DE102010006813A1 - Thin-film solar cell comprises substrate, transparent, electrically conductive front electrode layer provided on light-facing side, and semiconductor layer - Google Patents

Abstract

A thin-film solar cell comprises a substrate (1), a transparent, electrically conductive front electrode layer (2) provided on light-facing side (hv), and a semiconductor layer (3). The semiconductor layer is electrically connected to back electrode layer (15). The back electrode layer includes a reflective sublayer (6) and a structured layer (5). The structured layer for structuring reflective back electrode sublayer is coated with a part of the rear electrode layer. An independent claim is also included for a method for producing thin-film solar cell, which involves depositing reflective back electrodes sublayer on structured layer through sol-gel process, where structured layer is provided with transparent electrically conductive back electrode layer, semiconductor layer or substrate with a printed plate.

Description

The This invention relates to a thin film solar cell the preamble of claim 1 and a method for their preparation

thin Film solar Cells or thin solar cells based on a silicon semiconductor layer Do not come without light scattering measures, because silicon is an indirect semiconductor and has a minimum layer thickness in the range several 100 μm for a complete Light absorption needed.

On the other hand, thin film solar cells based on a compound semiconductor layer such as II-VI semiconductor (eg cadmium telluride) or I-III-VI ₂ semiconductor (eg copper indium diselenide) always play due to their high efficiency increasing role. Because they are direct semiconductors, they are able to completely absorb light already with a layer thickness of a few μm. However, material savings, in particular high-risk elements such as, for example, indium and a reduction in costs are becoming increasingly important for compound semiconductor layers.

Around to extend the path of light in the semiconductor layer and thus to increase the efficiency or the semiconductor layer to be able to train thinner, so-called "light-trapping" concepts are used, which increase the optical path length. This contains various measures, such as the introduction of a (additional) reflector layer on the back, a structuring of the light-facing side of the solar cells or Structuring the back reflector layer. Is advantageous the achievement of structuring via an intermediate layer compared to the direct structuring of functional layers, such as direct etching of the front electrode layer, since such a structure regardless of other features can be realized simultaneously higher degree of freedom.

This is off Journal of Non-Cystralline Solids 218 (1997) 391-394 a thin film solar cell is known to bring to a glass substrate by the sol-gel method, a layer of silica (SiO ₂ ) gel, in which a periodic pattern is embossed to obtain a structured layer having a template for the on z. B. by vapor deposition, sputtering or the like deposited layers to finally obtain the highly reflective layer / or layer stack on the solar cell back with the structured surface.

Out WO 92/14270 A1 is a wafer-based solar cell with point or line-shaped back contacts known, which is provided to enhance the reflection on the back with an incident light relief grid. For this purpose, a dielectric, that is electrically non-conductive layer is applied to the provided with the back contacts semiconductor layer, which is patterned for example by embossing, whereupon a reflective metal layer is applied to the dielectric layer.

Out DE 197 30 975 A1 For the production of a structured silicon wafer, it is known to use a structured silicon substrate with a porous silicon layer, which serves as a seed layer for the epitaxial growth of the patterned wafer and as a predetermined breaking point. For separation at the predetermined breaking point, an adhesive material is used, which may be a glass prepared by the sol-gel process.

task The invention is the power collection and thus the efficiency of solar cells to increase substantially.

This is according to the invention with the characterized in claim 1 Thin-film solar cell reached. Ie. which are both electric conductive as well as reflective back electrode layer is structured by direct deposition on the structured layer. The back electrode layer or the back electrode layer composite characterized by the back electrode sub-layers characterized that she or he is electrically conductive and a electrical contact to the semiconductor layer is to ensure the functionality to ensure the solar cell.

The structured layer can except the reflective sublayer with an electrically conductive back electrode sublayer be coated. To dissipate the current of the solar cell can be the reflective sub-layer or the electrically conductive Partial layer to be contacted with a power bus.

there For example, the back electrode layer may be different depending on the cell design will be realized. For one thing, it can consist of a layer stack a conductive transparent sub-layer and at least one another sub-layer, for example one or more metal layers be formed. The layer stack as a whole then forms the back electrode layer, which both the function of a reflector and a back contact Has.

On the other hand, instead of one or more metal layers, at least one electrically nonconductive highly reflective partial layer can also be introduced. In this back electrode layer, the transparent conductive layer alone performs the function of the back contact, and the composite of transparent conductive layer and non-conductive reflective layer performs the function of the reflector. Furthermore, it is possible to use both functions, Conductivity and high reflectivity to realize in a single back electrode layer.

The structured layer can directly with the reflective back electrode sublayer be coated. Also, the back electrode layer between the structured layer and the reflective back electrode sublayer have a further sub-layer.

moreover can be between the back electrode layer or the electric conductive transparent sub-layer of the back electrode layer and the semiconductor layer may be provided with an intermediate layer, for example as a barrier layer to diffusion from the back electrode layer to prevent the semiconductor layer.

For the structured layer according to the invention means this is either directly in front of the back electrode layer (This applies to both a back electrode layer from a layer stack as well as a back electrode layer from only one layer) or in the case of layer stacks between the the back electrode layer forming sub-layers deposited can be.

By The invention will be a much higher collection of photogenerated Carriers and thus a significant increase in the Solar cell efficiency achieved, through an increased light scattering at the back electrode layer. The introduction of the structured Layer has the consequence that the surface structure of the Back electrode layer or one of its sub-layers exactly the structured layer is modeled. The structured layer thus represents directly a texture template. The surface structure the back electrode layer or one of its partial layers So is according to the invention of the surface structure the foregoing layers, such as those provided on the glass substrate structured layer according to the above-mentioned literature decoupled.

