals, of from 0.65 to 1.15. In some embodiments, a dopant is incorporated into a perovskite structure at a precursor mole ratio, of the dopant to the one or more metals and/or one or more transition metals, of from 0.65 to 1.15. In some embodiments, a perovskite structure has from 0.1% to 10% of the B site as dopant, in the ABX ₃ perovskite structure. In some embodiments, X comprises one or more halides. For example, the perovskite structure may be doped with manganese, e.g., as discussed in U.S. Provisional Application No. 62/586,846, filed on November 15, 2017, entitled“Manganese-Doped

Perovskite Structures for Light-Emitting Devices and Other Applications,” incorporated herein by reference in its entirety. In some cases, the perovskite structure (e.g., nanocrystal, film, bulk structure) may be doped with a dopant (e.g., manganese, ytterbium, nickel), e.g., as discussed in a PCT application filed on even date herewith, entitled“DOPED PEROVSKITE

STRUCTURES FOR LIGHT-EMITTING DEVICES AND OTHER APPLICATIONS,” incorporated herein by reference in its entirety.

The dopant may be present in the perovskite structure at a variety of suitable

compositions. In some embodiments, the dopant may be present in the perovskite structure at a percent of B site, in the ABX ₃ perovskite structure, of at least 0.1%, at least 0.15%, at least 0.2%, at least 0.25%, at least 0.3%, at least 0.35%, at least 0.4%, at least 0.45%, at least 0.5%, at least 0.55%, at least 0.6, at least 0.65%, at least 0.69%, at least 0.7%, at least 0.75%, at least 0.8%, at least 0.85%, at least 0.9, at least 0.95%, at least 0.97%, at least 1%, at least 1.05%, at least 1.1%, at least 1.11%, at least 1.15%, at least 1.2%, at least 1.24%, at least 1.25%, or at least 1.30%. In some embodiments, the dopant may be present in the perovskite structure at a percent of B site, in the ABX ₃ perovskite structure, of at most 10%, at most 8%, at most 6%, at most 5%, at most 4%, at most 3%, at most 2%, at most 1.8%, or at most 1.5%. For example, 1.5% of the B sites having dopant corresponds to 15 dopant atoms and 985 Pb atoms out of every 1000 B sites, i.e., a mole ratio. Combinations of the above-referenced ranges are also possible (e.g., from 0.1% to 10%, from 0.1% to 5%, from 0.1% to 1.5%, etc.). For example, in some embodiments, a perovskite structure has from 0.1% to 10% of the B site as dopant, or any of the other percentages described herein.

Without wishing to be bound by theory, changing the composition of the perovskite nanocrystal with respect to at least one halide may change a bandgap of the perovskite nanocrystal relative to a perovskite nanocrystal of the same size, which may influence the peak emission wavelength of the perovskite nanocrystal (e.g., the observed color emitted by the perovskite nanocrystal). The composition of the perovskite nanocrystal may be determined by a variety of methods of elemental analysis known to those of ordinary skill in the art, e.g., energy dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, wavelength dispersive spectroscopy, Fourier-transform infrared spectroscopy, and/or x-ray diffraction.

In some embodiments, the peak emission wavelength of the perovskite nanocrystal is at least 200 nm, at least 300 nm, at least 350 nm, at least 400 nm, at least 450 nm, at least 465 nm, at least 470 nm, at least 500 nm, at least 511 nm, at least 520 nm, at least 600 nm, at least 700 nm, at least 800 nm, or at least 900 nm. In some embodiments, the peak emission wavelength of the perovskite nanocrystal is at most 1000 nm, at most 900 nm, at most 800 nm, at most at most 700 nm, at most 800 nm, at most 520 nm, at most 511 nm, at most 500 nm, at most 470 nm, at most 465 nm, at most 450 nm, at most 400 nm, at most 350 nm, or at most 300 nm.

Combinations of the above-referenced ranges are also possible (e.g., from 200 nm to 2000 nm, from 400 nm to 800 nm, from 465 nm to 511 nm). In some embodiments, the peak emission wavelength the perovskite nanocrystal is 468 nm. In some embodiments, the peak emission wavelength of the perovskite nanocrystal is 469 nm. The peak emission wavelength can be measured, e.g., by photoluminescence spectroscopy.

In some embodiments, as mentioned, the light-emitting region is positioned between the electron transport region and the hole transport region. In some embodiments, at least a portion of the light-emitting region is in direct contact with at least a portion of the electron transport region. In some embodiments, at least a portion of the light-emitting region is in direct contact with at least a portion of the hole transport region. In some embodiments, the light-emitting region has a maximum cross-sectional dimension of at least at least 1 nm, at least 3 nm, at least 5 nm, at least 10 nm, at least 15 nm, at least 18 nm, at least 20 nm, at least 22 nm, at least 25 nm, at least 30 nm, at least 35 nm, at least 40 nm, at least 45 nm, at least 50 nm, at least 60 nm, at least 70 nm, at least 80 nm, at least 90 nm, at least 100 nm, or at least 500 nm. In some embodiments, the perovskite nanocrystal has a maximum cross-sectional dimension of at most 900 nm, at most 500 nm, at most 100 nm, at most 90 nm, at most 80 nm, at most 70 nm, at most 60 nm, at most 50 nm, at most 45 nm, at most 40 nm, at most 35 nm, at most 30 nm, at most 25 nm, at most 22 nm, at most 20 nm, at most 18 nm, at most 15 nm, at most 10 nm, at most 5 nm, or at most 3 nm. Combinations of the above-reference ranges are also possible (e.g., from 1 nm to 900 nm, from 3 nm to 100 nm, from 5 nm from 30 nm, from 5 nm to 20 nm, from 10 nm to 30 nm, from 15 nm to 25 nm, from 18 nm to 22 nm). The perovskite nanocrystal in some embodiments has a maximum cross-sectional dimension of 20 nm.

