WO2008012079A1

WO2008012079A1 - Organic solar cell

Info

Publication number: WO2008012079A1
Application number: PCT/EP2007/006596
Authority: WO
Inventors: Ulrich Schindler; Achim Hansen; Andreas Schilling; Michael Heilmann
Original assignee: Leonhard Kurz Stiftung & Co. Kg
Priority date: 2006-07-26
Filing date: 2007-07-25
Publication date: 2008-01-31

Abstract

The invention relates to an organic solar cell comprising at least one light-permeable, particularly transparent, organic functional layer which increases the efficiency of the solar cell and is provided with light-scattering and/or luminescent particles, and/or at least one light-permeable, particularly transparent, organic or inorganic functional layer that increases the efficiency of the solar cell, has a refractive index lying between the refractive index of air and the refractive index of a light-permeable electrode layer of the solar cell, and/or is fitted with at least one first relief structure reducing reflection.

Description

Organic solar cell

The invention relates to an organic solar cell comprising at least three functional layers, wherein a first functional layer in the form of at least one electrically conductive first electrode layer, a second functional layer in the form of at least one organic semiconductor layer and a third functional layer in the form of at least one translucent, in particular transparent, electrically conductive second Electrode layer is formed, wherein the at least one organic semiconductor layer is photovoltaic active and is disposed between the at least one first electrode layer and the at least one second electrode layer.

Organic solar cells and methods for their production are known. An organic component is generally understood to be one which has at least one functional layer which is based at least partially on an organic material. A functional layer is in particular an electrically conductive layer, a semiconductor layer, an electrically insulating layer or a substrate. As organic materials, all kinds of organic, organometallic and / or inorganic plastics are referred to, wherein a restriction to a carbonaceous material is not provided. Rather, silicones, polymers or oligomers as well as the so-called "small molecules" are included.

DE 102004045211 A1 describes a flexible film body comprising an organic solar cell, which in the simplest case comprises a layer conjugated polymer which is disposed between a transparent electrode layer and a metallic electrode layer. In order to increase the efficiency of the solar cell, light from the areas surrounding the solar cell is guided by means of relief structures in the direction of the solar cell. Here, the solar cell optionally of an optically variable element such as a Kinegram ^® covered.

Currently, organic solar cells have an efficiency of about 3 to 5%, which is far below the efficiencies already achieved with silicon-based solar cells.

It is an object of the invention to provide an organic solar cell with improved efficiency.

The task is for the solar cell, comprising at least three

Functional layers, wherein a first functional layer in the form of at least one electrically conductive first electrode layer, a second functional layer in the form of at least one organic semiconductor layer and a third functional layer in the form of at least one transparent, in particular transparent, electrically conductive second electrode layer is formed, wherein the at least one organic semiconductor layer is photovoltaically active and is arranged between the at least one first electrode layer and the at least one second electrode layer, in which the solar cell has at least one light-transmitting, in particular transparent, organic functional layer which increases the efficiency of the solar cell and comprises light-scattering and / or luminescent particles Seen perpendicular to the at least one semiconductor layer are arranged overlapping with and / or next to this, and / or at least one of the efficiency of the solar cell enhancing translucent, in particular transparent, organic or inorganic functional layer having a refractive index, which is between the refractive index of air and the refractive index of the second electrode layer, wherein the at least one organic or inorganic functional layer on the at least A side of the second electrode layer facing away from the semiconductor layer is arranged, and / or at least one translucent, in particular transparent, organic or inorganic functional layer increasing the efficiency of the solar cell, wherein the at least one organic or inorganic functional layer on the, the at least one semiconductor layer facing away from the second Electrode layer is arranged and at its the at least one semiconductor layer facing away from the interface at least one first relief structure having a reflection of in the solar cell e incident light at this functional layer compared to a reflection at such a functional layer with a planar interface, in particular by at least 20%, reduced.

If an organic functional layer with light-scattering particles is used, they scatter and / or direct the incident light. The light is thereby deflected in one or more directions, so that the light travels on the one hand in the active layer of the solar cell or the at least one organic semiconductor layer a longer distance than would be the case without the particles. In this case, the light beams which have already been deflected impinge, if appropriate, on further particles which scatter the light again, so that an exit of the light or of parts of the light from the active layer can be completely prevented in the most favorable case. Light scattering particles that are perpendicular to at least one semiconductor layer seen next to this or are not overlapped with this, serve the light that would have missed the active layer and would have remained unused, redirecting towards the active layer of the solar cell. The light incident on and next to the solar cell is thus better utilized, thereby increasing the efficiency of the solar cell by up to 100%.

If an organic functional layer with luminescent particles is used, these are excited by incident light of at least one wavelength and emit light of a different wavelength. The luminescent particles are chosen so that the emitted wavelength can be better utilized or at least used by the active layer of the solar cell. In this case, the light exciting the luminescent particles can in particular be light of a wavelength which can not be utilized or only poorly utilized by the active layer of the solar cell. The light emitted by a luminescent particle light is radiated uniformly on all sides and is thus usable independent of direction. The light incident on and next to the solar cell is thus better utilized, thereby increasing the efficiency of the solar cell by up to 100%.

As the luminescent particles, fluorescent particles or phosphorescent particles may be used, and a combination thereof may be used.