In order to is an increase of the invention Reflection as well as an increased diffuse scattering of the Light achieved at the back electrode layer and thus a higher short-circuit current generated in the solar cell.

In order to the structured layer is the texture template for it forms deposited back electrode layer, the thin-film solar cell according to the invention both in the substrate configuration as in the superstrate configuration getting produced.

at the production in the substrate configuration becomes the structured one Layer on a rigid or flexible substrate, for example made of glass, ceramics, z. As glass-ceramic, metal, polymer or the like applied, then the back electrode layer z. B. deposited by sputtering and subsequently successively the semiconductor layer, possibly a buffer layer or further semiconductor layer and the front electrode layer is deposited, the front electrode layer usually with a transparent front cover, z. B. off Glass, glass ceramic or a polymer is provided. In special cases However, the substrate may also be coated, for example. With a Diffusion barrier.

To In another embodiment of the invention, the structured Layer applied between the back electrode layer and the semiconductor layer be, however, for example, by recesses in the structured layer with an electrical contacting of the semiconductor layer the reflective back electrode layer or the reflective one Rear electrode layer layer is to be provided.

at in superstrate configuration are referred to as "superstrate" transparent substrate, for example glass, glass ceramic or polymer, successively the front electrode layer, possibly a buffer layer or further semiconductor layer and the actual semiconductor layer For example, deposited by gas phase deposition.

Between However, the substrate and the front electrode layer can also additional functional layers, such as a structuring Layer and / or a diffusion barrier can be deposited.

In Dependence of cell design is followed by the deposition of the first Partial layer of the back electrode layer on which then the structured layer is applied, whereupon the at least a further sub-layer of the back electrode layer, ie for example, one or more metal layers are deposited, z. B. by sputtering.

Instead The structured layer may also be directly on the semiconductor layer are deposited and then the back electrode layer z. B. by sputtering. The back electrode layer then becomes usually with a back cover z. Glass, Ceramic, for example, glass ceramic, metal, or polymer provided.

If the production takes place in the superstrate configuration, electrical contact has to be established between the sublayers of the back electrode layer or of the semiconductor and back electrode layer, if the structured layer lies between two electrically conductive sublayers of the back contact or directly onto the semiconductor layer is applied. This does not apply to the case where the back electrode layer has a non-conductive highly reflective layer. In order to produce the contact, the structured layer preferably has recesses, by means of which, in the case of the superstrate configuration, a sufficiently good contacting of the corresponding layers is realized.

in the Case of a transparent back electrode sublayer, to a total reflection of the light at the back electrode layer To prevent the refractive index of the structured layer to the transparent back contact layer adapted, d. H. she gives way preferably at most 0.5 to 1, in particular at most 0.3 of the Refractive index of the transparent back electrode part layer. That is, in a back electrode part layer of an electrically conductive, transparent metal oxide, such as zinc or tin oxide, with a refractive index of 1.9 to 2.0 according to the invention is the Refractive index of the structured layer preferably 1.5 to 2.4, in particular 1.7 to 2.2.

The Thin film solar cell according to the invention also preferably has a buffer layer and / or another Semiconductor layer between the front electrode layer and the semiconductor layer is deposited.

The Substrate is preferably with at least one functional layer Mistake. The functional layer can be formed by a barrier layer be. In addition, on the substrate as a functional layer another be provided structured layer.

The structured layer preferably has a periodic pattern on, with the distance between the elevations and / or Recesses of adjacent patterns preferably in the submicrometer range is, and preferably less than 5 microns, preferably less than 2 microns, especially less than 1000 nm, especially preferably between 100 to 500 nm.

If the period of the pattern of the patterned layer in the submicron range is, the falling on the back electrode layer Deflected light with a large solid angle.

The Aspect ratio, ie the ratio of the Height of the elevations or the depth of the depressions the pattern to the distance from each other is preferably 0.01 to 2, especially 1.0 to 0.6. That is, the pattern is relatively flat to scatter the light at a shallow angle.

The average layer thickness of the structured layer is preferably at most 5 μm and can be 0.05 to 20 μm, in particular 0.1 to 5 microns.

On the periodic pattern of the structured layer in the submicrometer range preferably periodic superstructures are modulated, which are formed by elevations and / or depressions. These superstructures have a period, ie a distance between the elevations and / or depressions of more than 1 micron, in particular 5 to 20 microns. By the modulated superstructures of the structured layer an additional light scattering is achieved. The aspect ratio The superstructure may also be 0.01 to 2, especially 0.1 to 0.5.

The periodic patterns in the submicrometer range and / or the modulated Periodic superstructures are preferably isotropic, ie independent of direction. These can be the periodic patterns in the nanometer range and / or the modulated periodic superstructures through cross lattice, moth eyes, Pyramids or inverted pyramids may be formed.

To a preferred embodiment of the invention is in the layer material is a cross lattice with a period of 500 to 1200 nm, in particular about 800 nm, and a depth of 300 to 900 nm, in particular impressed about 600 nm.

The structured layer is preferably by a metal oxide and / or Semi-metal oxide network formed, which is preferably glassy, ie amorphous, hybrid polymer, nanocrystalline and / or partially crystalline formed is.

The structured layer can in particular consist of silicon dioxide (SiO ₂ ) as a semi-metal oxide and contain transparent metal oxides. The silicon dioxide can be in amorphous or hybrid polymeric form, that is, have organic residual constituents. A hybrid polymer is a crosslinking and / or crosslinked polymeric material of organic and inorganic constituents. Organic residues can z. For example, be methyl, ethyl or phenyl groups. Furthermore, the layer may contain polysiloxanes or their decomposition products.