In some embodiments, the light-emitting region has a minimum cross-sectional thickness of at least 1 nm, at least 2 nm, at least 3 nm, at least 4 nm, at least 5 nm, at least 6 nm, at least 7 nm, at least 8 nm, at least 9 nm, at least 10 nm, at least 20 nm, at least 30 nm, at least 50 nm, at least 80 nm, at least 90 nm, at least 100 nm, or at least 500 nm. In some embodiments, the perovskite nanocrystal has a cross-sectional thickness of at most 900 nm, at most 500 nm, at most 100 nm, at most 90 nm, at most 80 nm, at most 50 nm, at most 30 nm, at most 20 nm, at most 10 nm, at most 9 nm, at most 8 nm, at most 7 nm, at most 6 nm, at most 5 nm, at most 4 nm, at most 3 nm, or at most 2 nm. Combinations of the above-reference ranges are also possible (e.g., from 1 nm to 900 nm, from 1 nm to 10 nm, from 2 nm to 8 nm, from 4 nm to 6 nm). The perovskite nanocrystal in some embodiments has a cross-sectional thickness of 5 nm.

In some embodiments, the light-emitting region may comprise one or more layers of perovskite nanocrystals. In some cases, the perovskite nanocrystals in a light-emitting region have an average concentration in a layer of from 25 nanometers squared per nanocrystal to 400 nanometers squared per nanocrystal, as can be measured by, for example, atomic force microscopy or transmission electron microscopy.

In some embodiments, the light-emitting device may further comprise an electrode. In some embodiments, the light-emitting device may comprise a first electrode and a second electrode. The electrode in some embodiments may be optically transparent (e.g. to wavelengths of from 300 nm to 700 nm). The first electrode in some embodiments may comprise indium tin oxide. The electrode, in some embodiments, may comprise (as non-limiting examples) a metal, an alloy, a transition metal, copper, graphite, gold, titanium, brass, silver, aluminum, or platinum, or a combination thereof. The second electrode, in some embodiments, comprises aluminum.

In some embodiments, the light-emitting device has a surprisingly large external quantum efficiency. External quantum efficiency generally refers to a ratio of the number of photons emitted from the light-emitting device, to the number of electrons passing through the light-emitting device, e.g., during an application of a voltage between the electron transport region and the hole transport region. The external quantum efficiency can be calculated from the measured intensity, wavelength, and current of the light-emitting device. The intensity and wavelength of the light-emitting device may be measured by photoluminescence spectroscopy, and current can be measured by e.g. an ammeter.

The light-emitting device in some embodiments has an external quantum efficiency of at least 0.01%, at least 0.05%, at least 0.1%, at least 0.2%, at least 0.3%, at least 0.4%, at least 0.5%, at least 0.6%, at least 0.7%, at least 0.8%, at least 0.9%, at least 1%, at least 2%, at least 3%, at least 5%, at least 7%, at least 10%, at least 15%, at least 20%, or at least 25%, etc., at a peak emission wavelength of from 400 nm to 800 nm. The light-emitting device in some embodiments has an external quantum efficiency of at most 25%, at most 20%, at most 15%, at most 10%, at most 5%, or at most 3%, at a peak emission wavelength of from 400 nm to 800 nm. The light-emitting device in some embodiments has an external quantum efficiency of at most 1%, at most 0.9%, at most 0.8%, at most 0.7%, at most 0.6%, at most 0.5%, at most 0.4%, at most 0.3%, at most 0.2%, at most 0.1%, or at most 0.05%, at a peak emission wavelength of from 400 nm to 800 nm. Combinations of the above-reference ranges are also possible (e.g., from 0.01% to 0.1%, from 0.1% to 1%, from 0.1% to 0.5%). Other combinations of the above reference ranges are also possible (e.g., from 0.2% to 25%, from 0.2% to 20%). The light- emitting device in some embodiments has an external quantum efficiency of 0.5% at a peak emission wavelength of 469 nm.