If an organic or inorganic functional layer which has a refractive index which lies between the refractive index of air and the refractive index of the second electrode layer is arranged on the light incidence side of the solar cell, ie substantially in front of the second electrode layer, it is achieved that the reflection of the light is reduced when hitting the solar cell. There is more light crossing the interface Air and solar cell in the solar cell over than without this measure. Previously reflected at the interface light that has been diverted unused by the solar cell is now largely available for energy, the efficiency of the solar cell is increased by up to 20%.

Such organic or inorganic functional layers, which have a defined refractive index, are preferably each formed in a layer thickness in the range from 15 to 300 nm. Particularly suitable materials for forming functional layers are dielectric materials which are translucent, in particular transparent, in such a layer thickness, such as SiO ₂ , ZnS, Al ₂ O ₃ , ZrO ₂ , MgF ₂ , Ca ₂ O ₃ , etc.

Furthermore, an organic or inorganic functional layer, which has at least one first relief structure, which reduces a reflection of the light when hitting the solar cell, on the light incident side of the

Solar cell, so be arranged substantially in front of the second electrode layer. More light passes through the interface between the air and the solar cell into the solar cell than without this measure. Previously reflected at the interface light that has been diverted unused by the solar cell is now largely available for energy, the efficiency of the solar cell is increased by up to 20%.

It has proven useful if the at least one first relief structure is designed in the form of a matt structure. Matt structures have on a microscopic scale fine relief structure elements that determine the scattering power and can only be described with statistical parameters such. B. mean rough value Ra ₁ correlation length Ic etc., wherein the values for the average roughness Ra are in the range 20 nm to 2000 nm with preferred values in the range of 50 nm to 1000 nm, while the correlation length lc in at least one direction has values in the range of 200 nm to 50,000 nm, preferably in the range of 500 nm to 10,000 nm.

Furthermore, it has proven useful if the at least one first relief structure is in the form of a periodic structure, in particular as a blazed grating, line structure, cross grating, linear or crossed sine grating, circular grating, lens structure or a combination of two or more of these structures.

It is particularly preferred for the at least one first relief structure to have a depth-to-width ratio of> 0.3 and in particular of> 1, since this generally results in an improved function, ie. a reduced reflection is achieved.

Depth is the distance between the highest and the lowest consecutive point of such a re-structure, that is, the distance between "mountain" and "valley". Width is the distance between two adjacent highest points, ie between two "mountains." The higher the depth-to-width ratio is, the steeper the "mountain flanks" are formed. For example, the first relief structure may be periodic relief structures or quasi-periodic relief structures having discretely distributed line-shaped regions formed only as a "valley", the distance between two "valleys" being many times greater than the depth of the valley The calculated depth-to-width ratio of quasi-periodic relief structures can be approximately zero, so that in discretely arranged relief structures, which are essentially formed only from a "valley", the depth of the "valley" Width of the "valley" is to determine the depth-to-width ratio. It has proven useful if the at least one first periodic relief structure has a spatial frequency in the range of 300 to 4000 lines / mm.

In this case, to form a translucent, in particular transparent organic functional layer, printing media are preferably used which have at least one organic binder and to which light-scattering and / or luminescent particles are added or into which the first relief structures are embossed.

Organic or inorganic functional layers, whose refractive index has to be set in a defined manner, are selected as a function of the refractive index of the materials used for the formation, with in particular up to three functional layers being stacked on top of one another. Inorganic functional layers having a refractive index which is between that of air and that of the second electrode layer are in particular formed from magnesium fluoride or SiÜ ₂ .

Organic materials for forming organic functional layers are preferably dissolved in an organic solvent or solvent mixture, a printing medium is prepared and this is preferably gravure printed. Alternatively, flexographic printing, screen printing or a nozzle for structured application of the printing medium can be used.

The first electrode layer is preferably formed of a metal, in particular of gold, silver, copper, aluminum, nickel or alloys of at least two of these metals and may, depending on the layer thickness, opaque or translucent, in particular also transparent, be formed. It has proven useful if the second electrode layer is formed from indium tin oxide (ITO). This is usually deposited by sputtering. But also doped polyethylene, polyaniline, silver, gold, organic semiconductors, nanoparticulate solutions and so on are usable. A second electrode layer of a material with inherent color, such as gold, is formed in particular in a small layer thickness or as a lattice structure in order to be sufficiently transparent.

Between an electrode layer and the organic semiconductor layer of the solar cell, a hole blocker layer, in particular of TiO ₂ , can be arranged, which improves the electrical discharge of charges. On the side of the organic semiconductor layer which faces away from the hole blocker layer, a layer is sometimes arranged which assumes the function of an electron blocker layer. In this case, electrically conductive polymer, in particular poly-3,4-Ethylenedioxythiophene (PEDOT), has proven.

The at least one photovoltaically active organic semiconductor layer preferably has a layer thickness in the range from 50 to 300 nm, in particular in the range from 100 to 250 nm. It has proven particularly useful if the at least one organic semiconductor layer is formed by at least two organic semiconductor materials by forming a composite of at least one electron donor and at least one electron acceptor in a ratio of 2: 0.5 to 0.5: 2 , in particular in the ratio of 1: 0.9 to 1: 1, is formed. In this case, it is particularly preferred if the at least one electron donor is formed from a polythiophene, in particular from poly (3-hexylthiophene) (P3HT), and the at least one electron acceptor is formed from a fullerene derivative, in particular from PCBM. As a solar cell, not only one of the "single junction" type having a photovoltaic active semiconductor layer made of a material but also a "multi-junction" solar cell having two or more photovoltaically active semiconductor layers made of different materials can be used wherein the different materials can utilize different wavelengths of incident light.

