EP2044630A1

EP2044630A1 - Polymer-based solar cell

Info

Publication number: EP2044630A1
Application number: EP07786139A
Authority: EP
Inventors: Ulrich Schindler; Achim Hansen; Andreas Schilling
Original assignee: Leonhard Kurz Stiftung and Co KG
Current assignee: Leonhard Kurz Stiftung and Co KG
Priority date: 2006-07-20
Filing date: 2007-07-18
Publication date: 2009-04-08
Also published as: WO2008009428A1; US20090314340A1

Abstract

Methods are described for enlarging the surface of a polymer-based solar cell relative to a smooth surface, and/or for enlarging the active surface of the organic semiconductor layer of the solar cell relative to a smooth surface. A polymer-based solar cell (1) is further described, in which the active surface of the organic semiconductor layer (13) has a surface profile which enlarges the surface in relation to a smooth surface profile. The surface has elevations and/or indentations.

Description

Solar cell based on polymer

The invention relates to a polymer-based solar cell and to processes for producing the same.

Polymer-based solar cells (e.g., flexible solar cells) have heretofore had efficiencies ranging from 3 to 5%. These are efficiencies that are significantly lower than those of inorganic solar cells.

If inexpensive production processes, such as, for example, the roll-to-roll process, are used for the production of flexible polymer-based solar cells, mass production of solar cells is conceivable to a considerable extent.

The invention is based on the object of providing a polymer-based solar cell with improved efficiency and of specifying the production method.

The object of the invention is achieved by a method for producing a solar cell unit with a polymer-based solar cell having at least one organic semiconductor layer with a top side facing a light source and a rear side facing away from the light source, wherein it is provided that the solar cell after its completion is deformed so that at least the top of the solar cell has a surface profile which increases the surface of the top in relation to a flat surface profile. The object is further achieved by a method for producing a polymer-based solar cell having at least one carrier substrate and at least one organic semiconductor layer with a top side facing a light source and a rear side facing away from the light source it is provided that a surface relief is molded into a layer of the solar cell, and that on the molded surface relief one or more electrical functional layers containing the organic semiconductor layer (s) are applied so that the upper surface of the organic semiconductor layer has a surface profile which increases the surface area of the organic semiconductor layer with respect to a planar surface profile. The object is further achieved by a polymer-based solar cell having at least one carrier substrate and an organic semiconductor layer with a top side facing away from a light source and a rear side facing away from the light source, wherein it is provided that at least the upper side of the organic semiconductor layer has a surface profile which forms the surface of the Enlarged upper side in relation to a flat surface profile.

By virtue of the method according to the invention, a polymer-based solar cell, referred to below as a polymer solar cell, can be provided with an enlarged surface in a very simple and effective manner, so that the efficiency of the solar cell thus formed is increased compared with a polymer solar cell provided with a planar top side , for example due to multiple reflections. The proposed methods provide both microscopic and macroscopic deformations to form the enlarged surface, wherein further advantageous embodiments are possible by combining the method, as described in more detail below.

Thus, with the same mounting surface of the polymer solar cell, an enlarged surface of the responsible for the conversion of the radiation energy of the light into electrical energy semiconductor layer can be provided, whereby the efficiency of the polymer solar cell according to the invention is also increased due to multiple reflections over a polymer solar cell with a smooth surface ,

The organic semiconductor layer is generally a system of multiple semiconductor layers that interact with each other.

Further advantageous embodiments are designated in the subclaims. It can be provided that the solar cell is laminated on a shrink film, and that thereafter, the solar cell unit is subjected to a temperature treatment. The solar cell can thus be prepared as before, for example in a roll-to-roll process as a mass product and by a

Temperature treatment can be provided with an increased active surface by the shrink film by the action of elevated temperature, for example in a range of 80 ⁰ C to 250 ⁰ C, which unfolds on their laminated solar cell. One or more solar cells may be laminated to the shrink film to form the solar cell unit.

However, it can also be provided that a shrink film is used for the carrier substrate of the solar cell and the solar cell is subjected to a temperature treatment after its completion. While this process is less expensive, it has a narrower process window during roll-to-roll printing because it must be ensured that the shrink film does not change dimensions during the printing and drying process. In this embodiment, the process step "laminating", whereby the manufacturing cost can be reduced.

It is possible that a unidirectional shrink film is used. With such a shrink film, the solar cell can receive a corrugated-shaped training.

It is also possible that a bidirectional shrink film is used. The surface of the solar cell can thus be designed knob-shaped after shrinking, so that over the aforementioned training, a further enlarged active surface of the solar cell is reached.

It can be provided that an opaque or transparent or semi-transparent shrink film is used. A transparent shrink film may be advantageous if light is to strike the active layer of the solar cell from the back of the solar cell or if it is intended to stack solar cells one above the other, as explained below. It can further be provided that an electrically nonconductive shrink film is used. Such a non-conductive shrink film can be formed, for example, with plated-through holes in order to electrically connect a plurality of solar cells to one another or to lead all the connections of the solar cells to a connection area.

It can also be provided that an electrically conductive shrink film is used. The shrink film may be partially conductive. For example, the shrink film may include conductive traces suitable for electrically connecting a plurality of solar cells to each other, i. To make series connections and / or parallel circuits of solar cells. In this way, solar cell units can be produced, which provide a higher output voltage than a single solar cell.

It is possible that the shrink film is at least partially painted and / or coated before the temperature treatment. Such a coating or coating can be provided, for example, to form electrical conductors on the shrink film or to influence the shrinkage behavior of the shrink film targeted. By a non-shrinking strip-shaped, parallel aligned coating, for example, the corrugated-shaped deformation profile described above can be particularly well formed because coated areas can act as desired bending lines, between which the shrink film bulges. It can be influenced by the shrinkage process on the layer thickness of the painted areas, the degree of curvature.

It can further be provided that light-refractive and / or light-scattering and / or light-conducting and / or light wavelength-changing particles and / or particle mixtures are added to the paint and / or the coating material. As a result of the admixtures mentioned, the shrink film can at the same time be provided for directing the light incident on the solar cell onto the active regions of the solar cell. By changing the wavelength of light spectral ranges can be used to obtain the solar power, the lie outside of the sensitization of the active layer.

