DE102009006719A1 - Thin film solar cell - Google Patents

Abstract

A thin-film solar cell has a transparent substrate (1) on which a structured layer (2) with a periodic pattern (10) formed by elevations and / or depressions is applied, onto which successively several layers, including a front electrode layer (3), if necessary , a buffer layer, at least one semiconductor layer (4) and a back electrode layer (12) are deposited. In special cases, one or more further functional layers, such as, for example, a diffusion barrier, can be deposited above or below the structured layer. The patterned layer (2) is formed by embossing or printing a layer made by the sol-gel method. The structured layer (21) has a refractive index which is greater than the refractive index of the substrate (1) and at most as large as the refractive index of the front electrode layer (3). The distance (a) between the elevations and / or depressions of adjacent periodic patterns (10) is in the submicrometer range.

Description

The The invention relates to a thin film solar cell after The preamble of claim 1 and a method for the production thereof.

thin Film solar Cells or thin Solar cells come based on a silicon semiconductor layer not without light-scattering measures because silicon is an indirect semiconductor and has a minimum layer thickness in the range of several 100 μm for a complete absorption of light 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 so to increase the efficiency or the semiconductor layer thinner to be able to train are used so-called "light-trapping" concepts, which the optical path length increase. The involves various measures such as, for example, the introduction of an additional reflector layer the solar cell back, a structuring of the front electrode or light-facing surface of Semiconductor layer or structuring of the back electrode layer. Advantageous is the achievement of a structuring over an intermediate layer opposite the direct structuring of functional layers, such as direct etching of the Front electrode, as the structure is independent of other functions at the same time higher Degree of freedom can be realized.

To is from Journal of Non-Cystralline Solids 218 (1997) 391-394 a Thin-film solar cell according to the preamble of claim 1.

In this case, a layer of silica (SiO ₂ ) gel is applied to a substrate made of glass by the sol-gel method, in which a periodic pattern is embossed to obtain a patterned layer containing a texture template for the z , B. deposited by deposition from the gas phase, sputtering or the like deposited layers, to finally provide the reflector layer with the structured surface. As a pattern pyramids are described in this reference with a period, ie with a distance of adjacent pyramid peaks of 10 microns. The targeted selection of the period length in the micron range and the aspect ratio produces a geometrically optimized light trap structure which is intended to increase the yield of the thin-film solar cell.

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

This is inventively for solar cells (with Superstrate configuration) achieved by the fact that the structured Layer has a refractive index which is greater than the refractive index of Substrate and at most as big as the refractive index of the front electrode layer on the structured Layer is deposited, further characterized in that the period, ie the distance between the elevations and / or depressions of adjacent periodic patterns in the submicrometer range.

In particular embodiments can or below the structured layer one or more functional layers, such as a diffusion barrier, be deposited.

ever according to the refractive index of the substrate and the refractive index of the front electrode layer is the refractive index of the structured layer is between 1.3 and 2, preferably 1.4 to 1.9 and especially 1.6 to 1.8.

The transparent substrate can be flexible or stiff. It can do that glass, glass-ceramic or a transparent polymer, e.g. B. polyimide consist.

The Front electrode layer may be a transparent, electrically conductive metal oxide, such as zinc or tin oxide. However, it can also go through a high doped sub-layer on the substrate-facing side of the semiconductor layer be formed.

In special cases may be a diffusion barrier, such as silicon nitride (SiNx), or one or more other functional layers. or applied above the structured layer. In In this case, the refractive index is adjusted accordingly.

In the case of the solar cell according to the invention, a plurality of layers are deposited in succession on the substrate provided with the structured layer, in particular a front electrode layer, a semiconductor layer and a back electrode layer. In this case, further layers may be provided, for example a buffer layer, a further semiconductor layer and / or the mentioned diffusion barrier. The layers may also be composed of partial layers, for example the back electrode layer consisting of a transparent, electrically conductive sub-layer and a reflective sub-layer. The back electrode layer may also be formed by a partial layer, in particular a highly doped, electrically conductive partial layer of the semiconductor layer.