In a preferred embodiment, the SiO ₂ network is present as a hybrid polymer or as a vinyl-, allyl-, methacrylate- or epoxide-functionalized silane.

The transparent metal oxides are present in the layer preferably as amorphous, partially crystalline or crystalline nanoparticles which are bound in an amorphous SiO ₂ or SiO ₂ network functionalized with organic radical constituents. A typical particle or crystallite size of the metal oxides is 0.5-100 nm, preferably 1 to 50 nm, more preferably 2-20 nm.

Spherical SiO ₂ nanoparticles having a particle diameter of 4 to 100 nm, in particular 6 to 50 nm, very particularly 6 to 30 nm, are preferably present in the structured layer. In particular, spherical SiO ₂ nanoparticles are used as SiO ₂ nanoparticles, spherical ellipsoidal, acicular or fibrous SiO ₂ nanoparticles.

fibrous For example, nanoparticles can be made from chains several juxtaposed, spherical nanoparticles consist of a diameter of 8 to 20 nm.

The mean chain length is between 30 and 200 nm.

The Metal oxides can be in amorphous or nanocrystalline form also in the form of hybrid polymer derivatives or compounds or as a particle.

The transparent metal oxides may include titanium dioxide (TiO ₂ ), zirconium dioxide (ZrO ₂ ), niobium oxide (NbO ₂ ), manganese oxide (MnO ₂ , Mn ₂ O ₃ ), hafnium oxide (HfO ₂ ), germanium oxide (GeO ₂ ), calcium or magnesium. or yttrium stabilized zirconia, alumina (Al ₂ O ₃ ), zinc oxide (ZnO), tin oxide (SnO ₂ ), gadolinium oxide (Gd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ), lanthanum oxide (La ₂ O ₃ ), magnesium oxide (MgO), calcium oxide (CaO) and / or boron oxide (B ₂ O ₃ ), yttrium titanate (Y ₂ Ti ₂ O ₇ ), lanthanum zirconate (La ₂ ZrO ₇ ). The zinc oxide can be indium-, antimony- or aluminum-doped zinc oxide. Preference is given to metal oxides and their crystalline or amorphous nanoparticles having a refractive index> 2.0.

With these metal oxides, the refractive index of the structured layer can be set exactly. For example, the refractive index of titanium oxide in the anatase crystal modification is 2.54. The refractive index of ZrO ₂ is for example 2.1.

In particular embodiments, the metal oxides can also be introduced directly as nanoparticles. Redispersible nanoparticles or their colloidally disperse dispersion in water, alcohols or apolar solvents are preferably used for this purpose. Optionally, of the hydroxides, acetates or propionates of metal oxides such. B. Al (OH) ₃ , La (acetate) ₃ , Sm (acetate) ₃ , Gd (propionate) _{3 are} assumed. In a particular embodiment of the invention, the nanoparticles, in particular the TiO ₂ nanoparticles with a SiO ₂ , ZrO ₂ or Al ₂ O ₃ layer z. B. over the sol-gel method has been coated.

In a preferred embodiment, SiO ₂ nanoparticles are present in the structured layer in addition to other oxidic nanoparticles, by way of example preferably high-index nanoparticles. The high-index nanoparticles preferably have a particle size of 4 to 80 nm. The volume ratio of the high-index nanoparticles to other layer material, including the pores, is between 1: 10 to 1: 1, preferably 1: 5 to 1: 2.

In a preferred embodiment according to the invention, the SiO ₂ nanoparticles and the high-index nanoparticles are fixed in the structured layer with a glassy and / or hybrid polymer binder. The volume ratio of SiO ₂ and high-index nanoparticles to binders is for example 1 to 10 to 10 to 1, preferably 1 to 2 to 5 to 1.

The hydrolyzed and polycondensed sol-gel precursors amorphous or crystalline and molecular or colloidal-disperse, the particle size of these precursors preferably less than 20 nm. This particle size can by small angle scattering (SAXS), dynamic light scattering (DLS) and / or Fraunhofer diffraction are determined.

The structured layer can be made by embossing or printing a Formed by the sol-gel process from hydrolysing and polycondensable silicon compounds, in particular silicon-organic Compounds and optionally hydrosilyl and polycondensable titanium, Zirconium, aluminum, zinc, magnesium, calcium, cerium, samarium, gadolinium, Lanthanum, boron, yttrium and / or tin compounds produced is. In this case, the silicon or silicon organic compound be photochemically polymerizable.

D. H. the structured layer can be made by the sol-gel method hydrolyzable and condensable silicon and optionally titanium, Zirconium, niobium, aluminum, zinc, germanium, magnesium, calcium and tin compounds of the general formulas SiORxR'y, TiORxXy, ZrORxXy, NbORxXy, AlORxXy, ZnORxXy, GeORxXy MgORxXy, CaORxXy and / or SnORxXy where O is oxygen and R and R 'are the same or different organic radicals or R 'is hydrogen, X is a halide, preferably chlorine, and x and y together are the Forming number of residual valences. Organic residues can for example, methyl, ethyl, phenyl, propyl, butyl.

Further compounds are used for the silicon alkoxide precursors SiORxR'y, in which O is oxygen and R and R 'are identical or different organic radicals, which can be crosslinked in part thermally or photochemically via a free-radical and / or ionic polymerization reaction. Organically crosslinkable groups are z. 3-glycidoxypropyl, 3-methacryloxypropyl, allyl, vinyl. Particular preference is given to compounds such as 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, allyltriethoxysilane, vinyltriethoxysilane.

