Photovoltaic structures having a composite conductor

Abstract

A photovoltaic structure includes a transparent substrate and a transparent bottom electrode provided over the substrate. The transparent bottom electrode includes a first set of metal lines in contact with a first conducting layer. The first set of metal lines is characterized by an average height (H) of at least about 150 nm, an average width (W), and an aspect ratio H / W of at least about 1 / 250. A self-assembled molecular charge selective layer (SAM-CSL) is disposed over the transparent bottom electrode. A perovskite absorber layer overlays the SAM-CSL, an upper carrier transport layer overlays the perovskite absorber layer, and a top electrode overlays the upper carrier transport layer.

Description

[0001] PHOTOVOLTAIC STRUCTURES HAVING A COMPOSITE CONDUCTOR

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to perovskite photovoltaic (PV) devices having a transparent composite conductor and a self-assembled molecular charge selective layer.

[0004] BACKGROUND

[0005] Since their first report in 2009, rapid improvements have enabled perovskite solar cells (PSCs) to become a promising technology for converting light to electricity as part of optoelectronic devices. To date, the power conversion efficiencies (PCEs) of solution-processed PSCs have been certified above 25 percent, which is higher than the current dominant photovoltaic technology based on multi-crystalline silicon. Whereas crystalline silicon is rigid, brittle, and requires costly, energy-intensive fabrication procedures, perovskites are flexible, easily processed at low temperatures, and up to a thousand times thinner. Furthermore, perovskites are solution-processable, which enables their manufacture with scalable, low-cost methods. These attributes open new opportunities to integrate solar power creatively and inexpensively into previously inaccessible markets, such as electric vehicles and buildings. PSCs also have the important advantage of maintaining acceptable PCE as the temperature increases, unlike silicon-based solar cells, which exhibit significant power loss in typical operating environments. The manufacturing and PCE advantages of PSCs have put them on the path to be the next generation technology for utility, commercial, and residential photovoltaic applications.

[0006] Most top performing PSCs reported in the literature have been fabricated by lab-scale, spin-coating methods, which are unsuitable for high throughput and scalable module production. Forming high-performing, uniform, and defect-free multilayer structures on flexible substrates to make PSCs in a cost-effective manner remains a great challenge. Some of this complexity is due to the complexity of depositing and drying a perovskite solution with high-speed production equipment, but other layers can be challenging as well. Some non-limiting factors to consider in the manufacture of multilayer PSCs may include the adhesion of one layer to another, the chemical compatibility of a coating solution with an underlying layer, thermal treatments and compatibility of such with other layers, surface energy or structures and their effect on coatability, layer flexibility, thermal expansion properties, and optical properties, just to name a few. High efficiency PSCs benefit from electrodes that have low electrical resistance and high optical transparency, but such electrodes can be difficult to produce at high manufacturing speeds in a manner compatible with other layers of the PSC, which are typically very thin. Low resistance transparent electrodes arc particularly desired for high area devices where photogenerated currents may need to travel a significant distance to current collectors or other device components.

[0007] Despite research into various approaches, PVs based primarily on perovskites have yet to make a large market impact due at least in part to some of the unresolved problems noted above.

[0008] SUMMARY

[0009] There remains a desire for PSC devices that can be reliably manufactured at large scale at low cost, have high PCEs, and that can be made having large sizes or surface areas without unacceptable power loss.

[0010] In accordance with an embodiment of this disclosure, a photovoltaic structure includes a transparent substrate and a transparent bottom electrode provided over the substrate. The transparent bottom electrode includes a first set of metal lines in contact with a first conducting layer. The first set of metal lines is characterized by an average height (H) of at least about 150 nm, an average width (W), and an aspect ratio H / W of at least about 1 / 250. A self-assembled molecular charge selective layer (SAM-CSL) is disposed over the transparent bottom electrode. A perovskite absorber layer overlays the SAM-CSL, an upper carrier transport layer overlays the perovskite absorber layer, and a top electrode overlays the upper carrier transport layer.

[0011] The present disclosure provides for PV devices that may have one or more of the following advantages relative to conventional PV devices: improved PCE; lower resistance electrodes; electrodes with higher optical transparency; improved manufacturing scalability; simplified manufacturing process; reduced manufacturing defects; more reproducible manufacturing process; reduced environmental impact manufacturing process; increased physical durability or increased lifetime.

[0012] BRIEF DESCRIPTION OF DRAWINGS

[0013] FIG. 1A is a cross-scctional view of a non-limiting example of a perovskite photovoltaic structure according to some embodiments.

[0014] FIG. IB is an enlarged view of area B from FIG. 1 A.

[0015] FIGS. 1C and ID are cross-sectional views of some non-limiting examples of composite conductors according to some embodiments.

[0016] FIGS. 2A - 2D show some non-limiting examples of chemical structures of hole selective SAM-CSL materials.

[0017] FIG. 3 shows some non-limiting examples of chemical structures of electron selective SAM-CSL materials.

[0018] FIG. 4A is a cross-sectional view of non-limiting examples of metal lines according to some embodiments.

[0019] FIG. 4B is a top view of a non-limiting example of a set of metal lines according to some embodiments.

[0020] FIG. 5A is a top view of a non-limiting example of a perovskite PV module according to some embodiments.

[0021] FIG. 5B is a cross-sectional view along cutline B-B in FIG. 5A.

[0022] DETAILED DESCRIPTION

[0023] It is to be understood that the drawings are for purposes of illustrating the concepts of the disclosure and may not be to scale. Terms like “overlaying”, “over” or the like include, but do not necessarily require, direct contact (unless such direct contact is noted or clearly required for functionality). Additional details of certain features useful in certain embodiments of the present application may be found in U.S. Patent No. 11,108,007, U.S. Patent No. 11,342,130, U.S. Application Publication No. 2020 / 0377532, U.S. Application Publication No. 2022 / 0238807, PCT Application No. PCT / US2023 / 030527, PCT Application No. PCT / US2023 / 030576, PCT Application No. PCT / US2023 / 034120, PCT Application No. PCT / US2023 / 034146, PCT Application No. PCT / US2023 / 034137, and PCT Application No. PCT / US2023 / 078892, the entire contents of which are incorporated herein by reference for all uses.

[0024] A perovskite photovoltaic structure is intended to receive light (typically visible, IR, or UV light) and convert it into electricity. As such, various layers and features may need to be reasonably transparent to this light to ensure that an appropriate amount reaches the perovskite layer(s). Herein, unless otherwise noted, the terms “transparent”, “transparency”, “transmissivity” or the like, arc generally relative to the target wavelength or wavelength range for conversion to electricity. This target wavelength or wavelength range may be different for different systems. In some embodiments, the target wavelength range may correspond to the solar radiation spectrum or a portion thereof. In some cases, the target wavelength range may correspond to the visible light spectrum or a portion thereof. In some cases, the target wavelength range may correspond to the infrared or UV spectrum, or a portion thereof. In some embodiments, the target wavelength range may be defined as a particular wavelength, e.g., 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, or 750 nm, or any other wavelength of interest in the IR, visible, or UV portions of the spectrum intended for energy conversion. In some cases, a target wavelength range may be defined as an explicit range, e.g., 400 - 425 nm, 425 - 450 nm, 450 - 475 nm, 475 - 500 nm, 500 - 525 nm, 525 - 575 nm, 575 - 600 nm, 600 - 625 nm, 625 - 650 nm, 650 - 675 nm, 675 - 700 nm, 700 - 725 nm, 725 - 750 nm, or any combination of ranges thereof, or any other wavelength range of interest.

[0025] In some embodiments, something (e.g., a layer, a component, a structure, or the like) that is “transparent” transmits at least 50% of incident radiation within the target wavelength range, i.e., a transmittance (%T) of 50%. Something that is considered light transmissive generally transmits at least 10% of incident radiation within the target wavelength range. Transmi ttivities in the range of 10% up to 50% may be considered partially transparent. A light-transmissive component, layer, or structure may be either transparent or partially transparent.

[0026] Besides the light-absorbing properties of a layer, a component, a structure, or the like, its apparent transparency may in some cases be affected by refractive index mismatches, surface structures, or other factors that may result in reflective losses and / or light scattering. Another way to describe transparency is in terms of absorptance (%A). In some embodiments, something that is “transparent” may have an absorptance of 50% or less with respect to incident radiation within the target wavelength range. Something that is considered light transmissive may have an absorptance of 90% or less of incident radiation within the target wavelength range. Absorptances in a range of 50% up to 90% may be considered partially transparent.

[0027] FIG. 1 A is a cross-sectional view of a non-limiting example of a perovskite photovoltaic structure according to some embodiments. For added perspective, XYZ coordinate axes are also shown. FIG. IB is an enlarged view of area B from FIG. 1 A. The photovoltaic structure 100 may include a transparent substrate 161, which may in some cases be flexible. A transparent bottom electrode 162 (which may also be referred to herein as a first composite conductor or bottom composite conductor) is provided overlaying the transparent substrate 161. The bottom electrode may include a first set of conductive metal lines 103 and a first conducting layer 105 provided in contact with the first set of metal lines. In some preferred embodiments and as shown in FIG. 1A, the first set of conductive metal lines 103 may be provided over the transparent substrate 161 and the first conducting layer 105 may be provided over the first set of metal lines and the transparent substrate. In some cases, the first set of metal lines 103 have a height that is greater than the thickness of the first conducting layer 105. As illustrated, the conducting layer may form a substantially confomial coating over the metal lines and substrate, but in some cases, the conducting layer may be thinner at the sidewalls, edges, or tops of the metal lines relative to the substrate. For example, if the metal lines are formed of metal nanoparticles then they may have a roughness dependent on the size of the metal nanoparticles that is much larger than the roughness of the substrate, which increases the surface area and may decrease the local thickness conducting layer in certain regions.

