Photoelectrodes and methods of making and use thereof

Abstract

The disclosed subject matter relates to photoelectrodes and methods of making and use thereof. Disclosed herein are photoelectrodes comprising: an insulator layer disposed on a light absorbing layer; a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer; and a plurality of particles disposed on the insulator layer, wherein a least a portion of a particle is in physical and electrical contact with at least a portion of a protrusion. Also disclosed herein are methods of making said photoelectrodes, comprising: patterning a reactive material in an ordered array on the insulator layer; annealing such that the reactive material reacts with and diffuses through the insulator layer, thereby forming a plurality of spikes comprising the reactive material which penetrate through the insulator layer to the light absorbing layer; subsequently removing the reactive material; and subsequently depositing the catalyst material.

Description

[0001] 10046-662W01; 8574 YU PHOTOELECTRODES AND METHODS OF MAKING AND USE THEREOF CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority to U. S. Provisional Application No.

[0002] 63 / 745,899, filed January 16, 2025, which is hereby incorporated herein by reference in its entirety.

[0003] STATEMENT OF GOVERNMENT SUPPORT

[0004] This invention was made with government support under Grant no. CBET2109842, Grant no. DMR1720595, Grant no. DMR2308817 and Grant no. ECCS2025227 awarded by the National Science Foundation. The government has certain rights in the invention.

[0005] BACKGROUND

[0006] Solar powered water splitting and other photoelectrochemical reactions offer routes to the generation of hydrogen or other high-value chemicals using renewable energy sources.

[0007] Commercially viable technologies for solar water splitting and fuel generation have been hampered by cost and the tendency of efficient solar absorbing materials to degrade in the presence of water splitting or fuel generating reactions. Metal-insulator-semiconductor (MIS) photoelectrodes for solar water splitting and fuel generation offer a route to addressing the latter issue by covering the semiconductor with a chemically stable protective layer, but these layers are typically electrically insulating and block the flow of photogenerated electrons and / or holes to the surface of the device at which the water splitting or fuel generation reactions take place. Successfully addressing these issues would provide a foundation for the development of a clean, economically viable technology for generation of hydrogen and other high-value chemicals for energy storage, transport, and chemical synthesis applications. The compositions, devices, and methods discussed herein address these and other needs.

[0008] SUMMARY

[0009] In accordance with the purposes of the disclosed compositions, methods, and systems as embodied and broadly described herein, the disclosed subject matter relates to photoelectrodes, such as metal-insulator-semiconductor photoelectrodes, and methods of making and use thereof.

[0010] For example, disclosed herein are photoelectrodes comprising: a light absorbing layer; an insulator layer disposed on the light absorbing layer; and a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer, such that each protrusion is in physical and electrical contact with the light absorbing layer; and a plurality of particles disposed on the insulator layer, wherein a least a portion of at least one of the particles is in physical and electrical contact with at least a portion of one of the protrusions (preferably, wherein at least a portion of each of the particles is in10046-662W01; 8574 YU physical and electrical contact with at least a portion of one of the protrusions); and wherein the plurality of particles and optionally the plurality of protrusions comprise a catalyst material.

[0011] In some examples, the light absorbing layer comprises silicon, gallium arsenide, AlGaAs, InP, InGaP, InAlP, AlP, InGaAsN, InGaAs, GaN, InGaN, AlInGaN, AlGaN, SiGe, SiC, CdTe, CdSe, ZnO, ZnSe, ZnTe, CdZnTe, SnS2, Zn3P2, ZnP2, Zn3As2, TiO2, hybrid organic-inorganic perovskite compounds, copper oxides, SrTiO3, MoS2, GaSe, SnS, CuInGaSe2, a-Si:H (hydrogenated amorphous silicon), bismuth vanadate (BiVO4), iron oxide (Fe2O3), an organic / molecular material (e.g., such as those used as solar absorbers in organic solar cells), or a combination thereof. In some examples, the light absorbing layer comprises silicon.

[0012] In some examples, the light absorbing layer has an average thickness of from 50 nanometers (nm) to 500 micrometers (microns, pm).

[0013] In some examples, the light absorbing layer further comprises a doped region. In some examples, the doped region comprises doped silicon. In some examples, the doped region comprises p+doped silicon. In some examples, the doped region comprises boron doped silicon. In some examples, the doped region comprises a doped layer having an average thickness of from 10 nm to 500 pm.

[0014] In some examples, the light absorbing layer comprises Si with a buried pn junction. In some examples, the insulator layer comprises SiO2, TiO2, silicon nitride, silicon oxynitride, aluminum oxide, strontium titanate, tungsten oxide (WO3), aluminum nitride, boron nitride, aluminum gallium nitride, or a combination thereof. In some examples, the insulator layer comprises SiO2.

[0015] In some examples, the insulator layer has an average thickness of 20 nm or more, 50 nm or more, 75 nm or more, or 90 nm or more.

[0016] In some examples, the catalyst material comprises a metal selected from the group consisting of Ni, Pt, Mo, Co, Ru, Ir, Fe, or a combination thereof. In some examples, the catalyst material comprises Ni. In some examples, the catalyst material comprises an oxygen evolution reaction catalyst.

[0017] In some examples, each of the protrusions in the plurality of protrusions has an average characteristic dimension of from 0.1 nm to 10 pm.

[0018] In some examples, each of the protrusions in the plurality of protrusions has an average characteristic dimension that varies with the thickness of the insulator layer.

[0019] In some examples, the ordered array is a linear array, a triangular' array, a hexagonal array, or a quadrilateral array. In some examples, the ordered array is a hexagonal array.

[0020] In some examples, the ordered array is a two dimensional array defined by a first unit cell10046-662W01; 8574 YU having a first principle axis and a second principle axis with a first included angle between the first principle axis and the second principle axis. In some examples, the length of the first principle axis and / or the second principle axis independently is from 10 nanometers (nm) to 50 micrometers (microns, pm), such as from 50 nanometers to 10 micrometers. In some examples, the length of the first principle axis and the second principle axis are the same. In some examples, the first included angle is from 30° to 150°, such as from 60° to 120°. In some examples, the first unit cell is in the shape of a triangle or a quadrilateral.

[0021] In some examples, the plurality of protrusions are dispersed across the insulator layer laterally such that the areal density of the plurality of protrusions within the insulator layer is from 102to 1013protrusions per cm2of the insulator layer. In some examples, the plurality of protrusions are dispersed throughout the insulator layer such that the areal density of the plurality of protrusions within the insulator layer is from 2 x 107to 8 x 109protrusions per cm2of the insulator layer.

[0022] In some examples, the plurality of particles have an average height of from 1 nm to 1 pm, such as from 10 nm to 500 nm.

[0023] In some examples, the plurality of particles and / or the plurality of protrusions cover from 1% to 100%, from 5% to 90%, or from 5% to 80% of the top surface of the insulator layer. In some examples, the plurality of particles and / or the plurality of protrusions cover 10% or more, 25% or more, 35% or more, 50% or more, or 70% or more of the top surface of the insulator layer.

[0024] Also disclosed herein are methods of making a photoelectrode, the method comprising: patterning a reactive material on an insulator layer, the reactive material being patterned in an ordered array and the insulator layer being disposed on a light absorbing layer, such that the insulator layer is disposed between the light absorbing layer and the ordered array of the reactive material, thereby forming a precursor electrode; annealing the precursor electrode such that the reactive material reacts with and diffuses through the insulator layer, thereby forming a plurality of spikes comprising the reactive material, wherein each of the spikes penetrates through the insulator layer to the light absorbing layer, such that each of the spikes is in physical and electrical contact with the light absorbing layer, thereby forming a spiked electrode; removing the reactive material from the spiked electrode, thereby forming an intermediate electrode; and subsequently depositing a catalyst material on the intermediate electrode; thereby forming a photoelectrode comprising: the insulator layer disposed on the light absorbing layer; a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer, such that each of the protrusions is in physical and10046-662W01; 8574 YU electrical contact with the light absorbing layer; and a plurality of particles disposed on the insulator layer, wherein a least a portion of at least one of the particles is in physical and electrical contact with at least a portion of one of the protrusions (preferably, wherein at least a portion of each of the particles are in physical and electrical contact with at least a portion of one of the protrusions); and wherein the plurality of particles and optionally the plurality of protrusions comprise a catalyst material. In some examples, the photoelectrode comprises any of the photoelectrodes disclosed herein.

[0025] In some examples, the method further comprises forming the insulator layer on the light absorbing layer. In some examples, forming the insulator layer comprises thermal oxidation, electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof, or a combination thereof. In some examples, forming the insulator layer comprises thermal oxidation. In some examples, thermal oxidation comprises heating the light absorbing layer at a temperature of from 800°C to 1200°C in the presence of oxygen for an amount of time of from 10 seconds to 30 hours.

[0026] In some examples, the method further comprises doping the light absorbing layer to form a doped region prior to forming the insulator layer. In some examples, doping the light absorbing layer comprises annealing the light absorbing layer in the presence of a dopant source. In some examples, the dopant source comprises a boron source. In some examples, annealing comprises heating the insulator layer at a temperature of from 100°C to 1800°C in the presence of the dopant source for an amount of time of from 10 seconds to 100 hours.

[0027] In some examples, patterning the reactive material comprises lithography, such as electron beam lithography, optical lithography, nanoimprint lithography, nanoparticle lithography such as nanosphere lithography, focused ion beam lithography, photolithography, or a combination thereof. In some examples, patterning the reactive material comprises nanosphere lithography. In some examples, patterning the reactive layer comprises forming a self-assembled nanoparticle monolayer via the methods of WO 2025 / 096777 followed by depositing the reactive material, for example via thin film deposition such as sputtering.

[0028] In some examples, the reactive material comprises Al.

[0029] In some examples, annealing the precursor electrode comprises heating the precursor electrode at a temperature of from 300°C to 1500°C for an amount of time of from 1 minute to 48 hours.10046-662W01; 8574 YU In some examples, removing the reactive material comprises etching the reactive material. In some examples, etching the reactive material comprises contacting the reactive material with an etchant. In some examples, the etchant comprise H3PO4.

[0030] In some examples, depositing the catalyst material comprises electrodeposition, such as electroplating.

[0031] Also disclosed herein are methods of use of any of the photoelectrodes disclosed herein or a photoelectrode made by any of the methods disclosed herein. In some examples, the method comprises using the photoelectrode as an electrode in a photoelectrochemical reaction. In some examples, the method comprises using the photoelectrode as an electrode in an energy conversion device, a charge storage device, an electronic device, or a combination thereof. In some examples, the device comprises an energy conversion device, the energy conversion device comprising a solar cell, a fuel cell, a photovoltaic cell, or a combination thereof.

[0032] Also disclosed herein are photoelectrochemical cells comprising: a working electrode in electrochemical contact with a fluid and one or more additional electrodes in electrochemical contact with the fluid, wherein the working electrode comprises any of the photoelectrodes disclosed herein or a photoelectrode made by any of the methods disclosed herein. In some examples, the fluid comprises a fuel precursor. In some examples, the fuel precursor comprises water, carbon dioxide, or a combination thereof.

[0033] Also disclosed herein are methods of use of any of the photoelectrochemical cells disclosed herein for photoelectrochemical fuel generation. In some examples, the fluid comprises a fuel precursor and the method comprises illuminating the photoelectrode in contact with the fuel precursor with electromagnetic radiation that overlaps at least a portion of the photon energy range absorbed by the light absorbing, thereby providing photogenerated electrons or holes in the light absorbing which are transported to the catalyst material at the interface between the photoelectrode and the fuel precursor which participate in the desired electrochemical reaction to thereby convert the fuel precursor to a fuel. In some examples, the method further comprises collecting the fuel. In some examples, the electromagnetic radiation comprises light and the light is provided by a light source, wherein the light source comprises an artificial light source or a natural light source. In some examples, the electromagnetic radiation comprises sunlight. In some examples, the method comprises solar powered photoelectrochemical fuel production. In some examples, the fuel precursor comprises water and the method comprises photoelectrochemical water splitting. In some examples, the fuel precursor comprise water, the electromagnetic radiation comprises sunlight, and the method comprises solar water splitting. In some examples, the fuel comprises H2and the method comprises photoelectrochemical hydrogen10046-662W01; 8574 YU generation. In some examples, the fuel precursor comprises carbon dioxide and the method comprises photoelectrochemical reduction of CO2. In some examples, the fluid has a pH of 8 or more and the photoelectrode is stable for 24 hours or more. In some examples, the fluid has a pH of 14 and the photoelectrode is stable for 48 hours or more.

[0034] Also disclosed herein are devices comprising any of the photoelectrodes disclosed herein or a photoelectrode made by any of tire methods disclosed herein. In some examples, the device comprises an energy conversion device, a charge storage device, an electronic device, or a combination thereof. In some examples, the device comprises an energy conversion device, the energy conversion device comprising a solar cell, a fuel cell, a photovoltaic cell, or a combination thereof.

[0035] Additional advantages of the disclosed compositions, systems, and methods will be set forth in part in the description which follows, and in part will be obvious from the description. The advantages of the disclosed compositions, systems, and methods will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosed compositions, systems, and methods, as claimed.

[0036] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

[0037] BRIEF DESCRIPTION OF THE FIGURES

[0038] The accompanying figures, which are incorporated in and constitute a part of this specification, illustrate several aspects of the disclosure, and together with the description, serve to explain the principles of the disclosure.

[0039] Figure 1. Potential issues in Al thin film reaction.

[0040] Figure 2. Surface morphology of Al thin film reaction.

[0041] Figure 3. Surface morphology of Al thin film reaction.

[0042] Figure 4. Decay in photocurrent.

[0043] Figure 5. Colloidal lithography for Si -based MIS photoanodes.

[0044] Figure 6. Colloidal lithography for Si-based MIS photoanodes.

[0045] Figure 7. Ni coverage optimization.

[0046] Figure 8. PEC performance thin-film vs. patterned photoanode.

[0047] Figure 9. SEM image of a patterned photoanode.

[0048] Figure 10. LSV curve for patterned and thin-film photoanode.10046-662W01; 8574 YU Figure 11. Process flow and SEM images of fabrication of patterned photoanode.

[0049] Figure 12. SEM images of patterned photoanode with different Ni electrodeposition time (at the same voltage of 3.5 V) (a) 10 minutes (b) 15 minutes (c) 20 minutes (d) Unpatterned photoanode (electrodeposition at 3.5 V for 15 minutes).

[0050] Figure 13. Schematic diagram of an example photoelectrode as disclosed herein according to one implementation.

[0051] Figure 14. Schematic diagram of an example photoelectrode as disclosed herein according to one implementation.

[0052] Figure 15. Schematic diagram of an example photoelectrode as disclosed herein according to one implementation.

[0053] Figure 16. Schematic diagram of an example photoelectrode as disclosed herein according to one implementation.

