WO2024112968A1

WO2024112968A1 - Systems and methods nanofiber-reinforced metal halide perovskite optoelectronic devices

Info

Publication number: WO2024112968A1
Application number: PCT/US2023/081187
Authority: WO
Inventors: Adam Printz; Anton SAMOYLOV; Nikolaus SWENSON; Antonio MURRIETA; Juliana BALTRAM
Original assignee: University of Arizona
Current assignee: University of Arizona
Priority date: 2022-11-27
Filing date: 2023-11-27
Publication date: 2024-05-30
Anticipated expiration: 2025-05-27

Abstract

Examples of reinforced perovskite are described. The reinforced perovskite includes a layer of perovskite material and a mat of polymeric nanofibers. The layer of perovskite material is dispersed in the mat of polymeric nanofibers. The perovskite includes a metal halide perovskite material. The nanofibers have diameters smaller than ½ the perovskite film thickness.

Description

SYSTEMS AND METHODS NANOFIBER-REINFORCED METAL HALIDE PEROVSKITE OPTOELECTRONIC DEVICES

GOVERNMENT SUPPORT

[0001] This invention was made with support from U.S. Department of Energy under Grant No. DE-EE0009834. The government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

[0002] This is a PCT application that claims benefit to U.S. provisional application serial number 63/428,088 filed on November 27, 2023, which is incorporated by reference in its entirety.

FIELD

[0003] The present disclosure generally relates to solar cells; and in particular to examples of nanofiber-reinforced perovskite films or materials for use in making, e.g., optoelectronic devices.

BACKGROUND

[0004] Solar cells are commonly evaluated according to their efficiency in converting sunlight into electrical power. However, in order for a solar cell design to be practically viable, it must meet additional requirements having to do with lifetime, resistance to damage or failure in operation etc. These other requirements pose especially challenging difficulties when the use of mechanically fragile materials as active media for solar cells is considered. Accordingly, it would be an advance in the art to provide mechanically robust solar cells despite having mechanically fragile active media.

[0005] It is with these observations in mind, among others, that various aspects of the present disclosure were conceived and developed. SUMMARY

[0006] The present disclosure provides a number of examples associated with nanofiber-reinforced perovskite films or materials for use with e.g., optoelectronic devices. In the context of the disclosed methods, devices, techniques, apparatus, systems, and so on, the terms “operable to,” “configured to,” and “capable of” used herein are interchangeable.

[0007] In one set of illustrative examples, the nanofiber-reinforced perovskite techniques can be embodied by a reinforced perovskite film including a layer of perovskite material; and a mat of polymeric nanofibers; wherein the layer of perovskite material is dispersed in the mat of polymeric nanofibers. The perovskite material can be an active medium that provides electrical charge carriers in response to incident illumination. The perovskite material can comprise a metal halide perovskite. The polymeric nanofibers can comprise an organic polymer.

[0008] In another set of illustrative examples, the nanofiber-reinforced perovskite techniques can be embodied by an optoelectronic device comprising: an arrangement of layers comprising: a reinforced perovskite film layer comprising: a layer of perovskite material; and a mat of polymeric nanofibers; wherein the layer of perovskite material is dispersed in the mat of polymeric nanofibers; a first layer A comprising an electron transport layer (ETL) and/or hole blocking layer (HBL); and a second layer B comprising a hole-transport layer (HTL) and/or an electron blocking layer (EBL); and wherein the perovskite film layer is sandwiched between the first layer A and the second layer B. The stack of layers can be capped with at least one electrode. In some examples, the at least one electrode can be substantially transparent. The perovskite material can be an active medium that provides electrical charge carriers in response to incident illumination or a medium into which charge carriers are injected for radiative recombination. The polymeric nanofibers can comprise an organic polymer (e.g., a nylon such as nylon-6, 6, a methacrylate, polyethylene oxide/polyethylene glycol, or a polyvinyl alcohol; optionally cross-linked to improve properties). The polymeric nanofibers can be hydrophilic. The mat of polymeric nanofibers can be randomly ordered, axially oriented, or biaxially oriented. The layer of perovskite material can have a thickness in a range of from about 100 nm to about 2000 nm (or 300 nm to about 600 nm). The mat of polymeric nanofibers can have a thickness in a range of from about 300 nm to about 600 nm (range as above - preferably about 50-100 nm taller than the perovskite layer). The optoelectronic device can be configured as a device selected from the group consisting of solar cells, photovoltaic devices, light emitting diodes, perovskite tandem devices, and photodetectors.