[0028] Referring to FIG. 1C, in some cases, the transparent bottom electrode 162c may include an auxiliary conducting layer 104c provided between the first set of metal lines 103c and the substrate 161c, and also between the substrate 161c and the first conducting layer 105c.

[0029] In some embodiments, and referring now to FIG. ID, the transparent bottom electrode 162d may have the first conducting layer 105d provided over the substrate 16 Id with the first set of metal lines 103d provided on the first conducting layer 105d. However, this arrangement may result in unwanted migration of metal into active layers of the perovskite PV structure. In such an arrangement, an interfacial layer 106d may be provided over the metal lines 103d and conducting layer 105d. As discussed elsewhere herein, the interfacial layer may in some cases include a metal oxide deposited, e.g., by an atomic layer deposition process. Not only may this reduce unwanted migration of metal, it also provides a uniform surface onto which the SAM- CSL or lower carrier transport layer may be provided.

[0030] Bottom electrodes 162c and 162d are additional examples of composite conductors.

[0031] Referring again to FIG. 1 A, a first carrier transport layer 163 may be provided overlaying the bottom electrode 162. In some preferred embodiments, the first carrier transport layer 163 is generally not in direct contact with the first set of metal lines 103. In many cases, the first set of metal lines 103 have a height that is greater than the thickness of the first carrier transport layer 163. As illustrated, the first carrier transport layer may form a substantially conformal coating over the composite electrode, but in some cases, the first carrier transport layer may be thinner at the sidewalls, edges, or tops of the composite electrode corresponding to the metal lines. A selfassembled molecular charge selective layer (“SAM-CSL”) 1635 is conformally provided over the first carrier transport layer 163. The SAM-CSL may be very thin, typically thinner than the first conducting layer 105 or the first carrier transport layer 163. In some cases, the SAM-CTL may be just a few nanometers thick (e.g., less than or equal to 6 nm, or less than or equal to 2 nm) or alternatively a few monolayers thick or even a single monolayer thick.

[0032] A perovskite absorbing layer 164 (sometimes referred to herein simply as a perovskite layer) may be provided overlaying SAM-CSL 1635. A second carrier transport layer 165 may be provided overlaying the perovskite absorbing layer. A top electrode 166 may be provided overlaying the second carrier transport layer. The top electrode may be opaque, transmissive, or transparent. In some cases, the top electrode may be a second composite electrode.

[0033] Photovoltaic structure 100 may in some cases be a bifacial photovoltaic structure capable of receiving light 170 from its upper surface and light 172 from its lower surface. In some embodiments, light 172 may be more intense than light 170. For example, light 172 may include sunlight and light 170 may include reflected sunlight or some other ambient light source. Alternatively, light 170 may be more intense than light 172.

[0034] In preferred cases, the first carrier transport layer 163 is provided by a solution coating process, but it has been found that such a process may result in substantial thickness inhomogeneity, possibly including discontinuities, in the coating, particularly at edges or sidewalls of the composite conductor corresponding to the metal lines. If the metal lines are formed from large-sized particles (e.g., from a metal ink) this can create roughness resulting in substantial thickness inhomogeneity, possibly including discontinuities in the carrier transport layer between metal particles. Thus, not only at edges and sidewalls, but the top surface of the composite conductor corresponding to the metal lines may also or instead include thickness inhomogeneities and / or discontinuities in the first carrier transport layer. Unfortunately, substantial thickness inhomogeneity and / or discontinuities in the carrier transport layer can result in significant degradation in device performance. In addition to transporting a particular charge (holes or electrons), the first carrier transport layer is generally designed to also block transport of the opposite charge. Substantial thickness inhomogeneity in the carrier transport layer can severely impact both functions, as a thicker layer can create unacceptable resistance increases while a thinner layer is less effective at blocking transport of the opposite charge. In the case of discontinuities in the first carrier transport layer, the perovskite absorber layer may make direct contact with the bottom electrode. In this case photogenerated positive and negative charges can both find their way to the bottom electrode resulting in non-useful recombination and loss in photo efficiency.

[0035] A number of approaches have been tried to avoid substantial thickness inhomogeneity, but they have been found limiting or unsatisfactory. For example, a thicker first carrier transport layer can reduce discontinuities or relative thickness inhomogeneity. However, a thicker carrier transport layer can create unacceptable resistance increases in the device resulting in poor performance. Another approach is to use thinner metal lines and / or metal inks having smaller metal particles. While thinner lines can work in some cases, this limits the overall conductivity of the bottom electrode since thicker lines have lower resistance. Higher resistance in the electrodes causes device efficiency loss and limits the size of each photovoltaic cell in a module. Further, metal inks having smaller metal particles are typically much more expensive than other metal inks with larger metal particle size.

[0036] It has been found that the SAM-CSL, despite being very thin, can reliably coat both the carrier transport layer 163 and the bottom electrode exposed at discontinuities. Even such a thin layer of SAM-CSL can create a significant barrier to the unwanted charge transport between the perovskite and bottom electrode. Referring to FIG. IB, some discontinuities 170 are highlighted that are effectively coated by SAM-CSL layer 1635.

[0037] In some other embodiments, a SAM-CSL may be interposed between the first carrier transport layer and the bottom electrode instead of, or in addition to, a SAM-CSL interposed between the perovskite layer 164 and the first carrier transport layer 163. In some embodiments, there is no first carrier transport layer and only a SAM-CSL interposed between the bottom electrode 162 and the perovskite layer 164.

[0038] The layers between the top and bottom electrodes shown in FIG. 1A may sometimes be referred to herein as photovoltaic “active layers”. Although not illustrated in FIG. 1 A, in some embodiments, one or more interfacial layers may optionally be provided between any adjacent active layers, between an active layer and an electrode, over the second composite electrode or under the first composite electrode. Herein the term “interfacial layer” is used broadly, with the purpose, e.g., of altering one or more properties of the interface between two layers such as changing the work function, increasing the barrier properties to mobile ions, passivating defects in a neighboring layer, or altering the band gap. In some cases, an interfacial layer may more specifically act as a barrier to diffusion of water, solvents, molecules, ions (e.g., metal ions and / or halide ions). In some embodiments an interfacial layer may passivate, deactivate or otherwise ameliorate unwanted trap states or carrier transport barriers at layer interfaces or even grain boundaries. In some embodiments, an interfacial layer may aid in the deposition of a subsequent layer, e.g., by providing uniform chemical and / or physical properties across a surface such as surface tension, adhesion, reactive groups for bonding, or the like. An interfacial layer may in some embodiments include a generally electrically insulating metal oxide (e.g., aluminum oxide, titanium dioxide, or the like) that is sufficiently thin so as not to seriously impede the transport of charge between layers. In some embodiments, an interfacial layer may be less than 6 nm thick, alternatively less than 2 nm thick. In some cases, an interfacial layer may be a few monolayers thick, alternatively a single monolayer thick. In some cases, an interfacial layer may be a continuous layer or film, but in other cases may be discontinuous. In some embodiments, an interfacial layer may be applied by an inline tool compatible with roll-to- roll manufacturing. In some cases, an interfacial layer may be applied by spatial ALD (SALD), a reduced pressure metal oxide deposition tool, or coating (or other contact) with a solution, liquid, gas, or aerosol that includes an interfacial material. Additionally, anywhere the phrase “interfacial layer” or similar concepts appear herein, they may be replaced by “interfacial treatment”. In some cases, an interfacial treatment may not result in deposition of an interfacial layer but may instead treat a layer at its surface or even internally to provide the desired treatment result.

[0039] In operation, positive and negative charges (holes and electrons) are produced in the perovskite absorbing layer 164 in response to absorption of appropriate radiation. The first and second carrier transport layers (163, 165) receive these separated charges and transfer them to the respective bottom and top electrodes (162, 166). The electrodes may be in electrical contact with an electrical device (not shown) where the collected charges serve to power the device, or alternatively charge it in the case where the electrical device is an energy storage battery of some sort. In some embodiments, the first carrier transport layer or SAM-CSL may include a hole transporting material and the bottom electrode may act as an anode in the photovoltaic structure. In such embodiments, the second carrier transport layer may include an electron transporting material and the top electrode may act as a cathode in the photovoltaic structure. Such an arrangement of layers may for convenience be referred to as a PIN structure.

[0040] In some alternative embodiments, the first carrier transport layer or SAM-CSL may include an electron transporting material and the bottom electrode may act as cathode in the photovoltaic structure. In such embodiments, the second carrier transport layer may include a hole transporting material and the top electrode may act as an anode in the photovoltaic structure. Such an arrangement of layers may for convenience be referred to as a NIP structure.

[0041] In some embodiments, the materials and methods used for forming one or more layers of the photovoltaic structure are compatible with high-speed manufacturing. In some cases, one or more layers may be formed using roll-to-roll processes. In some embodiments, one or more manufacturing steps may instead use batch deposition methods or a series of substrates in a “cut sheet” format, e.g., with each mounted in a frame.