The following structure of a single-junction solar cell has proven particularly useful. In this case, the solar cell optionally has a transparent substrate, at least one second electrode layer, at least one light-transmissive photovoltaically active organic semiconductor layer, at least one, optionally transparent, first electrode layer and an encapsulation layer. Other layers, such as the blocker layers already mentioned above, may be present. The encapsulation layer serves to shield the functional layers of the solar cell from harmful ones

Environmental influences and is preferably made of an inorganic coated polymer film, wherein the coating is based in particular on tantalum, SiO _x or Siθχ / Na.

It has proved to be advantageous if the solar cell has at least two functional layers which increase the efficiency of the solar cell. This ensures that the efficiency of the solar cell is further increased. Thus, a plurality of organic functional layers comprising particles according to case a) may be present or one or more organic functional layers containing particles according to case a) with functional layers having a defined refractive index and / or first relief structure according to case b) are used in combination. Furthermore, a plurality of functional layers having a defined refractive index and / or a first relief structure can be produced according to case b) be used in combination

It has proven useful if the first electrode layer is transparent, in particular transparent, is formed. Thus, the formation of a substantially transparent or transparent solar cell is possible, which can be applied for example on a window, label, security element, a lettering or the like, after the organic semiconductor layer is usually translucent or transparent. A first electrode layer of a material with inherent color, such as gold, is formed in particular in a small layer thickness or as a lattice structure in order to be sufficiently transparent.

It is particularly preferred if the solar cell has at least one functional layer which has at least one diffractive and / or refractive second relief structure which, viewed at right angles to the plane of the semiconductor layer, overlaps and / or next to the semiconductor layer, in particular on the side of the semiconductor layer facing away from the semiconductor layer first electrode layer is arranged. The second relief structure makes it possible to deflect, focus or reflect light in a targeted manner in the direction of the active layer or at least one organic semiconductor layer or in areas thereof, thus resulting in a further increase in the efficiency of the solar cell. However, the second relief structure can also serve only decorative purposes, for example, to produce an optically variable element, such as a hologram or Kinegram ^® . A combination of light-guiding second relief structures and second relief structures serving for decorative purposes is also possible.

It has proven particularly useful if the at least one second relief structure in the form of a matt structure, an asymmetric relief structure, a linear one or crossed linear grating, a diffractive or refractive lens structure or a combination of at least two such structures is formed. Such relief structures are particularly well suited to scattering, collecting, focusing or distracting light incident thereon. Functional layers with second relief structures can, depending on the arrangement, be made translucent or opaque with regard to the incidence of light in the solar cell. Thus, at least one opaque reflective functional layer having at least one second relief structure may be arranged on the side of a light-permeable first electrode layer facing away from the at least one semiconductor layer and / or a light-permeable functional layer having at least one second relief structure on the side of the light-permeable second side facing away from the at least one semiconductor layer Electrode layer be arranged.

It has proved to be advantageous if the light-scattering and / or luminescent particles have a maximum particle size in the range from 5 nm to 10 μm. Since the layer thicknesses of the individual functional layers of an organic solar cell are usually each in the range below 1 μm, such small particles can readily be incorporated into a functional layer.

It is advantageous if the light-scattering particles are transparent or semitransparent, in particular made of an oxide, a sulfide, a carbide or a nitride. Particles of SiO ₂ or ZnS have proved to be particularly suitable. Particles of this type allow incident light to pass through, at least in part, so that the light distribution is improved compared to light-impermeable particles. Fluorescent particles are available, for example under the name -Lumogen ^®. Lumogen ^® Yellow S 0790, for example, does not scatter light and causes a displacement of wavelengths 300 to 500 nm in a range of 500 to 650 nm.

The light-scattering and / or luminescent particles preferably have a rod, platelet or spherical shape. In this case, rod-shaped or platelet-shaped particles can be present in a specific spatial orientation or disordered in the organic functional layer. Furthermore, it has proven useful if the at least one organic

Functional layer has a mixture of light-scattering and / or luminescent particles of different shapes.

Preferably, light-scattering and / or luminescent particles are contained in the range from 0.1 to 10% by weight in the at least one organic functional layer. Less, but also more particles lead to a reduction in the efficiency of the solar cell.

Furthermore, it is advantageous if the light-scattering and / or luminescent particles are selectively formed for a wavelength of the electromagnetic spectrum. In particular, it has proved favorable if the at least one organic functional layer has light-scattering and / or luminescent particles which are selectively formed for at least two different wavelengths of the electromagnetic spectrum.

Furthermore, it is advantageous if the light-scattering particles are also designed to be luminescent, and to convert a wavelength of the electromagnetic spectrum into another wavelength. As a result, in addition to the achievable scattering effects, wavelengths which can be exploited only slightly by the solar cell can be converted into wavelengths which can be better utilized. In particular, it has proven useful if the at least one organic functional layer has light-scattering particles which are of different fluorescence and / or phosphorescent design.

In this case, the light-scattering and / or luminescent particles can be distributed uniformly in the at least one organic functional layer. However, it can also offer advantages if the light-scattering and / or luminescent particles are distributed unevenly over an area and / or a layer thickness of the at least one organic functional layer. For example, it has proven useful if more light-scattering and / or luminescent particles are arranged in the edge region of the functional layers of the solar cell than in the middle of the solar cell

Functional layers to prevent leakage of light from the solar cell.