In some embodiments, the light-emitting device has a photoluminescence quantum yield, which may refer to a ratio of the number of photons emitted by photoluminescence by the light- emitting device to the number of photons absorbed by the light-emitting device. The number of photons emitted can be measured by photoluminescence spectroscopy. The light-emitting device in some embodiments has a photoluminescence quantum yield of at least 1%, at least 2%, at least 3%, at least 4%, at least 5%, at least 6%, at least 7%, at least 8%, at least 9%, at least 10%, at least 20%, at least 25%, at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, at least 90%, at least 95%, etc. The light-emitting device in some embodiments has a photoluminescence quantum yield of at most 100%, at most 99%, at most 80%, at most 70%, at most 60%, at most 50%, at most 40%, at most 30%, at most 27%, or at most 20%. The light-emitting device in some embodiments has a photoluminescence quantum yield of at most 10%, at most 9%, at most 8%, at most 7%, at most 6%, at most 5%, at most 5%, at most 3%, or at most 2%. Combinations of the above-reference ranges are also possible (e.g., from 1% to 10%, from 0.1% to 0.5%, etc.). Other combinations of the above reference ranges are also possible (e.g., from 1% to 100%, from 0.1% to 80%, etc.).

The light-emitting device in some embodiments has a maximum brightness of at least 1 cd/m ² , at least 5 cd/m ² , at least 10 cd/m ² , at least 20 cd/m ² , at least 30 cd/m ² , at least 50 cd/m ² , at least 80 cd/m ² , at least 100 cd/m ² , at least 120 cd/m ² , at least 140 cd/m ² , at least 160 cd/m ² , at least 200 cd/m ² , at least 500 cd/m ² , at least 1000 cd/m ² , or at least 1500 cd/m ² , at least 2000 cd/m ² , at least 3000 cd/m ² , at least 5000 cd/m ² , at least 10,000 cd/m ² , at least 20,000 cd/m ² , etc. at a peak emission wavelength of from 400 nm to 800 nm. In some cases, higher brightnesses are possible, e.g., for a green light-emitting device. For instance, the maximum brightness for green light may be at least 30,000 cd/m ² , at least 50,000 cd/m ² , at least 100,000 cd/m ² , at least 200,000 cd/m ² , at least 300,000 cd/m ² , at least 500,000 cd/m ² , at least 1,000,000 cd/m ² , etc.

The light-emitting device in some embodiments has a maximum brightness of at most 1,000,000 cd/m ² (e.g., for a green light-emitting device), at most 100,000 cd/m ² , at most 50,000 cd/m ² , at most 20,000 cd/m ² (e.g., for a blue light-emitting device), at most 10,000 cd/m ² , at most 5,000 cd/m ² , or at most 4,000 cd/m ² , at a peak emission wavelength of from 400 nm to 800 nm. The light-emitting device in some embodiments has a maximum brightness of at most 3000 cd/m ² , at most 1500 cd/m ² , at most 1000 cd/m ² , at most 500 cd/m ² , at most 200 cd/m ² , at most 160 cd/m ² , at most 140 cd/m ² , at most 120 cd/m ² , at most 100 cd/m ² , at most 80 cd/m ² , at most 50 cd/m ² , at most 30 cd/m ² , at most 20 cd/m ² , at most 10 cd/m ² , or at most 5 cd/m ² , at a peak emission wavelength of from 400 nm to 800 nm. Combinations of the above-reference ranges are also possible (e.g., from 1 cd/m ² to 3000 cd/m ² , from 100 cd/m ² to 200 cd/m ² ). Other combinations of the above-reference ranges are also possible (e.g., from 1 cd/m ² to 1,000,000 cd/m ² , from 100 cd/m ² to 50,000 cd/m ² ). The light-emitting device in some embodiments has a maximum brightness of 111 cd/m ² at a peak emission wavelength of 469 nm.

In some embodiments, methods for fabricating the light-emitting device (e.g., the light- emitting device of any of the embodiments herein) are provided. A method of fabricating the light-emitting device may comprise depositing a hole transport region, a light-emitting region, and an electron transport, e.g., on a substrate. A variety of deposition techniques may be used, such as spin coating, dip coating, lithography, chemical vapor deposition, physical vapor deposition, or the like. In addition, in some embodiments, one or more electrodes may be deposited on the device.

The hole transport region, in some embodiments, is deposited onto a first electrode, and/or onto a substrate comprising a first electrode. The light-emitting region may be deposited after (e.g., directly onto) the hole transport region. In some embodiments, the electron transport region is deposited after (e.g., directly onto) the light-emitting region and/or the hole transport region. In some embodiments, the method may comprise depositing a second electrode after (e.g., directly onto) the electron transport region.

In some embodiments, the electron transport region is deposited onto the second electrode, and/or onto a substrate comprising the second electrode. In some embodiments, the light-emitting region is deposited after (e.g., directly onto) the electron transport region. In some embodiments, the hole transport region is deposited after (e.g., directly onto) the light-emitting region and/or the electron transport region. In some embodiments, the method may comprise depositing the first electrode after (e.g., directly onto) the hole transport region.

In some embodiments, depositing (e.g., depositing a region, e.g., a hole transport region or a light-emitting region) comprises spin coating. The process of spin coating will may comprise adding a fluid (e.g., a solution or suspension comprising the composition of the electron transport region, a solution or suspension comprising the composition of the hole transport region, a solution or suspension comprising the composition of the light-emitting region) onto a substrate that is rotated before, during, and/or after the fluid is added onto the substrate, such that a composition from the fluid (e.g., a molecule and/or a particle dissolved and/or suspended in the fluid, or a plurality of the molecules and/or the particles) remains on the substrate.