If the substrate of glass or glass ceramic with a refractive index of about 1.5 and the front electrode layer is made of a metal oxide, such as zinc or tin oxide with a refractive index of 1.9 to 2.0 According to the invention, the refractive index the structured layer to 1.6 to 1.8, in particular about 1.7 set.

Especially in the case of glass and glass ceramics, the structured layer can simultaneously represent a diffusion barrier, which is a diffusion of alkali the glass into the thin-film solar cell prevented.

As could be found occurs in the known solar cells In the case of light, a reflection of the light at the front electrode layer facing side of the substrate. This reflection is reduced according to the invention, whereby a significant increase in the solar cell efficiency is achieved.

By the period of the pattern and texture of the structured layer, which is according to the invention in the submicrometer range is the light incident through the substrate in a larger solid angle bent.

Preferably is the period of the structured layer pattern is less than 800 nm, in particular 100 to 300 nm.

The Aspect ratio So the relationship the height the raises or the depth of the depressions of the pattern at their distance from each other is preferably 0.01 to 2, in particular 0.1 to 0.6. That is, that Pattern is relatively flat to the light at a shallow angle too bow.

The average layer thickness of the structured layer may be 0.05 to 20 microns, in particular 0.1 to 1.0 μm be.

On the periodic pattern of the structured layer in the submicrometer range are preferably by elevations modulated and / or recesses formed periodic superstructures, the one period, ie a distance between the elevations and / or Wells of more than 1 μm, in particular 5 to 20 microns exhibit. Due to the modulated superstructures of the structured Layer will be an extra Light scattering achieved. The aspect ratio of the superstructures may also be 0.01 to 2, in particular 0.1 to 0.5.

The periodic patterns in the submicrometer, ie nanometer range and / or the modulated periodic superstructures are preferably isotropic, that is formed direction independent. These can be the periodic patterns in the submicrometer range and / or the modulated periodic superstructures through cross lattices, moth eyes, pyramids or inverted pyramids be formed.

The structured layer may consist of silicon dioxide and transparent Contain metal oxides. The silica can be in amorphous or hybrid polymer form, ie organic residual constituents exhibit. Organic residues can z. Methyl, ethyl or Be phenyl groups. Furthermore, the layer may contain polysiloxanes or their decomposition products.

The transparent metal oxides are preferably present in the layer as amorphous, semicrystalline 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, particularly preferably 2-20 nm.

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 (SuO 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 ). The zinc oxide may be indium, antimony or aluminum doped zinc oxide.

With These metal oxides can the refractive index of the structured layer be set exactly. So is the refractive index of titanium oxide for example 2.54 in the anatase crystal modification.

The structured layer is prepared by the sol-gel process from hydrolysed and condensable silicon and optionally titanium, zirconium, niobium, Aluminum, zinc, germanium, magnesium, calcium and tin compounds the general formulas SiORxR'y, TiORxXy, ZrORxXy, NbORxXy, AlORxXy, ZnORxXy, GeORxXy MgORxXy, CaORxXy and / or SnOR x X y wherein 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 form the number of residual valences, where z. B. in Si, the total number of valences is 4. organic Leftovers can for example, methyl, ethyl, phenyl, propyl, butyl.

For the silicon alcoholate precursors SiORxR'y become furthermore used compounds in which 0 is oxygen and R and R 'same or are different organic radicals which are partially thermal or photochemically via crosslinked a radical and or ionic polymerization reaction can be. Organically crosslinkable groups are z. 3-glycidoxypropyl, 3-methacryloxypropyl, Allyl and vinyl. Particular preference is given to compounds such as 3-glycidoxypropyltrimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-methacryloxypropyltriethoxysilane, allyltriethoxysilane, Vinyltriethoxysilane.

When Adhesive to the substrate can the paint forming formulation with which the structured Layer is formed, aminosilanes such as 3-aminopropyltriethoxysilane or 3-aminopropyltrimethoxysilane.