[0054] Figure 17. Schematic diagram of an example photoelectrode as disclosed herein according to one implementation.

[0055] Figure 18. Schematic diagram of an example photoelectrode as disclosed herein according to one implementation.

[0056] Figure 19. Schematic diagram of an example spiked electrode as disclosed herein according to one implementation (e.g., the photoelectrode of Figure 13 before catalyst deposition).

[0057] Figure 20. Schematic diagram of an example spiked electrode as disclosed herein according to one implementation (e.g., the photoelectrode of Figure 14 before catalyst deposition).

[0058] Figure 21. Schematic diagram of an example spiked electrode as disclosed herein according to one implementation (e.g., the photoelectrode of Figure 15 before catalyst deposition).

[0059] Figure 22. Schematic diagram of an example spiked electrode as disclosed herein according to one implementation (e.g., the photoelectrode of Figure 16 before catalyst deposition).

[0060] Figure 23. Schematic diagram of an example spiked electrode as disclosed herein according to one implementation (e.g., the photoelectrode of Figure 17 before catalyst deposition).

[0061] Figure 24. Schematic diagram of an example spiked electrode as disclosed herein according to one implementation (e.g., the photoelectrode of Figure 18 before catalyst deposition).10046-662W01; 8574 YU DETAILED DESCRIPTION

[0062] Before the present compositions, methods, and systems are disclosed and described, it is to be understood that the aspects described below are not limited to specific synthetic methods or specific reagents, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0063] Also, throughout this specification, various publications are referenced. The disclosures of these publications in their entireties are hereby incorporated by reference into this application in order to more fully describe the state of the art to which the disclosed matter pertains. The references disclosed are also individually and specifically incorporated by reference herein for the material contained in them that is discussed in the sentence in which the reference is relied upon.

[0064] In this specification and in the claims that follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

[0065] Throughout the description and claims of this specification the word “comprise” and other forms of the word, such as “comprising” and “comprises,” means including but not limited to, and is not intended to exclude, for example, other additives, components, integers, or steps. As used in the specification and in the claims, the term “comprising” can include the aspects “consisting of” and “consisting essentially of.”

[0066] As used in the description and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a composition” includes mixtures of two or more such compositions, reference to “an agent” includes mixtures of two or more such agents, reference to “the component” includes mixtures of two or more such components, and the like.

[0067] “Optional” or “optionally” means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event or circumstance occurs and instances where it does not.

[0068] Ranges can be expressed herein as from “about” one particular value, and / or to “about” another particular' value. By “about” is meant within 5% of the value, e.g., within 4, 3, 2, or 1% of the value. When such a range is expressed, another aspect includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.10046-662W01; 8574 YU “Exemplary” means “an example of’ and is not intended to convey an indication of a preferred or ideal embodiment. “Such as” is not used in a restrictive sense, but for explanatory purposes.

[0069] Values can be expressed herein as an “average” value. “Average” generally refers to the statistical mean value.

[0070] By “substantially” is meant within 5%, e.g., within 4%, 3%, 2%, or 1%.

[0071] It is understood that throughout this specification the identifiers “first” and “second” are used solely to aid in distinguishing the various components and steps of the disclosed subject matter. The identifiers “first” and “second” are not intended to imply any particular order, amount, preference, or importance to the components or steps modified by these terms.

[0072] References in the specification and concluding claims to parts by weight of a particular element or component in a composition denotes the weight relationship between the element or component and any other elements or components in the composition or article for which a part by weight is expressed. Thus, in a compound containing 2 parts by weight of component X and 5 parts by weight component Y, X and Y are present at a weight ratio of 2:5, and are present in such ratio regardless of whether additional components are contained in the compound.

[0073] A weight percent (wt. %) of a component, unless specifically stated to the contrary, is based on the total weight of the formulation or composition in which the component is included.

[0074] The term “or combinations thereof’ as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB.

[0075] Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0076] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0077] Compositions, Systems, and Methods

[0078] Disclosed herein are compositions, systems, and methods. For example, disclosed herein are photoelectrodes and methods of making and use thereof.

[0079] Photoelectrodes

[0080] Disclosed herein are photoelectrodes. Referring now to Figure 13-Figure 18, disclosed10046-662W01; 8574 YU herein are photoelectrodes 100 comprising a light absorbing layer 110; an insulator layer 120 disposed on the light absorbing layer 110; a plurality of protrusions 130 arranged in an ordered array, wherein each protrusion penetrates through the insulator layer 120 to the light absorbing layer 110, such that each protrusion 130 is in physical and electrical contact with the light absorbing layer 110; and a plurality of particles 140 disposed on the insulator layer, wherein at least a portion of at least one of the particles 140 is in physical and electrical contact with at least a portion of one of the protrusions (preferably, wherein at least a portion of each of the particles 140 is in physical and electrical contact with at least a portion of one of the protrusions); wherein the plurality of particles 140 and optionally the plurality of protrusions 130 comprise a catalyst material (e.g., wherein the plurality of particles 140 comprise the catalyst material, or wherein the plurality of particles 140 and the plurality of protrusions 130 each comprise the catalyst material).

[0081] The light absorbing layer 110 can comprise any material consistent with the methods, devices, and systems disclosed herein. In some examples, the light absorbing layer 110 comprises a semiconductor and / or other light absorber (e.g., molecular absorber, light trapping structure, etc.). For example, the light absorbing layer 110 can comprise silicon, gallium arsenide, AIGaAs, InP, InGaP, InAlP, A1P, InGaAsN, InGaAs, GaN, InGaN, AlInGaN, AlGaN, Si Ge, SiC, CdTe, CdSe, ZnO, ZnSe, ZnTe, CdZn'Te, SnS2, Zn3P2, ZnP2, Zn? As2, T1O2, hybrid organic-inorganic perovskite compounds, copper oxides, SrTiCh, M0S2, GaSe, SnS, CuInGaSe2, a-Si: H (hydrogenated amorphous silicon), bismuth vanadate (BiVO-, iron oxide (R2O3), an organ! c / molecular material (e.g., such as those used as solar absorbers in organic solar cells), or a combination thereof. In some examples, the light absorbing layer 110 comprises silicon.

[0082] In some examples, the light absorbing layer comprises multiple semiconductor materials (e.g., Si plus amorphous Si (a-Si: H), Si plus SiC, GaAs plus other compound semiconductors, etc.), with each potentially being doped or in a pn junction structure.

[0083] The light absorbing layer 110 has a top surface 112 and a bottom surface 114 opposite and spaced apart from the top surface 112. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 are substantially parallel to each other.

[0084] The light absorbing layer 110 has an average thickness, the average thickness being the average dimension from the top surface 112 to the bottom surface 114. The average thickness of the light absorbing layer 110 can, for example, be 50 nanometers (nm) or more (e.g., 75 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 110046-662W01; 8574 YU micrometer (micron, pm) or more, 2 pm or more, 3 µm or more, 4 µm or more, 5 µm or more, 10 µm or more, 15 pm or more, 20 pm or more, 25 pm or more, 30 pm or more, 40 pm or more, 50 pm or more, 75 pm or more, 100 pm or more, 125 pm or more, 150 pm or more, 175 pm or more, 200 pm or more, 225 pm or more, 250 pm or more, 300 pm or more, 350 pm or more, 400 pm or more, or 450 pm or more). In some examples, the average thickness of the light absorbing layer 110 can be 500 micrometers (micron, pm) or less (e.g., 450 pm or less, 400 pm or less, 350 pm or less, 300 pm or less, 250 pm or less, 225 pm or less, 200 pm or less, 175 pm or less, 150 pm or less, 125 pm or less, 100 pm or less, 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, 10 pm or less, 5 pm or less, 4 pm or less, 3 pm or less, 2 pm or less, 1 pm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, or 75 nm or less). The average thickness of the light absorbing layer 110 can range from any of the minimum values described above to any of the maximum values described above. For example, the average thickness of the light absorbing layer can be from 50 nm to 500 pm (e.g., from 50 nm to 1 pm, from 1 pm to 10 pm, from 10 pm to 500 pm, from 50 nm to 400 pm, from 100 nm to 500 pm, or from 100 nm to 400 pm).

[0085] The top surface 112 and the bottom surface 114 of the light absorbing layer 110 can, independently, be any shape. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 can, independently, be substantially circular, ovate, ovoid, elliptic, triangular, rectangular, polygonal, etc. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 can be substantially the same shape. In some examples, the top surface 112 and the bottom surface 114 of the light absorbing layer 110 can be substantially rectangular. In some examples, the top surface 112 and / or the bottom surface 114 of the light absorbing layer 110 can have a texture or roughness.

[0086] The light absorbing layer 110 has an average lateral dimension (e.g., diameter when the light absorbing layer 110 is circular; diagonal when the light absorbing layer 110 is substantially rectangular, etc.) of 1 micrometer (micron, pm) or more (e.g., 2 pm or more, 3 pm or more, 4 pm or more, 5 µm or more, 10 pm or more, 15 pm or more, 20 pm or more, 25 pm or more, 30 pm or more, 40 pm or more, 50 pm or more, 75 pm or more, 100 pm or more, 125 pm or more, 150 pm or more, 200 pm or more, 250 pm or more, 300 µm or more, 400 pm or more, 500 pm or more, 750 pm or more, 1 millimeter (mm) or more, 1.25 mm or more, 1.5 mm or more, 2 mm or more, 2.5 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, 25 mm or more, 30 mm or more, 40 mm or more, 50 mm or more, 7510046-662W01; 8574 YU mm or more, 100 mm or more, 125 mm or more, 150 mm or more, 200 mm or more, 250 mm or more, 300 mm or more, 400 mm or more, 500 mm or more, 750 mm or more, 1 meter (m) or more, 2 m or more, 3 m or more, 4 m or more, or 5 m or more). In some examples, the average lateral dimension of the light absorbing layer 110 is 10 meters (m) or less (e.g., 9 m or less, 8 m or less, 7 m or less, 6 m or less, 5 m or less, 4 m or less, 3 m or less, 2 m or less, 1 m or less, 750 mm or less, 500 mm or less, 400 mm or less, 300 mm or less, 250 mm or less, 200 mm or less, 150 mm or less, 125 mm or less, 100 mm or less, 75 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less, 10 mm or less, 5 mm or less, 4 mm or less, 3 mm or less, 2.5 mm or less, 2 mm or less, 1.5 mm or less, 1.25 mm or less, 1 mm or less, 750 micrometer (pm) or less, 500 pm or less, 400 pm or less, 300 pm or less, 250 pm or less, 200 pm or less, 150 pm or less, 125 pm or less, 100 pm or less, 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, 10 pm or less, 5 pm or less, 4 pm or less, 3 pm or less, or 2 pm or less). The average lateral dimension of the light absorbing layer 110 can range from any of the minimum values described above to any of the maximum values described above. For example, the average lateral dimension of the light absorbing layer 110 can be from 1 pm to 10 m (e.g., from 1 pm to 1 mm, from 1 mm to 10 m, from 1 pm to 100 pm, from 100 pm to 10 mm, from 10 mm to 10 m, from 1 pm to 10 pm, from 10 pm to 100 pm, from 100 pm to 1 mm, from 1 mm to 10 mm, from 10 mm to 100 mm, from 100 mm to 1 in, from 1 m to 10 m, from 1 pm to 1 m, from 1 pm to 100 mm, from 1 pm to 50 mm, from 1 pm to 10 mm, from 10 pm to 300 mm, from 100 pm to 300 mm, from 1 mm to 300 mm, from 25 mm to 300 mm, or from 1 centimeter (cm) to 30 cm).

[0087] In some examples, the light absorbing layer 110 can further comprise a doped region, the doped region including a dopant. The dopant can, for example, comprise an n-type dopant or a p-type dopant. For example, the light absorbing layer can comprise a doped region such that the light absorbing layer comprises a buried pn junction.

[0088] In some examples, the doped region comprises doped silicon. In some examples, the doped region comprises n-type doped silicon (e.g., silicon doped with As and / or P). In some examples the doped region comprises p+doped silicon. In some examples, the doped region comprises boron doped silicon. In some examples, the light absorbing layer comprises Si with a buried pn junction.

[0089] The doped region can, for example, comprise a doped layer. In some examples, the doped layer can have an average thickness of 10 nanometers (nm) or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 75 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more,10046-662W01; 8574 YU 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, µm) or more, 2 µm or more, 3 µm or more, 4 µm or more, 5 µm or more, 10 µm or more, 15 µm or more, 20 µm or more, 25 µm or more, 30 µm or more, 40 µm or more, 50 µm or more, 75 µm or more, 100 µm or more, 125 µm or more, 150 µm or more, 175 µm or more, 200 µm or more, 225 µm or more, 250 µm or more, 300 µm or more, 350 µm or more, 400 µm or more, or 450 µm or more). In some examples, the average thickness of the doped layer can be 500 micrometers (micron, µm) or less (e.g., 450 µm or less, 400 µm or less, 350 µm or less, 300 µm or less, 250 µm or less, 225 µm or less, 200 µm or less, 175 µm or less, 150 µm or less, 125 µm or less, 100 µm or less, 75 µm or less, 50 µm or less, 40 µm or less, 30 µm or less, 25 µm or less, 20 µm or less, 15 µm or less, 10 µm or less, 5 µm or less, 4 µm or less, 3 µm or less, 2 µm or less, 1 µm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less, 100 nm or less, 75 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The average thickness of the doped layer can range from any of the minimum values described above to any of the maximum values described above. For example, the average thickness of the doped layer can be from 10 nm to 500 pm (e.g., from 10 nm to 1 µm, from 10 µm to 500 µm, from 10 nm to 100 nm, from 100 nm to 1 µm, from 1 µm to 10 µm, from 10 µm to 500 µm, from 10 nm to 400 µm, from 50 nm to 500 µm, or from 50 nm to 400 µm).

[0090] The insulator layer 120 can comprise any material consistent with the methods, devices, and systems disclosed herein. For example, the insulator layer 120 can comprise SiO2, TiO2, silicon nitride, silicon oxynitride, aluminum oxide, strontium titanate, tungsten oxide (WO3), aluminum nitride, boron nitride, aluminum gallium nitride, or a combination thereof. In some examples, the insulator layer 120 comprises SiO2. In some examples, the light absorbing layer 110 comprises silicon and the insulator layer 120 comprises SiO2.

[0091] The insulator layer 120 has a top surface 122 and a bottom surface 124 opposite and spaced apart from the top surface 122. The bottom surface 124 of the insulator layer 120 is disposed on the top surface 112 of the light absorbing layer 110. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 are substantially parallel to each other.