When Adhesion promoters to the substrate may be the paint formulation, with which the structured layer is made, aminosilanes such as 3-aminopropoyltriethoxysilane or 3-aminopropoyltrimethoxysilane be added. The hydrolyzed and polycondensed sol-gel precursors, may be amorphous or crystalline as well as molecular or colloidal be, the particle size of these precursors preferably less than 20 nm. This particle size can by small angle scattering (SAXS), dynamic light scattering (DLS) and / or Fraunhofer diffraction are determined.

to Stabilization of the reactive metal oxide precursors in particular the Alcoholates can be complexing agents such as beta-diketonates z. For example, acetylacetone, beta-carbonyl carboxylic acid ester such. For example, ethyl acetoacetate, carboxylic acids such as Propionic acid or methoxyethoxyacetic acid, monoethanolamine, Diethanolamine, triethanolamine, diols such as. As pentanediol and polymerizable Ligands such as methacrylic acid or acrylic acid used become.

In a particular embodiment, the sol-gel precursors can also be introduced in powder form using amorphous or crystalline sol-gel precursor powders known to those skilled in the art. For example, precursor powders of TiO ₂ , ZrO ₂ , Al ₂ O ₃ , ZnAl ₂ O ₄ , mullite (Al ₂ O ₃ / SiO ₂ ) and MgAl ₂ O ₄ with, for example, triethanolamine, acetylacetone or ethoxyacetic acid as chelate ligands are known.

The hydrolysis of the sol-gel precursors, in particular of the alcoholates, is generally carried out under neutral or acidic conditions. Acidic conditions are adjusted, for example, by the addition of mineral acid such as HCl, HNO ₃ , H ₂ SO ₄ and H ₃ PO ₄ . Alternatively, a hydrolysis or prehydrolysis can be carried out under acetic acid conditions. The hydrolysis and condensation can also be carried out in an alkaline medium, for example NH ₃ can be used for this purpose.

In particular embodiments are organic for hydrolysis Acid such as para-Toluolsulfonsäue used.

The crystalline nanoparticles can become liquid Phase in the synthesis as well as redispersible nanoparticles with an agglomerate size of the redispersed Nanoparticles <50 nm are introduced.

In a particular embodiment of the invention is the content of crystalline or amorphous nanoparticles with a refractive index> 2.0 more than 30, in particular more than 40 volumes of the total layer volume.

The Nanoparticles can be known by those skilled in the art Process such as precipitation from liquid phase, by Produces flame pyrolysis or under hydrothermal conditions have been.

In In a specific embodiment, the coating solution added an additionally crosslinkable organic monomer become. Such additives may include, for example, succinic anhydride, Tetraethylene glycol dimethacrylate, hexanediol diacrylate or trimethylolpropane triacrylate be.

special Sol-gel systems can be known to those skilled in the art such as the polyacrylates BYK 359 or BYK 301 added become.

In a special embodiment, the paint formulation for setting a special drying behavior and a special thixotropy a polysiloxane can be added.

Around the detachment behavior or reactions and / or the adhesion the paint formulation with the polymeric or silicone based stamping material To minimize or suppress, the Formulation fluorosilanes such as 1H, 1H, 2H, 2H-perfluorooctyltriethoxysilane, 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane, or other fluoroorganic compounds are added.

Around a photochemical curing of the structured thin films to be able to perform the sol-gel coating solutions, So the paint formulation, photoinitiators added, which z. B. a radical polymerization or crosslinking reaction Allyl, vinyl, methacrylate or acrylate groups can start. If epoxy groups are to be crosslinked photochemically, then cationic starter systems are used. Common to that Fachman photochemically excitable starter systems may, for. B 1-hydroxycyclohexylbenzophenone (Irgacure 184), benzophenone, mixtures from 1-hydroxycyclohexylbenzophenone and benzophenone, phosphineoxyphenyl bis (2,4,6-trimethylbenzoyl). By choosing the starter system For example, the excitation wavelength can be varied from 200-500 nm and each be set specifically. For a thermal Hardening is the brines, for example, the catalyst 1-methylimidazole added.

If the patterned layer is formed by embossing, in a substrate thin film solar cell, the patterned layer is passed through Coating the substrate or on a functional layer applied to the substrate, such as a diffusion barrier, with the sol, forming the gel layer, embossing the gel layer and curing the embossed gel layer. If the thin-film solar cell is fabricated in the superstrate configuration, the patterned layer is formed by coating a back electrode sublayer on the light-remote side with the sol, forming the gel layer, embossing the gel layer, and curing the embossed gel layer ,

The Coating can be done by dip coating, roller application, flooding or spraying. For serial production the roll application is preferred.

Out on the optionally coated with a functional layer substrate or a back electrode part or the semiconductor layer applied aqueous, solvent-containing Sol, the solvent is at least partially evaporated, an embossable, possibly even low viscosity or already more viscous dried gel film on the possibly coated substrate or a Rückelektrodenteil- or to form the semiconductor layer. The applied viscous gel film is then embossed and cured.

to Curing can be beam sources or their Combinations are used, which in the UV, in the visible wavelength range or emit NIR-IR or IR range.

When Embossing mold, for example, a polymeric film on a Embossing stamp or a stamping cylinder used become.

to Production of the mold is z. B. interference lithographic the periodic pattern with which the structured layer on the Substrate or the back contact layer to be provided on a master, z. B. made of nickel and from him to the polymeric Transfer film. The polymeric film thus has the negative of the periodic pattern and the aspect ratio of the structured ones Layer, and if the structured layer contains superstructures, also the negative of the superstructures and their aspect ratio. The polymeric film may be made of a rubber elastic material, for example Silicone rubber or perfluorinated polymer. The contact pressure when embossing is preferably 0.01 to 5 bar. At one higher pressure can damage the solar cell.