[0009] In another set of illustrative examples, the nanofiber-reinforced perovskite techniques can be embodied as a method of making an optoelectronic device, said method comprising: forming a reinforced perovskite film according to the previous example on an electron transport layer; and adding a hole transport layer on the perovskite film.

[0010] In another set of illustrative examples, the nanofiber-reinforced perovskite techniques can be embodied as a method of making a reinforced perovskite film, said method comprising: fabricating a mat of polymeric nanofibers; and applying a perovskite precursor solution onto the mat of polymeric nanofibers; and curing the perovskite precursor solution to form said reinforced perovskite film. The perovskite precursor solution can comprise an additive.

[0011] In another set of illustrative examples, the nanofiber-reinforced perovskite techniques can be embodied by a perovskite tandem device (e.g., 2-terminal or 4-terminal), said device comprising an arrangement of layers comprising: a reinforced perovskite film layer comprising: a layer of perovskite material; and a mat of polymeric nanofibers; wherein the layer of perovskite material is dispersed in the mat of polymeric nanofibers; a first layer A comprising an electron transport layer (ETL) and/or a hole blocking layer (HBL); and a second layer B comprising a hole-transport layer (HTL) and/or electron blocking layer (EBL); and wherein the perovskite film layer is sandwiched between the first layer A and the second layer B.

[0012] The foregoing examples broadly outline various aspects, features, and technical advantages of examples according to the disclosure in order that the detailed description that follows may be better understood. It is further appreciated that aspects of the above described in the context of the illustrative examples are not required and that one or more operations and/or features may be excluded and/or other additional features/operations discussed herein may be included. Additional features and advantages will be described hereinafter. The conception and specific examples illustrated and described herein may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Such equivalent constructions do not depart from the spirit and scope of the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 A is a simplified illustration of one example of a reinforced perovskite film.

[0014] FIG. 1 B is schematic cross sectional view of one example of an optoelectronic device described herein.

[0015] FIG. 1 C is a cross sectional view of another example of an optoelectronic device described herein.

[0016] FIGS. 2A-2D are cross-sectional views illustrating different possible configurations of layers next to the reinforced perovskite layer of the optoelectronic device examples described herein.

[0017] FIG. 3A is a schematic illustrating an example architecture of a nanofiber-reinforced perovskite solar cell.

[0018] FIG. 3B is another schematic illustrating an example architecture of a nanofiber-reinforced perovskite solar cell demonstrating non-limiting examples of polymers used in the reinforcing polymeric nanofibers.

[0019] FIG. 4 is a schematic representation of an example of a photovoltaic device described herein, showing a perovskite layer “MAPbh” disposed between a hole transport layer “PTAA” (poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]) and an SnO2 electron transport layer, with silver and ITO electrode layers.

[0020] FIG. 5A is a scanning electron micrograph image of the surface of a cured perovskite layer with integrated nylon-6, 6 nanofibers, showing good coverage of the fibers.

[0021] FIG. 5B is a SEM micrograph showing a profile of the surface of the perovskite with the integrated nylon-6, 6 nanofibers.

[0022] FIG. 5C is a (backside) image of the reverse side of the slide of ITO, showing good permeation of the perovskite precursor solution through the mat of nylon nanofibers, with no evidence of air trapped between the perovskite and the ITO slide.

[0023] FIG. 6 is a graph illustrating testing for fracture resistance demonstrating that fibers significantly increase toughness. [0024] FIG. 7 is a graph illustrating comparison of the champion solar cells (A=0.12 cm²): the MAPbh:nylon-6,6 device resulted in higher efficiencies than the pristine MAPbh device due to improved current density.

[0025] FIG. 8 is a graph illustrating results of comparison of formation of Pbh in perovskite layers using X-ray diffraction measurements.

[0026] Corresponding reference characters indicate corresponding elements among the view of the drawings. The headings used in the figures do not limit the scope of the claims.

DETAILED DESCRIPTION

[0027] Aspects of the present disclosure relate to examples of nanofiber- reinforced perovskite films or materials for use with e.g., optoelectronic devices. In general, the nanofiber-reinforced perovskite film can include a layer of perovskite material; and a mat of polymeric nanofibers, and the layer of perovskite material can be dispersed in the mat of polymeric nanofibers to mitigate mechanical stresses in the film. Various other non-limiting examples are described herein.