[0042] Transparent Substrate

[0043] The transparent substrate is generally electrically insulating and may be formed from any suitable transparent material(s) such as a glass, a polymer (plastic), or a combination of different materials. The transparent substrate may in some cases be rigid, but in preferred embodiments, the transparent substrate is flexible. Some non-limiting examples of transparent substrates may include thin flexible glass such as Corning® Willow® Glass, a polyethylene terephthalate (PET) (which may optionally be a heat-stabilized PET), a polyethylene naphthalate (PEN), a polycarbonate (PC), a polysulfone (PS), a polyether sulfone (PES), a polyamide, p- nitrophenylbutyrate (PNB), a polyetherketone (PEEK), a polyetherimide (PEI), a polyarylate (PAR), a polyvinyl acetate, a polyimide, a cyclic olefin polymer (COP), a cellulose triacetate (TAC), a polyacrylate, or an epoxide. For some applications, some particularly useful transparent substrates include thin flexible glass, PET and heat-stabilized PET. The transparent substrate may optionally include multiple materials or have a multilayer structure. The transparent substrate may include a surface treatment to modify the surface energy for improved coating quality and / or adhesion of subsequent layers. Some non-limiting examples of surface treatments include corona discharge, ozone (created, for example, with ultraviolet radiation), and plasma. Surface treatment devices may operate in ambient air, conditioned air (where temperature and relative humidity arc controlled), oxygen, or inert gas such as nitrogen or argon. In some embodiments, a surface-modifying treatment may involve a wet chemical treatment or even an additional surface layer deposited by a wet- or dry-coating method. In some cases, a surface layer may be referred to as a primer layer. In some cases, the transparent substrate may act as a water vapor or oxygen barrier, e.g., through choice of substrate material or by addition of one or more barrier layers.

[0044] Note that by “flexible” it is generally meant that the material can undergo some shape changes at least in one dimension in response to some force or stress without significant damage. In some cases, flexibility of a substrate or material may be measured by its bend radius, which is the minimum radius that it can be bent without functionally damaging it. In some embodiments, a flexible transparent support may have a bend radius of less than 100 cm, alternatively less than 50 cm, 20 cm, 10 cm, 5 cm, 4 cm, 3 cm, 2 cm, or 1 cm. In some preferred embodiments, a flexible transparent substrate may have a bend radius of less than 10 cm.

[0045] There are no particular limitations on the thickness of the substrate if flexibility is not desired, so long as it remains sufficiently transparent. In some preferred embodiments, a flexible transparent substrate is suitable for roll-to-roll manufacturing and may have a thickness of less than about 350 pm if it is flexible glass (e.g., a thickness in a range of 50 to 350 pm ), or alternatively less than about 200 pm if it is a flexible plastic (e.g., a thickness in a range of 20 to 250 pm). The transparent substrate preferably has a transmissivity (%T) of at least 80%, or more preferably 90%. Alternatively, the transparent substrate preferably has an absorptance (%A) of less than 20%, or more preferably, less than 10%.

[0046] First and Second Carrier Transport Layers

[0047] As mentioned, one carrier transport layer includes a hole transporting material, and the other carrier transport layer includes an electron transporting material. A carrier transport material that includes a hole transporting material may be referred to as a hole transport layer. In addition to transporting holes, a hole transporting material may also effectively block the transport of electrons. A carrier transport material that includes an electron transporting material may be referred to as an electron transport layer. In addition to transporting electrons, an electron transporting material may also effectively block the transport of holes. In some embodiments, a carrier transport layer may include multiple layers of materials. A non-limiting example of a multilayer charge transport layer may include embodiments where one sublayer is especially for transporting the desired charge and another sublayer especially for blocking the opposite charge. In some cases, a blocking sublayer may be adjacent to the perovskite layer. The thickness of a carrier transport layer depends in part on the properties of the overall photovoltaic stack, but in some embodiments, may have an average thickness in a range of 10 ’s to 100’s of nanometers.

[0048] Some non-limiting examples of hole-transporting materials may include a poly(triaryl amine) (e.g., poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine]), a poly-(N-vinyl carbazole), PEDOT complex, a poly(3-hexylthiophene), spiro-MeOTAD (also known as N2,N2,N2',N2',N7,N7,N7,NT-octakis(4-methoxyphenyl)-9,9'-spirobi[9H-fluorene]-2,2',7,7'- tetramine), poly-TPD, EH44, certain metal oxides (e.g. nickel oxide, molybdenum oxide, and vanadium oxide, any of which may optionally be doped), copper thiocyanate and copper iodide, and certain self-assembled monolayers (e.g. 2-(9H-Carbazol-9-yl)ethyl]phosphonic acid).

[0049] Some non-limiting examples of electron-transporting materials may include fullerenes, (e.g., phenyl-C 61 -butyric acid methyl ester (PCBM) and fullerene-C60), bathocuproine (BCP), TPBI, PFN, PC71BM, ICBA, graphene, reduced graphene oxide, certain metal oxides (e.g., tin oxide, zinc oxide, cerium oxide, and TiCh, any of which may optionally be doped).

[0050] Depending in part upon the particular material, a carrier transport layer may in some cases be deposited by a dry deposition process. Some non-limiting examples of dry processes may include sputtering, thermal evaporation, physical vapor deposition, chemical vapor deposition, atomic layer deposition, c-bcam deposition, or some other process that may in some cases operate under reduced pressure. In some cases, dry deposition may be performed inline in a roll-to-roll system, e.g., by using spatial ALD (SALD) or a reduced pressure material deposition (RPMD) tool. Such RPMD tools operate at pressures above normal vacuum deposition systems, e.g., in a range of 0.01 mBar to 200 mBar. In some embodiments, a carrier transport layer may be deposited from an aerosol of nanoparticles. Some non-limiting examples of aerosol-based deposition are described in US 10092926, which is incorporated by reference herein in its entirety for all purposes. In some cases, aerosol deposition has been found to be less damaging to underlying device layers.

[0051] In some embodiments, a carrier transport layer may be deposited by a coating process that does not require reduced pressure. Some non-limiting examples of coating processes may include gravure, slot die, spray, dip coat, inkjet, flexographic, rod, or blade coating methods. In some cases, a coating process may be followed by a thermal treatment to drive off solvent, anneal the carrier transport material, or the like.

[0052] In some embodiments, a carrier transport layer may be deposited by transfer of the carrier transport material from a donor sheet, e.g., by application of heat or some other stimulus to release it from the donor sheet with adherent transfer to the appropriate device layer or substrate.

[0053] In some cases, the deposition method is suitable for high-speed manufacturing. In some embodiments, the deposition of one or more carrier transport layers may be performed using a roll-to-roll manufacturing process. SAM-CSL

[0054] Self-assembled molecular charge selective layer (SAM-CSL) materials represent a specific class of carrier transport layer materials. Hole-selective SAM-CSL materials may be selective to passing holes between layers while blocking electrons. Electron-selective SAM-CSL materials may be selective to passing electrons between layers while blocking holes. A SAM- CSL material has properties that allow it to strongly adsorb or bond to a surface, often as thin as a few nanometers. The SAM-CSL material is typically a non-polymeric molecule capable of self-assembling a layer at a desired surface. A SAM-CSL molecule generally includes a functional group that provides the desired electrical properties, and may further include an anchoring group (including, but not limited to, carboxylic acids, phosphonic acids, siloxanes, cyanoacetic acids, or sulfonic acids) and optional spacer group (including, but not limited to, alkyl chains, aryl chains, or combinations thereof) that separates the functional group from the anchoring group.

[0055] Some non-limiting examples of functional groups for hole-selective SAM-CSL materials include aryl amines, carbazoles, phenothiazines, quinoxalines, thiophenes, and porphyrins. Some non-limiting examples of hole selective SAM-CSL materials are shown in FIGS. 2A - 2D.

[0056] Some non-limiting examples of functional groups for electron-selective SAM-CSL materials include fullerenes, aryl imides, and aryl diimides. Some non-limiting examples of electron selective SAM-CSL materials are shown in FIG. 3.

[0057] The SAM-CSL may be formed, for example, by contact with a solution of the desired SAM-CSL material. Contact may include a coating process such as gravure, slot die, spray, dip coat, inkjet, flexographic, rod, or blade coating methods. In some cases, a coating process may include a surface treatment, for example, corona discharge or plasma treatment, to modify the surface energy for improved self-assembly and adherence of the SAM-CSL with the surface. In some cases, a coating process may include a thermal treatment that can promote adherence of the SAM-CSL material to the substrate and / or drive off solvent. In some cases, there may be a solvent rinse following application of the SAM-CSL.

[0058] In some cases, the method for forming the SAM-CSL is suitable for high-speed manufacturing. In some embodiments, forming the SAM-CSL includes a roll-to-roll manufacturing process.

[0059] Although SAM-CSL materials have been discussed with reference to a location between the perovskite absorbing layer and the bottom electrode, SAM-CSL materials may in some cases be provided between the perovskite and the top electrode. In some cases, SAM-CSL material may even be provided in the perovskite coating mixture, and upon annealing of the perovskite layer, the SAM-CSL moves to perovskite grain-boundaries and / or interfaces between the perovskite absorbing layer and an adjacent electrode or charge transport layer. Perovskite absorbing layer

[0060] In some cases, perovskite materials and methods for forming perovskite absorbing layers may be as described in U.S. Patent No. 11,108,007, U.S. Patent No. 11,342,130, U.S. Application No. 2020 / 0377532, and U.S. Application Publication No. 2022 / 0238807, the entire contents of which are incorporated herein by reference. In some embodiments, a perovskite absorbing layer may be coated from a fluid mixture, which may be referred to as a perovskite solution. Any coating method suitable for coating a fluid mixture may be used including, but not limited to, gravure, slot die, spray, dip coat, inkjet, flexographic, rod, or blade coating methods. In some cases, the perovskite deposition method is suitable for high-speed manufacturing. In some embodiments, a perovskite absorbing layer may be performed using a roll-to-roll manufacturing process.