In a further advantageous embodiment it is provided that the shrink film is at least partially prestructured. It may thus be provided, for example, that the shrink film has particularly good deformable areas where the shrink film is preferably unfolded. These may be areas of lesser thickness, but it may also be provided, for example, that these areas are weakened by perforations in their flexural strength.

It can further be provided that a multilayer shrink film is used whose layers have a different shrinkage behavior. These may be full-surface-lying shrink films. However, one or more of the superimposed shrink films can be provided only in some areas and act in this way, for example, as introduced into a fabric rubber threads that put the fabric into folds.

In a further advantageous embodiment it is provided that the solar cell is deformed by an in-mold process. In the in-mold process, a film to be deformed is pressed under pressure into a mold by means of a medium injected behind the film and is deformed in this way. The injected medium may be, for example, a heated thermoplastic, such as ABS / PC or PMMA, which fixes the deformed film after solidification.

For example, the mold is an injection mold which has on one side the surface relief according to which the solar cell is to be deformed. The solar cell is part of an inmold film, which is inserted into the injection mold and then back-injected with liquid plastic injection molding from the side of the inmold film opposite this surface relief. In addition, it is still possible that a vacuum between the injection molding

Form half, which has the surface relief, and the resting Inmold- foil is applied, so that a correct impression of the surface relief in the inmold film is not hindered by air bubbles or the like. Due to the heat and pressure of the injected into the injection mold injection molding material is the Inmold film, which contains the solar cell, deformed according to the surface profile of the injection mold and the deformation then further stabilized and fixed by cooling the injection molding material. The in-mold film is preferably constructed of a 15 to 40 .mu.m thick PET film, a release layer and a transfer layer containing the solar cell. The polyester film is peeled off after cooling of the injection molding material or upon release of the molding from the injection mold. Furthermore, it is also possible that the in-mold film does not have a release layer and the polyester film remains on the molding. The latter process is less common.

It can further be provided that the solar cell is deformed by a touch-forming process. Here, the solar cell is applied to a specially dilatable polyester carrier whose thickness is in the range of 100 microns. With the help of a membrane press then takes place at a temperature in the range of 120 ⁰ C, the shaping by means of a molding. Important in this context are the individual cycle times, which strongly influence the final product and have to be individually tested.

A film with a solar cell suitable for such a process consists, for example, of the following layers:

- Carrier layer

- separating layer

- protective lacquer layer - solar cell / s

- adhesive layer

The release layer and the protective lacquer layer preferably have thicknesses in the range of 1 to 3 μm. The adhesive layer also preferably has a thickness in the range of 1 to 3 microns, wherein the thickness and composition of the adhesive layer may depend on the substrate.

Furthermore, it can be provided that the solar cell is deformed by a deep-drawing process. For this purpose, it can be provided that a film containing the Solar cell applied to a thermoformable substrate, such as an ABS plate with a thickness of 0.5 to 1 mm, preferably glued, and then the film is deformed with the substrate in a thermoforming process to form the surface relief. The solar cell is applied to the ABS plate exemplified here by means of a rolling process. Thereafter, the clamping takes place in a vacuum machine and via a partially heated metal mold deep drawing by means of vacuum, with the result that the coated ABS plate has assumed the shape of the metal mold.

It is also possible that the substrate consists of a film of ABS, PVC or Plexiglas. The structure of the film is similar to that already mentioned above. On a support there are one or more release layers, a protective varnish or a protective varnish package, the solar cell assembly and an adhesive layer. Further layers may be provided if special end properties are required.

In the case of both the touch-forming process and the thermoforming process, injection molding of the deformed film can be provided to permanently fix the deformation of the film.

The spray medium described above may be an electrically conductive spray medium if special applications are required.

It can also be provided that a partially electrically conductive spray medium is used or that an electrically non-conductive spray medium is used.

It can further be provided that an opaque or transparent or semitransparent spray medium is used. It is also envisaged to modify the spray medium in a comparable manner as the shrink film described above, wherein in principle any combinations are possible. So it is also possible to inject behind shrunken solar cells or to connect solar cells by injection molding together. It can also be provided that introduced metallized contact points in the back injection become.

As already explained above, at least two solar cells or solar cell units can be arranged one above the other, it also being possible to provide photovoltaic semiconductor layers which can absorb light from different wavelength ranges of light.

However, it can also be provided that the solar cell units are multifunctional cells. These cells have active areas that adsorb light from different wavelength ranges of light, so that an increase in efficiency is achieved.

It can be provided that two superimposed solar cells or solar cell units are applied on both sides of the shrink film.

It is possible for the solar cells or solar cell units provided on one side of the shrink film to be applied offset relative to the solar cells or solar cell units provided on the other side of the shrink film. In this way, for example, the spaces between adjacent solar cells can be filled by further, arranged on the opposite side of the shrink film or the back injection solar cells and so the active surface of the solar cell units are further increased.

The proposed design of the solar cells as a film body, further advantageous embodiments.

It can be provided that the solar cells and / or the solar cell units are shrunk onto mounting bodies. The mounting bodies may be, for example, plate-shaped bodies which, in addition to contact tracks for the purpose of establishing electrical connections, may have fastening elements.

It may also be provided that the solar cells or the solar cell units form a tubular shape, wherein it may further be provided to use the tubes as a conduit for a medium or the hoses if required on a generating line separate. The aforementioned medium can be water, which is circulated by a solar-powered pump. On the one hand, the water is heated by the solar radiation, on the other hand also promoted and fed the heat energy of the water to a heat exchanger.

It can further be provided that the solar cell units are encapsulated.

It is intended to assemble solar cells and / or solar cell units into solar cell modules. The solar cell modules can form marketable units that can be connected to photovoltaic systems. The aforementioned encapsulation may extend to all said units and / or be provided several times in succession.

The deformations of the surface of the solar cells formed by the shrink film as a result of the method steps described above are usually formed as elevations or depressions with a height or depth in the range from 1 mm to 20 mm. They preferably have a distance of 5 mm to 25 mm. It is therefore deformations that are generally visible to the naked eye and therefore can be referred to as macroscopic deformations. However, the elevations or depressions can also be made smaller and reach down to 30 μm. Similarly, far smaller distances can be provided, which reach down to 30 microns.