It has proven useful if the at least one organic functional layer comprising the light-scattering and / or luminescent particles corresponds to the at least one semiconductor layer. The light-scattering and / or luminescent particles are thus used distributed in the material of the at least one semiconductor layer. The distribution of the particles takes place in particular uniformly within the at least one photovoltaically active semiconductor layer.

Furthermore, it has proved favorable if the at least one organic functional layer containing the light-scattering and / or luminescent particles on the at least one semiconductor layer remote side of the second electrode layer is arranged. The distribution of the particles in the at least one organic functional layer takes place here either uniformly or only partially. A translucent, in particular transparent, spacer layer may be arranged between the functional layer containing the light-scattering and / or luminescent particles and the second electrode layer in order to change the path to be traced for the incident light, finally finally into the active layer or the at least one semiconductor layer couple. Instead of a spacer layer, or in combination with this, a translucent, in particular transparent substrate can also be used.

However, the at least one organic functional layer containing the light-scattering and / or luminescent particles can also be provided on the side of the first side facing away from the at least one semiconductor layer

Be disposed electrode layer, provided that it is transparent, in particular transparent. The distribution of the particles in the at least one organic functional layer also takes place here either uniformly or only partially. A translucent, in particular transparent spacer layer can be arranged between the functional layer containing the light-scattering and / or luminescent particles and the first electrode layer in order to change the path to be traced for the incident light, finally finally into the active layer or the at least one semiconductor layer couple. Instead of a spacer layer, or in combination with this, a translucent, in particular transparent substrate can also be used.

The at least one organic functional layer having a refractive index that is between the refractive index of air and the refractive index the transparent electrically conductive second electrode layer is located on the, the at least one semiconductor layer facing away from the second electrode layer. In this case, it has proven particularly advantageous if at least two transparent organic functional layers each having a refractive index which lies between the refractive index of air and the refractive index of the second electrode layer are present, the at least two transparent organic functional layers having a different refractive index and are stacked on the second electrode layer such that the refractive index of the at least two transparent organic functional layers decreases starting from the second electrode layer. The arrangement of at least one organic functional layer with a correspondingly defined refractive index on the second electrode layer has the effect of reducing reflection of the incident light at the air-solar cell interface and further increasing the efficiency of the solar cell. If light also impinges on the solar cell on the side of the first electrode layer and if it is translucent, it is of course also possible for at least one such organic functional layer, which has a refractive index, between the refractive index of air and the refractive index of the transparent electrically conductive first electrode layer lies, be arranged.

Preferably, the solar cell further comprises a light-transmitting, in particular transparent substrate. It has proven useful if the substrate has a thickness in the range of 6 μm to 1 mm, in particular in the range of 12 μm to 150 μm. The use of a substrate made of a flexible film allows the formation of flexible organic solar cells, since their functional layers usually have a much smaller layer thickness as the substrate and affect its flexibility not or only slightly. Suitable substrate materials are generally inorganic or organic materials, in particular PET, PEN, PVC or glass. On such a substrate, the functional layers of the solar cell can be readily applied in a continuous process, the active layer in particular in a printing process. In this case, the substrate is used in particular as an elongated, flexible film strip, which can be transported from roll to roll, so that a large number of solar cells can be formed thereon. In this case, the elongated film strip is provided wound onto a supply roll, deducted from this, successively formed the individual functional layers of the solar cells and finally the film strip including a plurality of formed thereon, optionally electrically interconnected solar cells wound on another supply roll. This can be a separation of solar cells and / or

Solar cell groups, in particular by cutting or punching, connect or other process steps are made, such as a thermal, chemical or mechanical treatment, a coating, irradiation, etc.

Within the structure of the solar cell, it has proven useful if the at least one organic semiconductor layer comprises the light-scattering and / or luminescent particles and / or if the at least one transparent organic functional layer containing the light-scattering and / or luminescent particles between the optionally present

Substrate and the at least one second electrode layer is arranged. If a translucent, in particular transparent substrate is present, it is also advantageous if the at least one transparent organic functional layer containing the light-scattering and / or luminescent particles on the, the second electrode layer facing away from the substrate is arranged. Furthermore, it has proven useful if the at least one transparent organic functional layer containing the light-scattering and / or luminescent particles is arranged between the at least one transparent first electrode layer and the encapsulation layer.

It is particularly preferred, if appropriate in combination with at least one functional layer comprising light-scattering and / or luminescent particles, if a transparent, in particular transparent substrate is present and at least three transparent functional layers with different refractive indices are arranged on the side of the substrate facing away from the second electrode layer. The refractive index of the substrate must be taken into account when selecting the functional layers.

Furthermore, it has proven useful if a translucent, in particular transparent substrate is present and at least one transparent organic functional layer, which has first and / or second relief structures, is arranged on the side of the substrate facing away from the second electrode layer.

It has proven to be advantageous if at least one reflective functional layer, which has the at least one second relief structure, on the side of the light-permeable first electrode layer facing away from the at least one semiconductor layer and directly to the

Encapsulation layer is disposed adjacent. The reflective functional layer is, in particular, an opaque metallic layer, but the use of transparent, high-index dielectric layers, known as HRI layers, has also proved successful. in particular, if the solar cell as a whole is to be made transparent.

Through a combination of different functional layers that increase the efficiency of the solar cell, it is possible to increase the efficiency of an organic solar cell by a total of up to 100%.