The hydrolyzed and polycondensed sol-gel precursors can be amorphous or crystalline as well as molecular or colloidally disperse, wherein the particle size of this Precursors preferably less than 20 nm. This particle size can be through Small angle scattering (SAXS), dynamic light scattering (DLS) and / or Fraunhofer diffraction can be determined.

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.

to Stabilization of the reactive metal oxide precursors, in particular the Alcoholates can Complexing agents such as beta-diketonates such as For example, acetylacetone, beta-carbonyl carboxylic acid ester such. For example ethyl acetoacetate, Carboxylic acids, like propionic acid, or methoxyethoxyacetic acid, Monoethanolamine, diethanolamine, triethanolamine, diols such as. B. Pentanediol and polymerizable ligands such as methacrylate or acrylic acid be used.

The hydrolysis of the sol-gel precursors, especially the alkoxides, is usually 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.

In particular embodiments are used for the hydrolysis of organic acid such as para-toluenesulfonic acid.

In a special embodiment can the solution with which the structured layer is formed, an additionally crosslinkable added organic monomer. Such additives may be, for example succinic anhydride, Tetraethylene glycol dimethacrylate, hexanediol diacrylate or trimethylolpropane triacrylate be.

Also can the formulation with which the structured layer is formed, Curable agents known to the person skilled in the art, for example the polyacrylate BYK 359 or BYK 301 may be added.

In a special embodiment the paint formulation with which the structured layer is formed can be used to set a special drying behavior and a specific thixotropy, a polysiloxane may be added.

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

Around a photochemical cure the structured thin films carry out to be able to be the sol-gel coating solutions, so the said formulation, Photoinitatoren added which z. B. a radical polymerization or crosslinking reaction with allyl, vinyl, methacrylate or acrylate groups can start. If epoxy groups are to be crosslinked photochemically, then cationic Starter systems are used. Pass the Fachman photochemically Excitable starter systems can z. B 1-hydroxycyclohexyl-benzophenone (Irgacure 184), benzophenone, mixtures of 1-hydroxycyclohexyl-benzophenone and Benzophenone, phosphine oxide phenyl bis (2,4,6-trimethylbenzoyl). By choosing the starter system, the excitation wavelength of 200-500 nm varied and each set specifically.

For a thermal hardening the sols, for example, the catalyst 1-methylimidazole is added.

The structured layer can be made by embossing or printing on the substrate be formed.

For embossing, the substrate is first coated with the sol, for example by dip coating, roller application, flooding or spraying. For serial production, the roller application is present drawn.

Out the applied to the substrate aqueous, solvent-containing sol is the solvent at least partially evaporated to an embossable partly still low viscosity or already higher viscous dried gel film to form on the substrate. The applied viscous gel film is then embossed and cured.

to curing can while beam sources or combinations thereof are used, which in the UV, in the visible wavelength range or emit NIR-IR or IR range.

When stamping die For example, a polymeric film on an embossing die or an embossing cylinder be used.

to Production of the stamping mold is z. B. interference-lithographically the periodic pattern with which the structured layer is to be provided on the substrate, 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 the structured layer, and if the structured layer has superstructures contains also the negative of the superstructures and their aspect ratio.

The polymeric film may be made of a rubbery elastic material, e.g. B. silicone rubber or silicone rubber or a perfluorinated polymer. The contact pressure during embossing is preferably 0.01 to 2 bar. At a higher pressure, the substrate can damaged become.

The Shape can be done in a vacuum, to prevent getting in the recesses of the embossed gel film liquid which can change the structure of the structured layer. Also can be a porous Embossing mold used Be that liquid receives.

in the The layering and embossing process becomes more or less continuous applied in a clean-room roll-to-plate process under clean room atmosphere. typical Process speeds are between 0.1 m to 10 m per minute.

