WO2009146845A2

WO2009146845A2 - Solar cell having light trap and solar module

Info

Publication number: WO2009146845A2
Application number: PCT/EP2009/003833
Authority: WO
Inventors: Karl-Heinz Stegemann; Steffen Krug
Original assignee: Signet Solar Gmbh; Nanooptics Gmbh
Priority date: 2008-06-05
Filing date: 2009-05-28
Publication date: 2009-12-10
Also published as: WO2009146845A3; EP2301082A2; DE102008026760A1

Abstract

One embodiment of the invention discloses a solar cell (100) having a light trap (104). The solar cell (100) comprises a photovoltaic element (101) having a front side (102) and an opposite rear side (103). The holographic element (104) is disposed on the front side of the photovoltaic element (101), wherein it allows at least part of the incident light (105) to pass and thus deflects said light into the photovoltaic element (101), without thereby concentrating said light, so that said light experiences an increase in optical path length between the front side (102) and rear side (103).

Description

Solar cell with light trap and solar module

description

The application relates to a device for photovoltaic conversion, such as a solar cell or solar cells connected to a solar module, which have a light trap.

Increasing the efficiency of solar cells is a continuing development goal of the photovoltaic industry. For this purpose, a reduction of the loss mechanisms in the solar cell is sought. Optical losses are due, for example, to the fact that light incident on the solar cell is reflected or the light passes through the photovoltaically active layers and re-flows the solar cell without being absorbed. This light is lost for the photovoltaic conversion of light into electricity.

Light traps are used to generate electron-hole pairs in the absorber layer suitable light, for. B. light with a photon energy above the band gap of the absorber layer to absorb as completely as possible in the solar cell and thus to reduce optical losses. In contrast to light concentrators, which focus light from a larger light incident surface onto a smaller surface of a solar cell, e.g. B. light collecting optics such as lenses, light traps direct the light incident on a solar cell at appropriate angles so in the photovoltaic active layers, without collecting it and concentrate that the path length of light within the solar cell longer and the absorption probability higher is as in omitting the light traps.

For monocrystalline silicon solar cells, for example, light traps can be texturized to the light incidence side produce directed surface of the monocrystalline silicon. An example of a textured surface are pyramidal structures that are formed utilizing a silicon etch rate dependent on the crystal direction. The texture of the surface causes less light to be reflected, and the light entering the cell is deflected such that, on average, it is path-extended.

Light-traps formed by texture for single-crystalline silicon solar cells typically have feature sizes that are substantially smaller than the layer thickness of the photovoltaically active layer. In the case of thin-film solar cells with layer thicknesses of the absorber layers in the order of magnitude of a few μm, the structure size of the texture would be in the region of the layer thickness of the photovoltaically active layer. The formation of a defined

Surface texture for non-monocrystalline materials appears expensive, eg. B. with regard to possible damage to the

Cell structure or the process control. Texturing takes place here, for example, by texturing a glass surface or a transparent, conductive electrode layer.

It is an object of the invention to provide a universally applicable and cost-effective light trap and a solar cell or connected to a module solar cells with such a light trap.

The object is achieved by the teaching of claims 1, 7 and 18. Advantageous embodiments are the subject of the dependent claims.

Fig. IA shows a schematic simplification a

Cross section through a solar cell with a holographic element on the front. Fig. IB shows a schematic simplification a

Cross section through a solar cell with a holographic element on the back.

Fig. 2A shows a schematic simplification of a

Cross section through a solar cell with a transmissive holographic element at the front and the light deflection caused by the holographic element.

Fig. 2B shows a schematic simplification a

Cross-section through a solar cell with a transmissive holographic element integrated into a front-side electrode and that caused by the holographic element

Light deflection.

Fig. 2C shows a schematic simplification

Cross section through a solar cell with a transmissive holographic element at the

Front as well as caused by the holographic element light deflection.