Furthermore, it is possible for the surface of the organic semiconductor layer to be enlarged in that the organic semiconductor layer and / or possibly further electrical functional layers of the solar cell are applied to a surface already having a corresponding surface profile, for example an embossing foil. This is preferably a surface structure introduced into a replication lacquer layer or a plastic film by means of an embossing process or UV replication process, which is a microscopic surface

Surface profile with a depth to width ratio of 0.1 to 5 and a distance of the elevations of 200 nm to 100 microns has. In a further advantageous embodiment, it is provided that the solar cell deformed after its completion is produced by means of one of the abovementioned methods. The solar cell with microscopic deformations described above is thus deformed after its completion so that at least the top of the solar cell has a surface profile which increases the surface of the top in relation to a flat surface profile. Thus, a method is proposed which forms both a (macroscopic) surface profile in the solar cell, which generally also follows the active layer of the solar cell, and also forms a (microscopic) surface profile at least in the active layer of the solar cell.

Further advantageous embodiments of the invention are directed to the design of the surface profile of the solar cells or solar cell units produced by the method described above.

It can be provided that the surface profile is designed such that it leads to multiple reflections and thus increases the efficiency of the solar cell. Apart from the special cases that a beam of light hits the surface of the solar cell perpendicularly - the energy of the light beam is maximally exploited - or is directed parallel to the surface of the solar cell - the energy of the light beam is not used - a part of the light is hit by the light beam Surface of the solar cell reflected. Consequently, some of the light energy is lost if the reflected beam does not strike the surface of the solar cell again. When using a surface with a flat surface profile, a light beam incident on the surface is reflected only once. An uneven

Surface profile, however, can lead to multiple reflections. If, for example, a sawtooth-shaped surface profile with a point angle of 90 ° is provided, the light beam is reflected twice on average, apart from the fact that the available surface is also enlarged relative to a flat surface. It can further be provided that the surface profile is formed from elevations and / or depressions of the carrier substrate and / or the semiconductor layer. It can also be provided that the carrier substrate is formed from a deformed foil or plate on which the polymer solar cell constructed of thin layers is arranged. The Semiconductor layer may be applied, for example, in a thickness of 150 nm to 200 nm. Each of the two electrode layers may have a thickness of 10 nm to 50 nm, but also thicknesses in the range of 50 to 1000 nm may be provided, depending on the required conductivity. It may further be provided to also form the semiconductor layer with elevations and / or depressions. By way of example, the carrier substrate may have macroscopic elevations and / or depressions and the semiconductor layer may have microscopic elevations and / or depressions.

Further embodiments are directed to the formation of the surface profile.

It can be provided that the surface profile is a stochastic surface profile. The stochastic surface profile may preferably be provided for microscopic surface profiles, i. preferably as a surface profile of the semiconductor layer. Stochastic surface profiles that

Structures below the resolution of an unarmed human eye are also known as matte structures. Electrode layers with the above-mentioned thickness of 10 to 50 nm can be applied to the semiconductor layer without "smearing" the microscopic surface profile of the semiconductor layer Thin layers can follow the surface profile exactly and form a surface corresponding to the surface profile a surface that no longer follows the surface profile at least in some areas, so it "smeared". However, by matching the refractive indices of the layer or layers arranged above the upper side of the semiconductor layer, for example an electrode layer, a smeared surface profile can also be tolerated. When the refractive index difference of the refractive indices of the surface profile partially or completely filling layer and the semiconductor layer is at least> 0.2, but is not so large that total reflection occurs at the interface between the layer and the semiconductor layer, the surface enlargement of the semiconductor layer is independent of Forming the surface profile covering layer optically effective. It can further be provided that the surface profile is a periodic surface profile. The periodic surface profile can be provided for both macroscopic and microscopic structures. It is particularly preferred for macroscopic surface structures or if a defined, the exact calculation accessible measure of

Surface enlargement is provided. It may also be preferred to reduce the tooling required to transfer the surface profile. A periodic profile is particularly suitable for a roll-to-roll production process in which the surface profile can be transferred from a rotating roll to the semiconductor layer. Another advantage of the periodic

Profiles is based on the fact that to optimize the properties of the periodic profile only one period of the profile has to be designed and designed.

Furthermore, it can be provided that the surface profile forms a cross lattice of two base lattices. The surface profile may, for example, be a cross lattice of two base lattices with periods smaller than a cutoff wavelength λ at the shortwave end in the spectrum of visible light, ie λ = 380 nm to λ = 420 nm and profile depths in the range of h = 50 nm to h = 500 nm exhibit. Such relief structures absorb almost all visible light incident on the surface and scatter only a small fraction of the incident light back. The percentage of light absorbed depends non-linearly on the tread depth and can be controlled between 50% and about 99% by choosing the texture depth, the more flat the surface profile, the more incident light will be backscattered and the less light will be emitted absorbed. As has been shown to be particularly advantageous, a depth-to-width ratio in the range of 0.5 to 5, as explained in more detail below. In a further embodiment, it is provided that the surface profile is a self-similar surface profile. The sections of self-similar profiles are similar to the profile itself. In this way, a surface profile can be further broken down without leaving the character of the surface profile. For example, the branches of a tree are similar to the tree itself. In mathematics, self-similar functions are also called fractals. It can be provided, for example, that a sinusoidal surface profile is superimposed with a sinusoidal function, which in turn can be superimposed on a sine function, and so on. If, for example, the elevations and / or the depressions have a height profile h = ± 100 μm, their elevations and / or a height profile h '= +10 μm may have, in turn, with a

A further profiling now generates structural elements in the order of magnitude of visible light, which covers wavelengths from 760 nm (red) to 380 nm (violet), but this could lead to diffraction-optical effects on such small structures in that the efficiency of the solar cell decreases again.

It can be provided that the mean width or the mean diameter of the elevations or depressions at the root point is in the range of 1 mm to 10 mm.

