WO2009062837A1

WO2009062837A1 - Solar cell having optical amplifier structures

Info

Publication number: WO2009062837A1
Application number: PCT/EP2008/064532
Authority: WO
Inventors: Martin Klenke; Matthias Henyk; Ralf Zastrau
Original assignee: Nanogate Advanced Materials Gmbh
Priority date: 2007-11-16
Filing date: 2008-10-27
Publication date: 2009-05-22
Also published as: EP2188846A1; TW200941746A

Abstract

The invention relates to a solar cell having a solar element (10) for converting solar rays into electrical energy. The solar element (10) is covered by a radiation-transparent cover element (16), through which the sunlight penetrates. According to the invention, diffractive surface elements (20) are provided on the cover element (16). The incident sun light is directed toward the solar element (10) by the surface elements (20). In this manner, the effectiveness of the solar cell (10) can be improved significantly.

Description

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SOLAR CELL WITH OPTICAL REINFORCEMENT STRUCTURES

The invention relates to a SoSarzeile.

Solar tents have a solar element which is usually designed as a semi-finished element. In the semi-finished area, the energy supplied in particular by the sunlight is converted into electrical current. This essentially takes place in that the radiation penetrates into the semiconductor component and generates free charge carriers there. With the help of an internal electric field then a current flow occurs. The efficiency of a solar cell depends, in addition to the materials used, in particular on how much radiation penetrates into the solar element and generates free charge carriers. This depends in part on the amount of radiation or the radiation density and on the other hand on the wavelength of the radiation. In this case, short-wave light is more effective, since this is high-energy radiation.

In known solar cells, there is the disadvantage that, especially in the morning and evening hours, the light strikes the soya line at a shallow angle, and thus a large part of the incident light is reflected. A large part of the light striking the solar cell is thus not converted into electrical current. The object of the invention is to provide a solar cell with improved efficiency, in particular an increase in efficiency at a flat angle of incidence of solar radiation to be achieved.

The object is achieved according to the invention by the features of claim 1.

The solar cell according to the invention has a solar element, which is in particular a semiconductor element. The solar element converts the incident solar radiation into electrical energy in a known manner. The solar panel is covered with a radiation-transparent cover element. The cover serves in particular to avoid contamination. The cover element can thus be a glass or plastic cover element which is transparent in particular to sunlight. The cover may be formed as a foil. The covering element is directly connected to the solar element or arranged at a distance therefrom. Preferably, the cover member is a planar cover member

According to the invention, diffractive surface elements are provided on the cover element. These surface elements, which are particularly small and are provided in a large number, are preferably elevations which, at least on one side, have a diffraction grating for directing incident sunlight. As a result, the surface elements are formed such that the incident sunlight is deflected in the direction of the solar element. In particular, in sunlight that strikes the solar cell at a shallow angle, therefore, no reflection of a major part of the light takes place. Rather, a large part of the incident sunlight is deflected and can thus be used for energy. As a result, the efficiency of the solar cell is considerably improved, since in particular in the morning and evening hours incident on the solar cell light can be used to a greater extent than in known solar cells.

Essential to the invention is that the sunlight by diffraction, ie diffraction on a grid and not by refraction to the effective surface of the Solar cell is deflected. Diffraction or diffraction occurs only in gratings with a small grating period which is at least smaller than 10,000 nm. In particular, the grating period is in the range of 300 to 900 nm. In addition, diffraction occurs only at the edge for wider columns. However, the light deflection is already essentially due to the laws of refraction. This also differs from the refraction, which is geometric Lichtienkung. Refraction describes light phenomena in geometric optics, such as lenses and the like, and is not to be equated with light diffraction as a special case of refraction.

Preferably, the surface elements, in particular their dimensions and their surface design are formed such that even light which strikes at an angle of less than 45 ° relative to the cover on this, is directed in the main part in the direction of Solareiements. In particular, a deflection of the incident light in the direction of the solar element takes place at angles of less than 30 °, more preferably at angles of less than 20 ° and more preferably at an angle of less than 10 °. According to the invention, more than 50%, in particular more than 80%, of the high-energy light, which lies in a wavelength range of 300 to 500 nm, is deflected in the direction of the solar element and can thus be used to generate electricity at a corresponding percentage. It is particularly preferable to redirect light through the surface elements in the direction of the solar element, which has a wavelength range of less than 500 nm, in particular less than 450 nm, and is therefore of high energy. In a preferred embodiment of the invention, by providing the surface elements according to the invention a Einfangeπ of light in angular ranges is possible in which takes place at today known solar lines total reflection. The angle of total reflection depends in particular on the material used. By providing the surface elements according to the invention, the angular range in which light is deflected in the direction of the solar element can thus be increased. As a result, the efficiency of the solar cell can be significantly improved. The individual Oberflächenelernente are preferably formed as a survey and have a substantially cuboid or cubic shape. In particular, at the top of the Oberflächenelernente acting as a diffraction grating surface structure is provided. This is in particular welienförmig and particularly preferably formed as a double sine wave. Depending on the distance of the waves or depending on the frequency of the structure of the structure, there is a diffraction of light of the corresponding wavelength. By choosing the surface structure, in particular the frequency and the amplitude of a wave-shaped surface structure, it can be defined which light of a certain wavelength range is diffracted and diffraction takes place in the soft direction.