[0061] The term “perovskite solution” refers to a solution or colloidal suspension that can be used to generate a continuous layer of organic-inorganic hybrid perovskite material (the perovskite absorber layer), e.g., one with an ABX3 crystal lattice where ‘A’ and ‘B’ are two cations of very different sizes, and X is an anion that coordinates to both cations. A perovskite solution typically includes an appropriate set of perovskite precursor materials and one or more solvents in which the precursor material is dissolved or suspended. A perovskite solution may also contain additives, e.g., to aid in crystal growth or to modify crystal properties or for some other purpose. A perovskite precursor material is typically an ionic species where at least one of its constituents becomes incorporated into the final perovskite layer ABX3 crystal lattice. Organic perovskite precursor materials are materials whose cation contains carbon atoms while inorganic perovskite precursor materials are materials whose cation contains metal but does not contain carbon.

[0062] When the perovskite solution dries, perovskite crystals or an intermediate precursor phase for hybrid perovskite crystals (intermediate phase) form. The intermediate phase is a crystal, adduct, or mesophase that is not the desired final crystal lattice, which is ABX3. The intermediate phase, if present, may be converted to the desired final crystal lattice by annealing. In some cases, annealing or other heating methods may include the use of heated nip rollers, optionally under nitrogen.

[0063] Some non-limiting examples of inorganic perovskite precursor materials for making perovskite solutions may include lead (II) iodide, lead (II) acetate, lead (II) acetate trihydrate, lead (II) chloride, lead (II) bromide, lead nitrate, lead thiocyanate, tin (II) iodide, rubidium halide, potassium halide, and cesium halide. In some cases, the halide may include iodide. Some non-limiting examples of organic perovskite precursor materials for making perovskite solutions may include methylammonium iodide, methylammonium bromide, methylammonium chloride, methylammonium acetate, formamidinium bromide, and formamidinium iodide. To produce a high-performance perovskite device, it is generally preferred in some cases that the organic perovskite precursor material has a purity greater than 99 percent by weight and the inorganic perovskite precursor has a purity greater than 99.9 percent by weight. The inorganic perovskite precursor material contains a metal cation, and in some preferred embodiments, the metal cation is lead. In some preferred embodiment, the molar ratio of organic perovskite precursor material to inorganic perovskite precursor material may be in a range of one to three.

[0064] In some cases, a perovskite solution may be formulated using a large proportion of a low boiling point solvent (e.g., at least 50 wt. % of total solvent, preferably at least 75 wt. % of total solvent, more preferably at least 90 wt. % of total solvent). In some embodiments, a low boiling point solvent is one having a boiling point of less than 150 °C, or preferably less than 135 °C. Such proportions may assist or enable high speed production of a uniform perovskite layer. Using an appropriate drying method, a low boiling point solvent can be made to evaporate quickly from the perovskite solution after deposition on a substrate thus minimizing movement of the crystals that form as the perovskite solution dries. Solvents that do not strongly coordinate with the perovskite precursors further enable short annealing times. Short annealing times arc desirable because they enable higher production speeds. Alcohol-based solvents have been identified that do not strongly coordinate with the perovskite precursors, can provide the proper solubility of the inorganic precursors, and have been shown to produce a perovskite solution that can be stable for use in high volume manufacturing of perovskite layers and photovoltaic devices. Some non-limiting examples of alcohol-based solvents suitable for use at high proportions in the perovskite solution may include 2-methoxyethanol, 2-ethoxyethanol, 2- butoxyethanol, 2-isopropoxyethanol, methanol, propanol, butanol, and ethanol. Mixtures of solvents are envisioned for use in the perovskite solution to tune the evaporation profile to further optimize the drying process. Some non-limiting examples of suitable solvent additives useful for modifying evaporation rate of the solvent may include dimethylformamide, acetonitrile, dimethyl sulfoxide, N-methyl-2-pyrrolidone, dimethylacetamide, gammabutyrolactone, phenoxyethanol, acetic acid, and urea.

[0065] In some preferred embodiments, a perovskite solution may be formulated with greater than 30 wt. % of solvent (e.g., 30-82 wt. %) and at least 18 wt. % of solids (e.g., 18-70 wt. %, preferably 25-60 wt. %, or 30-45 wt. %), where the total solids concentration of the perovskite solution is in a range of 30 - 70 % by weight of its saturation concentration at the provided solution temperature. In some preferred embodiments, a solution temperature may be in a range of 20 - 50 °C. In some preferred embodiments, the solvent is an alcohol and has a boiling point less than 135 °C. In some preferred embodiments, the solvent is 2-methoxyethanol, which has a boiling point of 125 °C. In some embodiments, such formulations may provide perovskite solutions that are stable at convenient handling and storage temperatures (e.g., in a range of 20 - 50 °C, and in particular, room temperatures in a range of 20 - 25 °C), and which can be used to manufacture uniform perovskite layers at high speed, thereby enabling low-cost production of high efficiency solar cells with low equipment costs.

[0066] Although uniform perovskite layers have been made at high production speeds with the above formulations, it has sometimes been found that the time required for the perovskite solution to form homogeneous nuclei and grow may be longer than the time required to evaporate the low boiling point solvent in such a way as to produce a uniform perovskite layer. A uniform perovskite layer with optimum sized crystals is desired to make perovskite devices with high photovoltaic energy output. Addition of a crystal growth modifier added to a perovskite solution having a low boiling point solvent has been found to improve the performance of perovskite photovoltaic devices. A crystal growth modifier refers to an additive that either alters the amount of time for homogeneous crystal growth or alters the rate of homogeneous crystal growth when drying a perovskite solution. Some non-limiting examples of crystal growth modifiers that are especially useful in perovskite solutions for making high performance perovskite layers include dimethyl sulfoxide, N-methyl-2 -pyrrolidone, gammabutyrolactone, 1,8-diiodooctane, N-cyclohexyl-2 -pyrrolidone, water, dimethylacetamide, acetic acid, cyclohexanone, alkyl diamines, and hydrogen iodide. In some preferred embodiments, the concentration of a crystal growth modifier may be less than about 10 % by weight of the coating solution (e.g., in a range of 0.01 - 10 % wt.). In some cases, a more preferred concentration of crystal growth modifier may be less than about 2 % by weight of the coating solution (e.g., 0.01 to 2 % wt.).

[0067] Another additive for a perovskite solution that may improve the performance of perovskite devices is a crystal grain boundary modifier. A crystal grain boundary modifier refers to an additive that improves the quality of the grain boundary, for example, be altering the electrical properties of the perovskite crystal grain boundary or reducing trap states at perovskite crystal grain boundary interfaces. Some non-limiting examples of crystal grain boundary modifiers that can be particularly useful in perovskite solutions for making high performance perovskite layers include choline chloride, phenethylamine, hexylamine, 1 -a- phosphatidylcholine, polyethylene glycol sorbitan monostearate, sodium dodecyl sulfate, Poly(methyl methacrylate), Polyethylene glycol, pyridine, thiophene, ethylene carbonate, propylene carbonate, fullerenes, polypropylene carbonate), and didodecyldimethylammonium bromide. A preferred concentration of crystal grain boundary modifier may be less than about 10 % by weight of the coating solution (e.g., in a range of 0.01 - 10 % wt.). In some cases, a more preferred concentration of crystal growth modifier may be less than about 2 % by weight of the coating solution (e.g., 0.01 to 2 % wt.).

[0068] In some embodiments, particularly in NIP structures, a multifunctional capping layer may be provided between the perovskite absorber layer and the hole transport carrier layer, e.g., as described in US20220246865, which is incorporated by reference herein in its entirety for all purposes. A multifunctional capping layer may include a thiophene-containing molecule functionalized with an ammonium group. A non-limiting example is 2-(3"',4'-dimethyl- [2,2':5',2":5'',2"'-quatcrthiophcn]-5-yl)cthan-l -ammonium iodide.

[0069] Electrodes

[0070] Many of the compositions and methods for forming each of the top and bottom electrodes may be individually selected from a similar set of material and coating technology options as described herein. In some embodiments, at least the bottom electrode is a transparent electrode, preferably a transparent composite conductor. The top electrode may be opaque, transmissive, or transparent. The transparency of a composite conductor depends in part on the width of the metal lines (which are typically mostly opaque), the transparency of the conducting layer, and may also depend in part on the layers adjacent the composite conductors, e.g., on their index of refraction.

[0071] A light-transmissive electrode may have a transmittance %T within a target wavelength range of at least 10%, or alternatively at least 15%, 20%, 25%, 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. In some cases, a light-transmissive electrode may (within a target wavelength range) have a %T in a range of 10 - 15%, 15 - 20%, 20 - 25%, 25 - 30%, 30

[0072] - 35%, 35 - 40%, 40 - 45%, 45 - 50%, 50 - 55%, 55 - 60%, 60 - 65%, 65 - 70%, 70 - 75%, 75

[0073] - 80%, 80 - 85%, 85 - 90%, or 90 - 95%, or any combination of ranges thereof. Higher %T values are usually favored, but other system factors (conductivity, manufacturing cost, device stability...etc.) may also be considered such that the bottom electrode may not have the highest possible %T, but rather have an effective %T for overall device performance.