Figures 1 to 9 are intended to exemplify solar cells according to the invention. So shows:

1 shows a first solar cell in cross-section, which has a semiconductor layer containing particles;

2 shows a second solar cell in cross section, which contains an organic functional layer containing particles on the second

Having electrode layer;

3 shows a third solar cell in cross-section, which has an organic functional layer containing particles on a transparent substrate;

4 shows a fourth solar cell in cross-section, which has an organic functional layer containing particles on a transparent first electrode layer formed;

Figure 5 shows a fifth solar cell in cross-section, which three

Having functional layers with different refractive indices; 6 shows a sixth solar cell in cross section, which three

Functional layers with different refractive index and a semiconductor layer containing particles;

Figure 7 is a seventh solar cell in cross section, which three organic

Functional layers containing particles of different shape and distribution;

8 shows an eighth solar cell in cross section, which is a

Functional layer having a defined refractive index and two organic functional layers containing particles of different shape and distribution; and

9 shows a ninth solar cell in cross section, which is a

Functional layer having a defined refractive index, an organic functional layer having second relief structures and two organic functional layers containing particles of different shape and distribution.

1 shows a first solar cell in cross section, which comprises a first electrode layer 1 made of gold, an active layer containing at least one organic functional layer in the form of a photovoltaically active organic semiconductor layer 2 of a composite of P3HT and PCBM in the ratio 1: 1, and a second electrode layer 3 indium tin oxide (ITO) has. The first electrode layer 1 is opaque and formed by cathode sputtering in a layer thickness of 25 nm. The semiconductor layer 2 is printed formed and has a layer thickness of 200 nm. The semiconductor layer 2 has 1% by weight of light-scattering particles 4 a which have a maximum diameter of 100 nm and which are distributed uniformly in the semiconductor layer 2. The second electrode layer 3 is transparent and formed by sputtering in a layer thickness of 10 nm. The functional layers 1, 2, 3 of the solar cell are located on a transparent substrate 10 made of PET with a layer thickness of 12 microns and are protected with an encapsulation layer 11 made of a tantalum-coated PET film from harmful environmental influences. The light incidence occurs in the first solar cell according to FIG. 1 from the side of the transparent substrate 10 and the second electrode layer 3. The light penetrates through the substrate 10 and the second electrode layer 3 and reaches the active layer comprising the semiconductor layer 2. At the light-scattering particles 4 a Light scattered and optimally distributed in the semiconductor layer 2.

FIG. 2 shows a second solar cell in cross section, which is constructed similarly to the first solar cell according to FIG. 1 (identical reference symbols designate the same components) and a first electrode layer 1 made of gold, a photovoltaically active layer containing at least one organic functional layer in the form of an organic semiconductor layer 2 a composite of P3HT and PCBM in a ratio of 1: 1, and a second electrode layer 3 of indium tin oxide (ITO). Here, however, the semiconductor layer 2 contains no light-scattering particles, but an organic functional layer 5b made of a transparent lacquer is provided on the second electrode layer 3, which contains light-scattering particles 4a.

The organic functional layer 5b has 1% by weight of light-scattering particles 4a which have a maximum diameter of 100 nm and which are uniformly distributed in the organic functional layer 5b. The incidence of light takes place in the second solar cell according to Figure 2 also from The light penetrates the substrate 10, the organic functional layer 5b and the second electrode layer 3 and reaches the active layer comprising the semiconductor layer 2. The light is scattered and optimally distributed at the light-scattering particles 4a in the organic functional layer 5b.

FIG. 3 shows a third solar cell in cross section, which is constructed similarly to the second solar cell according to FIG. 2 (identical reference symbols designate the same components) and an opaque first electrode layer 1 made of gold, a photovoltaically active layer containing at least one organic

Functional layer in the form of a semiconductor layer 2 made of a composite of P3HT and PCBM in the ratio 1: 1, and a transparent second electrode layer 3 of indium tin oxide (ITO). An organic functional layer 5 made of a transparent lacquer is provided on the side of the substrate 10 facing away from the second electrode layer 3, which contains light-scattering particles 4a. The organic functional layer 5 has 1% by weight of light-scattering particles 4 a which have a maximum diameter of 100 nm and which are uniformly distributed in the organic functional layer 5. The light is also incident on the side of the transparent substrate 10 in the case of the third solar cell according to FIG. 3. The light penetrates the organic functional layer 5, resulting in optimum scattering on the light-scattering particles 4a, the substrate 10 and the second electrode layer 3 and reaches the active layer comprising the semiconductor layer 2.

FIG. 4 shows a fourth solar cell in cross section, which is constructed similarly to the second solar cell according to FIG. 2 (identical reference symbols designate the same components) and a first electrode layer 1 made of gold, a photovoltaically active layer containing at least one organic layer Functional layer in the form of an organic semiconductor layer 2 made of a composite of P3HT and PCBM in the ratio 1: 1, and a transparent second electrode layer 3 of indium tin oxide (ITO). However, the first electrode layer 1 is designed to be transparent in a layer thickness of 8 nm. An organic functional layer 5a made of a transparent lacquer is provided on the first electrode layer 1, which contains light-scattering particles 4a. The organic functional layer 5a has a layer thickness of 100 nm and contains 1% by weight of light-scattering particles 4a which have a maximum diameter of 100 nm and are uniformly distributed in the organic functional layer 5a. 4, the light penetrates the substrate 10, the second electrode layer 3 and reaches the active layer comprising the semiconductor layer 2 pass through to the first electrode layer 1, are substantially transmitted by this, so that the remaining light is scattered at the light-scattering particles 4a of the organic functional layer 5a and thrown back into the semiconductor layer 2, so that a further utilization of these light components can take place.