[0092] The insulator layer 120 has an average thickness, the average thickness being the average dimension from the top surface 122 to the bottom surface 124. The average thickness of the insulator layer can, for example, be 2 nm or more (e.g., 3 nm or more, 4 nm or more, 5 nm or10046-662W01; 8574 YU more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, or 900 nm or more). In some examples, the average thickness of the insulator layer can be 1 µm or less (e.g., 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, or 5 nm or less). The average thickness of the insulator layer can range from any of the minimum values described above to any of the maximum values described above. For examples, the average thickness of the insulator layer can be from 2 nm to 1 pm (e.g., from 2 nm to 20 nm, from 20 nm to 100 nm, from 100 nm to 1 pm, from 2 nm to 900 nm, from 20 nm to 1 µm, or from 20 nm to 900 nm). In some examples, the average thickness of the insulator layer can be 20 nanometers (nm) or more. In some examples, the average thickness of the insulator layer can be 50 nanometers (nm) or more. In some examples, the average thickness of the insulator layer can be 75 nanometers (nm) or more. In some examples, the average thickness of the insulator layer can be 90 nanometers (nm) or more.

[0093] The top surface 122 and the bottom surface 124 of the insulator layer 120 can, independently, be any shape. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 can, independently, be substantially circular, ovate, ovoid, elliptic, triangular, rectangular, polygonal, etc. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 can be substantially the same shape. In some examples, the top surface 122 and the bottom surface 124 of the insulator layer 120 can be substantially rectangular. In some examples, the top surface 122 of the insulator layer 120, the bottom surface 124 of the insulator layer 120, the top surface 112 of the light absorbing layer 110, and the bottom surface 114 of the light absorbing layer 110 can each be substantially the same shape.

[0094] The insulator layer 120 has an average lateral dimension (e.g., diameter when the insulator layer 120 is circular; diagonal when the insulator layer 120 is substantially rectangular, etc.) of 1 micrometer (micron, pm) or more (e.g., 2 pm or more, 3 pm or more, 4 pm or more, 510046-662W01; 8574 YU µm or more, 10 µm or more, 15 µm or more, 20 pm or more, 25 pm or more, 30 pm or more, 40 pm or more, 50 pm or more, 75 pm or more, 100 pm or more, 125 pm or more, 150 µm or more, 200 pm or more, 250 pm or more, 300 pm or more, 400 pm or more, 500 pm or more, 750 pm or more, 1 millimeter (mm) or more, 1.25 mm or more, 1.5 mm or more, 2 mm or more, 2.5 mm or more, 3 mm or more, 4 mm or more, 5 mm or more, 10 mm or more, 15 mm or more, 20 mm or more, 25 mm or more, 30 mm or more, 40 mm or more, 50 mm or more, 75 mm or more, 100 mm or more, 125 mm or more, 150 mm or more, 200 mm or more, 250 mm or more, 300 mm or more, 400 mm or more, 500 mm or more, 750 mm or more, 1 meter (m) or more, 2 m or more, 3 m or more, 4 m or more, or 5 m or more). In some examples, the average lateral dimension of the insulator layer 120 is 10 meters (m) or less (e.g., 9 m or less, 8 m or less, 7 m or less, 6 m or less, 5 m or less, 4 m or less, 3 m or less, 2 m or less, 1 m or less, 750 mm or less, 500 mm or less, 400 mm or less, 300 mm or less, 250 mm or less, 200 mm or less, 150 mm or less, 125 mm or less, 100 mm or less, 75 mm or less, 50 mm or less, 40 mm or less, 30 mm or less, 25 mm or less, 20 mm or less, 15 mm or less, 10 mm or less, 5 mm or less, 4 mm or less, 3 mm or less, 2.5 mm or less, 2 mm or less, 1.5 mm or less, 1.25 mm or less, 1 mm or less, 750 micrometer (pm) or less, 500 pm or less, 400 pm or less, 300 pm or less, 250 pm or less, 200 pm or less, 150 pm or less, 125 pm or less, 100 pm or less, 75 pm or less, 50 pm or less, 40 pm or less, 30 pm or less, 25 pm or less, 20 pm or less, 15 pm or less, 10 pm or less, 5 pm or less, 4 pm or less, 3 pm or less, or 2 pm or less). The average lateral dimension of the insulator layer 120 can range from any of the minimum values described above to any of the maximum values described above. For example, the average lateral dimension of the insulator layer 120 can be from 1 pm to 10 m (e.g., from 1 pm to 1 mm, from 1 mm to 10 m, from 1 pm to 100 pm, from 100 pm to 10 mm, from 10 mm to 10 m, from 1 pm to 10 pm, from 10 pm to 100 pm, from 100 pm to 1 mm, from 1 mm to 10 mm, from 10 mm to 100 mm, from 100 mm to 1 m, from 1 m to 10 m, from 1 pm to 1 m, from 1 pm to 100 mm, from 1 pm to 50 mm, from 1 pm to 10 mm, from 10 pm to 300 mm, from 100 pm to 300 mm, from 1 mm to 300 mm, from 25 mm to 300 mm, or from 1 centimeter (cm) to 30 cm). In some examples, the insulator layer 120 and the light absorbing layer 110 can have substantially the same average lateral dimension.

[0095] The photoelectrodes further comprise a plurality of protrusions 130 arranged in an ordered array, wherein each protrusion 130 penetrates through the insulator layer 120 to the light absorbing layer 110, such that each protrusion 130 is in physical and electrical contact with the light absorbing layer 110. For example, each protrusion 130 can extend from the top surface 122 of the insulator layer 120 to the bottom surface 124 of the insulator layer 120, such that each10046-662W01; 8574 YU protrusion 130 is in physical and electrical contact with the top surface 112 of the light absorbing layer 110.

[0096] As used herein, “a plurality of protrusions 130” and “the plurality of protrusions 130” are meant to include two or more protrusions 130 of any size and in any ordered array. Thus, for example, “a plurality of protrusions 130” includes two or more protrusions 130 (e.g., 3 or more; 4 or more; 5 or more; 10 or more; 15 or more; 20 or more; 25 or more; 30 or more; 40 or more; 50 or more; 75 or more; 100 or more; 150 or more; 200 or more; 250 or more; 300 or more; 400 or more; 500 or more; 750 or more; 1000 or more; 1500 or more; 2000 or more; 2500 or more; 3000 or more; 4000 or more; 5000 or more; 7500 or more; 1 x 104or more; 2.5 * 104or more; 5 x 104or more; 7.5 * 104or more; 1 * 10’ or more; 2.5 * 105or more; 5 < 105or more; 7.5 * 103or more; 1 x 106or more; 5 x 106or more; 1 * 10?or more; 5 * 107or more; 1 * IO8or more; 5 x 108ormore; 1 x 109ormore; 5 * 109ormore; 1 * 1010ormore; 1 * 1011ormore; 1 * 10i2or more; 1 x 10l° or morel 1 x 1014or more; 1 * 1015or more; 1 * 1016or more; 1 * 101' ormore; 1 x 10lsormore; 1 * 1039ormore; or 1 * IO20or more).

[0097] The plurality of protrusions 130 can, independently, be any shape, such as a regular shape, an irregular shape, an isotropic shape, or an anisotropic shape. For example, the plurality of protrusions 130 can, independently, be a polyhedron (e.g., a platonic solid, a prism, a pyramid), a cylinder, a hemicylinder, an elliptical cylinder, a hemi-elliptical cylinder, a cone, a semi cone, etc.

[0098] In some examples, each of the protrusions 130 can, independently, have a longitudinal axis, a first surface, and a second surface opposite and axially spaced apart from the first surface. In some examples, the longitudinal axis of each of the protrusions 130 can, independently, extend through the insulator layer 120 at an angle of 90° or less relative to the top surface of the insulator layer (e.g., 85° or less, 80° or less, 75° or less, 70° or less, 65° or less, 60° or less, 55° or less, 50° or less, 45° or less, 40° or less, 35° or less, 30° or less, 25° or less, 20° or less, or 15° or less), wherein an angle of 90° means that the longitudinal axis is disposed perpendicular to the top surface of the insulator layer and 0° is parallel to the top surface of the insulator layer. In some examples, the longitudinal axis of each of the protrusions 130 can, independently, extend through the insulator layer 120 at an angle of 10° or more relative to the top surface of the insulator layer (e.g., 15° or more, 20° or more, 25° or more, 30° or more, 35° or more, 40° or more, 45° or more, 50° or more, 55° or more, 60° or more, 65° or more, 70° or more, 75° or more, 80° or more, or 85° or more). The angle at which the longitudinal axis of each of the protrusions 130 independently extends through the insulator layer 120 can range from any of the minimum values described above to any of the maximum values described above. For example,10046-662W01; 8574 YU the longitudinal axis of each of the protrusions 130 can, independently, extend through the insulator layer 120 at an angle of from 10° to 90° relative to the top surface of the insulator layer (e.g., from 10° to 45°, from 45° to 90°, from 10° to 30°, from 30 ° to 50°, from 50° to 70°, from 70° to 90°, from 30° to 90°, from 10° to 80°, or from 30° to 80°). In some examples, the longitudinal axis of one or more of the protrusions can be disposed at an angle of 90° relative to the top surface of the insulator layer, such that the longitudinal axis is disposed perpendicular to the top surface of the insulator layer. In some examples, the longitudinal axis of each of the protrusions 130 are substantially parallel to each other.

[0099] Each of the protrusions 130 can have a cross-sectional shape in a plane parallel to the top surface of the insulator layer, wherein the cross-sectional shape can be any shape, such as a regular shape, an irregular shape, an isotropic shape, or an anisotropic shape. In some examples, the cross-sectional shape of each of the plurality of protrusions can be substantially circular, ovate, ovoid, elliptic, triangular, rectangular, polygonal, etc. In some examples, the cross- sectional shape of each of the plurality of protrusions 130 is substantially the same. In some examples, the cross-sectional shape of the plurality of protrusions 130 can vary with the thickness of the insulator layer 120.

[0100] In some examples, the cross-sectional shape of the plurality of protrusions 130 can be selected in view of the thickness of the insulator layer 120 (e.g., for different thicknesses of the insulator layer 120, the cross-sectional shape of the plurality of protrusions 130 can vary). In some examples, the cross-sectional shape of a given protrusion 130 can vary along the depth (e.g., within) of the insulator layer 120.

[0101] The plurality of protrusions 130 can have an average characteristic dimension. The term "‘characteristic dimension,” as used herein refers to the largest straight line distance spanning the protrusion 130 in a plane parallel to the top surface 122 of the insulator layer 120. “Average characteristic dimension” and “mean characteristic dimension” are used interchangeably herein, and generally refer to the statistical mean characteristic dimension of the protrusions in a population of protrusions. For example, for a cylindrical plurality of protrusions, the cross- sectional shape can be substantially circular and the average characteristic dimension can refer to the average diameter. In some examples, the average characteristic dimension of the plurality of protrusions 130 can be substantially the same for the entire thickness of the insulator layer 120. In some examples, the average characteristic dimension of the plurality of protrusions 130 can vary with the thickness of the insulator layer 120 (e.g., tapered or stepped).

[0102] The plurality of protrusions can, for example, have an average characteristic dimension of 0.1 nm or more (e.g., 0.2 nm or more, 0.3 nm or more, 0.4 nm or more, 0.5 nm or more, 1 nm10046-662W01; 8574 YU or more, 1.5 nm or more, 2 nm or more, 2.5 nm or more, 3 nm or more, 4 nm or more, 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, pm) or more, 1.25 microns or more, 1.5 microns or more, 1.75 microns or more, 2 microns or more, 2.25 microns or more, 2.5 microns or more, 3 microns or more, 3.5 microns or more, 4 microns or more, 4.5 microns or more, 5 microns or more, 6 microns or more, 7 microns or more, 8 microns or more, or 9 microns or more). In some examples, the plurality of protrusions can have an average characteristic dimension of 10 micrometers (microns, pm) or less (e.g., 9 microns or less, 8 microns or less, 7 microns or less, 6 microns or less, 5 microns or less, 4.5 microns or less, 4 microns or less, 3.5 microns or less, 3 microns or less, 2.5 microns or less, 2.25 microns or less, 2 microns or less, 1.75 microns or less, 1.5 microns or less, 1.25 microns or less, 1 micron or less, 900 nanometers (nm) or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 5 nm or less, 4 nm or less, 3 nm or less, 2.5 nm or less, 2 nm or less, 1.5 nm or less, 1 nm or less, or 0.5 nm or less). The average characteristic dimension of the plurality of protrusions can range from any of the minimum values described above to any of the maximum values described above. For examples, the average characteristic dimension of the plurality of protrusions can be from 0.1 nm to 10 pm (e.g., from 0.1 nm to 100 nm, from 100 nm to 100 microns, from 0.1 nm to 1 nm, from 1 nm to 10 nm, from 10 nm to 100 nm, from 100 nm to 1 micron, from 1 micron to 10 microns, from 0.1 nm to 9 microns, from 1 nm to 10 microns, or from 1 nm to 9 microns). The average characteristic dimension of the protrusions can be measured using methods known in the art, such as evaluation by electron microscopy.

[0103] In some examples, the average characteristic dimension of the plurality of protrusions 130 can be substantially monodisperse. “Monodisperse” and “homogeneous characteristic dimension distribution,” as used herein, and generally describe a population of protrusions where10046-662W01; 8574 YU all of the protrusions have the same or nearly the same characteristic dimension. As used herein, a monodisperse distribution refers to distributions in which 80% of the distribution (e.g., 85% of the distribution, 90% of the distribution, or 95% of the distribution) lies within 25% of the mean characteristic dimension (e.g., within 20% of the mean characteristic dimension, within 15% of the mean characteristic dimension, within 10% of the mean characteristic dimension, or within 5% of the mean characteristic dimension).

[0104] The plurality of protrusions 130 are arranged in an ordered array. For example, the plurality of protrusions 130 can form a linear array, a triangular array, a hexagonal array, or a quadrilateral array. In some examples, the ordered array is a hexagonal array.

[0105] In some examples, the ordered array is a two dimensional array defined by a first unit cell. As used herein, a “unit cell” is the smallest group of protrusions in the array that constitutes the repeating pattern of the array. The first unit cell can have a first principle axis and a second principle axis with a first included angle between the first principle axis and the second principle axis. The ordered array is built up of repetitive translations of the first unit cell along its principle axes.