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

While the stamping die pressed against the plastic gel film on the substrate, the gel film is also cured, around the one to be transmitted Structure to fix. Optionally, the curing can also by the stamp medium UV light or IR radiation respectively. A cure with other beam sources such as high energy radiation is also possible. Usually closes after the pre-hardening before the embossing process and curing while of the embossing process still a post-hardening at.

The Advance hardening, the hardening while of the embossing process the final one Harden For example, thermally and / or with UV light or IR radiation respectively. For this purpose, the gel film, while it is pressed against the embossing mold, when pre-hardening first at 50 to 140 ° C heated become. After a duration of pre-curing of preferably 0.1 Seconds to 1 minute is the embossed structure fixed so that the stamping mold can be removed from the structured layer on the substrate.

When It has proven to be particularly advantageous to cure by means of UV radiation in a wavelength range from 200-300 nm, since This ensures a sufficiently high process speed is. It is also possible to achieve an exact and defect-free structure impression.

With inorganic, hybrid or organic only thermally crosslinkable Systems which do not contain photochemically polymerizable functionalities this is not possible with a sufficiently high process speed. Prefers be for this Beschichtungssol formulations, which on Methylmethacrylat- or Acrylate or vinyl groups functionalized particles and silanes based.

to Achieving a sufficiently long life of the solar cell However, it is necessary to have a glassy-crystalline structured layer with little to no residual organic content as a template to use. Therefore, a burn-out of the organics is required to the glassy nanocrystalline invention Composite layers which preferably have a residual organic content of <5% by mass, to obtain.

To can the abovementioned organic radicals R, R 'of the compounds from which the sol and thus the gel film is formed at elevated temperature and / or under UV radiation be cleavable radicals, such as epoxy or methacrylate radicals to the curing temperature decrease.

However, this usually requires that due to the high residual organic content in the sols, the layers are exposed to high shrinkage, which can level the embossed structure. Also, due to the strong shrinkage voltage cracks in the layers arise. Also, a high proportion of organic causes a high degree of residual porosity, which often leads to a porous layer after organic burnout and significantly reduces the refractive index of the layer.

Amazingly, showed that over a UV cure of the layers and a subsequent thermal work-up of the layer systems structured according to the invention glassy-crystalline layers could be obtained, which is sufficient high structure size to suitability as a structural template for Highly efficient thin-film solar cells represent.

The final curing can then be carried out at a temperature of preferably 400 to 900 ° C, if the substrate z. As glass or glass ceramic and thus accordingly is temperature stable.

metal substrates could optionally under a protective gas atmosphere hardened become.

In contrast, will in a substrate of a polymer z. As polyimide, due to low temperature stability a curing temperature from normally at most 300 ° C, in particular at most 200 ° C, applied.

Around the bonding of the gel film to the embossing mold when removing the embossing mold from To prevent the structured layer, the embossing, 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.

Further For example, the substrate may be subjected to a pretreatment to prevent the To improve adhesion of the structured layer to the substrate. Thus, a primer can be used, e.g. B. in glass or glass ceramic as the substrate an epoxy silane or a flame-pyrolytically deposited Silicon oxide layer. In a polymer substrate, for. B. a corona treatment before carried out the application of the sol become.

Instead of coating the substrate with the sol and embossing the substrate Gelfilms on the substrate can also be printed on the substrate be provided with the structured layer. In the printing form, which can be a cylinder or a plate can then deepened the negative of the periodic pattern with the aspect ratio of the be provided structured layer, and if the structured Layer superstructures contains also the negative of the superstructures and their aspect ratio.

The structured layer is made by printing the substrate with the With the gel provided printing form, holding the printing form against the Substrate during of pre-curing the structured layer, removing the printing form from the precured printed structured layer and final curing the structured layer formed.

The advance hardships and final Curing can doing so in the same way as described above in connection with embossing. The same applies to the pretreatment of the printing form and the substrate.

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 and mono-, 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 is 0 to 1.