The Embossing can be done in a vacuum to prevent being in the depressions of the embossed Gel-film liquid accumulates the structure of the structured Shift can change. Also can be a porous Embossing mold to be used, this liquid receives.

While the embossing mold against the plastic gel film on the substrate is pressed, the gel film is also cured, to fix the structure to be transferred. Optional Curing can also be effected by the embossing stamp, medium UV light or IR radiation. A hardening with other beam sources such as high energy radiation is also possible. Usually closes after pre-hardening before the embossing process, the curing during the embossing process still a post-curing.

The Pre-curing, hardening during the embossing process and the final cure may be, for example thermally and / or with UV light or IR radiation. To can the gel film while he is against the the embossing mold is pressed, when pre-curing first be heated to 50 to 140 ° C. After a duration pre-curing of preferably 0.1 seconds to 1 minute, the embossed structure is fixed so that the embossing form from the structured layer on the optionally coated substrate or a back electrode part or the semiconductor layer can be removed.

In Usually, the wet gel film is already before the actual embossing process medium UV or IR radiation or thermally pre-dried or pre-cured.

The Curing the embossed structured gel layer as explained in more detail below Printed structured gel layer can be thermally performed be, preferably at 300 to 750 ° C.

So can be the final cure at a temperature be carried out from preferably 450 to 740 ° C, when the substrate prepared according to the substrate configuration Thin-film solar cell or referred to as "superstrate" Substrate of the solar cell produced after the superstrate configuration is thermally stable accordingly.

In contrast, is in a substrate of a polymer z. As polyimide due the low temperature stability, a curing temperature of normally at most 300 ° C, especially at most 200 ° C applied.

To the abovementioned radicals R, R 'of the compounds, from which the sol and thus the gel film is formed, at elevated temperature and / or radicals which can be split off under UV radiation, for example Epoxy or methacrylate residues to the curing temperature decrease.

When it has proven to be particularly advantageous to cure by means of UV radiation in a wavelength range of 200-300 nm, as this results in a sufficiently high process speed is guaranteed. It is also possible through this to achieve an exact and defect-free structure impression.

With inorganic, hybrid or organic only thermally crosslinkable Systems which do not have photochemically polymerizable functionalities This is not with a sufficiently high process speed possible. For this coating sol formulations are preferred, which are functionalized on methyl methacrylate, acrylate, vinyl and / or epoxy groups Particles and silanes are based.

Around the connection of the gel film to the embossing mold when removing to prevent the embossing mold from the structured layer can the embossing mold, so for example the stamping foil, be provided with surfactants or the like entendenenden compounds, for example with perfluorinated hydrocarbons, fluorinated Silanes or the like.

at Production of the thin-film solar cell according to the substrate configuration In addition, the substrate can be subjected to a pretreatment in order to to improve the adhesion of the structured layer to the substrate. Thus, a primer can be used or a corona treatment of the substrate before applying the sol become.

Instead of the coating of the substrate or the back contact layer with the sol and embossing the gel film on the optionally coated Substrate or a back electrode part or the semiconductor layer If necessary, the coated substrate or a back electrode part or the semiconductor layer also by printing with the structured Layer be provided. In the printing form, a cylinder or a Plate can then deepen the negative of the periodic Pattern with the aspect ratio of the structured layer be provided, and if this structured layer superstructures contains, also the negative of superstructures with their aspect ratio.

The structured layer can thus by printing the possibly coated Substrate or a back electrode part or the semiconductor layer with the gel provided printing form, holding the printing form against the substrate or the back contact layer during precoating the structured layer, removing the printing form of the precured structured layer and final curing of the structured layer be formed.

The Pre-curing and final curing can be carried out in the same way as above described in the context of embossing. same for for the pretreatment of the printing form.

On the structured layer on the optionally coated substrate or a back electrode part or the semiconductor layer then, for example, by sputtering the back electrode layer or their further partial layer (s) deposited.

Around the electrical contact between the back electrode sublayers or the semiconductor layer and the back electrode layer can be used when embossing or printing the structured layer creates recesses in the structured layer be, for example, overmodulated recesses in the Embossing or printing form structure.

The Semiconductor layer has the usual for thin-film solar cells Thickness of less than 2 microns, especially less than 1 micron on.

The semiconductor layer of the thin film solar cell according to the invention preferably consists of a semiconductor based on silicon, that is to say in particular amorphous, microcrystalline or micromorphous or mono- or nano- or polycrystalline silicon or a compound semiconductor. The compound semiconductor is preferably made of II-VI semiconductors such as cadmium telluride or I-III-VI ₂ semiconductors such as Cu (In _x Ga _1-x) (S _y Se _{1-y) 2,} wherein x and y 0 to 1 is. Preferably, the semiconductor layer has more than one pn junction.

The Back electrode layer or one of its sub-layers can a metal layer of, for example, molybdenum, vanadium, Tungsten, nickel, titanium, palladium, silver, aluminum, copper or be an alloy of these metals. She can be at the back be provided with additional metal layers.

In In a particular embodiment, one of the back electrode sublayers but also by a white color layer, for example be formed of titanium dioxide or barium sulfate, in which case the further back electrode sub-layer on the light-facing Side of a transparent electrically conductive layer, in particular from an oxide (TCO), for example tin or zinc oxide exists to form the back electrode. In further embodiments The back electrode may also be through one or more metal layers and a transparent electrically conductive layer are formed.