[0028] 1.0 Introduction

[0029] Perovskite-based solar cells (PSC) have exhibited efficiencies in recent years competitive with the best silicon-based photovoltaics. Metal halide perovskites (“perovskites”) are a promising family of next-generation semiconducting materials, frequently demonstrated in photovoltaic (PV) applications with power conversion efficiencies (PCEs) comparable to crystalline silicon, but at a fraction of the processing cost and material usage. There are many possible compositions of metal halide perovskites, enabling tunability of performance and bandgaps that make perovskites ideal optoelectronic materials for applications including photodiodes, phototransistors, and photoconductors.

[0030] Despite these useful material properties, significant chemical and mechanical instabilities pose a major hurdle for the commercialization of perovskitebased technologies. These perovskite-based technologies require substantial improvements in thermomechanical and chemical stability to realize the long service lifetimes necessary to achieve the DOE SunShot goal of a $0.02-0.03 kWh^-1 Levelized Cost of Electricity (LCOE) by 2030. Studying approaches to improve the mechanical robustness of perovskites is a critical task, since the ionic bonding in these materials imparts an intrinsic fragility that must be overcome when scaling devices from lab-scale to module scale (given that shear stresses scale linearly with size).

[0031] There is a need to improve the stability of PSCs without sacrificing device efficiency or compatibility with applications that require physical flexibility. Electrospinning of nanofibers is inherently scalable and can be readily integrated with roll-to-roll industry-scale manufacturing on flexible substrates. A low-cost and scalable pathway to improve the thermomechanical and chemical stability of PSCs — two of the most significant hurdles to commercial viability - are important goals.

[0032] As described herein, the incorporation of polymer nanofibers into perovskite has the potential to overcome the exceptionally low fracture energies of the perovskite layer, by behaving much like rebar in concrete. Analysis of the effects of commodity polymer nanofibers on the overall chemical and thermomechanical stability of perovskite provides insight into understanding how different reinforcement frameworks help mitigate mechanical stresses in thin films.

[0033] It was surprisingly discovered that by providing a perovskite layer reinforced with polymeric nanofiber, a substantial improvement in fracture resistance of perovskite layers can be achieved, while retaining good power conversion efficiency when the reinforced perovskite layer is incorporated into, e.g., an optoelectronic device. Inspired by rebar in concrete, the present concept provides an alternative toughening strategy yet to be explored in perovskites - compositing with a tougher nanoscale material, such as nanoparticles or nanofibers. In addition to toughening, these nanofiber materials can also provide multifunctional enhancements such as improved optical properties demonstrated in applications such as color filters, LED encapsulation, and lenses.

[0034] One example of the inventive concept encompasses a reinforced perovskite film including a reinforced perovskite layer that comprises a mat of polymeric nanofibers permeated with a perovskite material. The film can further be implemented and/or embodied as an optoelectronic device and methods of making and using the same, where the optoelectronic device comprises a reinforced perovskite layer as an active medium that provides electrical charge carriers in response to incident illumination (for example, solar illumination), or as a medium into which charge carriers are injected for radiative recombination. In further examples, the reinforced perovskite layer comprises a mat of polymeric nanofibers permeated with a perovskite material. Other examples are described herein.

[0035] In some examples, a mat of nanofibers may comprise a material other than or in addition to polymeric nanofibers. However, without wishing to be limited by any particular theory, polymeric nanofibers may contribute to or otherwise facilitate light propagation and/or scattering throughout an optoelectronic device (e.g., a photovoltaic device), thereby increasing an amount of current that may be generated by the optoelectronic device. In some embodiments, optical properties of the polymeric nanofibers may be controlled during fabrication to optimize light propagation and/or scattering.

[0036] 2.0. Reinforced Perovskite Examples

[0037] Various examples (100) of reinforced perovskite shall now be described. In general, examples 100 include a reinforced layer of a metal halide perovskite material, comprising a layer of perovskite material and a mat of polymeric nanofibers, wherein the layer of perovskite material is dispersed in the mat of polymeric nanofibers. The perovskite material can be an active medium that provides electrical charge carriers in response to incident illumination. In some embodiments, the perovskite material is a metal halide perovskite, where the monovalent anion is a halide.