In some embodiments, depositing (e.g., depositing a region) comprises inkjet printing or dip coating a composition from a fluid onto the substrate. The fluid may include, for instance, e.g., a solution or suspension comprising a precursor composition of the electron transport region, a solution or suspension comprising a precursor composition of the hole transport region, a solution or suspension comprising a precursor composition of the light-emitting region, etc.

In some embodiments, one or more regions of the device may be annealed. In some embodiments, annealing comprises heating an article (e.g., comprising a substrate and/or any added material) to a maximum temperature of at least 50 degrees Celsius, at least 100 degrees Celsius, at least 110 degrees Celsius, at least 120 degrees Celsius, at least 125 degrees Celsius, at least 130 degrees Celsius, at least 135 degrees Celsius, at least 140 degrees Celsius, at least 145 degrees Celsius, at least 160 degrees Celsius, at least 180 degrees Celsius, at least 200 degrees Celsius, at least 300 degrees Celsius, at least 400 degrees Celsius, at least 500 degrees Celsius, at least 600 degrees Celsius, at least 700 degrees Celsius, at least 800 degrees Celsius, or at least 900 degrees Celsius. In some embodiments, annealing comprises heating an article to a maximum temperature of at most 1000 degrees Celsius, at most 900 degrees Celsius, at most 800 degrees Celsius, at most 700 degrees Celsius, at most 600 degrees Celsius, at most 500 degrees Celsius, at most 400 degrees Celsius, at most 300 degrees Celsius, at most 200 degrees Celsius, at most 180 degrees Celsius, at most 160 degrees Celsius, at most 145 degrees Celsius, at most 140 degrees Celsius, at most 135 degrees Celsius, at most 130 degrees Celsius, at most 125 degrees Celsius, at most 120 degrees Celsius, or at most 110 degrees Celsius, or at most 110 degrees Celsius. Combinations of the above-reference ranges are also possible (e.g., from 50 degrees Celsius to 1000 degrees Celsius, from 100 degrees Celsius to 200 degrees Celsius, from 140 degrees Celsius to 150 degrees Celsius).

In some embodiments, depositing (e.g., depositing a region such as an electron transport region, depositing an electrode) comprises physical vapor deposition or chemical vapor deposition. In certain cases, physical vapor deposition comprises thermal evaporation (e.g., using an evaporation chamber). The process of thermal evaporation may comprise positioning a substrate above a material to be evaporated (e.g., at a distance of from 200 mm to 1 m), and then evaporating the material to be deposited by reducing the external pressure and increasing the temperature to which the material is exposed. At least some of the evaporated material then coats the substrate.

In some embodiments, methods of operating a light-emitting device (e.g., a light- emitting device of any of the embodiments of this disclosure) are provided. A method of operating a light-emitting device according to certain embodiments comprises applying a voltage across the light-emitting device. The voltage may be applied between the electron transport region and the hole transport region. For example, applying the voltage across the light-emitting device may comprise applying the voltage to a first electrode and a second electrode, wherein the first electrode is electrically connected to the hole transport region and the second electrode is electrically connected to the electron transport region of the light-emitting device. In some embodiments, the light-emitting region is in physical contact with both the electron transport region and the hole transport region.

In some embodiments, the voltage applied across the light-emitting device is at least 0.1 V, at least 0.2 V, at least 0.3 V, at least 0.4 V, at least 0.5 V, at least 0.6 V, at least 0.7 V, at least 0.8 V, at least 0.9 V, at least 1 V, at least 2 V, at least 3 V, at least 4 V, at least 5 V, at least 6 V, at least 6.5 V, at least 7 V, at least 7.5 V, at least 8 V, at least 9 V, at least 10 V, at least 12 V, at least 14 V, at least 16 V, or at least 18 V. In some embodiments, the voltage applied across the light-emitting device is at most 20 V, at most 18 V, at most 16 V, at most 14 V, at most 12 V, at most 10 V, at most 9 V, at most 8 V, at most 7.5 V, at most 7 V, at most 6.5 V, at most 6 V, at most 5 V, at most 4 V, at most 3 V, at most 2 V, at most 1 V, at most 0.9 V, at most 0.8 V, at most 0.7 V, at most 0.6 V, at most 0.5 V, at most 0.4 V, at most 0.3 V, or at most 0.2 V.

Combinations of the above-reference ranges are also possible (e.g., from 0.1 V to 20 V, from 0.1 V to 7.5 V).

U.S. Provisional Application No. 62/586,837, filed November 15, 2017 and entitled “LIGHT-EMITTING DEVICE STRUCTURES FOR BLUE LIGHT AND OTHER

APPLICATIONS,” is incorporated herein by reference in its entirety for all purposes.

U.S. Provisional Application No. 62/586,846, filed November 15, 2017 and entitled “MANGANESE-DOPED PEROVSKITE STRUCTURES FOR LIGHT-EMITTING DEVICES AND OTHER APPLICATIONS,” is incorporated herein by reference in its entirety for all purposes.