[0106] The first principle axis of the first unit cell has a length that is the distance separating each protrusion in the ordered array from its neighboring protrusion (center-to-center) along the first principle axis. In some examples, the length of the first principle axis in the ordered arraycan be 10 nanometers or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, pm) or more, 1.25 microns or more, 1.5 microns or more, 1.75 microns or more, 2 microns or more, 2.25 microns or more, 2.5 microns or more, 3 microns or more, 3.5 microns or more, 4 microns or more, 4.5 microns or more, 5 microns or more, 6 microns or more, 7 microns or more, 8 microns or more, 9 microns or more, 10 microns or more, 15 microns or more, 20 microns or more, 25 microns or more, 30 microns or more, 35 microns or more, 40 microns or more, or 45 microns or more). In some examples, the length of the first principle axis in the ordered array can be 50 nanometers or more. In some examples, the length of the first principle axis in the ordered array can be 50 micrometers (microns, pm) or less (e.g., 45 microns or less, 40 microns or less, 35 microns or less, 30 microns or less, 25 microns or less, 20 microns or less, 1 microns10046-662W01; 8574 YU or less, 10 microns or less, 9 microns or less, 8 microns or less, 7 microns or less, 6 microns or less, 5 microns or less, 4.5 microns or less, 4 microns or less, 3.5 microns or less, 3 microns or less, 2.5 microns or less, 2.25 microns or less, 2 microns or less, 1.75 microns or less, 1.5 microns or less, 1.25 microns or less, 1 micron or less, 900 nanometers (nm) or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The length of the first principle axis in the ordered array can range from any of the minimum values described above to any of the maximum values described above. For example, the length of the first principle axis in the ordered array can be from 10 nanometers (nm) to 50 micrometers (microns, pm) (e.g., from 10 nm to 1 micron, from 1 micron to 50 microns, from 10 nm to 500 nm, from 500 nm to 5 microns, from 5 microns to 50 microns, from 10 nm to 25 microns, from 10 nm to 10 microns, from 10 nm to 500 nm, from 10 nm to 50 nm, from 25 nm to 50 microns, from 50 nm to 50 microns, from 100 nm to 50 microns, from 500 nm to 50 microns, from 10 microns to 50 microns, from 25 nm to 25 microns, or from 50 nm to 10 microns). In some examples, the length of the first principle axis in the ordered array can be from 50 nanometers to 10 micrometers.

[0107] The second principle axis of the first unit cell has a length that is the distance separating each protrusion in the ordered array from its neighboring protrusion (center-to-center) along the second principle axis. In some examples, the length of the second principle axis in the ordered array can be 10 nanometers or more (e.g., 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 110 nm or more, 120 nm or more, 130 nm or more, 140 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, 900 nm or more, 1 micrometer (micron, pm) or more, 1.25 microns or more, 1.5 microns or more, 1.75 microns or more, 2 microns or more, 2.25 microns or more, 2.5 microns or more, 3 microns or more, 3.5 microns or more, 4 microns or more, 4.5 microns or more, 5 microns or more, 6 microns or more, 7 microns or more, 8 microns or more, 9 microns or more, 10 microns or more, 15 microns or more, 20 microns or more, 25 microns or more, 30 microns or more, 35 microns or more, 40 microns or more, or 4510046-662W01; 8574 YU microns or more). In some examples, the length of the first principle axis in the ordered array can be 50 nanometers or more. In some examples, the length of the second principle axis in the ordered array can be 50 micrometers (microns, pm) or less (e.g., 45 microns or less, 40 microns or less, 35 microns or less, 30 microns or less, 25 microns or less, 20 microns or less, 15 microns or less, 10 microns or less, 9 microns or less, 8 microns or less, 7 microns or less, 6 microns or less, 5 microns or less, 4.5 microns or less, 4 microns or less, 3.5 microns or less, 3 microns or less, 2.5 microns or less, 2.25 microns or less, 2 microns or less, 1.75 microns or less, 1.5 microns or less, 1.25 microns or less, 1 micron or less, 900 nanometers (nm) or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 140 nm or less, 130 nm or less, 120 nm or less, 110 nm or less, 100 nm or less, 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, or 15 nm or less). The length of the second principle axis in the ordered array can range from any of the minimum values described above to any of the maximum values described above. For example, the length of the second principle axis in the ordered array can be from 10 nanometers (nm) to 50 micrometers (microns, pm) (e.g., from 10 nm to 1 micron, from 1 micron to 50 microns, from 10 nm to 500 nm, from 500 nm to 5 microns, from 5 microns to 50 microns, from 10 nm to 25 microns, from 10 nm to 10 microns, from 10 nm to 500 nm, from 10 nm to 50 nm, from 25 nm to 50 microns, from 50 nm to 50 microns, from 100 nm to 50 microns, from 500 nm to 50 microns, from 10 microns to 50 microns, from 25 nm to 25 microns, or from 50 nm to 10 microns). In some examples, the length of the first principle axis in the ordered array can be from 50 nanometers to 10 micrometers..

[0108] In some examples, the length of the first principle axis in the ordered array can be the same as the length of the second principle axis in the ordered array.

[0109] The first included angle between the first principle axis and the second principle axis of the first unit cell can, for example, be 30° or more (e.g., 35° or more, 40° or more, 45° or more, 50° or more, 55° or more, 60° or more, 65° or more, 70° or more, 75° or more, 80° or more, 85° or more, 90° or more, 95° or more, 100° or more, 105° or more, 110° or more, 115° or more, 120° or more, 125° or more, 130° or more, 135° or more, 140° or more, or 145° or more). In some examples, the first included angle between the first principle axis and the second principle axis of the first unit cell can be 60° or more. In some examples, the first included angle between the first principle axis and the second principle axis of the first unit cell can be 150° or less (e.g., 145° or less, 140° or less, 135° or less, 130° or less, 125° or less, 120° or less, 115° or less, 110°10046-662W01; 8574 YU or less, 105° or less, 100° or less, 95° or less, 90° or less, 85° or less, 80° or less, 75° or less, 70° or less, 65° or less, 60° or less, 55° or less, 50° or less, 45° or less, 40° or less, or 35° or less). In some examples, the first included angle between the first principle axis and the second principle axis of the first unit cell can be 120° or less. The first included angle between the first principle axis and the second principle axis of the first unit cell can range from any of the minimum values described above to any of the maximum values described above. For example, the first included angle between the first principle axis and the second principle axis of the first unit cell can be from 30° to 150° (e.g., from 30° to 90°, from 90° to 150°, from 30° to 60°, from 60° to 90°, from 90° to 120°, from 120° to 150°, from 30° to 120°, from 60° to 150°, or from 60° to 120°). In some examples, the first included angle between the first principle axis and the second principle axis of the first unit cell can be from 60° to 120°.

[0110] The first unit cell can be of any shape. In some examples, the first unit cell is in the shape of a triangle. In some examples, the first unit cell is in the shape of a quadrilateral (e.g., a rectangle, a parallelogram, or the like).

[0111] The plurality of protrusions can be dispersed across the insulator layer laterally such that the areal density of the plurality of protrusions within the plane of the top surface of the insulator layer can be 102protrusions per cm2of the insulator layer or more (e.g., 5 x 102protrusions / cm2or more, 1× 103protrusions / cm2or more, 5 x 103protrusions / cm2or more, 1 x 104protrusions / cm2or more, 5 x 104protrusions / cm2or more, 1 x 105protrusions / cm2or more, 5 x 105protrusions / cm2or more, 1 x 106protrusions / cm2or more, 5 x 106protrusions / cm2or more, 1 x 107protrusions / cm2or more, 5 x 107protrusions / cm2or more, 1 x 10sprotrusions / cm2or more, 5 x 108protrusions / cm2or more, 1 x 109protrusions / cm2or more, 5 x 109protrusions / cm2or more, 1 x 1010protrusions / cm2or more, 5 x 1010protrusions / cm2or more, 1 x 1011protrusions / cm2or more, 5 x 1011protrusions / cm2or more, 1 x 1012protrusions / cm2or more, 5 x 1012protrusions / cm2or more, 1 x 1013protrusions / cm2or more, or 5 x 1013protrusions / cm2or more). In some examples, the areal density of the plurality of protrusions within the plane of the top surface of the insulator layer can be 1013protrusions / cm2or less (e.g., 5 x 1013protrusions / cm2or less, 1 x 1013protrusions / cm2or less, 5 x 1012protrusions / cm2or less, 1 x 1012protrusions / cm2or less, 5 x 1011protrusions / cm2or less, 1 x 1011protrusions / cm2or less, 5 x 1010protrusions / cm2or less, 1 x 1010protrusions / cm2or less, 5 x 109protrusions / cm2or less, 1 x 109protrusions / cm2or less, 5 x 108protrusions / cm2or less, 1 x 108protrusions / cm2or less, 5 x 107protrusions / cm2or less, 1 x 107protrusions / cm2or less, 5 x 106protrusions / cm2or less, 1 x 106protrusions / cm2or less, 5 x 105protrusions / cm2or less, 1 x 105protrusions / cm2or less, or 5 x 104protrusions / cm2or less). The areal density of the plurality of protrusions within the plane10046-662W01; 8574 YU of the top surface of the insulator layer can range from any of the minimum values described above to any of the maximum values described above. For example, the areal density of the plurality of protrusions within the plane of the top surface of the insulator layer can be from 102to 1013protrusions / cm2(e.g., from 1 x 102to 1 x 107protrusions / cm2, from 1 x 107to 1 x 1013protrusions / cm2, from 1 x 102to 1 x 104protrusions / cm2, from 1 x 104to 1 x 106protrusions / cm2, from 1 x 106to 1 x 108protrusions / cm2, from 1 x 108to 1 x 1010protrusions / cm2, from 1 x 1010to 1 x 1013protrusions / cm2, from 1 x 102to 1 x 1012protrusions / cm2, from 1 x 103to 1 x 1013protrusions / cm2, from 1 x 103to x 1012protrusions / cm2, from 1 x 104to 1 x 1010protrusions / cm2, or from 1 x 105to x 109protrusions / cm2).

[0112] In some examples, the plurality of protrusions are dispersed throughout the insulator layer such that the areal density of the plurality of protrusions within the insulator layer is from 2 x 107to 8 x 109protrusions per cm2of the insulator layer.

[0113] The photoelectrodes further comprise a plurality of particles 140 on the insulator layer, wherein at least a portion of each of the plurality of particles 140 are in physical and electrical contact with at least a portion of one of the protrusions. For example, the plurality of particles 140 can be disposed on the top surface 122 of the insulator layer 120.

[0114] As used herein, “a plurality of particles” and “the plurality of particles” are meant to include particles of any size and in any arrangement. Thus, for example, “a plurality of particles” includes two or more particles (e.g., 3 or more; 4 or more; 5 or more; 10 or more; 15 or more; 20 or more; 25 or more; 30 or more; 40 or more; 50 or more; 75 or more; 100 or more; 150 or more; 200 or more; 250 or more; 300 or more; 400 or more; 500 or more; 750 or more; 1000 or more; 1500 or more; 2000 or more; 2500 or more; 3000 or more; 4000 or more; 5000 or more; 7500 or more; 1 * 104or more; 2.5 * 104or more; 5 * 104or more; 7.5 * 104or more; 1 * 105or more; 2.5 x 105or more; 5× 105or more; 7.5 × 105or more; 1 x 106or more; 5 x 106or more; 1 x 107or more; 5 * 107or more; 1 × 108or more; 5 × 108or more; 1 x 109or more; 5 × 109or more; 1 x 1010or more; 1 x 1011or more; 1 × 1012or more; 1 x 1013or more; 1 x 1014or more; 1 x 1015or more; 1 x 1016or more; 1 x 1017or more; 1 x 1018or more; 1 x 1019or more; or 1 x 1020or more). In some examples, the plurality of particles 140 can be arranged in an ordered array (e.g., the same ordered array as the plurality of protrusions). In some examples, the plurality of particles 140 and the plurality of protrusions 130 are monolithic (e.g., the portion of the protrusion extending above the surface of the insulator layer are referred to as “particles”, but are integrally formed with the protrusion).

[0115] The plurality of particles 140 can have an average height, the average height being the10046-662W01; 8574 YU average dimension extending above the top surface 122 of the insulator layer 120. Mean particle height can be measured using methods known in the art, such as evaluation by electron microscopy.

[0116] The plurality of particles 140 can, for example, have an average height of 1 nm or more (e.g., 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, 25 nm or more, 30 nm or more, 35 nm or more, 40 nm or more, 45 nm or more, 50 nm or more, 55 nm or more, 60 nm or more, 65 nm or more, 70 nm or more, 75 nm or more, 80 nm or more, 85 nm or more, 90 nm or more, 95 nm or more, 100 nm or more, 125 nm or more, 150 nm or more, 175 nm or more, 200 nm or more, 225 nm or more, 250 nm or more, 300 nm or more, 350 nm or more, 400 nm or more, 450 nm or more, 500 nm or more, 600 nm or more, 700 nm or more, 800 nm or more, or 900 nm or more). In some examples, the plurality of particles 140 can have an average height of 10 nm or more. In some examples, the plurality of particles 140 can have an average height of 1 micrometer (micron, pm) or less (e.g., 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 450 nm or less, 400 nm or less, 350 nm or less, 300 nm or less, 250 nm or less, 225 nm or less, 200 nm or less, 175 nm or less, 150 nm or less, 125 nm or less 95 nm or less, 90 nm or less, 85 nm or less, 80 nm or less, 75 nm or less, 70 nm or less, 65 nm or less, 60 nm or less, 55 nm or less, 50 nm or less, 45 nm or less, 40 nm or less, 35 nm or less, 30 nm or less, 25 nm or less, 20 nm or less, 1 nm or less, or 10 nm or less). In some examples, the plurality of particles 140 can have an average height of 500 nm or less. The average height of the plurality of particles 140 can range from any of the minimum values described above to any of the maximum values described above. For example, the plurality of particles 140 can have an average height of from 1 nm to 1 pm (e.g., from 1 nm to 500 nm, from 500 nm to 1 pm, from 1 nm to 200 nm, from 200 nm to 400 nm, from 400 nm to 600 nm, from 600 nm to 800 nm, from 800 nm to 1 pm, from 1 nm to 800 nm, from 1 nm to 600 nm, from 1 nm to 400 nm, from 1 nm to 100 nm, from 1 nm to 50 nm, from 1 nm to 25 nm, from 1 nm to 10 nm, from 5 nm to 1 pm, from 10 nm to 1 pm, from 25 nm to 1 pm, from 50 nm to 1 pm, from 100 nm to 1 pm, from 200 nm to 1 pm, from 400 nm to 1 pm, from 600 nm to 1 pm, from 5 nm to 900 nm, from 10 nm to 800 nm, or from 10 nm to 500 nm). In some examples, the plurality of particles 140 can have an average height of from 10 nm to 500 nm.

[0117] In some examples, the average height of the plurality of particles 140 can be substantially monodisperse. “Monodisperse” and “homogeneous height distribution,” as used herein, and generally describe a population of particles where all of the particles have the same or nearly the same height. As used herein, a monodisperse height distribution refers to distributions in which 80% of the distribution (e.g., 85% of the distribution, 90% of the distribution, or 95% of the10046-662W01; 8574 YU distribution) lies within 25% of the mean particle height (e.g., within 20% of the mean particle height, within 15% of the mean particle height, within 10% of the mean particle height, or within 5% of the mean particle height).