The Back electrode layer, which are both electrically conductive As well as being highly reflective, a metal layer can, for example titanium, palladium, nickel, tungsten, vanadium, molybdenum, silver, Aluminum, copper or their alloys or a layer stack z. B. consisting of a transparent electrically conductive metal oxide, such as For example, tin or zinc oxide, and a metal layer, such as titanium, palladium, Nickel, tungsten, vanadium, molybdenum, silver, aluminum, copper or their alloys.

In particular embodiments can they functionalities the return electrode also be separated. In this case, the metal layer by a white Color layer can be replaced, wherein the conductive layer of the back electrode then through an upstream layer of a transparent electric conductive Metal oxide is realized or the semiconductor layer is a highly doped, may have electrically conductive sub-layer in front of the white ink layer. The White Color layer can z. B. consist of titanium dioxide or barium sulfate.

The Solar cell according to the invention is characterized by a significantly increased power collection, so increasing the Short-circuit current and thus a high degree of efficiency.

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

1 a cross section through a portion of a thin film solar cell;

2 a plan view of a portion of the structured layer on the substrate; and

3 a cross section along the line III-III in 2 ,

According to 1 the solar cell consists of a transparent, electrically insulating substrate 1 , For example, a glass sheet on which the structured layer according to the invention 2 is deposited.

In particular embodiments can above or below the structured layer another Be applied functional layer, such as, for example, a diffusion barrier.

On the with the structured layer 2 provided substrate 1 are successively a transparent front electrode layer 3 , a semiconductor layer 4 , a transparent back electrode part layer 5 and a reflective back electrode part layer 6 deposited by vapor deposition, sputtering or the like. The back electrode sublayers 5 and 6 form the back electrode layer 12 the solar cell.

Optionally, the return electrode may also be formed by means of a layer. In particular embodiments, between the front electrode 3 and the semiconductor layer 5 a buffer layer or other semiconductor layer is introduced.

The semiconductor layer 4 has a positive-doped sub-layer 7 , an intrinsic sublayer 8th and a negative-doped sub-layer 9 on.

The structured layer 2 on the substrate 1 thus forms a texture template for the remaining layers 3 to 6 which are sequentially deposited on her. In this way, the back electrode layer becomes 12 provided with a structuring surface that scatters the incident light. In addition, the light enters the (possibly without absorption) passage through the structured layers 2 and 3 in a larger scattering angle in the semiconductor layer 4 one.

In particular embodiments The structured layer can also be used in so-called "multijunction devices", all ahead of the so-called tandem structure can be used.

How out 2 and 3 can be seen, the structured layer 2 a periodic pattern 10 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 So the height the pyramid to the distance a is z. B. 0.5.

Due to the increases in the distance of z. B. 200 nm, the layer 2 a texture so that the incident light hυ to the structured layer 2 is scattered.

In addition, the structured layer 2 Superstructures in the form of in cross-section z. B. V-shaped elevations on with a period, ie a distance b of z. B. 2 microns are arranged from each other, which can serve as a diffraction grating. The aspect ratio, ie the height of the elevations of the superstructure 11 to the distance b can z. B. 0.1.

At the back electrode layer 12 thus corresponding recesses in the form of inverted pyramids are formed with a distance of 200 nm, the reflection-enhancing effect, further V-shaped depressions, which lead to a further scattering of the light.

example 1

Preparation of the hydrolyzed paint formulation 1:

A vessel is charged with 50 g of isopropanol, 100 g (0.40 mol), methacryloxypropyltrimethoxysilane (MPTMS), 25.0 g (0.12 mol) of tetraethoxysilane (TEOS) and 0.1 g of paratoluene sulfonic acid dissolved in 2 g of water , The solution is stirred for 1 h. To this solution is then slowly under ice cooling and vigorous stirring a HNO ₃ -sure dispersion of 30 g of an aqueous nanoparticulate TiO ₂ dispersion (18% by mass, anatase, crystallite size 7-12 nm) with 15 g of ethanol and 12 g of distilled H ₂ O given.