2D shows, in a schematic simplification, a cross section through a solar cell with a reflective holographic element on the rear side and the light deflection effected by the holographic element.

Fig. 3 shows a schematic simplification a

Cross section through a reflective holographic element. Fig. 4 shows a schematic simplification a

Cross section through a transmissive holographic element.

Fig. 5 shows a schematic simplification a

Cross section through a solar module with a transmissive holographic element.

FIG. 6 shows a schematic representation of an exemplary transmission behavior of a holographic element at normal incidence of light as a function of a light deflection angle α.

7A shows a schematic representation of an exemplary spectral transmission behavior of a first hologram layer of a holographic element in the case of normal incidence of light.

FIG. 7B shows a schematic representation of an exemplary spectral transmission behavior of a first hologram layer of the holographic element when light is incident at an angle γ to the normal.

FIG. 7C shows a schematic representation of an exemplary spectral transmission behavior of a first hologram layer of the holographic element when light is incident at an angle δ to the normal.

7D shows a schematic representation of an exemplary spectral transmission behavior of a second hologram layer of the holographic element in the case of normal incidence of light. Fig. 7E shows a schematic representation of an exemplary spectral transmission behavior of a second hologram layer of the holographic element at light incidence at an angle γ to

Normal.

7F shows a schematic representation of an exemplary spectral transmission behavior of a second hologram position of the holographic

Elements at light incidence at an angle δ to the normal.

7G shows a schematic representation of an exemplary spectral transmission behavior of a third hologram layer of the holographic element in the case of normal incidence of light.

7H shows a schematic representation of an exemplary spectral transmission behavior of a third hologram layer of the holographic element when light is incident at an angle γ to the normal.

71 shows a schematic illustration of an exemplary spectral transmission behavior of a third hologram position of the holographic element when light is incident at an angle δ to the normal.

FIG. 7J shows a schematic representation of an exemplary spectral transmission behavior of the holographic element with superimposed first, second and third hologram position under normal incidence of light. The embodiments of the invention described below, as well as their features, can be combined with each other as desired, that is, there is no restriction that certain features that are described in connection with one embodiment could not be combined with features of another embodiment.

Fig. IA shows in schematic simplification a cross section through a solar cell with a holographic element on the front side.

The solar cell 100 comprises a photovoltaic element 101 having a front side 102 formed as a light entry surface and a rear side 103 opposite thereto. On the front side 102, a holographic element 104 acting as a light trap is arranged, which transmits at least part of the incident light 105 and thus into the photovoltaic Element 101 deflects without concentrating it undergoes an optical path extension WV between front 102 and back 103. For example, the back surface 103 of the photovoltaic element 101 may be reflective, such as by providing a reflective metal layer on the back surface 103, e.g. made of silver (Ag).

The optical path extension WV results here as an optical path difference compared to the case in which the light 105 passes through the photovoltaic element 101 without light trap 104 from the front side 102 to the rear side 103. In the schematic representation of FIG. 1A, the light 105 is incident perpendicularly on the front side 102 and is directed via the holographic element 104 at an angle α into the photovoltaic element 101. The optical path extension WV between front side 102 and rear side 103 taking into account a thickness d of the photovoltaic element 101, WV = d ([cosα] '- I). A

Deflection is not limited to perpendicularly incident light, but may be achieved for an angular range, which in turn may depend on the thickness of the holographic planes in the holographic element 104. If the holographic planes in the holographic element 104 have a total thickness in the range of a few 10 μm, e.g. 30μm to 50μm such as 40μm, a deflection in the angular range of several degrees, e.g. 1 ° to 4 ° can be achieved. If the thickness of the holographic planes in the holographic element 104 is less than 10 μm, then, for example, angular ranges of the deflection of about 5 ° to 20 ° or even 10 ° to 15 ° can be achieved.