It can further be provided that the mean width or the mean diameter of the elevations and / or depressions at the base point is in the range of 1 μm to 1000 μm. The resolution of the unarmed human eye is approximately 1 'under ideal conditions, i. 1 mm to 3.5 m or about 70 μm to 250 mm. In the range of 1 μm to 1000 μm, therefore, the boundary between macroscopic and microscopic structures runs.

Still further, it can be provided that the mean width or the mean diameter of the elevations and / or depressions at the base point is in the range of 100 nm to 1000 nm. For surface structures in the nanometer range, as stated above, it should be noted that the surface structures may be smeared by the layer adjacent to them.

It can further be provided that the depth-to-width ratio of the elevations and / or depressions is in the range of 0.5 to 5. The depth-to-width ratio, also referred to as the aspect ratio, gives as a dimensionless number information about the relationship between the depth of the "valleys" or the height of the "mountains" of the Surface structure to the distance between two adjacent structural elements are. As the depth-to-width ratio increases, the surface area of the surface structure is increased. Practical limits are set, inter alia, by the fact that the flanks of the elevations and / or depressions become steeper with increasing depth-to-width ratio, thereby making them flatter and flatter

Angle be hit by the incident light rays (at normal incidence on the surface) or at least partially no longer be hit (with oblique incidence on the surface).

On the one hand, as the slope increases, the likelihood of multiple reflections increases, which, as described above, increases the efficiency of the solar cell. On the other hand, steep flanks can have a shadowing effect, in particular for rays incident flat to the surface. Of importance for the occurrence of multiple reflections, which significantly increase the efficiency of the solar cell, a depth-to-width ratio of the structural elements between 0.5 to 5, preferably between 1 and 5 has been found. The flank shape can also influence the number of reflections. A planar flank, for example a flank of a sawtooth profile, acts as a plane mirror, while a curved flank can concentrate or disperse the beams, for example a concave flank can bundle the beams. The basic gratings mentioned above, which form a cross grid, can, for example, run according to a sine-square function, but also rectangular or pyramid structures are possible. This surface structures are formed, which resemble an egg carton. Even such structures lead to a wide increase in the efficiency of the solar cell.

Further embodiments are directed to the geometric shape of the elevations and / or depressions.

It can be provided that the lateral surfaces of the elevations and / or the depressions are formed as lateral surface areas of a spherical body.

It can further be provided that the spherical body is a sphere. It can also be provided that the lateral surfaces of the elevations and / or depressions are formed as lateral surface areas of a cone or a pyramid.

The achievable surface enlargement is now calculated, for example, on a square base pyramidal bump having a base edge length a and a height h = 2.96a, i. a depth-to-width ratio of 2.96.

The surface of the base O ₀ is

O ₀ = a • a = a ²

The surface of the lateral surface of the pyramid Ai is

Oi = 4 • a / 2 • (a ^2/4 + h ² ) ^1/2 = 2a ^« (a ^2/4 + 8,76a ² ) ^1/2 « 6 a ²

Thus, the surface enlargement O-ι / O ₀

The enlarged by a factor of 6 surface of the polymer solar cell can be further increased by applying the method described above, the formation of the lateral surfaces of the elevations and / or depressions with further elevations and / or depressions, for example, with three steps by a factor of 216. Even assuming that not all sub-areas are optimally aligned with the light source, the polymer solar cell according to the invention has a significantly increased effective surface area compared to a planar surface formed polymer solar cell with associated multiple reflections, which lead to an increase in efficiency. In a further advantageous embodiment it can be provided that the elevations and / or the depressions are formed with star-shaped cross-section. Under a star-shaped cross-section are understood all cross-sectional shapes, which have starting from a common starting point extensions.

It can further be provided that the lateral surfaces of the elevations and / or the depressions are formed as lateral surfaces of a horizontal prism or cylinder. Such unidirectional protrusions and / or depressions may have preferred orientations where the efficiency of the solar cell is greatest. However, it can also be provided to change the orientation of the elevations and / or depressions in regions, for example, in each case by 90 ° to reduce the directional dependence or cancel.

In particular, for the formation of microscopic surface profiles, the

Elevations are transmitted, for example by gravure printing on the surface of the semiconductor layer or semiconductor layers or the carrier substrate. If a carrier substrate forming the semiconductor layer is provided, the elevations can be formed, for example, from a radiation-curing lacquer, for example a UV-curing lacquer. But it can also be provided other paints or printing inks. It may also be reflective paints, so that incident light is directed to both the front and on the back of the polymer solar cell.

If the elevations and / or depressions are formed on the semiconductor layer, a semiconductor layer with a constant layer thickness can first be applied to the (plane) carrier layer, and then the elevations and / or the depressions can be applied by means of gravure printing. For this purpose, it can be provided, for example, that the areas of the gravure form which form the elevations are filled with semiconductor material and the areas which form the depressions represent as ungravierte areas on the gravure roll. Organic semiconductors may have a consistency which is then suitable for such a printing process. An immediate freezing of the Pressure points is necessary in this case.

It can further be provided that the height profile is formed from recesses and / or elevations introduced in the carrier layer. The depressions can be introduced, for example, by thermal impressions into the carrier layer, which can be formed as a replication layer, wherein the depressions can be dimensioned so that at the same time the elevations are formed. It may further be provided to form the carrier layer from a radiation-curing lacquer, such as the above-mentioned UV lacquer, and form the surface profile optically or by means of a profile roller in the radiation-curing lacquer and then cure it. But it may also be macroscopic depressions and / or elevations, as they may have, for example, packaging films.

In a further advantageous embodiment it is provided that the surface profile is formed by an additive superposition of a macroscopic surface profile with a microscopic surface profile.

The embodiments described above are not limited to polymer solar cells but can also be applied to organic solar cells in which the semiconductor layer is not formed from a polymer but from uncrosslinked organic molecules, and to inorganic solar cells, at least as far as the semiconductor layer is concerned, and to hybrid solar cells. Solar cells formed of organic and inorganic components.

Furthermore, the solar cells can be both single junction cells, ie cells with a photosensitive layer, as well as multi junction cells, ie cells with several photosensitive layers. The photosensitive layers of the multi-junction cell can be sensitized for different wavelength ranges, so that a comparatively larger wavelength spectrum than in the Sigle Junction cell can be used.