[0118] The plurality of particles 140 can, independently, be of any shape, such as a regular shape, an irregular shape, an isotropic shape, or an anisotropic shape (e.g., a sphere, a rod, a quadrilateral, an ellipse, a triangle, a polygon, etc.). In some examples, the plurality of particles 140 can have an isotropic shape. In some examples, the plurality of particles 140 can have an anisotropic shape.

[0119] The plurality of particles 140 and optionally the plurality of protrusions comprise a catalyst material (e.g., the plurality of particles 140 comprise the catalyst material, or the plurality of particles 140 and the plurality of protrusions comprise the catalyst material). In some examples, the plurality of particles 140 and the plurality of protrusions comprise the catalyst material.

[0120] The catalyst material can comprise any material consistent with the methods, devices, and systems disclosed herein. For example, the catalyst material can comprise a metal selected from the group consisting of Ni, Pt, Mo, Co, Ru, Ir, Fe, or a combination thereof. In some examples, the catalyst material comprises Ni. In some examples, the catalyst material comprises an oxygen evolution reaction catalyst. In some examples, the catalyst material comprises a hydrogen evolution reaction catalyst. In some examples, the catalyst material can comprise a metal containing compound, such as a metal oxide, metal sulfide, metal phosphide or combination thereof, wherein the metal, can, for example, comprise a metal selected from the group consisting of Ni, Pt, Mo, Co, Ru, Ir, Fe, or a combination thereof. In some examples, the catalyst material can comprise NiFe, NiFeOx, NiFe-layered double hydroxide, carbon nitrides, certain polymers, NiMo, MoS2, CoP, NiCoOx, RuO2, IrC2, or a combination thereof.

[0121] In some examples, the plurality of particles 140 and the plurality of protrusions comprise the catalyst material, and the catalyst material comprises Ni.

[0122] In some examples, the light absorbing layer 110 comprises silicon, the insulator layer 120 comprises SiO2, the plurality of particles 140 and the plurality of protrusions comprise the catalyst material, and the catalyst material comprises Ni.

[0123] The particles and / or the protrusions can, for example, cover 1% or more of the top surface of the insulator layer (e.g., 2% or more, 3% or more, 4% or more, 5% or more, 10% or more, 15% or more, 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, 45% or more, 50% or more, 55 ’ or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more). In some examples, the particles10046-662W01; 8574 YU and / or protrusions can cover 100% or less of the top surface of the insulator layer (e.g., 95% or less, 90% or less, 85% or less, 80% or less, 75% or less, 70% or less, 65% or less, 60% or less, 55% or less, 50% or less, 45% or less, 40% or less, 35% or less, 30% or less, 25% or less, 20% or less, 15% or less, 10% or less, or 5% or less). The amount of coverage of the top surface of the insulator by the particles and / or the protrusions can range from any of the minimum values described above to any of the maximum values described above. For example, the particles and / or the protrusions can cover from 1% to 100% of the top surface of the insulator layer (e.g., from 1% to 50%, from 50% to 100%, from 1% to 20%, from 20% to 40%, from 40% to 60%, from 60% to 80% from 80% to 100%, from 5% to 100%’, from 1% to 90%, from 5% to 90%, or from 5% to 80%). In some examples, the particles and / or the protrusions cover from 5% to 90% of the top surface of the insulator layer. In some examples, the particles and / or the protrusions cover from 5% to 80% of the top surface of the insulator layer. In some examples, the particles and / or the protrusions cover 10%’ or more, 25% or more, 35% or more, 50%’ or more, or 70% or more of the top surface of the insulator layer. The coverage of the top surface of the insulator layer by the catalyst material (e.g., by the particles and / or the protrusions) can, for example, be selected to enable a desired balance between available catalyst surface area and transmission of light into the light absorbing material.

[0124] In some examples, the catalyst material can comprise a metal, the light absorbing layer can comprise a semiconductor, and the photoelectrodes described herein comprise metal-insulator-semiconductor photoelectrodes.

[0125] Methods of Making

[0126] Also disclosed herein are methods of making photoelectrodes, such as any of the photoelectrodes disclosed herein. For example, disclosed herein are methods of making a photoelectrode, the method comprising: patterning a reactive material on an insulator layer, the reactive material being patterned in an ordered array and the insulator layer being disposed on a light absorbing layer, such that the insulator layer is disposed between the light absorbing layer and the ordered array of the reactive material, thereby forming a precursor electrode; annealing the precursor electrode such that the reactive material reacts with and diffuses through the insulator layer, thereby forming a plurality of spikes comprising the reactive material, wherein each of the plurality of spikes penetrates through the insulator layer to the light absorbing layer, such that each of the plurality of spikes is in physical and electrical contact with the light absorbing layer, thereby forming a spiked electrode (e.g., as shown in Figure 19-Figure 24); removing the reactive material from the spiked electrode, thereby forming an intermediate electrode; and subsequently depositing a catalyst material; thereby forming the photoelectrode10046-662W01; 8574 YU comprising: the insulator layer disposed on the light absorbing layer, a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer, such that each of the protrusions is in physical and electrical contact with the light absorbing layer; and a plurality of particles disposed on the insulator layer, wherein at least a portion of each of the particles is in physical and electrical contact with at least a portion of one of the protrusions; and wherein the plurality of particles and optionally the plurality of protrusions comprise the catalyst material.

[0127] In some examples, the methods can further comprise doping the light absorbing layer to form a doped region prior to forming the insulator layer. Doping the light absorbing layer can, for example, comprise annealing the light absorbing layer in the presence of a dopant source, ion implantation, epitaxial growth, or other methods such as those known in the art. In some examples, doping the light absorbing layer can comprise annealing the light absorbing layer in the presence of a dopant source. The dopant source can, for example, comprise a dopant, such as an n-type dopant or a p-type dopant. In some examples, the dopant source can comprise a compound or molecule that comprises a dopant atom, such as an n-type dopant or a p-type dopant. In some examples, the dopant source comprises a boron source. In some examples, annealing the light absorbing layer in the presence of a dopant source is performed in an inert atmosphere (e.g., nitrogen, argon, etc.).

[0128] In some examples, annealing comprises heating the insulator layer at a temperature of 100°C or more in the presence of the dopant source for an amount of time (e.g., 150°C or more, 200°C or more, 250°C or more, 300°C or more, 350°C or more, 400°C or more, 450°C or more, 500°C or more, 550°C or more, 600°C or more, 650°C or more, 700°C or more, 750°C or more, 800°C or more, 850°C or more, 900°C or more, 950°C or more, 1000°C or more, 1100°C or more, 1200°C or more, 1300°C or more, 1400°C or more, 1500°C or more, 1600°C or more, or 1700°C or more). In some examples, annealing comprises heating the insulator layer at a temperature of 1800°C or less in the presence of the dopant source for an amount of time (e.g., 1700°C or less, 1600°C or less, 1500°C or less, 1400°C or less, 1300°C or less, 1200°C or less, 1100°C or less, 1000°C or less, 950°C or less, 900°C or less, 850°C or less, 800°C or less, 750°C or less, 700°C or less, 650°C or less, 600°C or less, 550°C or less, 500°C or less, 450°C or less, 400°C or less, 350°C or less, 300°C or less, 250°C or less, 200°C or less, or 150°C or less). 'The temperature at which the insulator layer is annealed in the presence of the dopant source for an amount of time can range from any of the minimum values described above to any of the maximum values described above. For example, annealing can comprise heating the insulator layer at a temperature of from 100°C to 1800°C in the presence of the dopant source10046-662W01; 8574 YU for an amount of time (e.g., from 100°C to 950°C, from 950°C to 1800°C, from 100°C to 500°C, from 500°C to 900°C, from 900°C to 1300°C, from 1300°C to 1800°C, from 200°C to 1800°C, from 100°C to 1700°C, from 200°C to 1700°C, or from 900°C to 1000°C).

[0129] In some examples, annealing comprises heating the insulator layer at a temperature in the presence of the dopant source for an amount of time of 10 seconds or more (e.g., 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, 45 seconds or more, 50 seconds or more, 55 seconds or more, 1 minute or more, 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 12 hours or more, 14 hours or more, 16 hours or more, 18 hours or more, 24 hours or more, 30 hours or more, 36 hours or more, 42 hours or more, 48 hours or more, 60 hours or more, 72 hours or more, 84 hours or more, or 96 hours or more). In some examples, annealing comprises heating the insulator layer at a temperature in the presence of the dopant source for an amount of time of 100 hours or less (e.g., 96 hours or less, 84 hours or less, 72 hours or less, 60 hours or less, 48 hours or less, 42 hours or less, 36 hours or less, 30 hours or less, 24 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, 12 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, 1.5 minutes or less, 1 minute or less, 55 seconds or less, 50 seconds or less, 45 seconds or less, 50 seconds or less, 35 seconds or less, 30 seconds or less, 25 seconds or less, 20 seconds or less, or 15 seconds or less). The amount of time for which the insulator layer is annealed in the presence of the dopant source at a temperature can range from any of the minimum values described above to any of the maximum values described above. For example, annealing comprises heating the insulator layer at a temperature in the presence of the dopant source for an amount of time of from 10 seconds to10046-662W01; 8574 YU 100 hours (e.g., from 10 seconds io 1 minute, from 1 minute to 1 hour, from 1 hour to 24 hours, from 24 hours to 100 hours, from 10 seconds to 90 hours, from 1 minute to 100 hours, from 1 minute to 90 hours, or from 60 minutes to 1.5 hours). In some examples, annealing comprises heating the insulator layer at a temperature in the presence of the dopant source for an amount of time of from 10 seconds to 10 hours.

[0130] In some examples, the methods further comprise forming the insulator layer on the light absorbing layer. Forming the insulator layer can, for example, comprise thermal oxidation, electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof.

[0131] In some examples, forming the insulator layer comprises thermal oxidation. Thermal oxidation can, for example, comprise heating the light absorbing layer at a temperature of 800°C or more in the presence of oxygen for an amount of time (e.g., 800°C or more, 850°C or more, 900°C or more, 950°C or more, 1000°C or more, 1050°C or more, 1100°C or more, or 1150°C or more). In some examples, forming the insulator layer can comprise heating the light absorbing layer at a temperature of 1200°C or less in the presence of oxygen for an amount of time (e.g., 1150°C or less, 1100°C or less, 1050°C or less, 1000°C or less, 950°C or less, 900°C or less, or 850°C or less). The temperature at which the light absorbing layer is heated in the presence of oxygen for an amount of time can range from any of the minimum values described above to any of the maximum values described above. For example, forming the insulator layer can comprise heating the light absorbing layer at a temperature of from 800°C to 1200°C in the presence of oxygen for an amount of time (e.g., from 800°C to 1000°C, from 1000°C to 1200°C, from 800°C to 900°C, from 900°C, to 1000°C, from 1000°C to 1100°C, from 1100°C to 1200°C, from 850°C to 1200°C, from 800°C to 1150°C, or from 850°C to 1150°C).

[0132] In some examples, forming the insulator layer can comprise heating the light absorbing layer at a temperature in the presence of oxygen for an amount of time of 10 seconds or more (e.g., 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, 45 seconds or more, 50 seconds or more, 55 seconds or more, 1 minute or more, 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or10046-662W01; 8574 YU more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 12 hours or more, 14 hours or more, 16 hours or more, 18 hours or more, 20 hours or more, 24 hours or more, 26 hours or more, or 28 hours or more). In some examples, forming the insulator layer can comprise heating the light absorbing layer at a temperature in the presence of oxygen for an amount of time of 30 hours or less (e.g., 28 hours or less, 26 hours or less, 24 hours or less, 20 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, 12 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, 1.5 minutes or less, 1 minute or less, 55 seconds or less, 50 seconds or less, 45 seconds or less, 50 seconds or less, 35 seconds or less, 30 seconds or less, 25 seconds or less, 20 seconds or less, or 1 seconds or less). The amount of time for which the light absorbing layer is heated in the presence of oxygen at a temperature can range from any of the minimum values described above to any of the maximum values described above. For example, forming the insulator layer can comprise heating the light absorbing layer at a temperature in the presence of oxygen for an amount of time of from 10 seconds to 30 hours (e.g., from 10 seconds to 1 minute, from 1 minute to 1 hour, from 1 hour to 30 hours, from 10 seconds to 24 hours, from 1 minute to 30 hours, or from 1 minute to 24 hours, or from 60 minutes to 1.5 hours).

[0133] Patterning the reactive material can comprise any suitable method, such as, for example, lithography. Examples of lithography include, but are not limited to, electron beam lithography, optical lithography, nanoimprint lithography, nanoparticle lithography such as nanosphere lithography, focused ion beam lithography, photolithography, and combinations thereof.

[0134] In some examples, patterning the reactive material can comprise nanosphere lithography. In some examples, patterning the reactive layer comprises forming a self-assembled nanoparticle monolayer via the methods of WO 2025 / 096777 (which is hereby incorporated herein by reference for its description thereof) followed by depositing the reactive material, for example via thin film deposition. Examples of thin film depositions include, but are not limited to, electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin10046-662W01; 8574 YU coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, depositing the reactive material after forming the self- assembled nanoparticle monolayer via the methods of WO 2025 / 096777 comprises sputtering.

[0135] The reactive material can comprise any material consistent with the methods, devices, and systems disclosed herein. For example, the reactive layer can comprise Al.

[0136] Annealing the precursor electrode can, for example, comprise heating the precursor electrode at a temperature of 300°C or more (e.g., 350°C or more, 400°C or more, 450°C or more, 500°C or more, 550°C or more, 600°C or more, 650°C or more, 700°C or more, 750°C or more, 800°C or more, 850°C or more, 900°C or more, 950°C or more, 1000°C or more, 1100°C or more, 1200°C or more, 1300°C or more, or 1400°C or more). In some examples, annealing the precursor electrode can comprise heating the precursor electrode at a temperature of 1500°C or less (e.g., 1400°C or less, 1300°C or less, 1200°C or less, 1100°C or less, 1000°C or less, 950°C or less, 900°C or less, 850°C or less, 800°C or less, 750°C or less, 700°C or less, 650°C or less, 600°C or less, 550°C or less, 500°C or less, 450°C or less, 400°C or less, or 350°C or less). The temperature at which the precursor electrode is annealed can range from any of the minimum values described above to any of the maximum values described above. For example, annealing the precursor electrode can comprise heating the precursor electrode at a temperature of from 300°C to 1500°C (e.g., from 300°C to 900°C, from 900°C to 1500°C, from 300°C to 600°C, from 600°C to 900°C, from 900°C to 1200°C, from 1200°C to 1500°C, from 350°C to 1500°C, from 300°C to 1400°C. from 350°C to 1400°C, or from 300°C to 800°C).