The angular range can be further increased by stacking several hologram planes that are tuned to different wavelength ranges. Hereby, a changing angle of incidence of light, e.g. a wandering position of the sun can be accommodated by causing a desired light deflection of different hologram layers in different light incident angle ranges.

Possible material systems for absorber layers of the photovoltaic element are chalcopyrites such as CuIn _x Ga ₍ 1.x ₎ Se ₂ (CIGS) and derivatives thereof, such as CIGSSe, III-V

Semiconductor materials such as GaAs, silicon in various crystal states such as monocrystalline silicon, amorphous silicon (a-Si or a-Si.H), multicrystalline silicon (mc-Si), microcrystalline silicon (μc-Si), polycrystalline silicon (poly-Si), nanocrystalline silicon (nc-Si), CdTe, or organic semiconductors based on z. B. conjugated polymers.

The solar cell 100 may be on a single charge separating

Based transition, z. A pn junction or a pin junction, or on multiple charge-sharing junctions (Multi-junction solar cells). Examples of such multi-junction solar cells are tandem solar cells made of material systems such. As microcrystalline silicon / amorphous silicon or InGaP / GaAs, or triple junction solar cells such. B. a-Si: H / μc-Si: H / μc-Si: H, InGaP / GaAs / Ge or a-Si: H / aSiGe: H.

The holographic element 104 acting as a light trap merely redirects the incident light 105 without concentrating it. Thus, the holographic element 104 differs from light concentrators in that it does not collect incident light and thus does not concentrate light incident on a first surface onto a surface of a photovoltaic layer that is smaller than the first surface.

The light deflection shown in FIG. 1A is a simplified illustration. So the diversion, d. H. The angle α, for example, be location-dependent or wavelength-dependent, with various techniques such as spectral multiplexing or spatial multiplexing may come into play. For example, spatial multiplexing can counteract optical losses caused, for example, by the fact that light deflected by the holographic element 104 exits the photovoltaic device 100 again after the reflection on the rear side 103 through the holographic element 104. Also, a reflective holographic element may be positioned on the back surface which reflects the light at a suitable angle to the front surface so that it does not exit through the holographic element 104.

For example, between the holographic element 104 and a photovoltaically active structure within the photovoltaic element 101, for. B. pn absorber layers, an anti-reflection structure may be arranged. Such an anti-reflection structure reduces, for example, starting from the medium surrounding the solar cell 100, for. Air, Refractive index jumps in the transition of various media in the direction of the photovoltaically active layer. Reduced refractive index jumps reduce reflection losses and couple more light into the photovoltaic element 101.

The antireflection structure may for example consist of a single layer or of a layer stack. Layers of the antireflection structure have the highest possible transmissivity and are arranged approximately in such a way that the refractive indices increase in the direction of the photovoltaically active layer. The antireflection structure may, for example, comprise or consist of at least one of the materials silicon oxynitride and silicon nitride.

The holographic element 104 may be incorporated in a conductive and translucent front-side electrode layer. The front-side electrode layer derives the charge carriers separated in the photovoltaically active layers, ie the photovoltaically generated current, at the front side of the cell. Examples of the front-side electrode layer are layers of conductive polymers, e.g. Polymers with extended n-electron system such as polyacetylene, poly (para-phenylene), polythiophene or polypyrrole as well as conductive oxides such as In ₂ O ₃ : SnO ₂ (ITO), ZnO = Al, ZnO: B and SnO ₂ : F.

In the transmissive holographic element 104 shown in FIG. 1A, for example, one or more hologram layers (n) for reflection of heat radiation in the infrared region may be formed (not shown). The hologram layers may be the layers closest to the light incidence side. The holographic element 104 can then be used as a light trap to increase the light absorption in the photovoltaically active layers of the photovoltaic element 101 and additionally as a heat shield against heating of the photovoltaic element 101 by infrared radiation. Such a warming of the photovoltaic element 101 may lead to a decrease in the open-circuit voltage as well as to a slight increase in the short-circuit current and overall reduce the electric power provided by the solar cell.