In the following, the invention will be clarified by way of example with reference to several embodiments with the aid of the accompanying drawings. Show it:

1 shows a first embodiment of a polymer-based solar cell according to the invention;

FIG. 2 shows a second embodiment of a polymer-based solar cell according to the invention; FIG.

Fig. 3 is an enlarged detail view of Fig. 2;

4 is a schematic sectional view of a first exemplary embodiment of a solar cell unit according to the invention before a temperature treatment;

FIG. 5a shows a detailed view V from FIG. 4 with a first solar cell design; FIG.

FIG. 5b shows a detailed view V of FIG. 4 with a second solar cell design; FIG.

FIG. 6 is a schematic sectional view of the solar cell unit in FIG. 4 after the temperature treatment; FIG.

Fig. 7 is a schematic sectional view of a second

Embodiment of a solar cell unit according to the invention; Fig. 8 is a schematic sectional view of a third

Embodiment of a solar cell unit according to the invention;

9 shows an application example of the solar cell unit in FIG. 4 in a schematic sectional illustration; FIG. 10 shows a schematic illustration of the occurrence of

Multiple reflections on a surface according to the invention.

1 shows a polymer-based solar cell 1, referred to below as the polymer solar cell, which is constructed on a carrier substrate 10. In the carrier substrate 10th it may be, for example, a polyester film of about 20 to 125 microns thick.

Form elements 11 are arranged on the carrier substrate 10 and, as in the illustrated exemplary embodiment, can be arranged uniformly distributed on the carrier substrate 10 or can be distributed as desired. The mold elements 1 1 are formed in the embodiment shown in FIG. 1 as a spherical segment and have a height h of e.g. 6 microns and a diameter 2p, for example, 50 microns. They are printed on the carrier substrate 11 prior to the application of the first electrode layer 12. With the aid of the mold elements 11, the effective surface available for constructing the polymer solar cell 1 is increased relative to the planar surface of the carrier substrate 10.

The surface of a sphere segment is

O ₁ = 2π • r • h = π • (p ² + h ² )

Assuming a dense sphere packing each ball cap claimed a base O ₀ = πp ²

Thus, the maximum surface magnification is with the example values given above

d / Oo = 1 + h ² / p ² = 1 + 36/625 = 1, 05

In this way, the surface of the polymer solar cell 1 is enlarged with the same base area of the polymer solar cell 1. Because the sphere has the smallest surface area of all geometric bodies, the above calculation gives at the same time the smallest possible surface enlargement. The surface enlargement depends very much on the chosen parameters for p and h. For example, with p = When the value h is raised from 6 mm to 15 mm, the surface ratio changes from 1.05 to 1.28.

Assuming that the sphere segments are hemispheres, is

O ₁ ADo = (2Kr ² + Λi ² - πr ^ Mr ² = π / 4 + 1 = 1, 79

If, on the other hand, the elevations are formed from quadrilateral pyramids whose height is equal to the base side, the surface enlargement is

O ₁ ZO ₀ = (4/2 ^• a ^• _ = 2,236

It is advantageous in this context that in the choice of four-sided pyramids, the entire surface can be structured so that no gaps remain. While ball caps may have a maximum depth-to-width ratio of 1, for all other geometric shapes of the peaks, such as pyramids, cones, prisms, or the like, the depth-to-width ratio is not limited by the geometric shape ,

However, ball caps are particularly easy to produce, so that the disadvantage of having the lowest specific surface area of all embodiments can be compensated thereby. It may also be provided to design the mold elements as lying strip-shaped prisms, i. to make the surface of the solar cell corrugated.

For example, the mold elements 11 may be printed, preferably with a gravure printing process, or they may be replicated, as described further below in FIG. The mold elements 1 1 may be transparent or non-transparent, which depends on the structure of the solar cell and the light guide.

In the structural design of the mold elements 11, it should be noted that the effectiveness of a solar cell depends, inter alia, on the angle at which the radiation impinges and is guided into the solar cell. Parallel to Radiation direction aligned surface sections therefore contribute nothing to the energy from the incident radiation and do not increase the efficiency of the polymer solar cell.

Furthermore, the achievable surface enlargement depends on the number of mold elements 11 per unit area.

On the mold elements 11 and on the non-covered by the mold elements 11 portions of the carrier substrate 10, a first electrode layer 12 is applied, which is, for example, a layer of gold, silver, copper, aluminum or an alloy of these and / or other metals can act. However, the first electrode layer 12 can also be formed, for example, from a conductive ITO coating (indium / tin oxide). The first electrode layer 12 is formed as a transparent electrode layer of several nanometers in thickness. It may also be a semitransparent electrode layer, which may be formed, for example, as a metallic layer, a structured metallic layer or an optically closed layer.

On the first electrode layer 12, there is disposed a photosensitive semiconductor layer system 13, e.g. from a PEDOT / PSS layer, a photoelectric

Semiconductor layer and a TIO ₂ layer can exist. Other electron layers and / or hole blocking layers are also conceivable.

On the photosensitive semiconductor layer system 13, a second electrode layer 14 is arranged, which may be formed like the first electrode layer 12 described above.

The second electrode layer 14 is covered by an adhesive layer 15 on which a cover layer 16 is applied. It may also be provided to dispense with the adhesive layer. The cover layer can be a transparent plastic layer or a barrier layer structure that protects the system from external influences. The working principle of the polymer solar cell is based on the light-induced electron transfer in a so-called Donar acceptor system. As a result of the above-described enlargement of the surface of the polymer solar cell 1, the disadvantage of the lower efficiency of the polymer solar cell can be at least partially eliminated and positively influenced, which is also due to the multiple reflection caused by the enlarged surface.

2 now shows a second embodiment of the polymer solar cell according to the invention, in which the surface enlargement is not achieved as shown in FIG. 1, by elevations, but by depressions.

A polymer solar cell 2 has a replication layer 21, which is applied to the carrier substrate 10 and which is formed on its front side facing the first electrode layer 12 with recesses 21 v. The recesses 21v may similarly have a variety of shapes as the mold elements 11 described above. The replication layer 21 may be a layer or layers applied to a carrier substrate, into which by a heated mold that under pressure with the surface of the replication 21 is brought into contact, the recesses 21v are formed. It may also be provided that the replication layer is formed from a radiation-curing lacquer, for example from a UV-curing lacquer which is cured after the impressions 21 v have been shaped by irradiation with UV light.