[0137] In some examples, annealing the precursor electrode can comprise heating the precursor electrode at a temperature for an amount of time of 1 minute or more (e.g., 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, 10 hours or more, 12 hours or more, 14 hours or more, 16 hours or more, 18 hours or more, 24 hours or more, 30 hours or more, 36 hours or more, or 42 hours or more). In some examples, annealing the precursor electrode can comprise heating the precursor electrode at a temperature for an10046-662W01; 8574 YU amount of time of 48 hours or less (e.g., 42 hours or less, 36 hours or less, 30 hours or less, 24 hours or less, 18 hours or less, 16 hours or less, 14 hours or less, 12 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, or 1.5 minutes or less). The amount of time for which the precursor electrode is annealed at a temperature can range from any of the minimum values described above to any of the maximum values described above. For example, annealing the precursor electrode can comprise heating the precursor electrode at a temperature for an amount of time of from 1 minute to 48 hours (e.g., from 1 minute to 1 hour, from 1 hour to 48 hours, from 1 minute to 42 hours, from 10 minutes to 48 hours, from 10 minutes to 42 hours, or from 1 hour to 24 hours). For example, annealing the precursor electrode can comprise heating the precursor electrode at a temperature of from 450°C to 650°C for an amount of time of from 1 hour to 24 hours.

[0138] The precursor electrode can, for example, be annealed in vacuum or an atmosphere comprising nitrogen, argon, forming gas, etc.

[0139] In some examples, the methods can further comprise removing the reactive material from the spiked electrode before depositing the catalyst material, thereby forming an intermediate electrode. Removing the reactive material can, for example, comprise etching the reactive material. Etching the reactive material can, for example, comprise contacting the reactive material with an etchant. In some examples, the etchant can comprise H3PO4.

[0140] Depositing the catalyst material can, for example, comprise electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof. In some examples, depositing the catalyst material comprises electroplating.

[0141] Electroplating the catalyst material can, for example, comprise contacting light absorbing layer of the spiked electrode or the intermediate electrode with a plating solution and subsequently applying a voltage for an amount of time. The plating solution can, for example, comprise a salt of the metal. In some examples, the plating solution comprises NiCl2, NiSO4, or10046-662W01; 8574 YU a combination thereof. Different plating solutions can, for example, be used sequentially during an electroplating process.

[0142] The applied voltage can, for example, be -5 Volts (V) or more vs Ag / AgCl (e.g., -4.5 V or more, -4 V or more, -3.5 V or more, -3 V or more, -2.5 V or more, -2 V or more, -1.5 V or more, -1 V or more, -0.5 V or more, 0 V or more, 0.5 V or more, 1 V or more, 1.5 V or more, 2 V or more, 2.5 V or more, 3 V or more, 3.5 V or more, 4 V or more, or 4.5 V or more). In some examples, the applied voltage can be 5 V or less vs. Ag / AgCl (e.g., 4.5 V or less, 4 V or less, 3.5 V or less, 3 V or less, 2.5 V or less, 2 V or less, 1.5 V or less, 1 V or less, 0.5 V or less, 0 V or less, -0.5 V or less, -1 V or less, -1.5 V or less, -2 V or less, -2.5 V or less, -3 V or less, -3.5 V or less, -4 V or less, or -4.5 V or less). The applied voltage can range from any of the minimum values described above to any of the maximum values described above. For example, the applied voltage can be from -5 V to +5 V (e.g., from -5 V to 0 V, from 0 V to 5 V, from -5 V to -2.5 V, from -2.5 V to 0 V, from 0 V to 2.5 V, from 2.5 V to 5 V, from -5 V to 4 V, from -4 V to 5 V, from -4 V to 4 V, or from -0.5 V to -3.0 V). In some examples, the applied voltage is from -0.5 V to -3.0 V vs. Ag / AgCl.

[0143] In some examples, the voltage is applied for an amount of time of 10 seconds or more (e.g., 15 seconds or more, 20 seconds or more, 25 seconds or more, 30 seconds or more, 35 seconds or more, 40 seconds or more, 45 seconds or more, 50 seconds or more, 55 seconds or more, 1 minute or more, 1.5 minutes or more, 2 minutes or more, 2.5 minutes or more, 3 minutes or more, 3.5 minutes or more, 4 minutes or more, 4.5 minutes or more, 5 minutes or more, 6 minutes or more, 7 minutes or more, 8 minutes or more, 9 minutes or more, 10 minutes or more, 15 minutes or more, 20 minutes or more, 25 minutes or more, 30 minutes or more, 35 minutes or more, 40 minutes or more, 45 minutes or more, 50 minutes or more, 55 minutes or more, 1 hour or more, 1.5 hours or more, 2 hours or more, 2.5 hours or more, 3 hours or more, 3.5 hours or more, 4 hours or more, 4.5 hours or more, 5 hours or more, 6 hours or more, 7 hours or more, 8 hours or more, 9 hours or more, or 10 hours or more). In some examples, the voltage is applied for an amount of time of 12 hours or less (e.g., 11 hours or less, 10 hours or less, 9 hours or less, 8 hours or less, 7 hours or less, 6 hours or less, 5 hours or less, 4.5 hours or less, 4 hours or less, 3.5 hours or less, 3 hours or less, 2.5 hours or less, 2 hours or less, 1.5 hours or less, 1 hours or less, 55 minutes or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 35 minutes or less, 30 minutes or less, 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 9 minutes or less, 8 minutes or less, 7 minutes or less, 6 minutes or less, 5 minutes or less, 4.5 minutes or less, 4 minutes or less, 3.5 minutes or less, 3 minutes or less, 2.5 minutes or less, 2 minutes or less, 1.5 minutes or less, 1 minute or less, 55 seconds or less, 50 seconds or less, 4510046-662W01; 8574 YU seconds or less, 50 seconds or less, 35 seconds or less, 30 seconds or less, 25 seconds or less, 20 seconds or less, or 15 seconds or less). The amount of time for which the voltage is applied can range from any of the minimum values described above to any of the maximum values described above. For example, the voltage can be applied for an amount of time of from 10 seconds to 12 hours (e.g., from 10 seconds to 2 hours, from 2 hours to 12 hours, from 10 seconds to 1 minute, from 1 minute to 1 hour, from 1 hour to 12 hours, from 1 minute to 12 hours, from 10 seconds to 10 hours, from 1 minute to 10 hours, or from 1 minute to 6 hours). In some examples, voltage is applied for an amount of time of from 1 minute to 120 minutes. In some examples, the morphology and / or composition of the deposited catalyst material can be controlled by varying the applied bias, solution composition, and deposition time for electrodeposition during the electrodeposition process.

[0144] Devices and Methods of Use

[0145] Also disclosed herein are devices comprising any of the photoelectrodes described herein and methods of use of any of the photoelectrodes or devices described herein.

[0146] For example, also disclosed herein are methods of use of any of the photoelectrodes disclosed herein. The methods can, for example, comprise using the photoelectrode as an electrode in a photoelectrochemical reaction. In some examples, the methods can comprise using the photoelectrode as an electrode in an energy conversion device, a charge storage device, an electronic device, an optoelectronic device, or a combination thereof. In some examples, the methods can comprise using the photoelectrode as an electrode in an energy conversion device, wherein the energy conversion device comprises a solar cell, a fuel cell, a photovoltaic cell, another type of voltage or current source, or a combination thereof

[0147] Also disclosed herein are devices comprising any of the photoelectrodes described herein. For example, the device can comprise an energy conversion device, a charge storage device, an electronic device, an optoelectronic device, or a combination thereof. In some examples, the device can comprise an energy conversion device, such as a solar cell, a fuel cell, a photovoltaic cell, another type of voltage or current source, or a combination thereof.

[0148] Also disclosed herein are photoelectrochemical cells comprising any of the photoelectrodes described herein and methods of use thereof. For example, also disclosed herein are photoelectrochemical cells comprising: a working electrode in electrochemical contact with a fluid and one or more additional electrodes in electrochemical contact with the fluid, wherein the working electrode can comprise any of the photoelectrodes disclosed herein.

[0149] In some examples, the fluid can comprise a fuel precursor. Examples of fuel precursors include, but are not limited to, water, carbon dioxide, and combinations thereof. In some10046-662W01; 8574 YU examples, the fuel precursor comprises water in the form of an aqueous solution, such as, for example, contaminated water, nonpurified water, saline water, sea water, etc.

[0150] Also disclosed herein are methods of use of any of the photoelectrochemical cells disclosed herein. In some examples, the fluid comprises a fuel precursor and the method can comprise photoelectrochemical fuel generation. The method can, for example, comprise illuminating the photoelectrode in contact with the fuel precursor with electromagnetic radiation that overlaps at least a portion of the photon energy range absorbed by the light absorbing, thereby providing photogenerated electrons or holes in the light absorbing which are transported to the catalyst material at the interface between the photoelectrode and the fuel precursor which participate in the desired electrochemical reaction to thereby convert the fuel precursor to a fuel. In some examples, the methods can further comprise collecting the fuel.

[0151] The electromagnetic radiation can, for example, comprise light and the light can be provided by a light source.. The light source can be any type of light source. Examples of suitable light sources include natural light sources (e.g., sunlight) and artificial light sources (e.g., incandescent or other types of light bulbs, light emitting diodes, gas discharge lamps, arc lamps, lasers, etc.). In some examples, the electromagnetic radiation comprises sunlight. In some examples, the method comprises solar powered photoelectrochemical fuel production.

[0152] In some examples, the fuel precursor comprises water and the method comprises photoelectrochemical water splitting. In some examples, the fuel precursor comprise water, the electromagnetic radiation comprises sunlight, and the method comprises solar water splitting.

[0153] In some examples, the fuel comprises H2and the method comprises photoelectrochemical hydrogen generation.

[0154] In some examples, the fuel precursor comprises carbon dioxide and the method comprises photoelectrochemical reduction of CO2.

[0155] In some examples, the fluid has a pH of 8 or more and the photoelectrode is stable for 24 hours or more. As used herein, the photoelectrode being “stable” means that the photoelectrode has a photocurrent that is stable, e.g. wherein the photocurrent varies by 10% or less (e.g., 9% or less, 8% or less, 7% or less, 6% or less, 5% or less, 4% or less, 3% or less, 2% or less, or 1% or less) over the selected time period. In some examples, the fluid has a pH of 14 and the photoelectrode is stable for 48 hours or more (e.g., 72 hour or more, 96 hours or more, 120 hours or more, 144 hours or more, or 168 hours or more).

[0156] A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope10046-662W01; 8574 YU of the invention. Accordingly, other embodiments are within the scope of the following claims.

[0157] The examples below are intended to further illustrate certain aspects of the systems and methods described herein, and are not intended to limit the scope of the claims.

[0158] EXAMPLES

[0159] The following examples are set forth below to illustrate the methods and results according to the disclosed subject matter. These examples are not intended to be inclusive of all aspects of the subject matter disclosed herein, but rather to illustrate representative methods and results. 'These examples are not intended to exclude equivalents and variations of the present invention which are apparent to one skilled in the art.

[0160] Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.) but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in °C or is at ambient temperature, and pressure is at or near atmospheric. There are numerous variations and combinations of measurement conditions, e.g., component concentrations, temperatures, pressures and other measurement ranges and conditions that can be used to optimize the described process.

[0161] Example 1 - Patterned metal-insulator-semiconductor photoelectrodes for photoelectrochemical reactions

[0162] Described herein are patterned metal-insulator-semiconductor photoelectrodes for photoelectrochemical reactions created by micron-scale patterning (lithographic) techniques combined with a metal / dielectric, e.g., Al / SiCh, thin-film reaction process in which the metal, e.g., Al, forms nano- to micron-scale “spikes” penetrating the dielectric, e.g., SiCh, layer.

[0163] Removal of the Al following the spike-formation process, e.g., by wet chemical etching, and then subsequent electrodeposition of a suitable catalyst material into the voids left behind after etching of the metal spikes yields the final photoelectrode structure. In this structure, the underlying semiconductor layer serves to absorb light resulting in the formation of electron-hole pairs. The resulting electrons, holes, or both then diffuse to the semiconductor-catalyst contact and enter the metal catalyst to participate in the desired photoelectrochemical reaction at the catalyst surface. The dielectric layer serves to isolate the semiconductor from the aqueous solution in which the photoelectrode must be immersed, as the semiconductor will, if exposed to the solution, typically oxidize or corrode. This concept builds upon the technology disclosed elsewhere, in which the thin-film reaction process for spike formation to create photoelectrodes for photoelectrochemical reactions was disclosed, such as WO 2022 / 235423 which is hereby incorporated herein by reference for its description thereof. The additional element in the current disclosure is patterning of the Al that undergoes the thin-film reaction, resulting in minimization10046-662W01; 8574 YU or elimination of partial spiking and improved control over catalyst spatial distribution and morphology.

[0164] While the current disclosure is not specific to any particular lithographic patterning technology, the cost-effectiveness of the approach described here can depend on implementation using a highly scalable and low-cost patterning technique capable of producing micron-scale features. Conventional lithographic techniques such as optical or electron-beam lithography that are typically used in the semiconductor industry are likely to be too expensive for practical, cost- effective implementations of the technology described here. However, a technology disclosed in WO 2025 / 096777, which is hereby incorporated herein by reference for its description of the methods therein, on a method for self-assembly of nanostructures using ultrasonic aerosolization provides a promising approach for low-cost, highly scalable patterning that, combined with the thin-film reaction technology, could enable cost-effective realization of patterned photoelectrodes at large scale.

[0165] This disclosure builds upon the peculiar nature of certain metal / dielectric, e.g., Al / SiCh, thin-film reactions in which localized mass transport of the metal atoms into the dielectric to form pure regions of metal occurs, rather than diffusive transport to form alloys or mixtures. Previously, this behavior was implemented in unpatterned thin-film structures to create random arrays of metal spikes penetrating a dielectric with an average density suitable for fabrication of photoelectrodes. Using patterning to create regular arrays of metal, e.g., Al, islands atop the dielectric, e.g., SiO2, allows arrays of metal spikes to be formed that are highly uniform in both the spatial distribution of the spikes and the size of each spike. Catalysts electrodeposited into the voids left behind after etching of the metal spikes then exhibit much more uniform size and morphology. Uniformity in catalyst spatial distribution and morphology results in improved photoelectrode performance.

[0166] By combining the concept of photoelectrodes with patterned catalysts with the rapid, highly scalable nanoparticle self-assembly technology described elsewhere (e.g., WO 2025 / 096777), or potentially other low-cost lithographic techniques, scalability of this concept to large areas and rapid, cost-effective production becomes feasible.