FIG. 5 shows a fifth solar cell in cross section, which is constructed similarly to the third solar cell according to FIG. 3 (identical reference symbols designate identical components) and an opaque first electrode layer 1 made of gold, a photovoltaically active layer containing at least one organic functional layer in the form of an organic semiconductor layer 2 from a composite of P3HT and PCBM in a ratio of 1: 1, as well as a transparent second electrode layer 3 made of indium tin oxide (ITO). On the side of the transparent substrate 10 facing away from the second electrode layer 3, there are three functional layers 6, 7, 8 with different refractive indices arranged. An inorganic functional layer 6 is formed here from magnesium fluoride and has a refractive index ni which lies between the refractive index ΠL of air and the refractive index ΠE2 of the second electrode layer 3. An organic functional layer 7 is formed from a polymer and has a refractive index n ₂ which lies between the refractive index ni of the functional layer 6 and the refractive index ΠE2 of the second electrode layer 3. Another organic functional layer 8 is formed from a further polymer and has a refractive index n ₃ , which lies between the refractive index n _{2 of} the functional layer 7 and the refractive index ΠE2 of the second electrode layer 3. After the substrate 10 made of PET is also arranged in front of the second electrode layer 3, its refractive index n _s of approximately 1.6 is selected such that it lies between the refractive index n _{3 of} the functional layer 8 and the refractive index n _{E2 of} the second electrode layer 3 , The following relationship therefore applies to the layer stack of layers 6, 7, 8, 10, 3: n _L <ni <n ₂ <n ₃ <n _s <

The light incidence occurs in the fifth solar cell according to FIG. 5 from the side of the transparent substrate 10. The light penetrates the three functional layers 6, 7, 8 with different refractive indices, the substrate 10, the second electrode layer 3 and arrives at the photovoltaically active layer comprising the semiconductor layer 2 If the light were to impinge directly on the surface of the substrate 10, this would lead to portions of the light being reflected on the surface of the substrate 10 and not reaching the semiconductor layer 2. The functional layers 6, 7, 8 largely prevent such a reflection, so that far more light can now reach the semiconductor layer 2 and an exploitation of the otherwise reflected light components can take place. FIG. 6 shows a sixth solar cell in cross section, which has a construction combined according to FIG. 1 and FIG. According to the fifth solar cell, see FIG. 5, three functional layers 6, 7, 8 with different refractive indices are arranged on the transparent substrate 10, however, according to the first solar cell, see FIG. 1, a semiconductor layer 2 comprising refractive particles 4a is formed.

FIG. 7 shows a seventh solar cell in cross section, which has a transparent first electrode layer 1 made of gold, an active layer comprising at least one organic functional layer in the form of a photovoltaically active organic semiconductor layer 2 of a composite of P3HT and PCBM in a ratio of 1: 1, and a transparent second electrode layer 3 of indium tin oxide (ITO) has. Between the encapsulation layer 11 and the first electrode layer 1 is an organic functional layer 5a containing first refractive, fluorescent particles 4a, which are uniformly distributed.

The semiconductor layer 2 has, to the first light-scattering, fluorescent particles 4 a different, spherical second light-scattering phosphorescent particles 4 c, which have a maximum diameter of 15 nm and which are distributed unevenly in the semiconductor layer 2 or present only in their edge regions. Between the transparent second electrode layer 3 and the transparent substrate 10 there is a further organic functional layer 5b containing first light-scattering particles 4a as well as different third light-diffusing particles 4b. In this case, the first light-scattering particles 4a are arranged in a region above the second electrode layer 3, while the third light-scattering particles 4b are located only in an edge region of the further functional layer 5b, which is located next to the second electrode layer 3. Furthermore, the Concentration of the third particles 4b in the edge region selected to be greater than the concentration of the first particles 4a in the region above the second electrode layer 3. The third particles 4b are platelet-shaped and arranged in parallel spatial orientation.

The light incidence occurs in the seventh solar cell according to FIG. 7 from the side of the transparent substrate 10 and the second electrode layer 3. The light penetrates the substrate 10, the further organic functional layer 5 b, the second electrode layer 3 and reaches the active layer comprising the semiconductor layer 2 the first light-scattering particles 4a of the further organic functional layer 5b, the light is scattered and optimally distributed. At the third light-scattering particles 4b of the further organic functional layer 5b, the light is deflected in the direction of the semiconductor layer 2. The second light-diffusing particles 4c in the edge region of the semiconductor layer 2 prevent a coupling out of the light from the

Semiconductor layer 2 in this area. The first light-diffusing particles 4 a in the organic functional layer 5 a scatter light passing through the first electrode layer 1 and throw it back toward the semiconductor layer 2.

FIG. 8 shows an eighth solar cell in cross section, which has a similar construction to the seventh solar cell according to FIG. 7. Here, however, the organic functional layer 5 a has been omitted and instead a functional layer 6 with a defined refractive index n _1? which is between the refractive index ΠL of air and the refractive index n _{s of} the substrate 10, and wherein the refractive index n _{s of} the substrate 10 is between the refractive index of the functional layer 6 and the refractive index ng _{2 of} the second electrode layer 3, disposed on the substrate 10. Figure 9 shows a ninth solar cell in cross-section, which has a similar structure, as the seventh solar cell according to Figure 7. Here, the organic functional layer has also been omitted 5a and instead a transparent functional layer 7 of magnesium fluoride with a defined refractive index n ₂ arranged between the refractive index n _L of air and the refractive index n _{s of} the substrate 10 of PET having a refractive index n _s of about 1, 6, which in turn is greater than the refractive index n _{E2 of} the second electrode layer 3. Between the substrate 10 and the functional layer 7 with the refractive index n ₂ is a transparent organic functional layer 9 in the form of a

Lacquer layer arranged, which is stamped on its side facing away from the substrate 10 with a second relief structure 9a in the form of a sawtooth structure. The second structure Re 9a is located in the edge region above and next to the active layer of the solar cell, so that light from this area can be deflected to the semiconductor layer 2.