In the exemplary embodiment illustrated in FIG. 2, the replication layers on the carrier substrate 10 can be dispensed with. The carrier substrate in this case represents the replication layer 21 into which the structures (depressions) are directly molded. Alternatively, the recesses may be molded into the carrier substrate.

The second electrode layer 14 applied to the photosensitive semiconductor layer system 13 as the upper electrode is covered by the adhesive layer 15 on which the cover layer 16 or even several layers are applied, as in the first exemplary embodiment (FIG. 1) described above. 3 shows an enlarged section of the replication layer 21. The surface of the recesses 21v has a relief structure which is similar to the macrostructure molded into the surface of the replication layer 21. The surface of the recesses 21v thus has recesses 21v 'that are similar to the recesses 21v. The recesses 21v 'may in turn have recesses similar to the recesses 21v', and so on. It may therefore be provided, for example, that the recesses 21 v have a depth of 100 microns, the recesses 21 v 'have a depth of 10 microns and the following wells each have a depth that is 10% of the previous depth. The lower limit can be achieved, for example, if diffraction occurs at the surface structures and the light can no longer penetrate into the semiconductor layer 13.

The surface structuring increases the effective surface area of the pits from the effective surface of smooth pits (see Figs. 1 and 2). Such a formed surface structure may be designed as a self-similar structure or as a fractal structure. An example of a fractal structure is the so-called Koch curve, which is characterized by its triangular protuberances. This surface structure can lead to multiple reflections and thus to an increase in the efficiency of the cell.

4 now shows a solar cell unit 4, formed from a solar cell 41 and a shrink film 42. The shrink film 42 may preferably be a PE shrink film of 20 μm to 75 μm thickness. Other thicknesses are also conceivable.

The solar cell 41 is laminated after its completion on the shrink film 42, wherein it can be provided that a plurality of solar cells are laminated to the shrink film, which may be connected in parallel and / or in series, for example by interconnects. The interconnects may be formed on the shrink film 42 in a wiring layer not shown in FIG. 4. In the

The conductor layer may be a structured metal layer, for example formed from gold, silver or copper. FIG. 5 a shows an enlarged view of the layered structure of a solar cell unit 4 a, in which a polymer-based solar cell 41 a is applied to the shrink film 42. The solar cell 41 a is in principle constructed like the solar cell 1 in FIG. 1, but it has no form elements 11. It is therefore constructed with a flat active layer without a surface profile.

The carrier substrate 10 may be, for example, a polyester film of about 20 to 50 .mu.m thickness.

On the side of the carrier substrate 10 facing away from the shrink film 42, the first electrode layer 12, the photosensitive semiconductor layer system 13, the second electrode layer 14, the adhesive layer 15 and the cover layer 16 are applied successively. The layer structure is explained in detail above in Fig. 1.

5b now shows, in an enlarged representation, the layered structure of a solar cell unit 4b, in which a polymer-based solar cell 41b is applied to the shrink film 42. The solar cell 41b is constructed like the solar cell 1 in FIG.

On the side of the carrier substrate 10 facing away from the shrink film 42, as described above in FIG. 1, the mold elements 11 are arranged, which are printed onto the carrier substrate 10 before the first electrode layer 12 is applied. On the first electrode layer 12, the photosensitive semiconductor layer system 13, the second electrode layer 14, the adhesive layer 15 and the cover layer 16 are applied.

Fig. 6 shows the solar cell unit 4 in Fig. 4 after a temperature treatment of about 3 minutes at a temperature of 80 ⁰ C to 120 ⁰ C. The temperature range is chosen so that it is not reached during operation of the solar cell unit and that he Structure of the solar cell 41 not destroyed. In the embodiment shown in FIGS. 4 and 5, the shrink film 42 is a unidirectional shrink film that shrinks in one direction only when exposed to temperature.

As can be seen in FIG. 6, the solar cell unit 4 is now sinusoidally deformed in cross section, so that the surface of the upper side of the solar cell unit 4 is enlarged in relation to a planar surface profile.

Solar radiation directed to the solar cell is therefore reflected several times due to the curved larger area of the active layer, which is not the case with the undeformed solar cell unit 4 in FIG. 4.

When the solar cell 41 is of the type of solar cell 41a shown in FIG. 5a, in which the active layer has a planar surface profile, said surface enlargement of the solar cell unit 4a results only from the deformation of the solar cell 41a by the heat-treated shrink film 42 Solar cell 41 of the type of solar cell 41b shown in Fig. 5b in which the active layer has an uneven surface profile, said surface enlargement of the active layer of the solar cell unit 4b results from both the deformation of the solar cell 41b by the heat-treated shrink film 42 and the surface enlargement of the photosensitive semiconductor layer system 13 as a result of the mold elements 11. Thus, the surface profile thus produced is a superposition of a first (macroscopic) surface profile with a second (microscopic) surface profile, whereby a further Effiz Increasing the solar cell unit is achieved by multiple reflections. The macroscopic surface profile may be further configured such that it preferably directs incident light onto the active layer of the solar cell 41. It can further be provided that the shrink film is provided with lacquer and / or a coating material to which refractive and / or light-scattering and / or light-conducting and / or light wavelength-changing particles and / or particle mixtures are added. If the shrink film is formed as a transparent film, the light can also be brought through the shrink film on the solar cell and thereby be influenced by the said particles and / or particle mixtures. Instead of the solar cell shown in Fig. 5b, in which the surface profile is formed by mold elements 11, as shown in Fig. 1, also a solar cell may be provided, in which the surface profile is molded into the replication layer 21, as shown in Fig. 2 ,

The solar cell unit 4 shown in Fig. 6 may also be deformed by an in-mold process or by a touch-forming process. In this case, the solar cell 41 is inserted into an evacuatable mold and heated and then pressed by applying a vacuum against a provided with a surface structure film. In this case, the surface structure of said film is formed in the surface of the solar cell 41 or the solar cell 41 is deformed overall. To fix the deformation, the deformed solar cell 41 is back-injected with thermoplastic, which in this case assumes the function of the shrink film 42.