Preferably, different surface elements have surfaces with different diffraction characteristics. As a result, in a relatively large wavelength and angle range, the light striking the solar cell can be deflected in the direction of the solar elements, so that the efficiency of the solar line can be further improved. In particular, it is possible to design individual surface elements in such a way that, in a defined angular range, a defined range of wavelengths of the light occurring is deflected in the direction of the solar elements. The selection can also be made vice versa.

The individual surface elements preferably have a size of 0.04 μm ² to 10,000 μm ² , in particular 0.04 μm ² to 500 μm ² . The distance between the individual surface elements with one another is preferably 0 to 100 μm ² , in particular 0 to 50 μm ² and particularly preferably 0 to 15 μm ² . However, it is preferred that the spacing of the individual surface elements is greater than 0 μm ² , in particular greater than 1 μm ^2, and particularly preferably greater than 3 μm ² . This has the advantage that the production of the individual surface elements is simplified if the surface elements are arranged at a distance from one another. If the surface elements are produced, for example, by a hardening lacquer in conjunction with a molding element or a negative, the spacing of the surface elements avoids adulteration at the boundaries of the surface elements, for example as a result of resulting paint webs. In a preferred embodiment of the invention, the cover is arranged at a distance from the surface of the soi element. Surface elements according to the invention are provided on the inside, that is to say on the side of the covering element facing the base of the covering. As a result, light which is reflected at the top of the solar element is at least substantially exposed to light. thus deflected by the surface elements and / or reflected by the inside of the cover, that the light can be looped back to the Soiarelement and used there for energy. "In this embodiment, it is thus a kind of light trap. Of course, this embodiment of the invention with the embodiment described above, in which on the outer surface of the Abdeckeiements, that are provided by the Soiarelement facing surface, surface elements are combined.

In a further preferred embodiment, which can be combined in particular with the two above-described preferred essential embodiments, are with the cover coupling elements, such. B. Rippeπelemente connected. By way of example, the rib elements are cuboid-shaped elements which are connected to the cover element in such a way that they point away from it. In particular, the Rippenelemeπte are arranged perpendicular to the cover. The coupling elements may also be other geometric web or rod-shaped body, which are arranged on the upper side of the cover. For example, cylindrically shaped coupling elements are possible. These may also be pyramid or partially pyramidal elements or the like. The coupling elements have on at least one outer surface elements by which the incident light is deflected by diffraction at least partially in the direction of the solar element. The provision of rib elements with surface elements according to the invention represents an increase in surface area and thus a considerable improvement in the efficiency of the solar cell.

The coupling elements are preferably made of the same material as the cover. In particular, the rib elements are made of light-transparent Material. In particular, the material is the thermoplastics listed below or combinations of these materials:

- PP, PE, PC, PMMA, PVC, PET, PU, PVF, PVDF and ETFE.

Furthermore, mineral glass or FEP Teflon and EVA are also possible materials. The use is often via adhesive compounds using PVB _f silicone or EPDM. Preference is given to the use of material composites, such as PVF-PET-PVF, wherein packet layer thicknesses in the range of 0.1 to 0.4 mm are preferred.

In order to avoid leakage of light on the side facing away from the solar element outside of the rib elements, a Reflektionseiement, such as a Sptegelelement is preferably provided on these outer sides. This may be a vapor-deposited layer or the like.

Under light, the entire spectrum of sunlight, ie. H. also understood non-visible areas of electromagnetic radiation.

The invention will be explained in more detail with reference to preferred embodiments with reference to the accompanying drawings.

Show it:

Fig. 1 is a schematic perspective view of a first

Embodiment of a solar cell,

FIG. 2 shows a schematic enlargement of a region II in FIG. 1, FIG.

3 is a schematic enlarged sectional view of part of a second embodiment of a solar cell,

4 shows a schematic enlarged sectional view of part of a third embodiment of a solar cell, 5 shows a schematic perspective view of the third preferred embodiment of the solar cell,

FIGS. 6 and 7 are schematic diagrams of a simulation calculation based on the embodiment shown in FIGS. 4 and 5 and FIG

FIGS. 8 to 10 are schematic enlarged sectional views of further embodiments of a solar cell,

In the first embodiment of the solar cell according to the invention (FIGS. 1 and 2), a solar element 10, which is usually designed as a semiconductor element, is arranged on a carrier element 12. Within the solar element 10 is carried out by the penetrating radiation, a release of charges and due to an internal electric field generating electric current. This is discharged via lines 14.