It is obvious to a person skilled in the art that, using a wide variety of functional layers comprising light-scattering and / or luminescent particles and / or having defined refractive indices or at least one first relief structure, optionally also second

Relief structures, in a simple manner, the most varied variations of an efficient single junction or multi-junction solar cell can be formed, which are not explicitly shown in Figures 1 to 9.

Claims

claims

1. Organic solar cell, comprising at least three functional layers, wherein a first functional layer in the form of at least one electrically conductive first electrode layer (1), a second functional layer in the form of at least one organic semiconductor layer (2) and a third functional layer in the form of at least one translucent, in particular transparent , electrically conductive second electrode layer (3) is formed, wherein the at least one organic semiconductor layer (2) is photovoltaic active and between the at least one first electrode layer (1) and the at least one second electrode layer (3) is arranged, characterized in that the solar cell at least one of the efficiency of the solar cell increasing translucent, in particular transparent, organic functional layer (2, 5, 5a, 5b), the light scattering and / or luminescent particles (4a, 4b, 4c), which perpendicular to at least one Hal Conductive layer (2) seen overlapping with and / or arranged next to this, and / or at least one of the efficiency of the solar cell enhancing translucent, especially transparent, organic or inorganic

Functional layer (6, 7, 8) having a refractive index lying between the refractive index of air and the refractive index of the second electrode layer (3), wherein the at least one organic or inorganic functional layer (6, 7, 8) on the, the at least one Semiconductor layer facing away from the second electrode layer (3) is arranged, and / or at least one of the efficiency of the solar cell enhancing translucent, especially transparent, organic or inorganic

Functional layer, wherein the at least one organic or inorganic functional layer on the, at least one semiconductor layer (2) facing away from the second electrode layer (3) is arranged and at its the at least one semiconductor layer (2) facing away from the interface at least a first Re running structure which reduces a reflection of incident light into the solar cell at this functional layer compared to a reflection at such a functional layer with a planar interface.

2. Solar cell according to claim 1, characterized in that the at least one first relief structure, the reflection at the

Reduced interface by at least 20%.

3. Solar cell according to one of claims 1 or 2, characterized in that the solar cell has at least two, the efficiency of the solar cell increasing functional layers (2, 5, 5a, 5b, 6, 7, 8).

4. Solar cell according to one of claims 1 to 3, characterized in that the first electrode layer (1) transparent, in particular transparent, is formed.

5. Solar cell according to one of claims 1 to 4, characterized in that the at least one first relief structure is formed in the form of a matt structure.

6. Solar cell according to one of claims 1 to 4, characterized in that the at least one first relief structure in the form of a periodic structure, in particular as Blazegitter, line structure, cross lattice, linear or crossed sine, circular grating, lens structure or combinations of at least two of these structures is.

7. Solar cell according to one of claims 1 to 6, characterized in that the at least one first relief structure a Tϊefen-to-width

Ratio of> 0.3, in particular of> 1.

8. Solar cell according to one of claims 6 or 7, characterized in that the at least one first relief structure a Spatialfrequenz in

Range of 300 to 4000 lines / mm.

9. Solar cell according to one of claims 1 to 8, characterized in that the solar cell has at least one functional layer (9) having at least one diffractive and / or refractive second relief structure (9a), which is perpendicular to the plane of the semiconductor layer (2) overlapping with and / or next to the semiconductor layer (2), in particular on the, the semiconductor layer (2) facing away from the first side Electrode layer (1) is arranged.

10. Solar cell according to claim 6, characterized in that the at least one second relief structure (9a) in the form of a

Matt structure, a linear or crossed linear grating, an asymmetric relief structure, a diffractive or refractive lens structure, or a combination of at least two such structures is formed.

11. Solar cell according to one of claims 1 to 10, characterized in that the light-scattering and / or luminescent particles (4a, 4b, 4c) have a maximum particle size in the range of 5 nm to 10 microns.

12. Solar cell according to one of claims 1 to 11, characterized in that the light-scattering particles (4a, 4b, 4c) are transparent or semitransparent, in particular of an oxide, a sulfide, a carbide or a nitride.

13. Solar cell according to one of claims 1 to 12, characterized in that the light-scattering and / or luminescent particles (4a, 4b, 4c) have a rod, platelet or spherical shape.

14. Solar cell according to claim 13, characterized in that the at least one organic functional layer (5b) is a mixture from light-scattering particles (4a, 4b) of different shape.

15. Solar cell according to one of claims 1 to 14, characterized in that the light-scattering and / or luminescent particles (4a, 4b, 4c) in

Range of 0.1 to 10 wt .-% in at least one organic functional layer (2, 5, 5a, 5b) are included.

16. Solar cell according to one of claims 1 to 15, characterized in that the light-scattering and / or luminescent particles (4a, 4b, .4c) are selectively formed for a wavelength of the electromagnetic spectrum.

17. Solar cell according to claim 16, characterized in that the at least one organic functional layer (2, 5, 5a, 5b) has light-scattering and / or luminescent particles (4a, 4b, 4c) which are selective for at least two different wavelengths of the electromagnetic spectrum are formed.