As a further manufacturing method, the deep drawing can be provided, wherein instead of the shrink film 42 may be provided a thermoplastic film. The solar cell 41 and the thermoplastic film form a thermoforming sheet, which is placed in a thermoforming mold and heated and then pressed by pressure in the thermoforming mold and thereby deformed. The thermoforming mold is designed as a negative of the surface profile to be shaped into the thermoforming film. It may be provided to inject the thermoforming sheet after deformation in order to stabilize it against subsequent deformation.

FIG. 7 now shows a solar cell unit 7 in which two solar cells 41 b (see FIG. 5 b) are laminated on the shrink film 41 on both sides of the shrink film. In the embodiment shown in Fig. 7, a front solar cell 41 bv and a rear solar cell 41 bh are arranged opposite to each other, wherein each of the support substrate 10 of the solar cell is connected to the shrink film 41. The shrink film 41 is formed in this embodiment as a transparent film, so that incident light first on the photosensitive

Semiconductor layer system 13 of the front solar cell 41 bv then passes through the transparent shrink film 41 and finally hits the photosensitive semiconductor layer system 13 of the rear solar cell 41 bh. In this way, the solar cell unit 7 can use solar energy more effectively. It can also be provided be arranged to arrange the front solar cells 41 bv and the rear solar cells 41 bh to each other, so that, for example, the rear solar cells 41 bh are arranged in alignment with intended for contacting areas on the front of the shrink film 41, which do not contribute to energy. It is also conceivable that the photosensitive layers are formed differently and absorb the light from different wavelength ranges. Such cells are also referred to as multi-junction cells, in contrast to the single junction cells, which have only one photosensitive layer. A multi-junction cell can use a larger spectral range than a single-junction cell and therefore has a comparatively higher level

Energy conversion efficiency as a single junction cell.

8 shows a solar cell unit 8 which is formed from a front solar cell unit 8v facing the light source and a rear solar cell unit 8h arranged behind it. The two solar cell units 8v and 8h form a common multilayer body, it being possible to provide that their shrink films 41 and 41 are made of the same material and / or have the same shrinkage behavior. But it can also be provided that the shrink films 41 v and 41 h are formed of different materials and / or have different shrinkage behavior. Further

Training variants can be produced by varying the orientation of the interconnected solar cell units 8v and 8h. It can thus be provided, for example, that the shrink films 41 v and 41 h are unidirectional shrink films which are arranged crossed by 90 °, so that the solar cell unit 8 has a knob-shaped surface profile after the temperature treatment. Here it can also be provided that the different solar cell units are the same, different, formed from single and / or multi-junction cells.

The solar cell units 7 and 8 shown in Figs. 7 and 8 are in the state they have before the temperature treatment, that is, the shrink films 41, 41 v and 41 h are not yet deformed. It may preferably be provided in the embodiments described in FIGS. 4 to 8 to provide the solar cell units with protective coatings and / or to shrink them onto mounting bodies. Such an application example is shown in FIG. 9.

9 shows a solar cell module 9, which is arranged on a mounting surface 93 by means of fastening elements 94 and which faces a light source 95. The mounting surface 93 may be a roof surface of a building, preferably a roof surface on the south side of the building.

The solar cell module 9 has a solar cell unit 91, which is shrunk onto the front side of a mounting body 92. The mounting body 92 is formed as a plate-shaped body having a protruding mounting portion which is encompassed by the shrunk solar cell unit 91. The edge portions of the mounting body 92 have in the embodiment shown in Fig. 9 through holes, which are penetrated by the formed as a cylinder screws fasteners 94.

The solar cell unit 91 has one or more shrink films as described above. The surface profile of the solar cell unit 91 after shrinking increases the surface area of the solar cell unit 91 with respect to a planar surface profile. When shrinking further electrical connections with electrical contacts and / or traces of the mounting body 92 may be made. The electrical connections can be protected by the dome-shaped formation of the shrunken solar cell unit 91 at the same time against weathering and corrosion.

It can further be provided that the solar cell unit consists of water-flowed tubes with shrunk solar cell. In this case, in addition, the heat radiation of the sun can be used. 10 shows a diagrammatic representation of the occurrence of multiple reflections on a surface of a solar cell 100 according to the invention. The surface of the solar cell 100 has recesses 100v, into which recesses 100v 'are formed. An incident on the surface of the solar cell 100 Light beam 95s is reflected several times on the surface of the solar cell, giving off part of its energy to the solar cell at each reflection. In the embodiment shown in Fig. 10, the light beam 95s is reflected five times. Under the simplifying assumption that 50% of the energy is transferred into the solar cell 100 during each reflection, the following energy balance applies:

Reflection energy transfer

1st reflection 50%

2. Reflection 25%

3. Reflection 12.5%

4. Reflection 6.25%

5. Reflection 3.13%

96.66%

Although the five reflections mentioned in the example do not occur for every incident light beam (different impact point, different direction of incidence), two reflections, for example, already result in an energy transfer of 75%.

Structures with a depth-to-width ratio in the range of 0.5 to 5 have proven to be particularly advantageous for the formation of multiple reflections.

As has been further shown, suitable as a surface structure, in particular, cross gratings of two base gratings, which have said depth-to-width ratio. The structures may, for example, have sine-squared characteristics, but even rectangular or pyramidal structures are suitable. They are like an egg carton.

Claims

1. A method for producing a solar cell unit (4) with a solar cell (41) based on polymer with at least one carrier substrate (10) and at least one organic semiconductor layer (13) with a light source facing a top and a light source facing away from the back, characterized in that the solar cell (41) is deformed after its completion so that at least the upper side of the solar cell (41) has a surface profile which increases the surface of the upper side in relation to a planar surface profile.

2. The method according to claim 1, characterized in that the solar cell (41) on a shrink film (42) is laminated, and that thereafter, the solar cell unit (4) is subjected to a temperature treatment.

3. The method according to claim 1, characterized in that for the carrier substrate (10) of the solar cell (41) a shrink film is used and the solar cell (41) is subjected after its completion of a temperature treatment.