[0038] In some examples, the polymeric nanofibers comprise an organic polymer. Non-limiting examples of the organic polymer can include, for example, a nylon (e.g., nylon-6, 6), a polyethylene oxide/polyethylene glycol, a polyvinyl alcohol, or other hydrophilic material. Preferably, the organic polymer is resistant to solvents used in the making of the reinforced perovskite layer. The organic polymer may be crosslinked using technologies known in the art. Advantages of using crosslinked polymer can include, for example, minimizing solubility of the polymer nanofibers in organic solvents at processing temperatures, as well as strengthening the reinforcement provided by a mat of the polymeric nanofibers in the reinforced perovskite layer, or even modifying properties of the nanofibers to enhance power conversion efficiency of an optoelectronic device.

[0039] In some embodiments, said organic polymer may be hydrophilic. This is advantageous, inter alia, for optimizing performance and durability of the reinforced perovskite layer. In some embodiments, the nanofibers are monolithic. In some embodiments, said nanofibers may be of a type other than monolithic, for example, a co-axial core-shell nanofiber having an inner polymer component and an outer “sheath” component, said nanofiber generated by, for example, co-axial electrospinning techniques. In some embodiments, the polymeric nanofibers have an out diameter in a range of from about 50 nm to about 1000 nm (or about 100 nm to about 200 nm).

[0040] In further embodiments, the polymeric nanofibers are in the form of a mat. In some embodiments, the polymeric nanofibers are arranged randomly in the mat. The polymeric nanofibers may also be arranged with an axial orientation (i.e. , the fibers are substantially parallel), or with a biaxial orientation, including an orthogonal arrangement of nanofibers. The nanofibers may be arranged in a mat (e.g., randomly, axially, or biaxial ly) using techniques known in the art. The arrangement of polymeric nanofibers in the mat may be selected in order to optimize, for example, ease of formation of a reinforced layer of perovskite, mechanical strength and durability of the reinforced perovskite layer, and power conversion efficiency (PCE) in an optoelectronic device that incorporates the reinforced perovskite layer. In one aspect, the arrangement of polymeric nanofibers in the mat may ensure that 2 or more nanofibers “stack” on one another to improve mechanical strength and durability of the reinforced perovskite layer.

[0041] The inventors have surprisingly found that a reinforced perovskite layer of the inventive concept can exhibit at least an order of magnitude improvement in toughness of the layer when compared with a pristine perovskite layer (e.g., FIG. 6).

[0042] In some embodiments, the reinforced perovskite layer (and optoelectronic devices incorporating the reinforced perovskite layer) can exhibit improved thermomechanical and chemical stability, for example, under conditions of elevated humidity (e.g., 85% relative humidity) and temperature (e.g., 85°C) relative to the stability of pristine perovskite layers.

[0043] In some embodiments, a reinforced perovskite layer of the inventive concept has a thickness of the perovskite material in a range of from about 100 nm to about 2000 nm, from about 200 nm to about 1000 nm, from about 300 nm to about 600 nm, or even from about 300 nm to about 500 nm.

[0044] In some embodiments, a reinforced perovskite layer of the inventive concept has a thickness of the polymer nanofiber mat in a range of from about 100 nm to about 2000 nm, from about 200 nm to about 1000 nm, from about 300 nm to about 600 nm, or even from about 300 nm to about 500 nm, and most preferably the thickness of the polymer nanofiber mat is about 50 nm to 100 nm thicker than the layer of perovskite.

[0045] In a further aspect, the nanofibers within the mat of nanofibers may have diameters that are smaller than 1 of a thickness of the layer of perovskite material.

[0046] In some embodiments of the reinforced perovskite layer, the perovskite material is dispersed in the mat of polymeric nanofibers so as to leave no unfilled gaps within the perovskite layer. In some embodiments, the mat of polymeric nanofibers is essentially filled with perovskite material, leaving no gaps in the reinforced perovskite layer.

[0047] More specifically, referring to FIG. 1A, one example 100 of reinforced perovskite can take the form of reinforced perovskite film 102. In this example, the reinforced perovskite film 102 can include a perovskite layer 110 which is reinforced with a mat of nanofibers 120.

[0048] The perovskite layer 110 of the reinforced perovskite film 102 can include a metal halide perovskite. The nanofibers 120 can include polymeric nanofibers such as an organic polymer (e.g., nylon (such as nylon-6, 6), polyethylene oxide/polyethylene glycol, and polyvinyl alcohol; optionally cross-linked). Such polymeric nanofibers can be hydrophilic. In some examples, the mat of nanofibers 120 is randomly ordered. In some examples, the nanofibers of the mat of nanofibers 120 have diameters smaller than 14 the perovskite film thickness.