18. Solar cell according to one of claims 1 to 17, characterized in that the light-scattering particles (4a, 4b, 4c) are formed fluorescent or phosphorescent, and convert a wavelength of the electromagnetic spectrum into a different wavelength.

19. Solar cell according to claim 18, characterized in that the at least one organic functional layer (2, 5, 5a, 5b) has light-scattering particles (4a, 4b, 4c) which have different fluorescent or phosphorescent properties.

20. Solar cell according to one of claims 1 to 19, characterized in that the light-scattering particles (4a) are uniformly distributed in the at least one organic functional layer.

21. Solar cell according to one of claims 1 to 19, characterized in that the light-scattering particles (4c) unevenly over an area and / or a layer thickness of the at least one organic

Function layer (2, 5b) are distributed.

22. Solar cell according to one of claims 1 to 21, characterized in that the at least one organic functional layer (2) comprising the light-scattering and / or luminescent particles (4a, 4c) of the at least one semiconductor layer (2).

23. Solar cell according to one of claims 1 to 21, characterized in that the at least one organic functional layer (5b) containing the light-scattering and / or luminescent particles (4a, 4b) on the at least one semiconductor layer (2) facing away from the second Electrode layer (3) is arranged.

24. Solar cell according to claim 4 in conjunction with one of claims 5 to 21, characterized in that the at least one organic functional layer (5a) containing the light-scattering and / or luminescent particles (4a) on the, the at least one semiconductor layer (2) facing away Side of the light-transmissive first electrode layer (1) is arranged.

25. Solar cell according to claim 4 in conjunction with one of claims 5 to 24, characterized in that the at least one organic or inorganic functional layer (6, 7, 8) having a refractive index which is between the refractive index of the air and the refractive index of the transparent first electrode layer (1), on the at least one

Semiconductor layer (2) facing away from the first electrode layer (1) is arranged.

26. Solar cell according to one of claims 1 to 25, characterized in that at least two transparent functional layers (6, 7, 8), each having a refractive index lying between the refractive index of air and the refractive index of the second electrode layer (3), are present, wherein the at least two transparent functional layers (6, 7, 8) have a different refractive index and are stacked on the second electrode layer (3) stacked such that the refractive index of the at least two transparent functional layers (6, 7, 8) starting from the second Electrode layer (3) decreases.

27. Solar cell according to one of claims 1 to 26, characterized in that the solar cell further comprises a translucent, in particular transparent substrate (10), in particular made of PET, PEN, PVC or glass.

28. Solar cell according to claim 27, characterized in that the substrate (10) has a thickness in the range of 6 μm to 1 mm, in particular in the range of 12 μm to 150 μm.

29. Solar cell according to one of claims 1 to 28, characterized in that the at least one semiconductor layer (2) in a layer thickness in the range of 50 to 300 nm, in particular in the range of 100 to 250 nm, is formed.

30. A solar cell according to any one of claims 1 to 29, characterized in that the at least one organic semiconductor layer (2) is formed by at least two organic semiconductor materials by a composite of at least one electron donor and at least one electron acceptor in a ratio of 2: 0.5 to 0.5: 2, in particular in the ratio of 1: 0.9 to 1: 1, is formed.

31. Solar cell according to claim 30, characterized in that the at least one electron donor is formed from a polythiophene and the at least one electron acceptor is formed from a fullerene derivative.

32. Solar cell according to claim 31, characterized in that the at least one electron donor of poly (3-hexylthiophene)

(P3HT) and the at least one electron acceptor is formed from PCBM.

33. Solar cell according to one of claims 1 to 32, characterized in that the solar cell in this order optionally a transparent substrate (10), at least one second electrode layer (3), at least one organic semiconductor layer (2), at least one, optionally translucent, first electrode layer (1) and an encapsulation layer (11).

34. Solar cell according to claim 33, characterized in that the at least one organic semiconductor layer (2) comprises the light-scattering and / or luminescent particles (4a, 4b, 4c).

35. Solar cell according to claim 33, characterized in that the at least one transparent organic functional layer (5b) containing the light-scattering and / or luminescent particles (4a, 4b) between the optionally present substrate (10) and the at least a second electrode layer (3) is arranged.

36. Solar cell according to claim 33, characterized in that the transparent substrate (10) is present and the at least one transparent organic functional layer (5) containing the light-scattering and / or luminescent particles (4a) on the, the second electrode layer (3) facing away Side of the substrate (10) is arranged.

37. Solar cell according to claim 33, characterized in that the at least one transparent organic functional layer (5a) containing the light-scattering and / or luminescent particles (4a) is arranged between the at least one light-transmitting first electrode layer (1) and the encapsulation layer (11).

38. Solar cell according to one of claims 33 to 37, characterized in that the transparent substrate (10) is present and at least three transparent organic functional layers (6, 7, 8) with different

Refractive index on the, the second electrode layer (3) facing away from the substrate (10) are arranged.

39. Solar cell according to one of claims 33 to 38, characterized in that the transparent substrate (10) is present and at least one transparent organic functional layer (9), the first and / or second relief structures (9a), on the second Electrode layer (3) remote side of the substrate (10) is arranged.

40. Solar cell according to one of claims 33 to 39, characterized in that at least one reflective functional layer having the at least one second relief structure, on the at least one semiconductor layer (2) facing away from the light-transmitting first electrode layer (1) and directly to the encapsulation layer (11) is disposed adjacent.