In particular embodiments, the structured layer on the back electrode or between the back electrode sublayers may also be in so-called. "Multijunction devices", above all the so-called tandem structure, are used.

The Substrate of the thin-film solar cell according to the invention may be a soda lime, borosilicate or aluminosilicate glass.

The soda-lime glass preferably contains 40 to 80% by weight SiO ₂ , 0 to 5% by weight Al ₂ O ₃ , 3 to 30% by weight R ₂ O, 3 to 30% by weight R ' O and other ingredients of 0 to 10 wt .-%, wherein R is at least one element selected from the group consisting of Li, Na and K, and wherein R 'is at least one element selected from the group is, which consists of Mg, Ca, Sr, Ba and Zn, or
50 to 76 wt .-% SiO ₂ , 0 to 5 wt .-% Al ₂ O ₃ , 6 to 25 wt .-% R ₂ O, 6 to 25 wt .-%, R'O and other components from 0 to 10% by weight, wherein R is at least one member selected from the group consisting of Li, Na and K, and wherein R 'is at least one member selected from the group consisting of Mg, Ca , Sr, Ba and Zn, or at least 0.1 wt% Al ₂ O ₃ , preferably at least 0.5 wt% Al ₂ O ₃ .

The borosilicate glass preferably contains 60 to 85 wt .-% SiO ₂ , 1 to 10 wt .-% Al ₂ O ₃ , 5 to 20 wt .-% B ₂ O ₃ , 2 to 10 wt .-% R ₂ O and 0 to 10% by weight of other ingredients, wherein R is at least one member selected from the group consisting of Li, Na and K, or
70 to 83 wt .-% SiO ₂ , 1 to 8 wt .-% Al ₂ O ₃ , 6 to 14 wt .-% R ₂ O and 0 to 10 wt .-% of further constituents, wherein R is at least one element , which is selected from the group consisting of Li, Na and K.

The aluminosilicate glass preferably contains 55 to 70 wt.% SiO ₂ , 10 to 25 wt.% Al ₂ O ₃ , 0 to 5 wt.% B ₂ O ₃ , 0 to 2 wt.% R ₂ O, 3 to 25% by weight of R'O and other ingredients of 0 to 10% by weight, wherein R is at least one member selected from the group consisting of Li, Na and K, and wherein R 'is at least one Is element selected from the group consisting of Mg, Ca, Sr, Ba and Zn, or
at least 0.5% by weight of B ₂ O ₃ .

below the invention with reference to the accompanying drawings by way of example explained in more detail. In each case show schematically

1 and 2 a cross-section through a portion of a thin film solar cell in the superstrate configuration or substrate configuration;

3 a plan view of a portion of the patterned layer on a sub-layer of the back contact layer of the thin-film solar cell after 1 ; and

4 a cross section along the line IV-IV in 3 ,

According to 1 the thin-film solar cell consists of a transparent, electrically insulating substrate 1 , For example, a glass sheet, on the successively a transparent, electrically conductive front electrode layer 2 , a semiconductor layer 3 and a transparent, electrically conductive back electrode sublayer 4 , For example, deposited by gas phase deposition.

On the glass, so below the front electrode layer 2 , one or more functional layers, such as a patterned layer or diffusion barrier, may be deposited, and on the front electrode layer 2 , ie below the semiconductor layer 3 optionally a buffer layer or further semiconductor layer.

On the first back electrode partial layer 4 is a structured layer formed by the sol-gel method 5 applied, on which the further reflective back electrode sublayer 6 , z. B. is applied by sputtering. The back electrode sublayer 6 is with a back cover 7 Mistake.

So that an electrical contact between the two back electrode partial layers 4 and 6 are formed in the structured layer 5 recesses 8th provided when applying, for. B. by sputtering, the rear back electrode part layer 6 be filled.

The back electrode sublayer 6 on the structured layer 5 We can only have one single electrically conductive layer and one reflective layer. Furthermore, between the semiconductor layer 3 and front electrode layer 2 a buffer layer or further semiconductor layer may be provided.

According to 2 is on a substrate 1' a structured layer 5 ' applied. On the textured layer 5 ' is a back electrode sublayer 6 ' , deposited by sputtering, for example, on which a further (transparent) back electrode sublayer 4 ' is applied. Furthermore, a semiconductor layer is successively formed 3 , and a transparent front electrode layer 2 deposited. The front electrode layer 2 comes with a front cover 9 , For example, provided a glass.

In particular embodiments, the substrate 1' be coated with a further functional layer, such as, for example, a diffusion barrier. Also, the structured layer can be applied directly to the semiconductor layer 4 be applied. In addition, can only a single back electrode layer with the double function back contact and reflector can be provided.

The semiconductor layer 3 is with a positively-doped sublayer 10 , an intrinsic sublayer 11 and a negative-doped sub-layer 12 educated.

The structured layer 5 on the back electrode part layer 4 (or semiconductor layer 3 ) or the structured layer 5 ' on the substrate 1' thus forms a texture template for the deposited on the back electrodes (part) layer 6 respectively. 6 ' , In this way, the back electrodes (partial) layer 6 . 6 ' provided with a textured surface that scatters the incident light.

How out 3 and 4 can be seen, the structured layer 5 a periodic pattern 13 which is formed by elevations in the form of pyramids with a square base. The pyramids are at a distance (period) a of z. B. 200 nm from each other. The aspect ratio, ie the height of the pyramids to the distance a is z. B. 0.5.

Due to the increases in the distance of z. B. 200 nm of the structured layer 5 . 5 ' becomes at the reflector layer 6 respectively. 6 ' generates a complementary surface structure that forms a diffraction grating, so that the incident light hν at the reflector layer 6 . 6 ' is bent.