[0049] Referring to FIGS. 1 B and 10, other examples can include an optoelectronic device comprising a reinforced layer of a perovskite material, wherein the layer of perovskite material is reinforced with a mat of polymeric nanofibers. The reinforced layer of perovskite material can be incorporated into an optoelectronic device to increase the material toughness and durability of the optoelectronic device. For example, FIG. 1 B shows a simple schematic cross section of an exemplary embodiment of an optoelectronic device 112 comprising a stack 105, including a reinforced perovskite layer 110 which is reinforced with a mat of nanofibers 120. Reinforced perovskite layer 110 is sandwiched between a layer 130 and a layer 140. In some embodiments, layer 130 is an electron transport layer (ETL) and/or a hole blocking layer (HBL). In some embodiments, layer 140 is a hole-transport layer (HTL) and/or electron blocking layer (EBL).

[0050] In some examples, stack 105 is capped with at least one transparent electrode. The transparent electrode may include/be indium doped tin oxide, fluorine doped tin oxide, a nanowire network or mesh (e.g., nanowire comprising one or more previous oxides, or metallic nanowire), or a conductive polymer, such as PEDOT:PSS. In the example shown in FIG. 1 B, stack 105 comprises outer layers including an electrode layer (e.g., a metal electrode layer) 150 serving as a cathode, and an electrode layer (e.g., a metal electrode layer) 160 serving as an anode.

[0051] In another example embodiment, FIG. 1 C shows a schematic cross section of an exemplary embodiment of an optoelectronic device 112 comprising a stack 106 including a reinforced perovskite layer 110 reinforced with a mat of nanofibers 120, and the reinforced perovskite layer 110 is again sandwiched between layer 130 (ETL and/or HBL) and layer 140 (EBL and/or HTL). Stack 106 further comprises outer layers including electrode layer 150 serving as a cathode, and electrode layer 160 serving as an anode. A comparison of FIG. 1 B and FIG. 1 C shows that stacks 105 and 106 differ in the relative positions of the cathode and anode layers (i.e. , their positions are reversed).

[0052] Since layer 130 can be an ETL and/or an HBL, and layer 140 can be an HTL and/or an EBL, the stack can include several configurations of layers next to the reinforced perovskite layer, including those shown in FIGS. 2A-2D. Any suitable combination of these transport or blocking layers can be used in the optoelectronic device. A number of such types of transport and blocking layers are known to those having skill in the art. ETL and HBL can be interchangeable. Furthermore, HTL and EBL can be interchangeable.

[0053] In some example embodiments, the optoelectronic device 112 is a photovoltaic device, a light emitting diode, or a photodetector. The photovoltaic device may have an arrangement of components such as shown in FIGS. 1 B-1 C, 2A-2D (or other suitable arrangement of layers of the type commonly found in photovoltaic devices. [0054] FIGS. 3A-3B are schematics of example architectures of a nanofiber-reinforced perovskite solar cell, showing non-limiting examples of polymers used in the reinforcing polymeric nanofibers. While the nanofibers are shown this embodiment are in a biaxial configuration, in other embodiments the nanofibers can be in an axial configuration or even in a random configuration.

[0055] FIG. 4 is a schematic representation of an exemplary embodiment of a photovoltaic device of the inventive concept, showing a perovskite layer “MAPbh” with additives sandwiched between a hole transport layer “PTAA” (poly[bis(4- phenyl)(2,4,6-trimethylphenyl)amine]) and an SnO2 electron transport layer, with silver and ITO electrode layers.

[0056] Further Exemplary Features & Example Embodiments

[0057] In some embodiments, a perovskite layer reinforced with a mat of polymeric nanofibers can be used in metal halide perovskite-based optoelectronic devices such as light emitting diodes (LEDs).

[0058] In other aspects, the inventive concept includes a transistor comprising a perovskite layer as described herein. The inventive concept can also include an integrated circuit or a printed circuit board (PCB) that incorporates one or more perovskite layers as described herein.

[0059] In some embodiments, a process for making a photovoltaic device comprises depositing polymeric nanofibers through electrospinning onto atop a devicerelevant architecture (e.g., a glass/ITO/electron transport layer), forming a polymeric nanofiber mat. Subsequently, a perovskite ink (precursor perovskite solution) is deposited on top of the polymeric nanofiber mat, which then infiltrates the mat to make direct contact with the electron transport layer (ETL). On top of the perovskite/nanofiber nanocomposite so formed, a hole transport layer (HTL) is deposited, followed by a metallic cathode. Other stack architectures can be imagined, such as the nanofibers deposited on top of a cathode and HTL, with the ETL and anode then subsequently deposited on top of the perovskite/nanofiber nanocomposite.