An upper side of the solar element 10 is connected in the illustrated embodiment with a cover 16. The cover 16 is for example directly on the solar element 10 or is firmly connected thereto by gluing or the like.

The light-transparent cover element 16 has on its upper side 18 a plurality of individual Oberflächeneiementen 20. The individual surface elements are substantially cuboidal or litter-shaped and have at their top 22 a wave-shaped structure, so that a diffractive surface is formed. In particular, the structure is formed sinusoidal. Depending on the frequency and amplitude of a particular sinusoidal surface structure is a bending and thus deflecting light radiation, as shown simplified by the arrows 24, in the direction of the solar element 10. In particular, in sunlight, which radiates from the top 18 at a shallow angle, can by the invention a significant improvement in the efficiency of the solar cell can be achieved. In a further preferred embodiment of the invention (FIG. 3), identical or similar components are identified by the same reference numerals.

In this embodiment, the cover 16 is disposed at a distance from a top 26 of the solar element 10. The intermediate space 28 may in this case be hollow, that is filled with air, or be filled with another possibly solid medium. A schematically illustrated light beam 30 is partially reflected at a point 32 on the upper surface 26 of the solar cell and would be radiated without the inventive provision of surface elements substantially completely in the direction of a dotted arrow 34 and thus can not be used for energy.

In order to avoid this, a plurality of surface elements 20 are arranged on an inner surface 36 of the cover 16 according to the invention. These are preferably as described with reference to FIG. 2, formed. The provision of surface elements 20 on the inner surface 36 of the Abdeckeiements 16 causes the space essentially serves as a light trap.

In a further preferred embodiment of the invention (Figures 4 and 5) identical or similar components are again identified by the same reference numerals. According to the invention, rib elements 38 are provided on the outside 18 of the cover element in this embodiment. The rib members 38 are formed substantially cuboid and arranged perpendicular to the outer surface 18 of the cover 16. On at least one outer surface 40 of the rib members 38, in turn, a plurality of surface elements 20, which are formed as explained above, are provided. As indicated by the beam path 42, thus at least a portion of the light is reflected within the fin element and thus passes in the direction of the solar element 10. An unreflected portion 44 of the light is due to the corresponding diffraction by the surface elements of the adjacent rib member 38 within this fin element in Direction of the solar element 10 deflected. By providing rib elements with surface elements 20 provided at least on an outer surface 40 The effective surface of the solar cell can be significantly increased. In order to prevent leakage of a light beam from the rib element on a side facing away from the solar element 10 side, are provided on this reflection elements 46.

The three above-described essential embodiments of the invention for improving the efficiency of solar cells can be arbitrarily combined with each other.

With the aid of a suitable simulation software, calculations were carried out to determine the increase in efficiency on the basis of one of the embodiments of the solar line according to the invention shown in FIGS. 4 and 5. The corresponding graphical evaluations are shown in FIGS. 6 and 7.

Here, FIG. 6 shows a conventional solar cell 10, on the upper side of which, according to the exemplary embodiment illustrated in FIGS. 4 and 5, rib elements 38 are arranged. In order to be able to compare the simulation results, the rib elements 38 each have smooth surfaces 40 in the example shown in FIG. On the surfaces 40 no surface elements are provided. The material is a transparent material with a refractive index of nD = 1.52. The transmittance of the material is 95%, the degree of reflection 5% and the Absorbtionsgrad 0%, Furthermore, the course of a single incident light beam 48 is shown in Figure 6. As can be seen, only a small part of the light beam strikes the outside 18 of the solar element 10.

In FIG. 7, the identical component has now been used in the simulation as in FIG. 6, wherein diffractive surface elements 20 are arranged on the surfaces 40 of the rib elements 38. The surface elements have a grating period of 400 to 2000 nm.

In Figure 7, three beam paths are shown, which impinge on the rib members 38 at different angles. The respective upper or right beam 50 of the three beam paths is the 0-order beam path. This one will only broken and not bent. The other ray trajectories are those ray trajectories of the -1. Order. These rays are exclusively diffracted. It can be seen from FIG. 7 that a large part of the incident light is deflected onto the solar cell 10, in particular even in the case of very flat beam paths and the resulting diffraction. In the case of very steeply incident rays, the provision of the surface elements according to the invention on the rib elements 38 does not interfere.

The simulation has shown that an increase of approximately 30% can be achieved by providing the rib elements 38 with diffractive surface elements 20 in comparison to conventional solar cells. "In this case, the diffractions of higher orders were not taken into account. This would lead to a further increase in efficiency.

