DE102011001937A1 - Solar cell i.e. silicon solar cell, for converting solar radiation into electrical energy, has amorphous layer modulated by adjusting factors and/or refraction index of doped layer, where layer thickness is in preset values - Google Patents

Abstract

The cell (1) has heterojunction p-n transition (2) formed between a crystalline silicon substrate (3) and an amorphous doped layer (5). The amorphous doped layer comprises silicon monoxide, silicon nitride and/or silicon carbide layers modulated by adjusting factors and/or refraction index of the amorphous doped layer during deposition of the amorphous doped layer. The refraction index of the amorphous doped layer is about 2 and 3, conductivity of the amorphous doped layer is in preset values, and thickness of the doped layer is about 50 nm to 300 nm. The solar cell comprises a layer sequence made from ethyl vinyl acetate and glasses. An independent claim is also included for a method for manufacturing a solar cell.

Description

The present invention relates to a solar cell having a heterojunction pn junction formed between a crystalline silicon substrate of a first conductivity type and at least one amorphous doped layer of a second conductivity type. The present invention further relates to a method for producing a solar cell having a heterojunction pn junction, wherein at least one amorphous doped layer of a second conductivity type is formed to form the pn junction on a crystalline silicon substrate of a first conductivity type.

In the course of the rapid development of photovoltaics, a large number of different solar cell types has been developed. In a classical type of solar cell, a pn junction is formed in this silicon substrate within a single silicon substrate by doping the surface. Such a pn junction in a homogeneous material is also called homojunction. In other types of solar cells, another material with the inverse doping to the silicon substrate is deposited on a crystalline silicon substrate with a p- or n-type doping. In this way, a pn junction is made in which two different materials adjoin one another. Such a pn junction is also referred to as heterojunction or heterojunction. The other material besides the crystalline silicon may also be silicon, which has a different crystallinity or an amorphous structure. But it can also be a different chemical than silicon.

There is a concentration gradient of charge carriers between the n-doped and the p-doped region in a solar cell. This creates an electric field within the solar cell in the vicinity of the pn junction, which is also referred to as the space charge zone. Upon irradiation of the solar cell with light of sufficient energy, electrons that have absorbed light quanta are carried into the conduction band and electron-hole pairs are formed. As a result of the space charge zone formed in the solar cell, the generated charge carriers, i. H. Electrons and holes, moved in different directions and are available at the connection electrodes to an external circuit.

The efficiency of a solar cell depends on a number of factors. An important factor is preferably the lack of recombination centers within the solar cell. Such recombination centers are, for example, dislocations or other lattice defects within the silicon crystal. The recombined at the recombination centers electrons and holes can not get to the terminal electrodes of the solar cell and are therefore not available as a useful charge carriers.

In order to minimize the activity of the recombination centers, passivation layers, such as hydrogen-containing silicon or hydrogen-containing silicon nitride, are often deposited during solar cell production. The hydrogen is bound to the recombination centers and passivates them. As a result, recombinations occur less frequently and the efficiency of the solar cell increases. Further layers which are used in the production of solar cells are antireflection layers, which are intended to bring about the least possible reflection at the surface of the light incidence, and transparent or non-transparent electrode layers, which serve to dissipate charge carriers. For the deposition of each layer, coating systems are required whose price is reflected in the total price of the produced solar cell. For solar cells manufactured using many layers, the associated high production costs can be problematic.

From the publication WO 2009/078672 A2 a silicon heterojunction solar cell is known, in which on a crystalline silicon substrate, which is for example p-doped, directly a passivation layer is deposited, which serves not only as a passivation layer but also as an n-doped amorphous semiconductor layer, which contributes to the formation of the pn transition is involved. This passivation layer consists either of silicon oxide (SiO ₂ ), silicon carbide (SiC), silicon nitride (SiN _x ) or amorphous silicon (a-Si). This layer is n-doped, for example, by diffusion of phosphorus oxychloride (POCl ₃ ). If this layer is transparent, it can also be used as a sub-layer of a multilayer antireflection layer. On the passivation layer, an antireflection layer and electrode structures of a silver paste are applied. A disadvantage of this solar cell is that the deposition of passivation layer and antireflection layer is a total of consuming and associated with high costs. In one embodiment described, the amorphous layer is doped at 850 ° C. from POCl ₃ , wherein the amorphously deposited passivation layer crystallizes and forms recombination centers. Furthermore, the light-facing side of the solar cell is partially covered by a large number of silver terminal electrodes.