[0060] Without wishing to be limited by any particular theory, the polymeric nanofibers act to mechanically reinforce the metal halide perovskite; it has been demonstrated that nylon-6, 6 nanofibers reinforce methylammonium lead iodide perovskite (MAPbh) by 25-fold.

[0061] Another aspect of the inventive concept pertains to a process for forming a reinforced perovskite layer involves depositing a precursor solution of a perovskite material onto polymeric nanofibers (e.g. a mat of polymeric nanofibers). For example, in some embodiments, nylon nanofibers (e.g., nylon-6, 6 nanofibers) are deposited on a conductive substrate prior to depositing a perovskite precursor solution onto the nanofibers. The conductive substrate includes indium doped tin oxide (optionally coated with SnOx), fluorine doped tin oxide, a nanowire network or mesh (e.g., nanowire comprising one or more previous oxides, or metallic nanowire), or a conductive polymer, such as PEDOT:PSS. The conductive substrate may be in the form of a substrate.

[0062] Certain additives may be included in a precursor solution of perovskite material to, for example, improve penetration through a mat of polymeric nanofibers. Additives can include, for example, surfactants (e.g., Tween-20, Triton X- 100, or sodium dodecyl sulfate) and an organic ligand (e.g., ammonium/halide salt such as 5-AVAI and analogs thereof). Additives with amino and ammonium functional groups may also be used. In these additives, amine groups exhibit strong Lewis acidbase interactions with Pb²⁺, a soft Lewis acid, and attached hydrogen on ammonium groups may coordinate halide species on the surface of perovskite grains through hydrogen bonding, improving chemical stability by reducing surface reactivity. Examples of additives includes 5-aminovaleric acid (5-AVA) and its ammonium/halide salts 5-AVAX (X=l, Cl, or Br; including 5-AVAI). These bifunctional additives include amino (or ammonium) and carboxyl groups, which enable the passivation of multiple defect types and linking of adjacent grains via Lewis acid-base coordination and hydrogen bonding interactions, thus improving stability and performance of perovskites.

[0063] In some embodiments, said perovskite layer comprise said additive. Without wishing to be limited to a particular theory, when additives are used as an aid for permeation of perovskite precursor solution into the nanofiber mat, they become a component of the reinforced perovskite layer.

[0064] Example Applications & Testing [0065] Example 1: A mat of nylon-6, 6 nanofibers was deposited onto a slide of ITO using electrospinning, and a perovskite precursor solution in DMF was layered onto the mat of nanofibers. To facilitate permeation of the perovskite precursor solution through the polymer nanofiber layer, an ammonium/halide salt (such as 5- ammoniumvaleric acid iodide (5-AVAI)) was included in the perovskite precursor solution. FIG. 5A is a scanning electron micrograph image of the surface of a cured perovskite layer with integrated nylon-6, 6 nanofibers, showing good coverage of the fibers. FIG. 5B is a SEM micrograph showing a profile of the surface of the perovskite with the integrated nylon-6, 6 nanofibers. FIG. 5C is an image of the reverse side of the slide of ITO, showing good permeation of the perovskite precursor solution through the mat of nylon nanofibers, with no evidence of air trapped between the perovskite and the ITO slide. It was observed that in some instances, permeation or the perovskite precursor solution through the layer of polymer nanofibers was incomplete without an additive such as AVAL

[0066] Example 2: When a reinforced perovskite layer including a randomly ordered mat of nylon-6, 6 nanofibers and the additives 5-AVAI and Tween 20 was tested for fracture resistance, a significant improvement in cohesive fracture resistance was observed relative to a layer of the same perovskite material with the same additives but lacking a polymeric nanofiber mat (see FIG. 6).

[0067] Example 3 (Performance of solar cells including a perovskite layer with or without polymeric nanofiber or additives): Performance of solar cells having perovskite layers was measured with or without a mat of nylon-6, 6 nanofibers and additives (ammonium salt 5-AVAI and surfactant Tween 20). FIG. 7 shows efficiency data for the solar cells, showing comparison of the effect of including the reinforced perovskite layer and additives.