In addition, the structured layer 5 . 5 ' superstructures 14 in the form of cross-sectionally V-shaped elevations, with a period, ie a distance b of z. B. 2 microns are arranged from each other. The aspect ratio, ie the height of the elevations of the superstructure 13 to the distance b can z. B. 0.1.

The The following examples serve for further explanation the invention.

Paint formulation 1:

For the preparation, 1.5 mol of titanium tetraethylate are reacted with 1 mol of acetylactone and then hydrolyzed with 5 mol of water in which 0.1 mol of paratoluene sulfonic acid are dissolved. The solvent is removed and the powder is then dried for 4 hours at 125 ° C. The powder is redispersed in 10% strength by mass concentration in water and then hydrothermally treated for 15 hours at 160 ° C. in a metal bomb. The nanoparticles are then extracted from the aqueous phase with n-butanol. After removal of the n-butanol, redispersible TiO ₂ nanoparticles are obtained.

0.40 mol of methacryloxypropyltrimethoxysilane (MPTMS), 0.04 mol of tetraethoxysilane and 0.1 g of paratoluene sulfonic acid, dissolved in 16 g of water, are placed in a vessel. The solution is stirred for 1 h. 300 g of a dispersion of nanoparticulate TiO ₂ particles in n-butanol (15% by mass, anatase, crystallite size 7-12 nm) are then slowly added to this solution while cooling with ice and vigorously stirred.

The paint formulation 1 15 g of Photoinitators Irgagure 184 ^® was added and then performed one-sided coatings by means of roller coating. After the solvent has dried, a polymeric or silcon-like embossing stamp having an embossing pressure of 0.1-2.0 bar is pressed flat (10 × 10 cm ² ) into the low-viscosity plastic gel film. The embossing stamp is made of a material which is permeable in a wavelength range> 230 nm. The structure of the stamper is a periodic moth-eye structure having a period of 300 nm and an aspect ratio of on average 1. While the stamper is in contact with the layer material, is emitted by means of a UV lamp, which emits in the wavelength range of about 250 nm. performed a first hardening of the layer. After removal of the embossing stamp, a further UV-based layer hardening takes place.

The average glassy-ceramic layer thickness of the embossed layer is 500 nm. The aspect ratio of the embossed Structure is 0.5-0.6.

Paint formulation 2:

0.80 mol of glycidoxpropyltriethoxysilane (GPTMS) and 0.20 mol of tetraethoxysilane (TEOS) are introduced into a vessel and hydrolyzed with 0.13 mol of H ₂ O, which contains 0.0018 mol of paratoluene sulfonic acid. After 10 minutes, 0.10 mol of spherical SiO ₂ nanoparticles (8 nm particle diameter) as a 30% by mass dispersion in isopropanol and 2.4 mol of crystalline TiO ₂ nanoparticles in n-butanol are added. The solution is stirred for 24 hours.

Add 0.6 g of an iodonium salt as photoinitiator to the paint formulation. The photoinitiator is under the brand name irgagure 250 ^® available. Subsequently, a one-sided coating is carried out by roller coating. After the solvent has dried, a polymeric or silicone-containing embossing stamp having an embossing pressure of 0.1 to 2.0 bar (10 × 10 cm ² ) is pressed into the low-viscosity plastic gel film. The embossing stamp is made of a material which is permeable in a wavelength range> 230 nm. The structure of the stamper is a periodic cross lattice structure with a period of 500 nm and an aspect ratio of one mean. During the embossing stamp in contact with the layer material is, is carried out by means of a UV lamp, which emits in the wavelength range of about 250 nm, a first hardening of the layer. After removal of the embossing stamp, a further UV-based layer hardening and a thermal layer hardening takes place at 170 ° C. for 1 hour.

The average glassy-ceramic layer thickness of the embossed layer is between 800 to 900 nm. The aspect ratio the embossed structure is 0.75. The layer material has a refractive index of about 1.7.

Paint formulation 3:

In a vessel, 0.5 mol of vinyltriethoxysilane and 0.1 mol of tetraethoxysilane are hydrolyzed with 1.0 mol of H ₂ O containing 0.03 mol of HCl. The solution is stirred for 1 h. 0.5 mol of zirconium tetrapropylate, mixed with 0.5 mol of methacrylic acid, is slowly added dropwise to this solution while cooling with ice.

The Formulation 3 is then diluted with 100 ml of ethanol and mixed with 12 g Irgacure 189. The curing and Structuring takes place as described for Formulation 1 or 2.

Paint formulation 4:

For the preparation, 100 g of titanium tetrapropylate are mixed with 50 g of 1-propanol and 6 g of concentrated HCl. After one hour, hydrolyzed with 7.5 g of water in 15 g of 1-propanol. The solution is then hydrothermally treated for 1 hour at 200 ° C in a metal bomb. After removal of the 1-propanol, redispersible TiO ₂ nanoparticles are obtained.

In a vessel 100 g (0.40 mol), methacryloxypropyltrimethoxysilane (MPTMS) and 1.5 g of concentrated HCl in 14 g of water are introduced. The solution is stirred for 1 h. 300 g of a dispersion of nanoparticulate TiO ₂ particles in toluene (15% by mass, anatase, crystallite size 7-12 nm) are then slowly added to this solution while cooling with ice and vigorously stirred.