The illustrated in Fig. IB solar cell 1 10 has a photovoltaic element 1 1 1 with a designed as a light entrance surface front side 1 12 and one of these opposite back 1 13. On the back 1 13 of the photovoltaic element 1 1 1, a holographic element 1 14 is arranged, which acts as a light trap is tuned to the light absorption characteristic of the photovoltaic element 1 1 1 and at least a portion of the light transmitted through the photovoltaic element light 1 15 by reflection so deflects back into the photovoltaic element 1 1 1, without concentrating it, that it undergoes an optical path extension between the back of 1 13 and front 1 12.

The features and properties listed above for the photovoltaic element 101 and the holographic element 104 can be transferred in a corresponding manner to the solar cell 110 shown in FIG. 1B and to the embodiments shown in the further illustrations.

The angle α, which characterizes the angle of reflection for light incident perpendicularly on the holographic element 14, can be selected, for example, such that this light is totally reflected at the front side 12 of the photovoltaic element 11, and thus again into the photovoltaic element 1 1 1 is deflected, whereby the light absorption within the photovoltaic element 1 1 1 is further increased. In order to prevent that on the front side 1 12 totally reflected light on re-hitting the holographic element 1 14 by reflection from the photovoltaic element in the same way (ie, at the same angle) exits as it has occurred, the holographic element 1 14 may have a spatial multiplexing and thus have different diffraction vectors in different areas.

The holographic elements 104, 14 can be constructed such that the light is deflected on the entire light incident side. In this case, the hologram layers are formed over the entire surface and the holographic element has, for example, no areas in which incident light having a wavelength whose absorption length in the absorber corresponds to a multiple of the thickness of the absorber is transmitted without being deflected.

The holographic element 104, 14 has at least one hologram layer. The at least one hologram layer can be formed within a polymer layer, for example. The at least one hologram layer can be formed approximately with the aid of UV laser irradiation, for. In chromate gelatin. The polymer containing the at least one hologram layer can be a conductive polymer, so that the polymer, in addition to its function as a light trap, can also contribute to the transport of electricity, eg. In the form of a front side or rear side electrode of the photovoltaic element. For example, the polymer is formed as a polymer film or part thereof. Likewise, the polymer can be arranged on a transparent support, for. B. on a glass or a transparent plastic. The at least one hologram layer of the holographic element is constructed, for example, to provide at least 80% of the incident light at an angle α for a wavelength in the visible part of the spectrum at which an absorption length within the photovoltaic element is greater than the thickness of the photovoltaic element > 50 °, wherein the angle α describes the deflection angle relative to a normal of the light incident surface. The at least one hologram layer has, for example a sinoidal refractive index modulation and thereby differs from a conventional diffraction grating.

A deflection of the light in the holographic elements 104, 1 14 can be optimized, for example, to a wavelength range in which an optical absorption length within the photovoltaically active layer (s) (absorber layer (s)) of the photovoltaic elements 101, 1 1 1 is greater as the thickness of this layer (s). Thus, the hologram layers can be spectrally optimized. In particular for wavelengths whose optical absorption length is greater than the thickness of the absorber layer (s), a deflection of the light by the holographic elements leads to an increase in the short-circuit current contribution attributable to this spectral range.

The photovoltaic elements 101, 1 1 1 can be, for example, multi-junction solar cells with a certain number of Ia- tion separating junctions, z. B. Tandem cells with two charge-separating junctions or triple cells with three Ia- separating fusions, and a deflection of the light in the holographic element can be optimized for at least one of the number of corresponding number of wavelength ranges so that for each of these wavelength ranges one high light absorption takes place in a different cell of the multi-junction solar cell. For example, the holographic elements 104, 14 can be optimized for different wavelength ranges whose energy equivalents are in relation to the energy band gap of the various absorber layers of the multi-junction solar cell. For example, light having wavelengths at which absorption in a corresponding absorber layer is just beginning to be absorbed (ie, photon energy near the bandgap) is poorly absorbed. Here, light traps are particularly suitable for achieving a higher absorption in the absorber layers by way of light deflection. Another parameter for determining the wavelengths for which a spectral optimization of the holographic elements 104, 1 14 takes place, for example, the spectral energy distribution of the solar spectrum may be, for. B. AM 1, 5 (Air Mass 1, 5).