A PCT application filed on the same day as the instant application, entitled“Doped Perovskite Structures for Light- Emitting Devices and Other Applications,” by Congreve, et al, is incorporated herein by reference in its entirety for all purposes.

The following examples are intended to illustrate certain embodiments of the present invention, but do not exemplify the full scope of the invention.

EXAMPLE 1 In this example, CsPbBr _x Ch- _x perovskite nanocrystals were synthesized with moderate exciton confinement and improved charge injection properties. It was then demonstrated that the emission efficiency and lifetime of the CsPbBr _x Cl _{3 x} perovskite nanocrystals were significantly impaired when the perovskite nanocrystals were used with traditional hole transport layers (HTLs) such as NiO _x . A device architecture was then developed that did not affect the emission from the perovskite nanocrystals. Light-emitting device performance with increased to a maximum external quantum efficiency (EQE) of 0.50% and a brightness of 111 cd/m ² at an emission wavelength of 469 nm. Finally, it was demonstrated that these device improvements were beneficial across the visible spectrum, with high brightness and efficiency devices spanning from 511 nm to 469 nm.

FIG. 6 illustrates a CsPbBr _x Cl;v _x perovskite nanocrystal structure. The ligands 110 used in this example were a mix of octadecene, oleyl amine and trioctylphosphine.

FIG. 7 illustrates a transmission electron microscopy (TEM) image of synthesized CsPbBr _x Cb- _x perovskite nanocrystals, showing nanocrystals of approximately 20 nm lateral dimension and 5 nm thickness.

FIG. 8 illustrates an absorption spectrum and an emission spectrum of 469 nm

CsPbBr _x Cb- _x perovskite nanocrystals. The absorption spectrum showed slight quantum confinement and there was a narrow emission full width at half maximum (FWHM) of 23 nm.

FIG. 9 and FIG. 10 are energy level diagrams (in eV) of fabricated light-emitting diodes (LEDs). Either NiO _x or poly(3,4-ethylenedioxythiophene): (poly styrene sulfonate)/poly((9,9- dioctylfluorenyl-2,7-diyl)-co-(4,4’-(N-(4-sec-butylphenyl) diphenylamine)))/(perfluorinated ionomer) (PEDOT:PSS/TFB/PFI) was used as the hole transport layer (HTL) of the LEDs. PFI was represented in FIG. 10 by band bending to a deeper work function. 2,2’,2”-(l,3,5- Benzinetriyl)-tris( 1 -phenyl- l-H-benzimidazole) (TPBi) was used as the electron transport layer (ETL) of the LEDs.

CsPbBr _x Cb- _x perovskite nanocrystals were synthesized (see, e.g., Example 2) at low temperature to favor an asymmetric crystal growth. The yielded nanocrystals were

approximately 20 nm in the lateral dimension and 5 nm thick (see, e.g., FIG. 7).

Absorption and emission properties of the nanocrystals are presented in FIG. 8, which demonstrated a slight excitonic peak and a narrow emission of 23 nm FWHM. These

nanocrystals were robust to purification process by polar solvent (e.g., ethyl acetate) washing, and the washing preserved balanced properties of the nanocrystals, such as exciton confinement/emission and charge injection.

The transient decay of a thin film of nanocrystals was monitored as a function of the composition of an underlying layer. All data was measured in air with 379 nm excitation using a Hamamatsu streak camera integrated across the emission wavelength of the nanocrystals.

FIG. 20 illustrates subtracted TFB photoluminescence data. The integrated curve from the nanocrystals (e.g., dots) was determined by subtracting the PEDOT:PSS/TFB/PFI only emission from the PEDOT:PSS/TFB/PFI/Dots curve. The subtraction has been doubled for clarity. The subtraction was then scaled to best fit the data in FIG. 11.

FIG. 21 illustrates photoluminescence spectra of perovskite nanocrystals spun atop a variety of HTLs. NiOx showed a substantial reduction in luminescence relative to that of nanocrystals on glass, while the PEDOT:PSS/TFB/PFI HTL nanocrystal assembly had luminescence intensity on a similar order to that of the glass nanocrystal assembly.

FIG. 22 illustrates electroluminescence of the PEDOT:PSS/TFB/PFI/nanocrystal devices as a function of applied voltage. No change in shape of the electroluminescence spectrum was observed with change in applied voltage.

FIG. 23 illustrates electroluminescence (EL) from PEDOT:PSS/TFB HTL devices with and without PFI. The PFI layer suppressed EL from the TFB layer (440 nm peak).

FIG. 24 illustrates electroluminescence and photoluminescence from all four nanocrystal types (with different peak wavelengths) in the series used in this work. A small peak shift between EL and PL was observed for all nanocrystal types in the series.

In FIG. 11, the transient photoluminescence was compared for nanocrystals spun-cast on top of glass, PEDOT:PSS/TFB/PFI, and NiO _x in the first nanosecond after excitation. A clear decrease in lifetime was observed in the presence of NiO _x , which, when combined with the strong reduction in photoluminescence, indicated the appearance of a non-radiative decay channel, possibly decaying through defect states in the NiO _x . In order to obtain optimal emission efficiencies from the nanocrystals, PEDOT:PSS/TFB/PFI was chosen over NiO _x as a hole transport layer because it did not introduce any non-radiative decay channels.