[0074] A light-transmissive electrode may have an absorptance %A within a target wavelength range of less than 90%, or alternatively less than 85%, 80%, 75%, 70%, 60%, 50%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, or 5%. In some cases, a light-transmissive electrode may (within a target wavelength range) have a %A in a range of 5 - 10%, 10 - 15%, 15 - 20%, 20 - 25%, 25 - 30%, 30 - 35%, 35 - 40%, 40 - 45%, 45 - 50%, 50 - 55%, 55 - 60%, 60 - 65%, 65 - 70%, 70 - 75%, 75 - 80%, 80 - 85%, or 85 - 90%, or any combination of ranges thereof. Lower %A values are usually favored, but other system factors (conductivity, manufacturing cost, device stability...etc.) may also be considered such that the bottom electrode may not have the lowest possible %A, but rather have an effective %A for overall device performance.

[0075] The transparent electrode may have a %T within a target wavelength range of at least 50%, or alternatively, at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 95%. In some cases, the transparent electrode may (within a target wavelength range) have a %T in a range of 50 - 55%, 55 - 60%, 60 - 65%, 65 - 70%, 70 - 75%, 75 - 80%, 80 - 85%, 85 - 90%, or 90 - 95%, or any combination of ranges thereof. Higher %T values are usually favored and a significant consideration, but other system factors (conductivity, manufacturing cost, device stability...etc.) may also be considered such that the top electrode may not have the highest possible %T, but rather have an effective %T for overall device performance.

[0076] The transparent electrode may have a %A within a target wavelength range of less than 50%, or alternatively less than 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, or 5%. In some cases, the transparent electrode may (within a target wavelength range) have a %A in a range of 5 - 10%, 10 - 15%, 15 - 20%, 20 - 25%, 25 - 30%, 30 - 35%, 35 - 40%, 40 - 45%, or 45 - 50%, or any combination of ranges thereof. Lower %A values are usually favored, but other system factors (conductivity, manufacturing cost, device stability... etc.) may also be considered such that the bottom electrode may not have the lowest possible %A, but rather have an effective %A for overall device performance.

[0077] When an electrode is not opaque, it may include a light-transmissive conducting layer, optionally in combination with a set of electrode metal lines in the form of a composite conductor. In some embodiments, a conducting layer may include a conductive polymer material such as PEDOT:PSS, a poly(pyrrole), a polyaniline, a polyphenylene, or a poly(acetylene). Conductive polymers may be applied by a coating from a suspension or solution, e.g., using any of the coating methods described above with respect to the perovskite absorbing layer. After coating, the conducting layer may optionally be subjected to heating or some other drying step to drive off solvent or otherwise improve conductivity properties of the conductive polymer.

[0078] In some embodiments, a conducting layer may include high aspect ratio metal nanowires (e.g., silver nanowires) or carbon nanotubes. Such materials may be coated from a dispersion (optionally with a binder) at a density sufficient to form an interconnected, conductive mesh, but low enough to maintain transparency. After coating, the conducting layer may optionally be subjected to heating or some other drying step to drive off solvent or otherwise improve conductivity properties of the metal nanowires or carbon nanotubes.

[0079] In some embodiments, a conducting layer may include doped or undoped metal oxides such as tin oxide (e.g., doped with indium or fluorine), molybdenum oxide, and zinc oxide (e.g., doped with aluminum). Such metal oxides are sometimes referred to as transparent conductive oxides (TCOs). TCOs may in some cases be coated from a suspension of metal oxide particles or formed from a sol-gel precursor solution, typically followed by a heating step to drive off solvent and anneal or sinter the metal oxide particles. TCOs may in some cases be deposited using dry deposition methods such as sputtering, physical vapor deposition, chemical vapor deposition, atomic layer deposition, e-beam deposition, or the like.

[0080] In some preferred embodiments, a conducting layer may include a TCO deposited from an aerosol of nanoparticles (also considered a dry process). Some non-limiting examples of aerosol-based deposition are described in US 10092926, which is incorporated by reference herein in its entirety for all purposes. In some cases, aerosol deposition may be less damaging to underlying device layers. A heating step may optionally follow such dry deposition processes, e.g., to improve conductivity of the deposited layer.

[0081] In some embodiments, the applied conducting layer may have an intrinsic sheet resistance (i.e., as measured in the absence of metal lines) of less than 1000 / square, preferably less than 500 / square, and more preferably less than 300 / square. In some embodiments, the top electrode conducting layer may have a %T within a target wavelength range of at least 80%, alternatively at least 90%, at least 95%, or at least 97% (as measured in the absence of any metal lines).

[0082] The thickness of a conducting layer depends in part on the electrical and optical properties of the selected material and may also depend on the deposition method. In some embodiments, a conducting layer may have a thickness of less than 500 nm, alternatively less than 200 nm, alternatively less than 100 nm, alternatively less than 50 nm, alternatively less than 20 nm, or alternatively less than 10 nm. In some embodiments, the conducting layer may be an TCO having an average thickness in a range of 30 nm to 100 nm.

[0083] In some embodiments (including, but not limited to, embodiments where a plurality of perovskite photovoltaic structures or cells are connected in series) the average sheet resistance of the first composite conductor (bottom electrode) be similar to the average sheet resistance of the top electrode which may be second composite conductor. In some embodiments, the ratio of the average sheet resistance of the first composite conductor to the average sheet resistance of the second composite conductor may be in a range of 0.2 to 5, alternatively 0.5 to 2, alternatively 0.6 to 1.7, alternatively 0.7 to 1.4, alternatively 0.8 to 1.25, or alternatively 0.9 to 1.1. As discussed elsewhere herein, due in part to the composite nature of the conductor, the term “sheet resistance” may refer to a functional sheet resistance that depends not only upon the intrinsic resistivities of the metal lines and the conducting layer, but may also depend upon the geometries of the metal lines and the intended direction of current flow across the composite conductor.

[0084] Metal lines

[0085] There is no particular limitation on the conductive material that may be used for the metal lines of a composite conductor. In some preferred embodiments, the conductive / metal lines may be formed of a conductive material having a conductivity of at least 105S / m. In some embodiments, metal lines may include silver or copper, or alloys containing one or both of these metals. In some cases, other metals may be suitable including, but not limited to, gold, aluminum, molybdenum, tungsten, zinc, nickel, iron, tin, palladium, platinum, titanium, and alloys containing one or more of these metals.

[0086] Although dry deposition or electrochemical deposition methods may be used, in some preferred embodiments, metal lines may be formed by printing using a metal-containing fluid mixture or “metal ink” (e.g., a suspension, slurry, paste, or the like). In some cases, printing metal lines may be performed by flexographic printing, inkjet printing, gravure printing, or some other printing technology. The printed metal lines may in some cases be followed by a heat treatment to drive off solvent or cause metal particles to fuse or sinter, which can increase the metal conductivity. Heat treatments may include an oven, IR heaters, flashlamps, heated rollers (with or without pressure), or the like. US8907258, incorporated herein by reference for all purposes, discloses a non-limiting example of a pulsed radiation apparatus that may be suitable for metal particle sintering in a roll-to-roll manner. In some cases, a printed metal ink may be subjected to a secondary chemical treatment such as a reducing agent. The metal ink may include metal particulates of various shapes and sizes (e.g., spherical, oblong, nanoparticles, nanowires) in an appropriate liquid carrier and may further include other agents such as binders, surfactants, or the like. A few non-limiting examples of metal inks may include those disclosed in US20220025200, which is incorporated herein by reference for all purposes. In some embodiments, a surface receiving the metal ink may first be treated to modify its surface energy, e.g., by corona discharge, a plasma, UV / ozone, or a chemical treatment. Modification of this surface energy can in some cases be used to control the shape, dimension, and / or adhesion of the deposited metal ink. Metal line patterns

[0087] FIG. 4 A is a cross-scctional view of non-limiting examples of metal lines according to some embodiments. Metal line 244 may be provided on a surface 242. A metal line may be characterized in cross section by a height H (or thickness) and width W. Height H and width W may be measured at a particular point or may be reported as an average height H and average width W along a metal line. In some embodiments, the height or width may vary along the length of a metal line. An upper surface 246 of metal line metal line may further be characterized by a surface roughness, e.g., Roughness Average (Ra), RMS Roughness (Rq), Maximum Profile Peak Height roughness (RP), Average Maximum Height of the Profile (Rz), or Peak Density (Pc). As illustrated in FIG. IB, the sidewalls may also have a roughness.

[0088] Surface 242 may, for example, correspond to the surface of a substrate when metal line 244 is part of the bottom electrode set of metal lines. Alternatively, surface 242 may correspond to the upper portion of the second conducting layer or second carrier transport layer when metal line 244 is part of a top electrode set of metal lines. Metal line 244 may take on a variety of shapes and sizes. In FIG. 4A, metal line 244 is shown to have a trapezoidal shape in crosssection where the base is wider than the top, but such a shape is not limiting. In some embodiments, in particular for the first set of metal lines, it may be less preferred to use metal line structures such as metal line 244x where the top of the metal is wider than the base thereby creating an overhang. This may create electrical discontinuities when depositing the first conducting layer over the first set of metal lines, particularly when the first conducting layer is substantially thinner than the metal line. In some preferred embodiments, the cross-sectional shape of the metal line may have sidewalls that generally slope inwardly, i.e., away from the surface and toward the middle of the line, e.g., as shown in metal line 244. Although shown as symmetrical, the cross-sectional shape may not be symmetrical. Although shown as straight, the sidewalls may be rounded or irregular.