The photovoltaic elements 101, 11 may, for example, comprise one or more thin-film solar cell (s), e.g. a-Si: H, a-Si: H / μc-Si: H or a-Si: H / μc-Si: H / / μc-Si: H solar cells.

In the schematic cross-sectional view of Fig. 2A, a solar cell 201 is shown, in which on a transparent substrate 206, z. As glass or transparent plastic, a transparent front side electrode 207 is applied. The transparent front side electrode 207 can, for example, a transparent conductive oxide such as In ₂ O ₃ ISNO ₂ (ITO), ZnO.Al, ZnOrB or SnO ₂ = F, or a transparent conductive polymer. On the front side electrode 207, one or more photovoltaically active layers (absorber layer (s)) 208 are arranged. In the absorber layer 208, electron-hole pairs are generated by light absorption, which are dissipated via the charge-separating transition of the absorber layer 208 to the front-side electrode 207 or to a rear-side electrode 209 positioned at the absorber layer 208 and opposite the front-side electrode. The backside electrode 209 may be used as a backside reflector which reflects incident light back into the absorber layer 208.

The solar cell 201 may include other layers not shown in FIG. 2A, e.g. B. Passivierungsschichten to reduce the O- berflächenrekombination of optically generated minority charge carriers or anti-reflection layers to reduce reflection losses of the incident light. On the side facing away from the front side electrode 207 of the transparent substrate 206, a holographic element 204 acting as a light trap is arranged. As already explained in connection with the embodiments shown in FIGS. 1A and 1B, the holographic For example, based on the light absorption characteristic and the thickness of the absorber layer (s) 208, element 204, at least part of the incident light 205, can be converted into the absorber layer (s) 208 without concentrating on an optical path extension between one optical path Front 202 of the absorber layer (s) 208 and a rear 203 of the absorber layer (s) 208 experiences. The light deflections shown in Fig. 2A as well as in Figs. 2B-2D are shown only schematically.

The solar cell structure shown in FIG. 2A may, for example, be a solar cell with a single absorber layer 208 of amorphous silicon or a multi-junction solar cell with absorber layers of microcrystalline silicon and amorphous silicon.

FIG. 2B is a schematic cross-sectional view of a solar cell 221 having a holographic element 224 which also serves as a front-side electrode and is deposited on a transparent substrate 226. On the holographic element 224 one or more photovoltaically active layers 228 are arranged opposite to the substrate 226. An interface between the photovoltaic active layer 228 and the holographic element 224 defines a front side 222, ie the side from which the light penetrates into the photovoltaically active layers 228, ie the absorber layer (s) 228. On a rear side 223 of the absorber layer 228, a rear side electrode 229 is arranged. Incident light 225 is redirected to absorber layer 228 in holographic element 224, as discussed above, without being focused to undergo an optical path extension between front side 222 and back side 223. The backside electrode 229 may be reflective. The construction shown in FIG. 2B is suitable, for example, for solar cells made of amorphous silicon or else tandem solar cells made of amorphous and microcrystalline silicon. FIG. 2C is a schematic cross-sectional view of a solar cell 241 having a reflective backside electrode 249 disposed on a carrier substrate 246. Since the light does not enter through the carrier substrate 246, it may be permeable or non-transmissive to light. On the backside electrode 249, an absorber layer 248 is disposed opposite to the carrier substrate 246, and a front-side electrode 247 is disposed on the absorber layer 248 opposite to the backside electrode 249. On the front side electrode 247, ie on a front side 242 of the absorber layer 248, a holographic element 244 is arranged. The holographic element 244 redirects incident light 245 into the absorber layer 248, thereby increasing the light absorption and the photocurrent within the absorber layer 248.