[0167] In the absence of patterning, the thin-film reaction approach exploited here and elsewhere is susceptible to the formation of “partial” spikes in which the metal, e.g., Al, does not penetrate completely through the dielectric, e.g., SiO2layer. After the metal is etched away, the remaining dielectric layer is thinner at the locations of the partial spikes, and no catalyst is electrodeposited at those locations since the remaining dielectric blocks the flow of electric current required for the electrodeposition process. These thin regions of dielectric produced by partial spiking are10046-662W01; 8574 YU likely to reduce long-term stability of the photoelectrode since the dielectric serves as a protective layer separating the semiconductor absorber below it from the aqueous solution in which the photoelectrochemical reactions are occurring. Micron-scale patterning of metal islands prior to the annealing that drives the thin-film reaction ensures that spiking occurs only in the regions directly below the metal islands. Because the spiking reaction is occurring only at these locations, more aggressive annealing conditions can be employed to ensure that every spiking reaction occurs to completion, i.e., complete penetration of the metal spike through the dielectric layer. Thus, the process approach described here minimizes or eliminates the issue of partial spiking leading to thinned areas of the dielectric protective layer in a photoelectrode.

[0168] As noted above, this disclosure can improve the stability and performance of metal- insulator-semiconductor photoelectrodes fabricated using the approach described elsewhere (e.g., WO 2022 / 235423). As also noted above, in combination with the self-assembly technology described elsewhere (e.g., WO 2025 / 096777), or potentially other low-cost patterning techniques, this approach can enable these improvements to be realized with minimal impact on cost and scalability to high production volumes.

[0169] The technology described here requires the introduction of an additional process step into the photoelectrode fabrication process compared to that described elsewhere. There will be a nonzero increase in cost, manufacturing time, and process complexity associated with this additional step, but using the patterning approach described elsewhere, or other low-cost, rapid patterning techniques, these increases are expected to be modest.

[0170] An application for the photoelectrodes described here is solar-powered splitting of water molecules to form hydrogen and oxygen molecules, with hydrogen being the useful product. However, other photoelectrochemical reactions, e.g., conversion of CO2 to CO, could also be performed.

[0171] The technology described herein may be of interest to companies involved in green hydrogen production, including those in the fossil fuel industry. The technology described herein may be of interest to companies involved in solar cell manufacturing, as the processes and materials employed here are similar to those for silicon solar cells.

[0172] Example 2

[0173] Solar powered water splitting and other photoelectrochemical reactions offer routes to the generation of hydrogen or other high-value chemicals using renewable energy sources.

[0174] Commercially viable technologies for solar water splitting have been hampered by cost and the tendency of efficient solar absorbing materials, e.g., silicon or gallium arsenide, to degrade in the presence of water splitting reactions. Metal-insulator-semiconductor (MIS) photoelectrodes for10046-662W01; 8574 YU solar water splitting offer a route to addressing the latter issue by covering the semiconductor with a chemically stable protective layer, but these layers are typically electrically insulating and block the flow of photogenerated electrons and / or holes to the surface of the device at which the water splitting reactions take place. The use of low-cost materials, such as silicon, combined with low-cost, scalable processes for photoelectrode fabrication offers a route to addressing the former issue. Successfully addressing these issues would provide a foundation for the development of a clean, economically viable technology for generation of hydrogen and other high-value chemicals for energy storage, transport, and chemical synthesis applications.

[0175] Described herein are device designs and fabrication processes that enable the creation of silicon-based MIS photoelectrodes for solar water splitting or other photoelectrochemical reactions with thick, extremely stable protective insulating layers that enable excellent stability and high solar-to-hydrogen efficiency combined with low cost and excellent potential for scalability in manufacturing. Use of very low cost, highly scalable approaches for micron-scale patterning of catalysts on the photoelectrode surface enable precise control over catalyst density, spatial distribution, and morphology resulting in outstanding photoelectrode performance.

[0176] This technology leverages established, low-cost, highly scalable silicon semiconductor process technology combined with new self-assembly techniques for nanopatterning for fabrication of low cost, highly stable, high performance MIS photoelectrodes for solar driven water splitting and other photoelectrochemical reactions. MIS photoanode devices demonstrated experimentally are fabricated from standard silicon wafers, incorporate thick (-100 nm) insulating protective layers and low-cost, earth- abundant catalyst materials, and with minimal optimization have yielded wafer-scale photoanodes that, combined with commercial silicon solar cells in a self-contained solar-powered water splitting system, yield -7% solar-to-hydrogen (STH) efficiency with a clear route to STH efficiency of at least 12%.

[0177] 'This technology offers a clear route to highly scalable manufacturing of silicon-based photoelectrodes for solar-powered water splitting and other photoelectrochemical reactions with a cost structure similar to that for manufacturing of silicon photovoltaics. Combined with excellent performance and stability demonstrated to date, this technology has the potential to enable dramatic progress towards cost-effective green hydrogen production via photoelectrochemical techniques.

[0178] 'This technology may be of interest to energy companies, chemical companies, and auto manufacturers pursuing fuel cell vehicle technologies.

[0179] Example 3 - Patterned metal-insulator-semiconductor photoelectrodes for

[0180] ph otoelectroch emical reactions10046-662W01; 8574 YU Potential issues in Al thin film reaction are shown in Figure 1. Al thin film reaction in SiO2 layer produces random / uneven spiking morphology. A large portion of voids in SiCh layer will be attacked in KOH solution, which can decrease device stability.

[0181] Surface morphology of Al thin film reaction are shown in Figure 2 - Figure 3 (CHA#1 AlSi 150 nm + Annealed 480C 5hr + Ni Electrodepostion 3.5V 15min).

[0182] Colloidal lithography for Si-based MIS photoanodes is shown in Figure 5 - Figure 6. NSL-assisted Al spiking method provides localized hole arrays, which control the coverage ratio of the catalyst, which provides higher light transmission and device stability.

[0183] Ni coverage optimization is shown in Figure 7.

[0184] PEC performance thin-film vs. patterned photoanode is shown in Figure 8. The patterned photoanode has better PEC performance compared to thin-film photoanode. The patterned photoanode achieves a maximum ABPE of 1.39% at 1.06 V versus RHE.

[0185] Example 4 - Scalable Si-Based Metal-Insulator-Semiconductor Photoanodes for Water Oxidation Fabricated Using Nanosphere Lithography and Thin Film Reaction Photoelectrochemical (PEC) water splitting is a promising approach for converting solar energy into storable hydrogen, offering a sustainable alternative to fossil-based hydrogen production. PEC cells rely on semiconductor materials to absorb sunlight and generate mobile charge carriers that drive the hydrogen and oxygen evolution reactions. Si-based photoelectrodes are especially attractive due to their optimal bandgap, high charge mobility, long diffusion lengths, and cost-effective, scalable manufacturing process. To improve the stability of Si-based PEC cells, metal-insulator-semiconductor (MIS) structures have emerged as a promising approach [1], MIS photoanodes integrate ultrathin insulating layers that protect the Si surface while maintaining charge transfer efficiency. The thickness of the insulator is critical: ultrathin layers facilitate effective charge tunneling, whereas thicker layers enhance long-term stability in corrosive environments.

[0186] In previous work, it was demonstrated that localized conduction paths formed via an Al / SiO2thin-film reaction enable low-resistance charge extraction through thick insulating layers, while also providing excellent stability and scalability to full-wafer photoanodes [2], However, the performance of such photoelectrodes can be limited by nonuniformity in thin-film reaction behavior. Demonstrated herein is a method for creating more controllable and uniform localized conduction paths on the photoanode by employing nanosphere lithography (NSL), a low-cost and highly scalable patterning technique. NSL is used to create a patterned mask for Al deposition that enables the density and locations of Al / SiO2thin-film reactions and consequently metal catalysts to be precisely controlled, leading to improvements in both photocurrent density10046-662W01; 8574 YU and onset voltage. Moreover, a recently developed technique for extremely rapid large-area nanosphere monolayer formation [3] makes this patterning approach easily scalable to fabrication of full-wafer photoanodes and therefore, highly promising for large-scale PEC applications.

[0187] Figure 9 shows an SEM image of a patterned photoanode.

[0188] Figure 10 shows an LSV curve for patterned and thin-film photoanode.

[0189] Figure 11 shows process flow and SEM images of fabrication of patterned photoanode. Figure 12 shows SEM images of patterned photoanode with different Ni electrodeposition time (at the same voltage of 3.5 V) (a) 10 minutes (b) 15 minutes (c) 20 minutes (d) Unpatterned photoanode (electrodeposition at 3.5 V for 15 minutes).

[0190] References

[0191] [1] M. J. Kenney, M. Gong, Y. Li, J. Z. Wu, J. Feng, M. Lanza, H. Dai, Science, 342, 6160, 836-840, (2013)

[0192] [2] S. Lee, S. Wu, E. T. Yu, ACS Appl. Energy Mater. 2024, 7, 8, 3253-3262

[0193] [3] G. Cossio, R. Barbosa, B. Korgel, E. T. Yu, Adv. Mater. 2309775 (2023)

[0194] EXEMPLARY ASPECTS

[0195] In view of the described compositions, devices, systems, and methods, herein below are described certain more particularly described aspects of the inventions. The particularly recited aspects should not, however, be interpreted to have any limiting effect on any different claims containing different or more general teachings described herein or that the “particular” aspects are somehow' limited in some way other than the inherent meanings of the language and formulas literally used therein.

[0196] Example 1: A photoelectrode comprising: a light absorbing layer; an insulator layer disposed on the light absorbing layer; and a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer, such that each protrusion is in physical and electrical contact with the light absorbing layer; and a plurality of particles disposed on the insulator layer, wherein a least a portion of at least one of the particles is in physical and electrical contact with at least a portion of one of the protrusions (preferably, wherein at least a portion of each of the particles is in physical and electrical contact with at least a portion of one of the protrusions); and wherein the plurality of particles and optionally the plurality of protrusions comprise a catalyst material.

[0197] Example 2: The photoelectrode of any example herein, particularly example 1, wherein the light absorbing layer comprises silicon, gallium arsenide, AlGaAs, InP, InGaP, InAlP, A1P, InGaAsN, InGaAs, GaN, InGaN, AlInGaN, AlGaN, SiGe, SiC, CdTe, CdSe, ZnO, ZnSe, ZnTe,10046-662W01; 8574 YU CdZnTe, SnS2, Zn3P2, ZnP2, Zn3As2, TiO2, hybrid organic-inorganic perovskite compounds, copper oxides, SrTiO3, M0S2, GaSe, SnS, CuInGaSe2, a-Si: H (hydrogenated amorphous silicon), bismuth vanadate (BiVO4), iron oxide (Fe2O3), an organic / molecular material (e.g., such as those used as solar absorbers in organic solar cells), or a combination thereof.

[0198] Example 3: The photoelectrode of any example herein, particularly example 1 or example 2, wherein the light absorbing layer comprises silicon.

[0199] Example 4: The photoelectrode of any example herein, particularly examples 1-3, wherein the light absorbing layer has an average thickness of from 50 nanometers (nm) to 500 micrometers (microns, pm).

[0200] Example 5: The photoelectrode of any example herein, particularly examples 1-4, wherein the light absorbing layer further comprises a doped region.

[0201] Example 6: The photoelectrode of any example herein, particularly example 5, wherein the doped region comprises doped silicon.

[0202] Example 7: The photoelectrode of any example herein, particularly example 5 or example 6, wherein the doped region comprises p+doped silicon.

[0203] Example 8: The photoelectrode of any example herein, particularly examples 5-7, wherein the doped region comprises boron doped silicon.

[0204] Example 9: The photoelectrode of any example herein, particularly examples 5-8, wherein the doped region comprises a doped layer having an average thickness of from 10 nm to 500 pm.

[0205] Example 10: The photoelectrode of any example herein, particularly examples 1-9, wherein the light absorbing layer comprises Si with a buried pn junction.

[0206] Example 11: The photoelectrode of any example herein, particularly examples 1-10, wherein the insulator layer comprises SiO2, TiO2, silicon nitride, silicon oxynitride, aluminum oxide, strontium titanate, tungsten oxide (WO3), aluminum nitride, boron nitride, aluminum gallium nitride, or a combination thereof.

[0207] Example 12: The photoelectrode of any example herein, particularly examples 1-11, wherein the insulator layer comprises SiO2.

[0208] Example 13: The photoelectrode of any example herein, particularly examples 1-12, wherein the insulator layer has an average thickness of 20 nm or more, 50 nm or more, 75 nm or more, or 90 nm or more.

[0209] Example 14: The photoelectrode of any example herein, particularly examples 1-13, wherein the catalyst material comprises a metal selected from the group consisting of Ni, Pt, Mo, Co, Ru, Ir, Fe, or a combination thereof.10046-662W01; 8574 YU Example 15: The photoelectrode of any example herein, particularly examples 1-14, wherein the catalyst material comprises Ni.

[0210] Example 16: The photoelectrode of any example herein, particularly examples 1-15, wherein the catalyst material comprises an oxygen evolution reaction catalyst.

[0211] Example 17: The photoelectrode of any example herein, particularly examples 1-16, wherein each of the protrusions in the plurality of protrusions has an average characteristic dimension of from 0.1 nm to 10 pm.

[0212] Example 18: The photoelectrode of any example herein, particularly examples 1-17, wherein each of the protrusions in the plurality of protrusions has an average characteristic dimension that varies with the thickness of the insulator layer.

[0213] Example 19: The photoelectrode of any example herein, particularly examples 1-18, wherein the ordered array is a linear array, a triangular array, a hexagonal array, or a quadrilateral array.

[0214] Example 20: The photoelectrode of any example herein, particularly examples 1-19, wherein the ordered array is a hexagonal array.

[0215] Example 21: The photoelectrode of any example herein, particularly examples 1-20, wherein the ordered array is a two dimensional array defined by a first unit cell having a first principle axis and a second principle axis with a first included angle between the first principle axis and the second principle axis.

[0216] Example 22: The photoelectrode of any example herein, particularly example 21, wherein the length of the first principle axis and / or the second principle axis independently is from 10 nanometers (nm) to 50 micrometers (microns, pm), such as from 50 nanometers to 10 micrometers.

[0217] Example 23: The photoelectrode of any example herein, particularly example 21 or example 22, wherein the length of the first principle axis and the second principle axis are the same.

[0218] Example 24: The photoelectrode of any example herein, particularly examples 21-23, wherein the first included angle is from 30° to 150°, such as from 60° to 120°.

[0219] Example 25: The photoelectrode of any example herein, particularly examples 21-24, wherein the first unit cell is in the shape of a triangle or a quadrilateral.

[0220] Example 26: The photoelectrode of any example herein, particularly examples 1-25, wherein the plurality of protrusions are dispersed across the insulator layer laterally such that the areal density of the plurality of protrusions within the insulator layer is from 102to 1013protrusions per cm2of the insulator layer.10046-662W01; 8574 YU Example 27: The photoelectrode of any example herein, particularly examples 1-26, wherein the plurality of protrusions are dispersed throughout the insulator layer such that the areal density of the plurality of protrusions within the insulator layer is from 2 x 107to 8 x 109protrusions per cm2of the insulator layer.