[0089] FIG. 4B is a top view of a non-limiting example of a set of metal lines according to some embodiments. In some cases, the metal lines may be provided by roll-to-roll coating, and arrow 240 may correspond to the direction of web conveyance. Alternatively, arrow 240 may correspond to the direction of a cut sheet conveyance. The set of metal lines may be characterized by an average spacing Sx. In some preferred embodiments, the metal lines may be substantially parallel to each other and uniformly spaced. By substantially parallel, it is meant that the metal lines are within 30° of each other along a length dimension, alternatively within 15°, 10°, or 5°. The metal lines may be substantially parallel to the Y axis in FIG. 4B. When using roll-to-roll coating, such metal lines may be advantageously provided having a direction substantially orthogonal (within 15°, 10°, or 5° of 90°) to the web conveyance direction, e.g., when using flexographic printing methods for the metal lines. In some cases, however, the metal lines may be provided at a different angle, or at various angles. Similarly, in some cases, the spacing may not be uniform. Although shown as straight lines, the metal lines could include some curvature, a zig-zag pattern, or some other pattern.

[0090] In operation, positive or negative charges may generally flow in a direction 246, substantially parallel to the set of metal lines, to a first edge 251 of cell 250 where the current may be collected by a bus line or transferred in series to an adjacent cell (not shown). Although not shown, opposite charges may flow in the direction opposite of arrow 246 to the second edge 252 of cell 250 to be collected by a bus line or transferred in series to an adjacent cell.

[0091] A photovoltaic structure may be characterized by an active area, e.g., corresponding to the area of cell 250 in the XY plane that includes the active layers and which is intended to receive light in order to generate electricity. The metal lines such as 244 occupy some of the active area and block light. The metal lines (dimensions, # of lines, etc.) should be provided in a manner to yield the desired conductivity, but not block more light than necessary. In some embodiments, a set of metal lines may occupy may less than 15% of the active cell surface area, preferably less than 10%, more preferably less than 5%. In some cases, a set of metal lines occupies an active cell surface area in a range of 0.5% to 10%, or alternatively 1 to 5%. In some cases, the average spacing Sx of the metal lines is in a range of 0.1 to 2.0 mm. In some cases, a ratio Sx / W of average spacing Sx of the metal lines to the average width W of the metal lines is in a range of 10 to 100. In some embodiments, the average width W of the metal lines of is less than 40 pm, preferably less than 30 pm. In some embodiments, the average width W of the metal lines may be in a range of 1 to 30 pm, alternatively 2 to 25 pm. In some embodiments, the average height H of the metal lines is at least 50 nm, preferably at least 100 nm.

[0092] In some preferred embodiments, the bottom electrode is a composite conductor with a first set of metal lines having an average height H of at least 150 nm, alternatively, at least 200 nm, or at least 250 nm. In some cases, the first set of metal lines have an average height H in a range of 150 - 200 nm, 200 - 250 nm, 250 - 300 nm, 300 - 400 nm, 400 - 500 nm, 500 - 600 nm, 600 - 700 nm, 700 - 800 nm, 800 - 900 nm, 900 - 1000 nm, or any combination of ranges thereof. In some preferred eases, the first set of metal lines have a height H in a range of 200 nm to 600 nm, or alternatively, 250 - 400 nm. In the absence of the SAM-CSL, H above about 100 nm for metal lines in a bottom electrode has been difficult due to reasons mentioned elsewhere. With the SAM-CSL, thicker metal lines of greater than or equal to about 150 nm, preferably greater than or equal to about 200 nm, and more preferably greater than or equal to about 250 nm, can be used which reduces the resistance of the bottom electrode. In some preferred embodiments, a ratio of H / W is preferably at least about 1 / 250, more preferably at least about 1 / 200, and more preferably at least about 1 / 100. In various embodiments, useful H / W ratios may be, e.g., in a range of 1 / 250 to 1 / 8, in a range of 1 / 200 to 1 / 8, or more preferably in a range of 1 / 100 to 1 / 10. In some embodiments, the first set of metal lines has W less than 25 pm and average cross-sectional area (A) in a range of range of 2.5 to 8 pm2, or preferably W is less than 15 pm and A is in a range of 2.5 to 5 pm2. In some preferred embodiments, the first set of metal lines are substantially parallel having an average spacing of at least 200 pm, preferably in a range of 500 to 2000 pm. In some preferred embodiments, the first set of metal lines may occupy less than 6% of the active cell surface, e.g., in a range of 0.2% to 6%, and preferably less than 2.5%, e.g., in a range of 0.5% to 2.5%. In some preferred embodiments, the first set of metal lines have a surface roughness Rain a range of 10 - 100 nm. In some preferred embodiments, the first set of metal lines have a surface roughness Rzin a range of 50 - 200 nm. In some preferred embodiments, the first set of metal lines include metal nanoparticles having an average particle size in a range of 10 - 40 nm. In some preferred embodiments where the device is bifacial and the substrate is meant to face the albedo side, the first set of metal lines may occupy more than 6% of the active cell surface e.g., in a range of 6% to 30%, or alternatively between 6% and 15%.

[0093] Functional sheet resistance metrics

[0094] Although the conductivity or resistivity of a composite conductor can be described in party by intrinsic properties of the metal lines and conducting layer materials, it is important to understand the effective conductivity properties of the composite as it may behave in a device architecture. That is, simple sheet resistance measurements may not account for the spatial and directional asymmetries present in a composite conductor. In some cases, a functional or composite sheet resistance may instead be measured or calculated which better correlates to device performance.

[0095] For example, in the composite conductor shown in FIGs 4A-4B, the primary direction of current flow is in the direction of the metal lines along the Y axis. A functional sheet resistance (^functional’ measured in W) for this composite conductor may in some cases be defined by the geometric and material parameters of the metal lines and conducting layer as according to Equation 1: where W is the metal line width (cm), H is the metal line height (cm), / 'is a dimensionless number that defines the fraction of the W*H cross-section occupied by metal, rMLis the metal resistivity (W * cm), Sxis the average spacing of metal lines in the X-direction (cm), and RS,CL is the sheet resistance of the conducting layer (W * H-1). This functional resistance calculation is useful for composite conductors with metal lines parallel to direction 246, but may require modification where lines deviate from these axes, include curvature, or contain zig-zag patterns.

[0096] In some preferred embodiments, the bottom electrode is a composite conductor having a functional sheet resistance of less than 20 ohms, preferably less than 10 ohms, more preferably less than 5 ohms.

[0097] PV Module

[0098] The PV structures of the present disclosure may enable advantaged PV modules.

[0099] Referring to FIGS. 5 A, there is a top view of a non-limiting example of a perovskite PV module 500 according to some embodiments. FIG. 5B is a cross-sectional view along cutline B-B. Perovskite PV module 500 may include one or more sets of PV cells connected in series. For example, PV module 500 may include a first set of series-connected PV cells 500-R1 including first PV cell 502-1, second PV cell 502-2, third PV cell 502-3, fourth PV cell 502-4, and fifth PV cell 502-5. PV module 500 may further include a second set of series-connected PV cells 500-R2 including first PV cell 502-1’, second PV cell 502-2’, third PV cell 502-3’, fourth PV cell 502- 4’, and fifth PV cell 502-5’. The first and second sets may be separated by scribe structure 536, which may optionally be referred to herein as a second scribe structure or a P4 scribe for convenience. In operation, the first and second sets of series-connected PV cells may be connected in parallel (not shown here). Although only two sets are shown, the PV module may contain any number of such sets. Similarly, although 5 cells arc shown connected in series for each set, there may be more or fewer such PV cells.

[0100] The series interconnect region between first and second PV cells of a set are described with reference to FIG. 5B. For clarity, the structural details shown in FIG. 5B have been simplified to illustrate simply the transparent bottom electrode 562-x, the top electrode 566-x, and the photoactive layer 506-x which collectively includes the SAM-CSL, the perovskite absorber layer, and any other optional layers between the top and bottom electrodes. Further, although transparent bottom electrode 562-x is a composite conductor, the first set of metal lines and first conducting layer are not separately illustrated. Note that “x” is simply generic reference a cell number in the series. The PV cells may be provided over a common substrate 501.

[0101] The first and second PV cells are separated by a scribe structure 549 extending along a first dimension that may be generally parallel to the X axis of the present FIGS. 5A and 5B. Scribe structure 549 may be referred to herein as a first scribe structure or even a series scribe structure. In the illustrated embodiment, first scribe structure 549 includes an upper scribe portion 545 and a lower scribe portion 541. The lower scribe portion 541 defines a gap between bottom electrode 562-1 and bottom electrode 562-2. The upper scribe portion defines a gap between photoactive layer 506-1 and photoactive layer 506-2 and a gap between the top electrode 566-1 and top electrode 566-2. Structurally, the upper scribe portion 545 is generally wider than the lower scribe portion 541. The overall width of the first scribe structure may in most cases generally correspond to the width of the upper scribe portion. Referring to FIG. 5B, one end of lower scribe portion 541 (or alternatively upper scribe portion 545) generally defines an edge of first cell 502-1 and the opposite end of the lower scribe portion (or alternatively the upper scribe portion) generally defines an adjacent edge of second cell 502-2. Although the PV cell layers adjacent to the first scribe structure are shown as having vertical sidewalls, they may take on a different angle or shape (curved, sloped, or the like).