The layer structure shown in FIG. 2C is suitable, for example, for solar cells in whose production process a backside electrode is first applied to a carrier substrate, as for example in solar cells such as a-Si: H on metal or polymer film or in solar cells with chalcopyrite absorber layers Case is, for. B. CIS solar cells and their derivatives.

FIG. 2D is a schematic cross-sectional view of a solar cell 261 with a translucent substrate 266 of e.g. As glass or transparent plastic on which a transparent front side electrode 267 is applied. The front-side transparent electrode 267 may be, for example, a transparent conductive oxide or a transparent conductive polymer. Opposite the substrate 266, one or more absorber layers 268 are disposed on the front side electrode 267. Opposite the front-side electrode 267, a holographic element 264 is arranged on the absorber layer 268, which also serves as a back-side electrode. The holographic element 264 is thus disposed on a backside 263 of the absorber layer 268 and, unlike the holographic ones shown in FIGS. 2A-2C, causes Elements 204, 224, 244, a light deflection with simultaneous reflection.

The structure shown in FIG. 2D may be, for example, an amorphous silicon solar cell or else a tandem solar cell made of microcrystalline silicon and amorphous silicon.

FIG. 3 shows a reflective holographic element 300 having two hologram layers 301, 302 capable of reflecting and deflecting at least a portion of incident light 304 without concentrating it, the two hologram layers 301, 302 being embedded in a polymer 303.

4 shows a schematic cross-sectional view of a holographic element 400. Unlike the holographic element shown in FIG. 3, in which the deflection is associated with a reflection of light, the holographic element 400 causes a deflection during transmission. For redirecting the light 404, the holographic element 400 has hologram layers 401, 402 which are embedded in an approximately transparent polymer 403.

Although the embodiments shown each have two hoofogram positions 301, 302 and 401, 402, this is only to be regarded as an example and several hologram layers, but at least one, may be incorporated into the respective polymer 303 or 403. An increase in the number of hologram layers, for example, allows optimization of the spectral dependence of the deflection.

5 shows a schematic cross-sectional view of a solar module 500. The solar module 500 has solar cells with a holographic element 504, a transparent substrate 506, a front-side electrode 507, an absorber layer 508, and an For backlit electrode 509. For layer arrangement, material selection and light redirection of incident light 505, reference is made to the explanations of the respective layers 204, 206, 207, 208 and 209 of the example shown in FIG. 2A.

The front-side electrode 507, the absorber layer 508 and the rear-side electrode 509 are structured in such a way that a first cell associated with the absorber layer 508a is connected in series with a second cell associated with the absorber layer 508b. The series connection is made by connecting the rear side contact 509 of the absorber layer 508a with the front side contact of the absorber layer 508b. The cells may also be encapsulated to protect them from environmental influences (not shown).

FIG. 6 shows a schematic representation of an exemplary transmission behavior of a transmissive holographic element 604 as a function of a light deflection angle α. The transmission behavior is shown for a wavelength to which the deflection has been optimized. Vertical incident light 605 is passed undistracted to a small extent of less than 20%, eg, less than 10%, such as about 3%. The majority of the incident light 605, that is, more than 80%, eg more than 90% such as 97%, is deflected by a predetermined angle α _0th The holographic element 604, in contrast to conventional gratings, does not have any intensity contributions attributable to higher orders, to which further deflection angles are assigned.

7A shows a schematic representation of an exemplary spectral transmission behavior of a first hologram layer H _{0 of} a holographic element. The exemplary spectral transmission behavior shown as a diagram is based on a measuring arrangement simplified as sketched above the diagram. Light 705 falls perpendicular to the hologram H _{0 of} the holographic element. A detector D, which is positioned on the side opposite to the light incident side, measures the intensity component of the light 705 that has been passed undistracted.