[0068] Example 4 (Comparison of perovskite layers with and without mat of polymer nanofibers and additives): A comparison of formation of Pbb in perovskite layers was carried out, using X-ray diffraction measurements. Results are summarized in FIG. 8. The top line shows little to no formation of Pbh.

[0069] Example 5 (Surface Roughness): Atomic force microscopy was used to evaluate surface roughness of the nanofiber-incorporated perovskite films. Initial results showed that the root-mean-square (RMS) roughness of the film surface nearly doubled with the incorporation of the nanofiber mat, which was beyond a target roughness of less than 50% greater roughness than pristine perovskite films (i.e. , perovskite films without a mat of polymeric nanofibers). The pristine MAPbh roughness was measured to be 38 ± 9 nm compared to the MAPbh:nylon-6,6 nanocomposite roughness of 80 ± 20 nm. The film roughness was reduced by depositing a organic semiconductor hole transport layer PTAA, which brought down the RMS roughness within specification. After deposition of PTAA, the pristine MAPbh roughness was 31 ± 4 nm and the MAPbh:nylon-6,6 nanocomposite roughness was reduced to 46 ± 2 nm.

[0070] Example 6 (General procedure for fabricating devices):

[0071] The following procedure (previously conducted) may be used to fabricate certain embodiments of the inventive concept.

[0072] A conductive substrate (such as ITO-coated glass slides (2 cm x 2 cm)) was cleaned by first scrubbing the slides with a soft bristled toothbrush in a 1 % w/w aqueous Alconox detergent solution. The glass slides were then cleaned with sequential ultrasonic baths (10 min each) in dilute Alconox detergent solution, DI water, acetone, and then isopropanol before being dried with a N2 gas gun. The ITO layer was then coated with tin oxide as follows. A 15% tin oxide suspension in water was diluted to 5% tin oxide using deionized water and the resulting dilution was stirred for 15 min, which was then filtered with a 0.2 pm PTFE syringe filter. The ITO slides were treated in oxygen plasma at 60 W for 30 s (OptiGlow ACE) and the tin oxide solution was spin- coated on top of the ITO layer at 4000 RPM for 30 s. The resulting films were dried in air at 150 °C for 1 h. After drying, the ITO slides were treated in oxygen plasma at 30 W for 30 s.

[0073] Prior to depositing perovskite for the fiber-composite samples, electrospun nanofibers were deposited according to the following procedure. A 5% w/w solution of nylon-6, 6 in 98% formic acid was kept stirring at 60 °C for 4 h. The solution was drawn through a 0.2 pm filter while electrospinning. The following parameters were optimized for electrospinning: 22 kV, 120mm working distance, flow rate of 0.2 mL h^-1, 30 °C chamber temperature, and 15% relative humidity. A deposition time was calibrated to produce films 400 nm thick. [0074] Samples were treated in oxygen plasma at 30 W for 30 s after nanofiber deposition. For all samples, 0.9 M MAPbh perovskite precursor solution (1 :3 lead acetate trihydrate:methylammonium iodide) in DMF was spin-coated at 2000 RPM on top of the slides under nitrogen for 75 s. The slides were annealed at 100 °C for 5 min to form the perovskite. A 15 mg mL^-1 solution of PTAA in anhydrous toluene with 10 pL mL^-1 of 170 mg mL^-1 bis(trifluoromethane)sulfonamide lithium (LiTFSI) in anhydrous acetonitrile and 6 pL mL^-1 of 4-tert-butylpyridine (tBP) as dopants was then spin-coated on top of the perovskite at 4000 rpm for 45 s to form a layer 30 nm thick. Next, the slides were annealed on a hotplate at 75 °C for 5 min. Finally, a 150 nm thick layer of Ag was deposited using e-beam physical vapor deposition through a templated shadow mask.

[0075] Additional Examples for Integrating nanofibers into perovskite layers

[0076] Nanofibers are highly scalable through several fabrication pathways, including electrospinning, melt-blowing, and centrifugal spinning. Of these manufacturing approaches, electrospinning is the most attractive due to its low cost, scalability, and capacity for producing large quantities of nanofibers. Electrospinning also enables a high degree of tunability with process parameters and polymers that can be used, providing control over properties such as fiber dimensions, orientation, and surface chemistry.

[0077] In one example, electrospun nanofibers can be incorporated into methylammonium lead iodide perovskite layers, using nylon-6, 6 as the nanofiber material due to its excellent thermal, chemical, and mechanical properties. These nanofibers can first be deposited onto an electron transport layer and then subsequently infiltrated with the perovskite via one-step solution deposition. In example configurations, a significant increase in the cohesive fracture energy of the nanocomposite material was observed with no decrease in device efficiency; which was attributed to beneficial scattering of incident light off the nanofibers.