[0221] Example 28: The photoelectrode of any example herein, particularly examples 1-27, wherein the plurality of particles have an average height of from 1 nm to 1 pm, such as from 10 nm to 500 nm.

[0222] Example 29: The photoelectrode of any example herein, particularly examples 1-28, wherein the plurality of particles and / or the plurality of protrusions cover from 1% to 100%, from 5% to 90%, or from 5% to 80% of the top surface of the insulator layer.

[0223] Example 30: The photoelectrode of any example herein, particularly examples 1-29, wherein the plurality of particles and / or the plurality of protrusions cover 10% or more, 25% or more, 35%’ or more, 50% or more, or 70% or more of the top surface of the insulator layer.

[0224] Example 31: A method of making a photoelectrode, the method comprising: patterning a reactive material on an insulator layer, the reactive material being patterned in an ordered array and the insulator layer being disposed on a light absorbing layer, such that the insulator layer is disposed between the light absorbing layer and the ordered array of the reactive material, thereby forming a precursor electrode; annealing the precursor electrode such that the reactive material reacts with and diffuses through the insulator layer, thereby forming a plurality of spikes comprising the reactive material, wherein each of the spikes penetrates through the insulator layer to the light absorbing layer, such that each of the spikes is in physical and electrical contact with the light absorbing layer, thereby forming a spiked electrode; removing the reactive material from the spiked electrode, thereby forming an intermediate electrode; and subsequently depositing a catalyst material on the intermediate electrode; thereby forming a photoelectrode comprising: the insulator layer disposed on the light absorbing layer; a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer, such that each of the protrusions is in physical and electrical contact with the light absorbing layer; and a plurality of particles disposed on the insulator layer, wherein a least a portion of at least one of the particles is in physical and electrical contact with at least a portion of one of the protrusions (preferably, wherein at least a portion of each of the particles are in physical and electrical contact with at least a portion of one of the protrusions); and wherein the plurality of particles and optionally the plurality of protrusions comprise a catalyst material.

[0225] Example 32: The method of any example herein, particularly example 31, wherein the10046-662W01; 8574 YU photoelectrode comprises the photoelectrode of any example herein, particularly examples 1-30.

[0226] Example 33: The method of any example herein, particularly examples 31-32, wherein the method further comprises forming the insulator layer on the light absorbing layer.

[0227] Example 34: The method of any example herein, particularly example 33, wherein forming the insulator layer comprises thermal oxidation, electroplating, lithographic deposition, electron beam deposition, thermal deposition, spin coating, drop-casting, zone casting, dip coating, blade coating, spraying, vacuum filtration, chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), sputtering, pulsed layer deposition, molecular beam epitaxy, evaporation, or combinations thereof, or a combination thereof.

[0228] Example 35: The method of any example herein, particularly examples 33-34, wherein forming the insulator layer comprises thermal oxidation.

[0229] Example 36: The method of any example herein, particularly example 35, wherein thermal oxidation comprises heating the light absorbing layer at a temperature of from 800°C to 1200°C in the presence of oxygen for an amount of time of from 10 seconds to 30 hours.

[0230] Example 37: The method of any example herein, particularly examples 33-36, wherein the method further comprises doping the light absorbing layer to form a doped region prior to forming the insulator layer.

[0231] Example 38: The method of any example herein, particularly example 37, wherein doping the light absorbing layer comprises annealing the light absorbing layer in the presence of a dopant source.

[0232] Example 39: The method of any example herein, particularly example 38, wherein the dopant source comprises a boron source.

[0233] Example 40: The method of any example herein, particularly example 38 or example 39, wherein annealing comprises heating the insulator layer at a temperature of from 100°C to 1800°C in the presence of the dopant source for an amount of time of from 10 seconds to 100 hours.

[0234] Example 41: The method of any example herein, particularly examples 31-40, wherein patterning the reactive material comprises lithography, such as electron beam lithography, optical lithography, nanoimprint lithography, nanoparticle lithography such as nanosphere lithography, focused ion beam lithography, photolithography, or a combination thereof.

[0235] Example 42: The method of any example herein, particularly examples 1-41, wherein the patterning the reactive material comprises nanosphere lithography.

[0236] Example 43: The method of any example herein, particularly examples 31-42, wherein patterning the reactive layer comprises forming a self-assembled nanoparticle monolayer via the10046-662W01; 8574 YU methods of WO 2025 / 096777 followed by depositing the reactive material, for example via thin film deposition such as sputtering.

[0237] Example 44: The method of any example herein, particularly examples 31-43, wherein the reactive material comprises Al.

[0238] Example 45: The method of any example herein, particularly examples 31-44, wherein annealing the precursor electrode comprises heating the precursor electrode at a temperature of from 300°C to 1500°C for an amount of time of from 1 minute to 48 hours.

[0239] Example 46: The method of any example herein, particularly examples 31-45, wherein removing the reactive material comprises etching the reactive material.

[0240] Example 47: The method of any example herein, particularly example 46, wherein etching the reactive material comprises contacting the reactive material with an etchant.

[0241] Example 48: The method of any example herein, particularly example 47, wherein the etchant comprise H3PO4.

[0242] Example 49: The method of any example herein, particularly examples 31-48, wherein depositing the catalyst material comprises electrodeposition, such as electroplating.

[0243] Example 50: A method of use of the photoelectrode of any example herein, particularly examples 1-30 or a photoelectrode made by the methods of any example herein, particularly examples 1-49.

[0244] Example 51: The method of any example herein, particularly example 50, wherein the method comprises using the photoelectrode as an electrode in a photoelectrochemical reaction.

[0245] Example 52: The method of any example herein, particularly example 50, wherein the method comprises using the photoelectrode as an electrode in an energy conversion device, a charge storage device, an electronic device, or a combination thereof.

[0246] Example 53: The method of any example herein, particularly example 52, wherein the device comprises an energy conversion device, the energy conversion device comprising a solar cell, a fuel cell, a photovoltaic cell, or a combination thereof.

[0247] Example 54: A photoelectrochemical cell comprising: a working electrode in electrochemical contact with a fluid and one or more additional electrodes in electrochemical contact with the fluid, wherein the working electrode comprises the photoelectrode of any example herein, particularly examples 1-30 or a photoelectrode made by the methods of any example herein, particularly examples 1-49.

[0248] Example 55: The photoelectrochemical cell of any example herein, particularly example 54, wherein the fluid comprises a fuel precursor.

[0249] Example 56: The photoelectrochemical cell of any example herein, particularly example10046-662W01; 8574 YU 55, wherein the fuel precursor comprises water, carbon dioxide, or a combination thereof.

[0250] Example 57: A method of use of the photoelectrochemical cell of any example herein, particularly examples 54-56 for photoelectrochemical fuel generation.

[0251] Example 58: The method of any example herein, particularly example 57, wherein the fluid comprises a fuel precursor and the method comprises illuminating the photoelectrode in contact with the fuel precursor with electromagnetic radiation that overlaps at least a portion of the photon energy range absorbed by the light absorbing, thereby providing photogenerated electros or holes in the light absorbing which are transported to the catalyst material at the interface between the photoelectrode and the fuel precursor which participate in the desired electrochemical reaction to thereby convert the fuel precursor to a fuel.

[0252] Example 59: The method of any example herein, particularly example 58, wherein the method further comprises collecting the fuel.

[0253] Example 60: The method of any example herein, particularly example 58 or example 59, wherein the electromagnetic radiation comprises light and the light is provided by a light source, wherein the light source comprises an artificial light source or a natural light source.

[0254] Example 61: The method of any example herein, particularly examples 58-60, wherein the electromagnetic radiation comprises sunlight.

[0255] Example 62: The method of any example herein, particularly examples 57-61, wherein the method comprises solar powered photoelectrochemical fuel production.

[0256] Example 63: The method of any example herein, particularly examples 58-62, wherein the fuel precursor comprises water and the method comprises photoelectrochemical water splitting.

[0257] Example 64: The method of any example herein, particularly examples 58-63, wherein the fuel precursor comprise water, the electromagnetic radiation comprises sunlight, and the method comprises solar water splitting.

[0258] Example 65: The method of any example herein, particularly examples 58-64, wherein the fuel comprises H2and the method comprises photoelectrochemical hydrogen generation.

[0259] Example 66: The method of any example herein, particularly examples 58-62, wherein the fuel precursor comprises carbon dioxide and the method comprises photoelectrochemical reduction of CO2.

[0260] Example 67: The method of any example herein, particularly examples 57-66, wherein the fluid has a pH of 8 or more and the photoelectrode is stable for 24 hours or more.

[0261] Example 68: The method of any example herein, particularly examples 57-67, wherein the fluid has a pH of 14 and the photoelectrode is stable for 48 hours or more.10046-662W01; 8574 YU Example 69: A device comprising the photoelectrode of any example herein, particularly examples 1 -30 or a photoelectrode made by the methods of any example herein, particularly examples 31-49.

[0262] Example 70: The device of any example herein, particularly example 69, wherein the device comprises an energy conversion device, a charge storage device, an electronic device, or a combination thereof.

[0263] Example 71: The device of any example herein, particularly example 70, wherein the device comprises an energy conversion device, the energy conversion device comprising a solar cell, a fuel cell, a photovoltaic cell, or a combination thereof.

[0264] Other advantages which are obvious and which are inherent to the invention will be evident to one skilled in the art. It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

[0265] The compositions, systems, and methods of the appended claims are not limited in scope by the specific compositions, system, and methods described herein, which are intended as illustrations of a few aspects of the claims and any methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the compositions, systems, and methods in addition to those shown and described herein are intended to fall within the scope of the appended claims. Further, while only certain representative composition elements, system elements, and method steps disclosed herein are specifically described, other combinations of the composition elements, system elements, and method steps also are intended to fall within the scope of the appended claims, even if not specifically recited. Thus, a combination of steps, elements, components, or constituents may be explicitly mentioned herein or less, however, other combinations of steps, elements, components, and constituents are included, even though not explicitly stated.

Claims

10046-662W01; 8574 YU CLAIMSWhat is claimed:

1. A photoelectrode comprising:a light absorbing layer;an insulator layer disposed on the light absorbing layer;a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer, such that each protrusion is in physical and electrical contact with the light absorbing layer; anda plurality of particles disposed on the insulator layer, wherein a least a portion of at least one of the particles is in physical and electrical contact with at least a portion of one of the protrusions (preferably, wherein at least a portion of each of the particles is in physical and electrical contact with at least a portion of one of the protrusions);wherein the plurality of particles and optionally the plurality of protrusions comprise a catalyst material.

2. The photoelectrode of claim 1, wherein the light absorbing layer comprises silicon and / or the light absorbing layer has an average thickness of from 50 nanometers (nm) to 500 micrometers (microns, pm).

3. The photoelectrode of any one of claims 1-2, wherein the insulator layer comprises SiO2and / or wherein the insulator layer has an average thickness of 20 nm or more, 50 nm or more, 75 nm or more, or 90 nm or more.

4. The photoelectrode of any one of claims 1-3, wherein the catalyst material comprises a metal selected from the group consisting of Ni, Pt, Mo, Co, Ru, Ir, Fe, or a combination thereof.

5. The photoelectrode of any one of claims 1-4, wherein the catalyst material comprises Ni.

6. The photoelectrode of any one of claims 1-5, wherein each of the protrusions in the plurality of protrusions has an average characteristic dimension of from 0.1 nm to 10 pm.

7. The photoelectrode of any one of claims 1-6, wherein the ordered array is a linear array, a triangular array, a hexagonal array, or a quadrilateral array.

8. The photoelectrode of any one of claims 1-7, wherein the plurality of particles have an average height of from 1 nm to 1 pm, such as from 10 nm to 500 nm.10046-662W01; 8574 YU 9. A method of making a photoelectrode, the method comprising:patterning a reactive material on an insulator layer, the reactive material being patterned in an ordered array and the insulator layer being disposed on a light absorbing layer, such that the insulator layer is disposed between the light absorbing layer and the ordered array of the reactive material, thereby forming a precursor electrode;annealing the precursor electrode such that the reactive material reacts with and diffuses through the insulator layer, thereby forming a plurality of spikes comprising the reactive material, wherein each of the spikes penetrates through the insulator layer to the light absorbing layer, such that each of the spikes is in physical and electrical contact with the light absorbing layer, thereby forming a spiked electrode;removing the reactive material from the spiked electrode, thereby forming an intermediate electrode; andsubsequently depositing a catalyst material on the intermediate electrode;thereby forming a photoelectrode comprising:the insulator layer disposed on the light absorbing layer;a plurality of protrusions arranged in an ordered array, wherein each protrusion penetrates through the insulator layer to the light absorbing layer, such that each of the protrusions is in physical and electrical contact with the light absorbing layer; anda plurality of particles disposed on the insulator layer, wherein a least a portion of at least one of the particles is in physical and electrical contact with at least a portion of one of the protrusions (preferably, wherein at least a portion of each of the particles are in physical and electrical contact with at least a portion of one of the protrusions);wherein the plurality of particles and optionally the plurality of protrusions comprise a catalyst material.

10. The method of claim 9, wherein the photoelectrode comprises the photoelectrode of any one of claims 1-8.

11. The method of any one of claims 9-10, wherein the patterning the reactive material comprises nanosphere lithography.

12. The method of any one of claims 9-11, wherein patterning the reactive layer comprises forming a self-assembled nanoparticle monolayer via the methods of WO 2025 / 096777 followed by depositing the reactive material, for example via thin film deposition such as sputtering.

13. The method of any one of claims 9-12, wherein the reactive material comprises Al.10046-662W01; 8574 YU 14. The method of any one of claims 9-13, wherein annealing the precursor electrode comprises heating the precursor electrode at a temperature of from 300°C to 1500°C for an amount of time of from 1 minute to 48 hours.

15. The method of any one of claims 9-14, wherein removing the reactive material comprises etching the reactive material.

16. The method of any one of claims 9-15, wherein depositing the catalyst material comprises electrodeposition, such as electroplating.

17. A method of use of the photoelectrode of any one of claims 1-8 or a photoelectrode made by the methods of any one of claims 9-16.

18. A photoelectrochemical cell comprising: a working electrode in electrochemical contact with a fluid and one or more additional electrodes in electrochemical contact with the fluid, wherein the working electrode comprises the photoelectrode of any one of claims 1-8 or a photoelectrode made by the methods of any one of claims 9-16.

19. A method of use of the photoelectrochemical cell of claim 18 for photoelectrochemical fuel generation.

20. A device comprising the photoelectrode of any one of claims 1-8 or a photoelectrode made by the methods of any one of claims 9-16.

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