[0102] The top electrode of the first PV cell 502-1 is electrically connected to the bottom electrode of the adjacent second PV cell 502-2 thereby forming a series connection. In particular, electrically conductive connector 531 provides the series connection between cells. To avoid shorting of the electrically conductive connector with the first PV cell bottom electrode, an insulating material 521 may be provided along a sidewall of the first PV cell adjacent to the second PV cell. Similarly, to avoid shorting of the electrically conductive connector with the second PV cell top electrode, an insulating material 523 may be provided along a sidewall of the second PV cell adjacent to the first PV cell. In some cases, the insulating materials may also partially coat the respective top electrode near the edge of the scribe structure. In some preferred embodiments, the electrically conductive connector 531 is provided by printing a metal ink and the insulating materials 521 and 523 are provided by printing an insulating ink.

[0103] As previously explained, the PV structures of the present disclosure can provide PV cell electrodes having reduced resistance. In a module, this has numerous advantages. First, the PV module becomes more efficient, because the thicker, less resistive metal lines of the electrode are not as electrically lossy (power = current” * resistance). Since the resistance of the PV cell electrodes can be made lower, the cell length (e.g., measured between first scribe structures along the Y-axis in FIGS. 5 A and 5B) can be made longer (power loss along the electrode generally scales with square of its length). Longer cells means that a series of cells in a PV module requires fewer interconnections (scribe structures). Such series interconnections areas are not photoactive and reduce the overall active area of the PV module. By reducing the number of interconnects, the overall active area and PE of the module is increased.

[0104] In some embodiments, a PV cell has a cell length of at least 0.2 cm, alternatively, at least 0.3, at least 0.5 cm, or at least 1.0 cm. In some cases, a PV cell has a cell length in a range of 0.2 - 0.3 cm, 0.3 - 0.5 cm, 0.5 - 1 .0 cm, 1 .0 - 1 .5 cm, 1 .5 - 2.0 cm, 2.0 - 2.5 cm, or 2.5 - 3.0 cm, or any combination of ranges thereof.

[0105] Example

[0106] Without the use of SAM-CSLs, effective perovskite PV structures having a transparent bottom electrode with a first set of metal lines having a metal line height of about 150 nm to 200 nm have been made with metal particles of metal ink (used to print the metal lines) generally having a relatively low average particle diameter of about 7 nm and a relatively narrow size distribution. Beyond this height and / or particle size, problems may occur with other coated layers, e.g., the lower charge transport layer, leading to structural defects.

[0107] When using the SAM-CSL as described herein, it was unexpectedly found that the metal lines can be 3 or 4 or more times taller (e.g., 600 nm or even more) while avoiding such structural defects with other coated layers. Further, the metal ink used can have larger metal particle sizes, and the metal lines can have higher surface roughness without leading to structural defects.

[0108] Thus, with the SAM-CSL metal lines can be, e.g., 4x taller which allows the cell length to be twice as long. For example, without the SAM-CSL, the PV cell length was about 1.1 cm, but with the SAM-CSL, the PV cell length is 2.2 cm. As mentioned above, the longer cell length also reduces the number of first scribe structures which is beneficial to efficiency and cost.

[0109] It is also noted that the longer PV cells enable a simple design for lower voltage panels - since the cells are in series, doubling the cell length halves the module voltage. Lower voltage is beneficial for some applications, for example, on residential rooftops where high voltage systems are not allowed due to permitting restrictions for safety. A 1 -meter-long panel with 1.1 cm long cells would have 91 cells in series making an open circuit voltage of 100 V (for perovskite with 1.1 V open circuit voltage per cell). 2.2 cm long cells would make a 50 V panel with 45 cells.

[0110] Enumerated Embodiments

[0111] Still further embodiments herein include the following enumerated embodiments.

[0112] Enumerated embodiment 1. A photovoltaic structure including: a transparent substrate; a transparent bottom electrode provided over the substrate, the bottom electrode including a first set of metal lines in contact with a first conducting layer, wherein the first set of metal lines is characterized by an average height (H) of at least about 150 nm, an average width (W), and an aspect ratio H / W of at least about 1 / 250; a self-assembled molecular charge selective layer (SAM-CSL) disposed over the transparent bottom electrode; a perovskite absorber layer overlaying the SAM-CSL; an upper carrier transport layer overlaying the perovskite absorber layer; and a top electrode overlaying the upper carrier transport layer.

[0113] Enumerated embodiment 2. The photovoltaic structure of enumerated embodiment 1, further including a lower carrier transport layer interposed between the transparent bottom electrode and the SAM-CSL.

[0114] Enumerated embodiment 3. The photovoltaic structure of enumerated embodiment 2, further including a second SAM-CSL interposed between the transparent bottom electrode and the lower carrier transport layer. Enumerated embodiment 4. The photovoltaic structure of enumerated embodiment 1 , further including a lower carrier transport layer interposed between the SAM-CSL and the perovskite absorber layer.

[0115] Enumerated embodiment 5. The photovoltaic structure according to any of enumerated embodiments 1 - 4, wherein H is in a range of 0.15 to 1 pm, W is less than 25 gm, and H / W is in a range of 1 / 150 to 1 / 8.

[0116] Enumerated embodiment 6. The photovoltaic structure according to any of enumerated embodiments 1 - 5, wherein H is in a range of 0.2 to 0.6 gm, or optionally 0.25 to 0.4 gm, and H / W is in a range of 1 / 100 to 1 / 10.

[0117] Enumerated embodiment 7. The photovoltaic structure according to any of enumerated embodiments 1 - 6, wherein W is in a range of 8 to 15 pm.

[0118] Enumerated embodiment 8. The photovoltaic structure according to any of enumerated embodiments 1 - 7, wherein the metal lines of the first set have an average cross-sectional area A in a range of 2.5 to 8 pm2, or optionally, 2.5 to 5 pm2.

[0119] Enumerated embodiment 9. The photovoltaic structure according to any of enumerated embodiments 1 - 8, wherein the first set of metal lines include substantially parallel metal lines having an average spacing of at least 200 pm, optionally in a range of 500 pm to 2000 pm.

[0120] Enumerated embodiment 10. The photovoltaic structure according to any of enumerated embodiments 1 - 9, wherein the bottom electrode has a functional sheet resistance of less than 25 ohms, optionally less than 15 ohms.

[0121] Enumerated embodiment 11. The photovoltaic structure according to any of enumerated embodiments 1 - 10, wherein the first set of metal lines includes printed silver or copper.

[0122] Enumerated embodiment 12. The photovoltaic structure according to any of enumerated embodiments 1 - 11, wherein an upper surface of the first set of metal lines has an average roughness Ra in a range of 10 to 100 nm.

[0123] Enumerated embodiment 13. The photovoltaic structure according to any of enumerated embodiments 1 - 12, wherein an upper surface of the first set of metal lines has a peak roughness Rz in a range of 50 to 200 nm.

[0124] Enumerated embodiment 14. The photovoltaic structure according to any of enumerated embodiments 1 - 13, wherein the first set of metal lines includes sintered metal nanoparticles having an average particle size in a range of 10 to 40 nm. Enumerated embodiment 15. The photovoltaic structure according to any of enumerated embodiments 1 - 14, wherein the first conducting layer includes a transparent conductive oxide.

[0125] Enumerated embodiment 16. The photovoltaic structure according to any of enumerated embodiments 1 - 15, wherein the SAM-CSL is a hole-selective SAM-CSL.

[0126] Enumerated embodiment 17. The photovoltaic structure of enumerated embodiment 16, wherein the SAM-CSL has a chemical structure including an aryl amine, a carbazole, a phenothiazine, a quinoxaline, a thiophene, or a porphyrin.

[0127] Enumerated embodiment 18. The photovoltaic structure of enumerated embodiment 16 or 17, further including a metal oxide -based lower carrier transport layer interposed between i) the SAM-CSL and the first conducting layer, or ii) the SAM-CSL and the perovskite absorber layer.

[0128] Enumerated embodiment 19. The photovoltaic structure of enumerated embodiment 18, wherein the metal oxide -based lower carrier transport layer includes a nickel oxide.

[0129] Enumerated embodiment 20. The photovoltaic structure according to any of enumerated embodiments 1 - 19, wherein the SAM-CSL is an electron-selective SAM-CSL.

[0130] Enumerated embodiment 21. The photovoltaic structure of enumerated embodiment 20, wherein the SAM-CSL has a chemical structure including a fullerene, an aryl imide, or an aryl diimide.

[0131] Enumerated embodiment 22. The photovoltaic structure according to any of enumerated embodiments 1 - 21, wherein the perovskite absorber layer has a thickness in a range of 400 to 1300 nm, or optionally in a range of 500 to 1000 nm.

[0132] Enumerated embodiment 23. The photovoltaic structure according to any of enumerated embodiments 1 - 22, wherein the top electrode is transparent, the perovskite absorber layer has a thickness in a range of 100 to 300 nm, and the photovoltaic structure is transmissive to visible light.

[0133] Enumerated embodiment 24. The photovoltaic structure according to any of enumerated embodiments 1 - 22, wherein the top electrode is opaque or transmissive.

[0134] Enumerated embodiment 25. The photovoltaic structure according to any of enumerated embodiments 1 - 23, wherein the top electrode is transparent and includes a second conducting layer disposed over the upper carrier transport layer and a second set of metal lines disposed over the second conducting layer. Enumerated embodiment 26. The photovoltaic structure according to any of enumerated embodiments 1 - 25, wherein the bottom electrode has a functional resistance that is within 20% of a functional resistance of the top electrode.