The paint formulation 1 15 g of Photoinitators Irgagure 184 ^® was added and carried out 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 with a period of 300 nm and an aspect ratio of one mean. While the embossing stamp is in contact with the layer material, a first curing of the layer is carried out by means of a UV lamp which emits in the wavelength range of about 250 nm.

After removal of the embossing stamp another UV-based layer hardening and a thermal hardening at 450 ° C. The heating rate is 20 K / min.

The average glassy-ceramic layer thickness of the embossed layer is between 170 to 400 nm. The aspect ratio the embossed Structure is 0.5-0.6. The layer material has a refractive index of about 1.7.

Preparation of the hydrolyzed paint formulation 2:

50 g of isopropanol, 0.40 mol of methacryloxypropyltrimethoxysilane (MPTMS) are hydrolyzed in a vessel with 0.6 mol of H ₂ O containing 0.035 mol of HCl. The solution is stirred for 18 h.

To this solution will be first slowly with ice-cooling 0.04 mol of zirconium tetrapropylate, added with 0.04 mol of methacrylic acid, added dropwise. Subsequently, will to this solution under ice-cooling 0.04 mol of titanium tetraethylate added with 0.04 mol of methacrylic acid, add.

The paint formulation 2 12 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 silicone-containing 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 cross lattice structure with a period of 320 nm and an aspect ratio of one mean. While the embossing stamp is in contact with the layer material, a first hardening of the layer is carried out by means of a UV lamp which emits in the wavelength range of about 250 nm.

To removing the stamping die another UV-based is done layer hardening and a thermal layer hardening at 450 ° C. The heating rate is while 20 K / min.

The average glassy-ceramic layer thickness of the embossed layer is between 170 to 500 nm. The aspect ratio the embossed Structure is 0.5-0.6. The layer material has a refractive index of about 1.7-1.8.

Preparation of the hydrolyzed paint formulation 3:

0.7 mol of vinyltriethoxysilane, 0.1 mol of tetraethoxysilane, containing 1.0 mol of H ₂ O containing 0.03 mol of HCl are hydrolyzed in a vessel. The solution is stirred for 1 h. 0.2 mol of zirconium tetrapropylate, mixed with 0.2 mol of methacrylic acid, is slowly added dropwise to this solution while cooling with ice.

The Formulation 3 will follow diluted with 100 ml of ethanol and mixed with 12 g Irgacure 189. The curing and structuring takes place like in formulation 1 or 2 described.

Claims (33)