4. The method according to claim 2 or 3, characterized in that a unidirectional shrink film is used.

5. The method according to claim 2 or 3, characterized in that a bidirectional shrink film is used.

6. The method according to any one of claims 2 to 5, characterized in that an opaque or transparent or semi-transparent shrink film is used.

7. The method according to any one of claims 2 to 6, characterized in that an electrically non-conductive shrink film is used.

8. The method according to any one of claims 2 to 6, characterized in that an electrically conductive shrink film is used.

9. The method according to any one of claims 2 to 8, characterized in that the shrink film (41) before the temperature treatment at least partially painted and / or coated.

10. The method according to claim 9, characterized in that the paint and / or the coating material refractive and / or light-scattering and / or photoconductive and / or changing the wavelength of light particles and / or particle mixtures are added.

11.Verfahren according to any one of claims 2 to 10, characterized in that the shrink film (41) is at least partially prestructured.

12. The method according to any one of claims 2 to 11, characterized that a multilayer shrink film is used whose layers have a different shrinkage behavior.

13. The method according to any one of claims 2 to 12, characterized in that two superimposed solar cells (41 v, 41 h) or solar cell units are applied on both sides of the shrink film (42).

14. Method according to claim 13, characterized in that the solar cells or solar cell units provided on one side of the shrink film (42) are offset relative to the solar cells or solar cell units provided on the other side of the shrink film (42).

15. The method according to claim 1, characterized in that the solar cell (41) is deformed by an in-mold process.

16. The method according to claim 1, characterized in that the solar cell (41) is deformed by a touch-forming process.

17. The method according to claim 1, characterized in that the solar cell (41) is deformed by a deep-drawing process.

18. The method according to any one of the preceding claims, characterized in that the deformation of the solar cell (41) by means of one or more spacer

Layers is affected.

19. The method according to any one of the preceding claims, characterized that the solar cell (41) is injected behind.

20. The method according to claim 19, characterized in that an electrically conductive spray medium is used.

2 I.Verfahren according to claim 20, characterized in that a partially electrically conductive spray medium is used.

22. The method according to claim 19, characterized in that an electrically non-conductive spray medium is used.

23. The method according to any one of claims 19 to 22, characterized in that an opaque or transparent or semitransparentes spray medium is used.

24. The method according to any one of the preceding claims, characterized in that at least two solar cells (41b) or solar cell units (8v, 8h) are arranged one above the other.

25. The method according to any one of the preceding claims, characterized in that the solar cell units are encapsulated.

26. A method for producing a polymer-based solar cell (1, 2) having at least one carrier substrate (10) and an organic semiconductor layer (13) with a top side facing a light source and a rear side facing away from the light source, characterized in that a surface relief into a layer the solar cell (1, 2) is molded, and that one or more electrically functional layers containing the organic semiconductor layer (13) are applied to the molded surface relief such that the upper surface of the organic semiconductor layer (13) has a surface profile which increases the surface area of the organic semiconductor layer with respect to a planar surface profile ,

27. Method according to claim 26, characterized in that the surface profile is molded into the carrier substrate (10) or into a replication lacquer layer (21) applied to the carrier substrate.

28. A method for producing a solar cell unit with a solar cell according to one of claims 1 to 25, characterized in that the deformed after its completion solar cell (41b) by means of

A method according to claim 26 or claim 27 is made.

29. A solar cell (1, 2) based on polymer with at least one carrier substrate and at least one organic semiconductor layer (13) facing a light source top and a light source facing away from the back, characterized in that at least the top of the organic semiconductor layer (13) has a surface profile which enlarges the surface of the upper surface with respect to a planar surface profile.

30. Solar cell according to claim 29, characterized in that the surface profile is formed so that it leads to multiple reflections.

31. Solar cell according to claim 29 or 30, characterized in that the surface profile of elevations and / or depressions of the Carrier substrate (21) and / or the semiconductor layer (13) is formed.

32. Solar cell according to one of claims 29 to 31, characterized in that the surface profile is a stochastic surface profile.

33. Solar cell according to one of claims 29 to 31, characterized in that the surface profile is a periodic surface profile.

34. Solar cell according to claim 33, characterized in that the surface profile forms a cross lattice of two base lattices.

35. Solar cell according to one of claims 29 to 31, characterized in that the surface profile is a self-similar surface profile.

36. Solar cell according to one of claims 31 to 35, characterized in that the average width or the mean diameter of the elevations (11) or depressions (21 v) at the base in the range of 1 mm to 10 mm.

37. Solar cell according to claim 36, characterized in that the average width or the mean diameter of the elevations (11) and / or depressions (21 v) at the base point in the range of 1 .mu.m to 1000 .mu.m.

38. Solar cell according to claim 37, characterized in that the average width or the average diameter of the elevations (11) and / or depressions (21v) at the base point in the range of 100 nm to 1000 nm.

39. Solar cell according to one of claims 31 to 38, characterized in that the depth-to-width ratio of the projections and / or depressions is in the range of 0.5 to 5.

40. Solar cell according to one of claims 31 to 39, characterized in that the lateral surfaces of the elevations (11) and / or the recesses (21 v) are formed as lateral surface areas of a spherical body.

41. The solar cell according to claim 40, characterized in that the spherical body is a sphere.

42. Solar cell according to one of claims 31 to 39, characterized in that the lateral surfaces of the elevations (11) and / or the recesses (21 v) as

Lateral surface areas of a cone are formed.

43. Solar cell according to one of claims 31 to 39, characterized in that the lateral surfaces of the elevations (11) and / or the recesses (21 v) as

Lateral surface areas of a pyramid are formed.

44. Solar cell according to one of claims 31 to 39, characterized in that the elevations (11) and / or the recesses (21 v) with star-shaped

Cross section are formed.

45. Solar cell according to one of claims 31 to 39, characterized the lateral surfaces of the elevations (11) and / or the depressions (21 v) are formed as lateral surfaces of a horizontal prism or cylinder.

46. Solar cell according to one of claims 29 to 46, characterized in that the surface profile of an additive superposition of a macroscopic surface profile is formed with a microscopic surface profile.