Solar cells are also known in the prior art, in which transparent conductive layers are used as electrodes. Indium tin oxide (ITO) is often used as the material for such electrodes. In the use of this Transparent electrodes, the area density of non-transparent metal electrodes can be reduced. A disadvantage of such solar cells is that the refractive index of the ITO layer with values of about 1.9 is too small for an optimal antireflection layer, so that the solar cells have a large reflection and correspondingly large reflection losses.

It is therefore the object of the present invention to propose a solar cell with heterojunction pn junction and a method for its production, which is designed inexpensively with a few thin layers, which is well coated at least at a design wavelength and which has a high electrical efficiency.

The object is achieved by a solar cell of the type mentioned in the introduction, in which the at least one amorphous doped layer modulates at least one SiO _x , SiN _y and / or modulated in its refractive index by adjusting the factor x, y and / or z in the layer deposition SiC _z layer with x ≠ 2, y ≠ 4/3 and z ≠ 1 comprises; wherein the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer is between 2 and 3, the conductivity of the at least one SiO _x , SiN _y and / or SiC _z layer is between 50 Ω / □ and 500 Ω / □ and the layer thickness of the at least one SiO _x , SiN _y and / or SiC _z layer is between 50 nm and 300 nm.

In the solar cell according to the invention, therefore, an amorphous layer is used whose refractive index is modulated. That is, the refractive index of this layer changes over its layer thickness. In connection with the modulation of the refractive index, ie the gradient in optical properties, the electrical properties of the layer also change accordingly. For a simplified description of the layer with changes in the properties within the layer, a single-layer model with a mean refractive index and a total sheet resistance can be used, at least for the description of the optical properties. At the interface with the crystalline silicon substrate where the heterojunction pn junction is to be formed, the amorphous doped layer has predominantly semiconductive properties. Due to the amorphous structure of the amorphous doped layer, this hardly has recombination centers. By avoiding high temperatures, crystallization of the amorphous doped layer is prevented. At the interface with the crystalline silicon substrate, the amorphous doped layer is composed primarily of silicon alloyed with oxygen, nitrogen or carbon or of a layer which may already be termed unstoichiometric silicon carbide. By alloying with oxygen, nitrogen or carbon, the amorphous doped layer has a larger bandgap at the interface than crystalline silicon. Greater optical clarity is associated with the larger bandgap, which results in a greater portion of sunlight radiating onto the solar cell penetrating the solar cell and the crystalline region of the silicon substrate. As the distance to the crystalline silicon substrate increases, the concentration of oxygen, nitrogen or carbon is changed so that the transparency of the layer increases. With increasing transparency, a decreasing electrical conductivity is connected, which is basically unfavorable, but manageable.

Overall, the at least one amorphous doped layer can be surprisingly designed optimized so that all requirements are fulfilled that can otherwise be realized only by a plurality of layers and a correspondingly higher time and cost. In the solar cell according to the invention, one of the two parts of the pn junction is formed with the at least one amorphous doped layer, a sufficiently good electrically conductive connection between the semiconductor material of the solar cell and a collecting electrode is achieved, furthermore a passivation of the semiconductor of the solar cell and a achieved optical antireflection. The optical reflection coating is possible in that the refractive index of the amorphous doped layer can be adjusted to an optimum value by a suitable composition of the layer.

In a preferred embodiment of the solar cell according to the invention, the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer is between 2.1 and 2.5. Solar cells are built into housings to achieve long term stability, with the actual solar cell protected by the housing, which includes, for example, a glass sheet and an ethyl vinyl acetate (EVA) plastic lamination. The antireflection in a solar cell according to the invention is generally not limited to a single layer, but it can be formed in a known manner by the use of multiple layers also a further improved antireflection, depending on the requirements of the specific solar cell to find an optimum between effort and benefits is. Depending on the housing used and its optical properties, the refractive index optimum of the at least one amorphous doped layer may be at different values, the refractive index of this layer being preferably set between 2.1 and 2.5.

In a particularly preferred embodiment of the solar cell according to the invention, the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer is 2.3. This refractive index is on the preferred matched to EVA and glass based housing. The optimum refractive index n _{1 of} the antireflection layer between the silicon substrate and the housing can be calculated in a known manner as geometric mean according to the equation n ₁ = √ (n0 × n ₂ ), the refractive index of silicon n ₀ = 3.5 and the refractive index n ₂ of EVA and glass is about 1.5 each.

In a particularly advantageous embodiment of the solar cell according to the invention, at least one amorphous intrinsic layer is provided between the crystalline silicon substrate and the at least one amorphous doped layer. The intrinsic, that is undoped layer has proven to be suitable in practice to improve the quality of the pn junction, which is measurable, for example, at an increased open circuit voltage of the solar cell.