The deflection of the light 705 by the predetermined angle α ₀ is set by way of example for the hologram position H ₀ to a wavelength λ ₀ of 600 nm. The intensity component of undirected light 705 measured by the detector D is therefore minimal at λ ₀ . With increasing wavelength difference to λ ₀ , the intensity measured at the detector D increases, ie the transmission of the hologram layer increases and in the ideal case increases to 100%. Losses such as reflection or parasitic absorption can cause maximum transmission values that are less than 100%, eg between 80% and 100% or between 90% and 100%.

FIGS. 7B to 7C described below serve to explain the spectral transmission behavior of the first hologram layer H ₀ when the light incidence angle changes. Since these figures and the following FIGS. 7D to 7J are constructed to form further hologram layers such as FIG. 7A, only essential differences from FIG. 7A are discussed below.

7B shows a schematic representation of the spectral transmission behavior of the first hologram layer H ₀ when the light incidence from vertical (see FIG. 7A) changes to an angle γ to the normal. The angle γ is for example 10%. The change of the light incidence angle leads to a change of the light deflection angle at which the transmission at the detector D becomes minimal. By way of example, a change in the angle of incidence of light from 0 ° to the normal (see FIG. 7A) on γ leads to a change in the light deflection angle from α ₀ to α ₁ , accompanied by a change in the maximum deflection of the light. ordered wavelength of λ _o = 6OOnm (see Fig. 7A) to example

As shown in the schematic representation of the spectral transmission behavior of the first hologram layer H ₀ in FIG. 7C, a further change in the angle of incidence of light from γ (FIG. 7B) to δ, for example from 10 ° to 20 °, leads to a further change of the light deflection angle from Ct ₁ to α ₂ , accompanied by a change in the wavelength of λ ^ OOnm associated with the maximum light deflection (see Fig. 7B) to, for example, λ ₂ = 800 nm.

In the figures 7D to 7F are schematic representations for spectral transmission characteristics of a second hologram layer H ₁ for vertical incidence of light (FIG. 7D), light incident at an angle γ relative to the normal (see. Fig. 7E) and light δ at an angle to the normal (cf. Fig. 7F). The hologram position H ₁ differs from the hologram position H ₀ of FIGS. 7A to 7C in that a light deflection through the angle α ₀ at normal incidence of light is set by way of example to a wavelength of λ _o = 7OOnm.

FIGS. 7G to 71 show schematic representations of the spectral transmission behavior of a third hologram position H ₂ for vertical incidence of light (FIG. 7G), incidence of light at an angle γ to the normal (see FIG. 7H) and incidence of light at an angle δ to the normal (cf. Fig. 71). The hologram layer H ₂ differs from the hologram layers H ₀ and H ₁ of FIGS. 7A to 7F in that a light deflection through the angle α ₀ at normal incidence of light is set by way of example to a wavelength of λ _o = 800 nm.

The spectral transmission behavior of the holographic element with superimposed hologram layers H ₀ , H ₁ and H ₂ with vertically incident light 705 is shown schematically in FIG. 7J. By superposition of the hologram layers H ₀ , H ₁ and H ₂ , a light deflection is achieved in an exemplary spectral range of 600 to 800 nm.

Although the spectral transmission behavior of a holographic element is shown in FIG. 7J by way of example with three superimposed hologram layers H ₀ , H ₁ and H ₂ which optimally deflect perpendicularly incident light with wavelengths of 600 nm, 700 nm and 800 nm, the holographic element can of course be one of have three different numbers of hologram layers whose deflection can be set to predetermined wavelengths. The number and design of the hologram layers can be matched to a light deflection in a desired spectral range, for example. Also, the holographic element may be a reflective holographic element.