[0135] Enumerated embodiment 27. The photovoltaic structure according to any of enumerated embodiments 1 - 26, wherein the substrate includes polymer.

[0136] Enumerated embodiment 28. The photovoltaic structure of enumerated embodiment 27, wherein the polymer is PET, PEN, or PC.

[0137] Enumerated embodiment 29. The photovoltaic structure according to any of enumerated embodiments 1 - 28, wherein the first set of metal lines is disposed over the substrate and the first conducting layer is provided over the first set of metal lines and overlaying portions of the substrate between the metal lines.

[0138] Enumerated embodiment 30. The photovoltaic structure of enumerated embodiment 29, wherein the transparent bottom electrode further includes an auxiliary first conducting layer provided between the first set of metal lines and the substrate and between the substrate and the first conducting layer.

[0139] Enumerated embodiment 31. The photovoltaic structure of enumerated embodiment 30, wherein the auxiliary first conducting layer includes a transparent conductive oxide.

[0140] Enumerated embodiment 32. The photovoltaic structure according to any of enumerated embodiments 1 - 28, wherein the first conducting layer is provided over the substrate and the first set of metal lines is provided over the first conducting layer.

[0141] Enumerated embodiment 33. The photovoltaic structure according to any of enumerated embodiments 1 - 32, further including an interfacial layer interposed between the SAM-CSL and a lower carrier transport layer or between the SAM-CSL and the transparent bottom electrode.

[0142] Enumerated embodiment 34. The photovoltaic structure according to any of enumerated embodiments 1 - 33, wherein the first conducting layer is a transparent metal oxide having an average thickness in a range of 30 nm to 100 nm.

[0143] Enumerated embodiment 35. A photovoltaic cell including the photovoltaic structure according to any of enumerated embodiments 1 - 34, wherein the photovoltaic cell is characterized by an active cell area, and wherein first set of metal lines cover less than 6% of the active cell area, optionally less than 2.5% of the active cell area. Enumerated embodiment 36. The photovoltaic cell of enumerated embodiment 35, characterized by a cell length in a range of 0.3 to 2.0 cm.

[0144] Enumerated embodiment 37. A photovoltaic module including two or more photovoltaic cells according to enumerated embodiment 35 or 36, wherein the photovoltaic cells are connected in series.

[0145] The specific details of particular embodiments may be combined in any suitable manner without departing from the spirit and scope of embodiments of the invention. However, other embodiments of the invention may be directed to specific embodiments relating to each individual aspect, or specific combinations of these individual aspects.

[0146] The above description of example embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above.

[0147] In the preceding description, for the purposes of explanation, numerous details have been set forth in order to provide an understanding of various embodiments of the present technology. It will be apparent to one skilled in the art, however, that certain embodiments may be practiced without some of these details, or with additional details.

[0148] Having described several embodiments, it will be recognized by those of skill in the art that various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the invention. Additionally, a number of well-known processes and elements have not been described in order to avoid unnecessarily obscuring the present invention. Additionally, details of any specific embodiment may not always be present in variations of that embodiment or may be added to other embodiments. It should be noted that, unless otherwise explicitly noted or required by context, the word “or” is used in this disclosure in a non-exclusive sense.

[0149] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context clearly dictates otherwise, between the upper and lower limits of that range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in that stated range is encompassed. The upper and lower limits of these smaller ranges may independently be included or excluded in the range, and each range where either, neither, or both limits are included in the smaller ranges is also encompassed within the invention, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included.

[0150] As used herein and in 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 method” includes a plurality of such methods and reference to “the device” includes reference to one or more devices and equivalents thereof known to those skilled in the art, and so forth. The invention has now been described in detail for the purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the appended claims.

[0151] All publications, patents, and patent applications cited herein are hereby incorporated by reference in their entirety for all purposes. None is admitted to be prior art.

Claims

We claim:

1. A photovoltaic structure comprising: a transparent substrate; a transparent bottom electrode provided over the substrate, the bottom electrode comprising a first set of metal lines in contact with a first conducting layer, wherein the first set of metal lines is characterized by an average height (H) of at least about 150 nm, an average width (W), and an aspect ratio H / W of at least about 1 / 250; a self-assembled molecular charge selective layer (SAM-CSL) disposed over the transparent bottom electrode; a perovskite absorber layer overlaying the SAM-CSL; an upper carrier transport layer overlaying the perovskite absorber layer; and a top electrode overlaying the upper carrier transport layer.

2. The photovoltaic structure of claim 1, further comprising a lower carrier transport layer interposed between the transparent bottom electrode and the SAM-CSL.

3. The photovoltaic structure of claim 2, further comprising a second SAM-CSL interposed between the transparent bottom electrode and the lower carrier transport layer.

4. The photovoltaic structure of claim 1, further comprising a lower carrier transport layer interposed between the SAM-CSL and the perovskite absorber layer.

5. The photovoltaic structure of claim 1, wherein H is in a range of 0.15 to 1 pm, W is less than 25 pm, and H / W is in a range of 1 / 150 to 1 / 8.

6. The photovoltaic structure of claim 1, wherein H is in a range of 0.2 to 0.6 pm, and H / W is in a range of 1 / 100 to 1 / 10.

7. The photovoltaic structure of claim 1, wherein W is in a range of 8 to 15 pm.

8. The photovoltaic structure of claim 1, wherein the metal lines of the first set have an average cross-sectional area A in a range of 2.5 to 8 pm2.

9. The photovoltaic structure of claim 1, wherein the first set of metal lines comprise substantially parallel metal lines having an average spacing of at least 200 pm.

10. The photovoltaic structure of claim 1, wherein the bottom electrode has a functional sheet resistance of less than 25 ohms.

11. The photovoltaic structure of claim 1, wherein the first set of metal lines comprises printed silver or copper.

12. The photovoltaic structure of claim 1 , wherein an upper surface of the first set of metal lines has an average roughness Ra in a range of 10 to 100 nni.

13. The photovoltaic structure of claim 1, wherein an upper surface of the first set of metal lines has a peak roughness Rz in a range of 50 to 200 nm.

14. The photovoltaic structure of claim 1, wherein the first set of metal lines comprises sintered metal nanoparticles having an average particle size in a range of 10 to 40 nm.

15. The photovoltaic structure of claim 1 , wherein the first conducting layer comprises a transparent conductive oxide.

16. The photovoltaic structure of claim 1, wherein the SAM-CSL is a hole-selective SAM-CSL.

17. The photovoltaic structure of claim 16, wherein the SAM-CSL has a chemical structure comprising an aryl amine, a carbazole, a phenothiazine, a quinoxaline, a thiophene, or a porphyrin.

18. The photovoltaic structure of claim 16 or 17, further comprising a metal oxidebased lower carrier transport layer interposed between i) the SAM-CSL and the first conducting layer, or ii) the SAM-CSL and the perovskite absorber layer.

19. The photovoltaic structure of claim 18, wherein the metal oxide -based lower carrier transport layer comprises a nickel oxide.

20. The photovoltaic structure of claim 1, wherein the SAM-CSL is an electron- selective SAM-CSL.

21. The photovoltaic structure of claim 20, wherein the SAM-CSL has a chemical structure comprising a fullerene, an aryl imide, or an aryl diimide.

22. The photovoltaic structure of claim 1, wherein the perovskite absorber layer has a thickness in a range of 400 to 1300 nm.

23. The photovoltaic structure of claim 1, wherein the top electrode is transparent, the perovskite absorber layer has a thickness in a range of 100 to 300 nm, and the photovoltaic structure is transmissive to visible light.

24. The photovoltaic structure of claim 1, wherein the top electrode is opaque or transmissive.

25. The photovoltaic structure of claim 1 , wherein the top electrode is transparent and comprises a second conducting layer disposed over the upper carrier transport layer and a second set of metal lines disposed over the second conducting layer.

26. The photovoltaic structure of claim 1, wherein the bottom electrode has a functional resistance that is within 20% of a functional resistance of the top electrode.

27. The photovoltaic structure of claim 1, wherein the substrate comprises polymer.

28. The photovoltaic structure of claim 27, wherein the polymer is PET, PEN, or PC.

29. The photovoltaic structure of claim 1, wherein the first set of metal lines is disposed over the substrate and the first conducting layer is provided over the first set of metal lines and overlaying portions of the substrate between the metal lines.

30. The photovoltaic structure of claim 29, wherein the transparent bottom electrode further comprises an auxiliary first conducting layer provided between the first set of metal lines and the substrate and between the substrate and the first conducting layer.

31. The photovoltaic structure of claim 30, wherein the auxiliary first conducting layer comprises a transparent conductive oxide.

32. The photovoltaic structure of claim 1, wherein the first conducting layer is provided over the substrate and the first set of metal lines is provided over the first conducting layer.

33. The photovoltaic structure of claim 1, further comprising an interfacial layer interposed between the SAM-CSL and a lower carrier transport layer or between the SAM-CSL and the transparent bottom electrode.

34. The photovoltaic structure of claim 1, wherein the first conducting layer is a transparent metal oxide having an average thickness in a range of 30 nm to 100 nm.

35. A photovoltaic cell comprising the photovoltaic structure of claim 1, wherein the photovoltaic cell is characterized by an active cell area, and wherein first set of metal lines cover less than 6% of the active cell area.

36. The photovoltaic cell of claim 35, characterized by a cell length in a range of 0.3 to 2.0 cm.

37. A photovoltaic module comprising two or more photovoltaic cells according to claim 35 or 36, wherein the photovoltaic cells are connected in series.

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