Thin-film solar cell with a transparent substrate ( 1 ), on which a structured layer with a periodic pattern formed by elevations and / or depressions (US Pat. 10 ), on the succession of several layers, including a front electrode layer ( 3 ), at least one semiconductor layer ( 4 ) and a back electrode layer ( 12 ), wherein the structured layer ( 2 ) is formed by embossing or printing a layer produced by the sol-gel process, characterized in that the structured layer ( 2 ) has a refractive index which is greater than the refractive index of the substrate ( 1 ) and at most as large as the refractive index of the front electrode layer ( 3 ), and the distance (a) between the elevations and / or depressions of adjacent periodic patterns ( 10 ) lies in the submicrometer range. Thin-film solar cell according to claim 1, characterized in that the back electrode layer ( 12 ) a transparent back electrode sublayer ( 5 ) on its semiconductor layer ( 4 ) facing side. Thin-film solar cell according to claim 1, characterized in that the transparent substrate ( 1 ) made of glass or glass ceramic and the front electrode layer ( 3 ) consists of zinc or tin oxide and the refractive index of the structured layer ( 2 ) Is 1.6 to 1.8. Thin-film solar cell according to claim 1, 2 or 3, characterized in that a diffusion barrier below or above the structured layer ( 2 ) is deposited. Thin-film solar cell according to claim 4, characterized in that the diffusion barrier consists of silicon nitride (SiN _x ), silicon oxide (SiO ₂ ), silicon oxynitride (SiO _x N _y ), silicon oxycarbide (SiO _x C _y ), at least one metal oxide and / or at least one metal nitride , Thin-film solar cell according to claim 5, characterized in that the metal oxide is alumina (Al ₂ O ₃ ) or zirconium oxide (ZrO ₂ ). Thin film solar cell according to any one of the preceding claims, that they have more than one pn junction having. Thin-film solar cell according to claim 1, characterized in that the distance (a) between the elevations and / or depressions of adjacent periodic patterns ( 10 ) is less than 600 nm. Thin-film solar cell according to claim 1, characterized in that the average layer thickness of the structured layer ( 2 ) is at most 20 microns. Thin-film solar cell according to claim 1, characterized in that the periodic patterns ( 10 ) in the submicrometer range are modulated on periodic superstructures formed by elevations and / or depressions with a spacing between the elevations and / or depressions of more than 1 μm. Thin-film solar cell according to one of the preceding claims, characterized in that the periodic patterns ( 10 ) in the submicrometer range and / or the modulated periodic superstructures ( 11 ) are formed isotropically. Thin-film solar cell according to one of the preceding claims, characterized in that the aspect ratio of the elevations and / or depressions of the periodic patterns ( 10 ) in the submicrometer range and / or the elevations and / or depressions ( 11 ) of the modulated superstructures is 0.01 to 2. Thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 2 ) consists of silicon dioxide and at least contains transparent metal oxide. Thin-film solar cell according to claim 13, characterized in that the transparent metal oxide 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, magnesium and / 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 ). Thin-film solar cell according to one of the preceding claims, characterized in that the proportion of organic constituents in the structured layer ( 2 ) is at most 5% by mass. Thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 2 ) according to the sol-gel process of hydrolyzable and polycondensable silicon or organosilicon compounds and optionally hydrolyzable and polycondensable titanium, zirconium, aluminum, zinc, magnesium, calcium, cerium, samarium, gadolimium, Lanthanum, boron, yttrium, and / or tin compounds is produced. Thin film solar cell according to claim 16, characterized in that the silicon or Silicon organic compound is photochemically polymerizable. Thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 2 ) has been prepared by the sol-gel method with a photochemical curing process and subsequent thermal decomposition of the organic constituents, so that the proportion of organic constituents in the structured layer ( 2 ) is at most 5% by mass. Thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 2 ) has been applied to glass as a substrate and has been thermally treated at a temperature of at least 300 ° C. Thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 2 ) is formed photoluminescent. Thin-film solar cell according to one of the preceding claims, characterized in that the semiconductor layer ( 4 ) consists of a silicon-based semiconductor or a compound semiconductor. Process for producing the thin-film solar cell according to one of the preceding claims, characterized in that the structured layer ( 2 ) by coating 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 22, characterized in that the layer ( 2 ) is patterned by embossing the gel layer with an embossing punch. Method according to claim 22 or 23, characterized in that the structured layer ( 2 ) is cured by the die. A method according to claim 22, characterized in that the coating of the substrate ( 1 ) by dip coating, roller application, flooding or spraying. Process for producing the thin-film solar cell according to one of Claims 1 to 21, characterized in that the structured layer ( 1 ) by printing the substrate ( 2 ) is formed with a printing form provided with the gel and hardening of the printed gel layer. Method according to claim 23 or 26, characterized that the embossing stamp or the printing form based on a polymer or silicone. Method according to one of claims 22 to 27, characterized that the embossed or printed structured gel layer photochemically and / or thermally cured becomes. Method according to Claim 28, characterized that the thermal curing at 300 to 700 ° C carried out becomes. Method according to one of claims 22 to 29, characterized that the sol is formed by hydrolysis and polycondensation of silicon, Titanium, zirconium, aluminum, zinc, magnesium, calcium and / or Tin compounds is produced. Method according to claim 30, characterized in that 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 represent different organic radicals or R 'is hydrogen, X is a halide and x and y together are the number of residual valences form. Method according to claim 31, characterized in that that R and / or R 'a organic radical with a vinyl, allyl, epoxy or methacrylate group is. Method according to claim 22, characterized in that that curing at less than 300 ° C carried out becomes.