FIG. 11 illustrates time-resolved photoluminescence data for nanocrystals spuncast on top of glass, PEDOT:PSS/TFB/PFI, and NiO _x in the first nanosecond after excitation. FIG. 11 shows the clear emergence of a non-radiative decay channel in nanocrystals on top of NiO _x .

Data was taken from the integration of streak camera data. As shown in FIG. 11, PEDOT:PSS/TFB/PFI demonstrated dynamics identical to those of nanocrystals on glass, allowing for unaltered emission inside the device.

To improve the emission from a light-emitting device, an HTF constructed of a trilayer made of PEDOT:PSS/TFB/PFI was used. The TFB is an electron-blocking, hole-transport polymer with a strong hole mobility of 0.01 cm ² /Vs. PFI can be used as part of a buffer hole injection layer leading to high brightness devices. Without wishing to be bound by theory, it may be that strong surface dipole induced by PFI led to a band bending of the HTF to a higher work function, favorable for hole injection, while the isolation of the perovskite layers helped to reduce their exciton quenching process.

In order to better understand the dynamics of the luminescence of the nanocrystals, due to the luminescence of TFB overlapping with that of the nanocrystals, the TFB -only emission was first subtracted from the data taken for samples. The final subtracted data was plotted in FIG. 11, PEDOT :PSS/TFB/PFI. The transient decay with PEDOT:PSS/TFB/PFI was virtually identical to the emission behavior from glass, demonstrating that the nanocrystals were not significantly perturbed by the presence of the HTF, and thus this HTF could substantially improve the emission from the nanocrystals relative to current HTFs.

To more clearly quantify the benefits of this HTF switch, devices were fabricated utilizing both NiO _x and PEDOT:PSS/TFB/PFI as the HTF, following the device structures in FIG. 9 and FIG. 10. ITO coated glass was cleaned via solvent washing and plasma cleaning immediately before sequential spin coating of the HTF layers, either PEDOT:PSS, TFB, and PFI, or the NiO _x precursor (followed by heating to form NiO _x ). Without wishing to be bound by theory, the presence and/or relative position of the PFI layer helped to maintain nanocrystal emission. Without PFI, electroluminescence from primarily TFB was observed. The nanocrystals were then spuncast from octane, and the partial device was then transferred to a thermal evaporator, where 40 nm of TPBi was evaporated, followed by evaporation of FiF/Al to form the top contact and the device was patterned with a diameter of 2 mm. All device fabrication was performed inside a glovebox in an inert gas atmosphere (e.g., nitrogen, argon). All device testing was done on unpackaged devices in air.

After device fabrication, clear electroluminescence was observed from the perovskite nanocrystal layer (see, e.g., FIG. 12) in both structures of NiO _x and PEDOT:PSS/TFB/PFI. FIG. 12 illustrates electroluminescence spectra for NiO _x and PEDOT:PSS/TFB/PFI. The

electroluminescence spectra from both devices were nearly identical to each other, with a peak of 469 nm and a FWHM of 24 nm for the NiO _x and 25 nm for the PEDOT:PSS/TFB/PFI. The emission was unchanged as a function of applied voltage.

FIG. 13 and FIG. 14 illustrate electrical characteristics of perovskite light-emitting devices. The NiO _x device, relatively a more conductive structure than PEDOT:PSS/TFB/PFI, demonstrated a low turn-on voltage and high brightness, but was limited by high dark current and the non-radiative recombination of the nanocrystals discussed previously, leading to a maximum EQE of 0.03%. The PEDOT:PSS/TFB/PFI device, in contrast, demonstrated a higher tum-on voltage but a much lower dark current, indicating strong film formation and reduced pinholes. The EQE for PEDOT:PSS/TFB/PFI devices reached a value as high as 0.50% before rolling off at higher current densities. This high quantum efficiency demonstrated the value of PEDOT:PSS/TFB/PFI as an HTL and showed significant efficiency for blue perovskite nanocrystals.

FIG. 13 illustrates J-V-L curves for light-emitting diodes (LEDs) fabricated using 469 nm perovskite nanocrystals and either NiO _x or PEDOT:PSS/TFB/PFI as the hole transport layer. FIG. 14 illustrates EQE curves for LEDs fabricated using 469 nm perovskite nanocrystals and either NiO _x or PEDOT:PSS/TFB/PFI as the hole transport layer.

Finally, to demonstrate the versatility of the PEDOT:PSS/TFB/PFI device structure, the bromide to chloride ratio was tuned to adjust the emission wavelength as shown in FIG. 15, while keeping the device structure constant. The fabricated devices had emission wavelengths at 469 nm, 481 nm, 488 nm, and 511 nm, with narrow FWHM. The J-V-L characteristics were similar for all devices with low dark currents and turn-on voltages that increased with increased bandgap. The EQEs for these devices were plotted in FIG. 17. There was a substantial increase in efficiency as the emission wavelength redshifted; indeed, a small 7 nm emission wavelength difference between the 481 nm and 488 nm device resulted in a threefold difference in maximum EQE.