The Formulation 4 is then mixed with 15 g Irgacure 189 offset. The curing and structuring takes place as described in Formulation 1 or 2.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• WO 92/14270 A1 [0006]
• DE 19730975 A1 [0007]

Cited non-patent literature

• - Journal of Non-Cystralline Solids 218 (1997) 391-394 [0005]

Claims (20)

Thin-film solar cell with a substrate ( 1 . 1' ), a transparent, electrically conductive front electrode layer ( 2 ) on the light-facing side (hν), at least one semiconductor layer ( 3 ), one with the semiconductor layer ( 3 ) electrically connected back electrode layer ( 15 ) comprising at least one reflective sub-layer ( 6 . 6 ' ) and a structured layer ( 5 . 5 ' ), characterized in that the structured layer ( 5 . 5 ' ) for structuring the reflective back electrode sublayer ( 6 . 6 ' ) with the reflective back electrode sublayer ( 6 . 6 ' ) is coated. Thin-film solar cell according to claim 1, characterized in that the structured layer ( 5 . 5 ' ) is formed by an amorphous, hybrid polymer, nanocrystalline and / or semicrystalline metal oxide and / or semimetal oxide network. Thin-film solar cell according to claim 1 or 2, characterized in that it has a substrate configuration in which the substrate ( 1' ) is arranged on the side facing away from the light-facing side (hν) side, wherein the structured layer ( 5 ' ) on the substrate ( 1' ) is applied. Thin-film solar cell according to one of the preceding claims, characterized in that the back electrode layer ( 15 ) one of the semiconductor layer ( 3 ) adjacent, transparent and electrically conductive back electrode sublayer ( 4 . 4 ' ) having. Thin-film solar cell according to claim 1 or 4, characterized in that it has a superstrate configuration with a transparent substrate ( 1 ) on the light-facing side (hν), wherein the structured layer ( 5 ) formed transparent and on the side facing away from the light-facing side (hν) side with the reflective back electrode sub-layer ( 6 ) is coated. Thin-film solar cell according to claim 5, characterized in that the structured layer ( 5 ) for electrically contacting the semiconductor layer ( 3 ) with the reflective back electrode sublayer ( 6 ) is trained. Thin-film solar cell according to claim 4 or 6, characterized in that the structured layer ( 5 ) for electrically contacting the semiconductor layer ( 3 ) or the electrically conductive, transparent back electrode sublayer ( 4 ) with the reflective back electrode sublayer ( 6 ) Recesses ( 8th ) having. Thin-film solar cell according to claim 2, characterized in that the semimetal oxide is silicon dioxide and the structured layer ( 5 . 5 ' ) contains at least one transparent metal oxide. Thin-film solar cell according to claim 8, characterized in that the transparent metal oxide titanium dioxide (TiO ₂ ), niobium oxide (NbO ₂ ), manganese oxide (MnO ₂ , Mn ₂ O ₃ ), hafnium oxide (HfO ₂ ), germanium oxide (GeO ₂ ), calcium or Magnesium or yttrium stabilized zirconia (Z _r O ₂ ), alumina (Al ₂ O ₃ ), zinc oxide (ZnO), tin oxide (SnO ₂ ), gadolinium oxide (Gd ₂ O ₃ ), samarium oxide (Sm ₂ O ₃ ) , Lanthanum oxide (La ₂ O ₃ ), magnesium oxide (MgO), calcium oxide (CaO) lanthanum zirconate (La ₂ Zr ₂ O ₇ ), yttrium titanate (Y ₂ Ti ₂ O ₇ ) and / or boron oxide (B ₂ O ₃ ). Thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 5 . 5 ' ) is formed photoluminescent. Thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 5 . 5 ' ) consists in part of nanoparticles with a refractive index of at least 2.0. Thin-film solar cell according to claim 11, characterized in that the content of the structured partial layer ( 5 . 5 ' ) of nanoparticles having a refractive index of at least 2.0 more than 30, in particular more than 40% by volume of the total volume of the intermediate layer ( 5 . 5 ' ) is. Thin-film solar cell according to claim 11 or 12, characterized in that the nanoparticles by hydrothermal synthesis and / or a liquid phase precipitation reaction are made. Method for producing the thin-film solar cell according to one of the preceding claims, characterized in that the reflective back-electrode sub-layer ( 6 . 6 ' ) on a structured layer ( 5 . 5 ' ), which has been prepared by the sol-gel process. Method according to claim 14, characterized in that the structured layer ( 5 . 5 ' ) by coating the transparent, electrically conductive back electrode sublayer ( 4 ) or semiconductor layer ( 3 ) or the substrate ( 1' ) is formed with the sol, formation of the gel layer, embossing of the gel layer and curing of the embossed gel layer. Method according to claim 15, characterized in that that the coating by dip coating, roller application, flooding or spraying or screen printing. A process for producing the thin-film solar cell according to any one of claims 1 to 12, as characterized in that the structured layer ( 5 . 5 ' ) by printing the transparent electrically conductive back electrode sublayer ( 4 ), the semiconductor layer ( 3 ) or the substrate ( 1' ) is formed with a printing form provided with the gel and hardening of the printed gel layer. Method according to one of claims 14 to 17, characterized in that the sol by hydrolysis and polycondensation of silicon, titanium, zirconium, aluminum, zinc, magnesium, calcium and / or Tin compounds is produced. Method according to claim 18, characterized that the compounds have the general formula SiORxR'y, TiORxXy, ZrORxXy, AlORxXy, ZnORxXy, MgORxXy, CaORxXy and / or SnORxXy, wherein O oxygen and R and R 'same or different organic Represent radicals or R 'is hydrogen, X is a halide and x and y together form the number of residual valences. Method according to claim 19, characterized R and / or R 'are an organic radical containing a vinyl, allyl, Epoxy or methacrylate group.