Claims

claims

A solar cell (100, 110) comprising: a photovoltaic element (101, 111) having a front surface (102, 112) formed as a light entrance surface and a rear surface (103, 113) opposite the front surface (102, 112); a holographic element (104, 114) on the front

(102, 112) of the photovoltaic element (101, 111); wherein the holographic element (104, 114) transmits at least a portion of incident light (105, 115) and thus redirects it into the photovoltaic element (101, 111), without concentrating it to an optical path extension between Front (102, 112) and back (103, 113) learns.

2. Solar cell according to claim 1, wherein between the holographic element (104, 114) and a photovoltaically active structure of the photovoltaic element (101, 111) an antireflection structure is arranged.

A solar cell according to any one of the preceding claims, wherein the holographic element (104, 114) is incorporated in a conductive and light-transmissive front-side electrode layer.

The solar cell according to claim 3, wherein the front-side electrode layer contains a conductive polymer.

5. Solar cell according to one of the preceding claims, wherein one or more hologram layers of the holographic element (104, 114) are formed for the reflection of heat radiation in the infrared range.

A solar cell according to claim 5, wherein the one or more hologram layers for reflecting heat radiation are hologram layers of the holographic element (104, 114) formed adjacent to the front side (102, 112).

7. A solar cell (100, 110) comprising: a photovoltaic element (101, 111) having a front surface (102, 112) formed as a light entry surface and a rear surface (103, 113) opposite the front surface (102, 112); a holographic element (104, 114) on the back side (103, 113) of the photovoltaic element (101, 111); wherein the holographic element (104, 114) deflects at least a portion of the light passing through the photovoltaic element (101, 111) back into the photovoltaic element (101, 111) without concentrating it an optical path extension between the back (103, 113) and front side (102, 112) experiences.

8. Solar cell according to claim 7, wherein the deflection is such that to the front side (102, 112) of the photovoltaic element (101, 111) returned light is totally reflected.

9. A solar cell according to any one of claims 7 or 8, wherein the Holographic element (104, 114) is incorporated in a conductive and translucent back electrode layer.

10. The solar cell according to claim 9, wherein the backside electrode layer comprises a conductive polymer.

11. Solar cell according to one of the preceding claims, wherein the holographic element (104, 114) is constructed so that a light deflection takes place in the entire region of its light incident side.

12. Solar cell according to one of the preceding claims, wherein the holographic element (104, 114) has at least one introduced into a polymer hologram layer.

13. Solar cell according to claim 1 1 or 12, wherein the at least one hologram layer is introduced into chromat gelatin.

14. Solar cell according to one of the preceding claims, wherein a deflection of the light in the holographic element (104, 1 14) is optimized to a wavelength at which an optical absorption length within the photovoltaic element (101, 1 1 1) is greater than its thickness ,

15. Solar cell according to one of the preceding claims, wherein the photovoltaic element (101, 1 1 1) is a Multijunction- solar cell with a certain number of charge-separating transitions and a deflection of the light in the holographic element (104, 1 14) on at least one of a certain number of corresponding number of wavelengths is optimized so that as complete as possible absorption of light takes place in a different cell of the multi-junction solar cell for each of these wavelengths.

16. Solar cell according to one of the preceding claims, wherein the photovoltaic element (101, 1 1 1) comprises a thin film solar cell.

17. Solar module comprising at least one solar cell according to one of the preceding claims.

18. A holographic element (300, 400) comprising: at least one hologram layer (301, 302, 401, 402) adapted to pass and deflect at least a portion of incident light (304, 404) or to reflect and deflect without Concentrate it, wherein the at least one hologram layer (301, 302, 401, 402) is incorporated in a polymer (303, 304).

The holographic element (300, 400) of claim 18, wherein more than four hologram layers are stacked.

20. A method for producing a solar module, wherein a holographic element according to claim 18 is applied to a solar cell.