FIG. 15 to FIG. 18 demonstrated the versatility of the PEDOT:PSS/TFB/PFI device structure. Device parameters were tabulated in Table 1. Devices were fabricated across the blue- green spectrum. FIG. 15 illustrates the electroluminescence spectra of devices with

electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm. FIG. 16 illustrates the J-V- L curves of devices with electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm. FIG. 17 illustrates EQE of devices with electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm. FIG. 18 illustrates photographs of devices with electroluminescence peaks at 469 nm, 481 nm, 488 nm, and 511 nm.

FIG. 25 illustrates current efficiencies of the devices presented in FIG. 15, FIG. 16, FIG. 17, and FIG. 18.

FIG. 26 illustrates spin conditions for each of the devices presented in FIG. 15, FIG. 16, FIG. 17, and FIG. 18.

As the energetics were shifted towards green, a small gain in quantum efficiency resulted. While the 469 nm device showed a strong efficiency enhancement with the HTL change, the bromide device peaked at 2.3% EQE and 3423 cd/m ² . Without wishing to be bound by theory, it was hypothesized that the energetic requirements for lower bandgap nanocrystals were much less restrictive than those for higher bandgap nanocrystals, and thus the benefits of the PEDOT:PSS/TFB/PFI structure faded as the emission peak redshifted and other structures provided an equally favorable environment. The full set of device parameters are shown in Table 1.

As another comparison test, LEDs using different materials as the HTL were excited in a standard setup by sourcing 1 mA to a given device and measuring the spectrum with a spectrometer. FIG. 19 illustrates the electroluminescence spectra of light-emitting diodes with the same nanocrystals and a variety of hole transport layers. Competing HTLs either had significantly reduced luminescence (see, e.g., FIG. 19, NiO _x and PEDOT:PSS/PFI) or impure spectra (see, e.g., FIG. 19, poly(9-vinylcarbazole), PVK) relative to the PEDOT:PSS/TFB/PFI device (see, e.g., FIG. 19, A3232).

This example demonstrated high efficiency blue perovskite LEDs. In this example, one of the efficiency barriers in blue perovskite nanocrystal LEDs, the architecture itself, was both demonstrated and overcome. The HTL comprising NiO _x was shown to induce non-radiative recombination of the emissive state, fundamentally limiting device performance. A new HTL, PEDOT:PSS/TFB/PFI, that did not significantly influence the nanocrystals, was introduced and provided a strong overall boost in efficiency, with values reaching as high as 0.50% EQE for 469 nm emitting devices. It was further demonstrated that this structure provided strong benefits across the blue-green portion of the spectrum.

EXAMPLE 2

This example demonstrates the synthesis of perovskite nanocrystals used in Example 1.

For synthesis of the perovskite nanocrystals, all synthetic materials were purchased from Sigma Aldrich and used as received unless otherwise noted. 0.814 g of CS2CO3 (purity 99.9%), 40 mL of octadecene (purity 90%) and 2.5 mL of oleic acid (purity 90%) were loaded into 100 mL flask, dried under vacuum at 120 degrees Celsius for 1 h, and then heated to 150 degrees Celsius under N ₂ protection, yielding a clear solution. The solution was cooled to room temperature for storage, and re-heated up to 100 degrees Celsius under vacuum before use.

179 mg PbBr _{2 (} 0.488 mmol, purity 98%), 73.2 mg PbCb (0.2632 mmol, purity 98%), 20 mL of octadecene, 2 mL of oleylamine (purity 98%), 2 mL of oleic acid, and 2 mL of trioctylphosphine (purity 97%) were loaded into a 100 mL three-neck flask, dried under vacuum at 130 degrees Celsius for 45 min., and then heated to 150 degrees Celsius. A resulting clear solution was heated to 165 degrees Celsius under N ₂ protection. 1.75 mL of pre-heated Cs-oleate precursors was swiftly injected into the aforementioned solution, and the solution turned to a yellow color immediately. After having reacted for 10 s, a crude product was cooled to room temperature in an ice/water bath. For the 511 nm emission device, only PbBr ₂ precursors were used to synthesize CsPbBr ₃ . To tune emission wavelength of the perovskite nanocrystals, a Br post-exchanging method was used.

To purify the nanocrystals, an equal volume of anhydrous ethyl acetate (purity 99.8%) was added to the aforementioned crude product to precipitate the nanocrystals. After

centrifuging at 4000 rpm) for 5 min., the pellet was dissolved in 10 mL of anhydrous hexane (purity 95%). The nanocrystals were washed again by anhydrous ethyl acetate (volume ratio of ethyl acetate:hexane 3:1), centrifuged at 7000 rpm for 5 min., and re-dispersed in 8 mL of octane or hexane. The solution was filtered by a polytetrafluoroethylene (PTFE) filter (0.2 um) before use. For light-emitting device fabrication, Ni(N0 ₃ ) ₂ *6H ₂ 0, Nafion® perfluorinated resin solution 5 wt. % in lower aliphatic alcohols and water, PFI, LiF (evaporation grade), and Aluminum were purchased from Sigma- Aldrich and used as received. Indium tin oxide (GGO) substrates, TPBi and TFB were purchased from Luminescence Technology, Inc. and used as received. PEDOT:PSS was purchased from Heraeus (Clevios P VP AI 4083) and used as received.