Due to this considerable increase in efficiency, for example, it is no longer necessary to track a solar cell panel to the course of the sun. The provision of a corresponding electric motor with the associated mechanism, etc. can thus be omitted. Furthermore, the simulation has shown that angles of incidence in a range of approximately +/- 90 ° are acceptable.

A further increase in efficiency can be achieved by reducing the distance between the rib members 38. Furthermore, it is possible to provide a semi-permeable mirror opposite the surface 18 of the soya element 10, for example at the top of the rib elements 38, so that radiation which is deflected upwards away from the solar element 10 is reflected back.

In FIGS. 8 to 10, different embodiments of coupling elements, which replace the ribbed elements 38, are shown on the solar element 10. Of course it is possible to combine all illustrated embodiments with each other.

In Figure 8 are shown as Einkoppelelemente 52 substantially teilpyramidenförmige elements. These have two with respect to the surface 18 of the solar element 10 inclined surfaces 54 and one of the surface 18 of the Solar element 10 parallel surface 56 on. It is preferred here that surface elements 20 with a different surface lattice are arranged on the surfaces 54, 56. This makes it possible, depending on the position of the sun, to provide gratings adapted to the angle of incidence.

Also arranged according to Figure 9 on the solar element 10 Einkoppelelemente 58, which are formed kreiszylindrisch are designed such that a good coupling of the sun's rays is possible, although the angle of incidence changes during the day. On the cylindrical outer side of the coupling elements 58 in turn diffractive surface elements 20 are arranged. Diffractive surface elements 20, which likewise have a different lattice constant than the diffractive surface elements 20 arranged on the surface 60, can likewise be provided on the flat top 62. Likewise, on surface 32, a particularly semitransparent mirror may be provided, the function of which corresponds to mirror 46 (FIGS. 4 and 5).

Another embodiment, which has a lower overall height, is shown schematically in FIG. The individual coupling elements 64, 66 are in a right angle! arranged to each other and stacked according to a grid structure. On different outer sides of the coupling elements 64, 66 surface elements 20 may be provided, which optionally have different grating structures. Furthermore, it is possible to provide semipermeable mirrors, in particular on the side facing away from the solar element.

Claims

claims

1. solar cell, with

a solar cell (10) for converting solar radiation into electrical energy,

a radiation-transparent cover member (16) through which the sunlight passes through the solar element (10) and

on the cover (16) arranged diffractive surface elements (20) for steering incident sunlight in the direction of the solar element (10).

2. Solar cell according to claim 1, characterized in that the surface elements (20) are formed such that in particular light at an angle of less than 45 °, in particular less than 30 ° and more preferably less than 20 ° to the cover (16 ), is directed in the direction of the Soiarelements (10),

3. Solar cell according to claim 1 or 2, characterized in that the surface elements (20) are formed such that high-energy light, which in particular has a wavelength of 500 nm and particularly preferably of less than 450 nm, in the direction of the soiareelement (10). being steered

4. Solar cell according to one of claims 1 to 3, characterized in that the surface elements (20) have a size of 0.04 to 10,000 nm ² , in particular 0.04 to 500 nm ² .

5. Solar cell according to one of claims 1 to 4, characterized in that the individual surface elements (20) with each other at a distance of 0 to 100 nm ² , in particular 0 to 50 nm ^z and more preferably 0 to 15 nm ² have.

6. Solar cell according to one of claims 1 to 5, characterized in that the surface elements (20) on at least one outer side (22), in particular on a cover member (16) opposite the outside have a diffraction grating,

7. Solar cell according to one of claims 1 to 6, characterized in that the Oberfiächenelemente (20) on one of the Solareiement (10) pioneering Außenfiäche (18) of the Abdeckeiements (16) are arranged.

8. Solar cell according to one of claims 1 to 7, characterized in that the cover (16) is arranged at a distance from the solar element (10) and on the solar element (10) facing the inner surface (36) surface elements (20) are arranged,

9. Solar cell according to one of claims 1 to 8, characterized by coupling elements (38, 52, 58, 64, 66) connected to the cover element (16), which have surface elements (20) on at least one outer side (40).

10. Solar cell according to claim 9, characterized in that the coupling elements (38, 52, 58, 64, 66) have light-transparent material,

11. Solar cell according to claim 9 or 10, characterized in that the Einkoppeleiemente (38, 52, 58, 64, 66) are arranged substantially perpendicular to one of the solar element (10) pioneering outer surface (18).

12. Solar line according to one of claims 9 to 11, characterized in that the Einkoppeielemente (38, 52, 58, 64, 66) on one of the solar element (10) facing away from a Refiexionselement (46).