[0078] Stated another way, methylammonium lead iodide (MAPbh) can be nanocomposited with nylon-6, 6 nanofibers to augment the film toughness. The fracture resistance, Gc, increases over 500% in nylon-6, 6 reinforced films to 2.34 ± 1 .67 J m^-2 from 0.40 ± 0.16 J m^-2 for pristine MAPbh. The nanocomposites were observed via scanning electron microscopy (SEM) and atomic force microscopy (AFM) to show complete penetration of the perovskite through the nanofibers, and x-ray diffraction (XRD) showed similar quality films, but with some decrease in crystalline orientation for the nanocomposite films. Furthermore, we show an increase in power conversion efficiencies between the pristine and nylon-6, 6:MAPbh devices from 11 .0 ± 2.1 % to 13.8 ± 1 .1 %, respectively. The surprising device efficiency for the nanocompsites is shown to likely be due to beneficial in-plane light scattering from the nanofibers.

[0079] As used herein, the term “perovskite” can include “metal halide perovskite” which encompasses as a material with a chemical formula ABXs where A is a monovalent cation, B is a divalent metal cation, and X is a monovalent halide (or halide containing) anion. All three components (i.e. , A, B, or X) can comprise either a homogeneous or heterogeneous mixture of elements and molecules (e.g., A can be some composition of methylammonium (CH3NH3 ⁺), formamidinium (CH3(NH2)2 ⁺), Cs⁺, etc., B some composition Pb²⁺, Sn²⁺, Ge²⁺, and/or other divalent metal cations, and X is typically some composition of Cl", Br", I", BF4", PFe", SCN", etc.). One example of a perovskite molecular formula would be CHsNHsPbh while another would be CSO O5[(CH3NH3)o.17(CH3(NH2)2)o.83]o.95Pb(lo.83Bro.17)3.

[0080] It should be understood from the foregoing that, while particular embodiments have been illustrated and described, various modifications can be made thereto without departing from the spirit and scope of the inventive concept as will be apparent to those skilled in the art. Such changes and modifications are within the scope and teachings of this inventive concept as defined in the claims appended hereto.

Claims

CLAIMS What is claimed is:

1 . A reinforced perovskite film comprising: a layer of perovskite material; and a mat of polymeric nanofibers; wherein the layer of perovskite material is dispersed in the mat of polymeric nanofibers.

2. The reinforced perovskite film of claim 1 , wherein the perovskite material is an active medium that provides electrical charge carriers in response to incident illumination.

3. The reinforced perovskite film of claim 1 , wherein the perovskite material comprises a metal halide perovskite.

4. The reinforced perovskite film of claim 1 , wherein the polymeric nanofibers comprise an organic polymer.

5. The reinforced perovskite film of claim 1, wherein the polymeric nanofibers are hydrophilic.

6. The reinforced perovskite film of claim 1 , wherein the mat of polymeric nanofibers is randomly ordered.

7. The reinforced perovskite film of claim 1 , wherein the layer of perovskite material has a thickness in a range of from about 300 nm to about 600 nm.

8. The reinforced perovskite film of claim 1 , wherein the mat of polymeric nanofibers has a thickness in a range of from about 300 nanometers to about 600 nanometers. The reinforced perovskite film of claim 1 , wherein the mat of nanofibers have diameters smaller than 1 a thickness of the layer of perovskite material. The reinforced perovskite film of claim 1 , wherein the reinforced perovskite film is sandwiched between a hole blocking layer and an electron blocking layer. An optoelectronic device, comprising: a plurality of layers comprising: a reinforced perovskite film layer comprising: a layer of perovskite material, and a mat of polymeric nanofibers, wherein the layer of perovskite material is dispersed in the mat of polymeric nanofibers. The optoelectronic device of claim 11 , further comprising: a first layer A comprising an electron transport layer (ETL); and a second layer B comprising a hole-transport layer (HTL), wherein the reinforced perovskite film layer is sandwiched between the first layer A and the second layer B. The optoelectronic device of claim 11 , wherein the plurality of layers is capped with at least one electrode. The optoelectronic device of claim 11 , wherein the perovskite material is an active medium that provides electrical charge carriers in response to incident illumination. A method of making a reinforced perovskite film as in one of claims 1 -10.