To make the NiO _x precursor, 1.5 M of each Ni(N0 ₃ ) ₂ *6FbO and ethylene diamine were dissolved in ethylene glycol to obtain a blue colored complex. After stirring for 10 min, the solution was filtered by a 0.4 micrometer PVDF filter.

15 Ohm ITO patterned glass was cleaned by sequential sonicating once in Micron-90 detergent, 2 times in water, 2 times in acetone, and then soaking in boiling isopropanol, for 10 min. each. The films were dried under blowing air and treated with O2 plasma at 200 W using 0.5 Torr O2 gas for 5 min. On these clean ITO substrates, a thin layer of PEDOT:PSS (Clevios PVP AI 4083, filtered using 0.4 micrometer PVDF filter) was spun at 4000 rpm for 45 s (ramp = 2500 rpm/s), and annealed at 140 degrees Celsius for 30 min in a nitrogen glovebox. After cooling, a TFB (4 mg/mL in chlorobenzene) layer was spin coated at 3000 rpm for 45 s (2000 rpm/s ramp), and annealed at 125 degrees Celsius for 15 min. A thin layer of PFI (0.05 wt% in isopropanol) was then coated at 3000 rpm for 45 s and dried at 145 degrees Celsius for 10 min.

For NiO _x thin films, the precursor solution was spun on plasma cleaned ITO at 2000 rpm for 90 s (2000 rpm/s), and annealed at 300 degrees Celsius for 1 h in air.

On top of these layers of either PEDOT:PSS/TFB/PFI or NiO _x , CsPbX ₃ perovskite quantum dots in octane were coated using different spin conditions to achieve a uniform layer. These films were then taken in the evaporation chamber, where 40 nm TPBi, 1.1 nm LiF, and 60 nm Al were deposited at 6 x 10 ⁶ mbar at 2 Angstroms/s, 0.2 Angstroms/s, and 3 Angstroms/s respectively. Devices were unpackaged and measured in air.

In use of the streak camera, samples were excited by a 379 nm laser from Hamamatsu (C 10196) with an 81 ps pulse width. Optical density (OD) filters were used to reduce the excitation intensity. The excitation was incident at a 45 degree angle to the glass face. The photoluminescence (PL) was collected with a 25.4 mm focal length lens normal to the glass face. The PL was focused through a 400 nm longpass filter into an SP2l50i spectrograph coupled to a Hamamatsu C 10627 streak unit and C9300 digital camera. Data was integrated across the nanocrystal emission wavelength to obtain the curves presented in FIG 11. For device characterization, electroluminescence (EL) spectra were taken with an Ocean Optics QE Pro with 100 ms integration time with 1 mA sourced to the device from a Keithley 2400. Current density- voltage and EQE characteristics were measured with an HP 4145A with a calibrated half inch ThorLabs photodetector physically pressed to the face of the device, removing the need for a geometric correction. The device (2 mm radius) was much smaller than the photodetector (PD) (9.7 mm). The PD was smaller than the glass slide (12.2 mm), which, combined with the black material construction of the EQE holder, blocked the collection of wave-guided light, which prevented overestimation of the EQE. Luminance was calculated from the J-V-L curves and the spectra of the device. Pictures were taken with 1 mA sourced to the device from a Keithley 2400.

While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or

configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present invention.

In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control. If two or more documents incorporated by reference include conflicting and/or inconsistent disclosure with respect to each other, then the document having the later effective date shall control.

All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and/or ordinary meanings of the defined terms.

The indefinite articles“a” and“an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean“at least one.”

The phrase“and/or,” as used herein in the specification and in the claims, should be understood to mean“either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e.,“one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to“A and/or B”, when used in conjunction with open-ended language such as“comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

As used herein in the specification and in the claims,“or” should be understood to have the same meaning as“and/or” as defined above. For example, when separating items in a list, “or” or“and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as“only one of’ or“exactly one of,” or, when used in the claims,“consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term“or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e.“one or the other but not both”) when preceded by terms of exclusivity, such as“either,”“one of,”“only one of,” or“exactly one of.”

As used herein in the specification and in the claims, the phrase“at least one,” 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 non-limiting 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.

When the word“about” is used herein in reference to a number, it should be understood that still another embodiment of the invention includes that number not modified by the presence of the word“about.”

It should also be understood that, unless clearly indicated to the contrary, in any methods claimed herein that include more than one step or act, the order of the steps or acts of the method is not necessarily limited to the order in which the steps or acts of the method are recited.

In the claims, as well as in the specification above, all transitional phrases such as “comprising,”“including,”“carrying,”“having,� �“containing,”“involving,”“holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases“consisting of’ and“consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.