This amorphous intrinsic layer is preferably an amorphous undoped silicon layer. Since silicon is also used as the substrate, silicon atoms are particularly well suited from an atomistic point of view to form a low-interference layer on the substrate. However, the amorphous undoped layer need not necessarily be made of silicon, but may be formed of other materials such as silicon carbide.

In a favorable embodiment of the solar cell according to the invention, the at least one amorphous intrinsic layer has a layer thickness of 5 nm to 15 nm. In this layer thickness range, optimal properties of the solar cell have been found in experiments. The optimal layer thickness depends on the technology used. Therefore, in other solar cells according to the invention, other optimal layer thicknesses may also be found.

In a preferred solar cell according to the invention, the factor x, y and / or z of the at least one SiO _x , SiN _y and / or SiC _z layer is changed with the layer thickness _such that the at least one SiO _x , SiN _y and / or SiC _z layer has different refractive indices over its layer thickness. By set in the layer concentration gradients of their constituents, the catalog of requirements to the layer can be favorably met. However, it is also possible to produce layers with, for example, opposing oxygen and carbon gradients, in which the effects on the refractive index are compensated for and the refractive index over the layer is substantially constant.

In a further variant of the solar cell according to the invention, the at least one SiO _x , SiN _y and / or SiC _z layer has a higher refractive index on its side facing the crystalline silicon substrate than on its opposite surface. At the interface with silicon, the electrical properties, in particular the conductivity and the band gap, are more important than the optical properties. In this part of the layer, it is important that the layer is a conductive silicon or silicon carbide layer rather than a transparent but insulating silicon oxide or silicon nitride layer. Overall, however, the amorphous doped layer should have a high transparency. High transparency is achieved above all by partial formation of the amorphous doped layer with similarities to silicon monoxide, silicon dioxide, silicon nitride or silicon oxynitride layers, which have a lower refractive index than required for the amorphous doped layer. This transparent part of the lower refractive index layer is provided where the more conductive layer having the higher refractive index is not already provided.

It is particularly advantageous to change the doping of the at least one SiO _x , SiN _y and / or SiC _z layer with the layer thickness so that the at least one SiO _x , SiN _y and / or SiC _z layer via their layer thickness has changed conductivities. The conductivity of the amorphous doped layer is influenced not only by its silicon, oxygen, nitrogen and carbon content, but additionally by its doping. The doping of the amorphous doped layer is inverse to the doping of the crystalline silicon substrate, ie, when the crystalline silicon substrate is n-doped, the amorphous doped layer is p-doped or vice versa. As n-type dopants, atoms of the fifth main group, such as phosphorus or arsenic, are generally used and, as p-type dopants, elements of the third main group, such as boron or aluminum. To achieve a doping, various methods are known, such as, for example, the diffusion of doping atoms from a layer or from the gas phase or the implantation. However, the doping can be controlled in a particularly favorable manner if the doping is achieved during the layer deposition by addition of suitable precursors. This in situ doping during the deposition is often associated with considerable difficulties, for example, the addition of arsine as an arsenic source to a silane-containing CVD atmosphere causes a strong impediment to silicon deposition. However, by means of suitable process control, for example of plasma-assisted CVD depositions, insitu-doped amorphous hydrogenated silicon layers have already been successfully deposited, for example using borane. Depending on the dopant and deposition process, however, a multi-stage deposition for the preparation of a doped layer may be required, for example, arsenic and silicon may be deposited in layers. The activation of the doping can be carried out, for example, by ion bombardment or by laser pulses.

In this case, the doping in the layer is preferably modified in such a way that the at least one SiO _x , SiN _y and / or SiC _z layer has a higher conductivity on its side facing the crystalline silicon substrate than on its opposite surface.

With an antireflection layer, the reflection can be minimized only for a certain wavelength. With increasing difference of the wavelength of the incident light to this optimum wavelength, the antireflective effect is reduced and the reflection of the solar cell increases accordingly. With a silicon solar cell, the part of the solar radiation can be converted into electrical energy, in which the energy of the photons is greater than the band gap of silicon or, in other words, in which the wavelength is smaller than 1100 nm. Sun-ray radiation and a silicon solar cell usable radiation is therefore in a wavelength range between about 400 nm and 1100 nm. The efficiency of the solar cell is generally greatest when the antireflection layer is optimized to a wavelength between 600 nm and 700 nm. In this wavelength range, the reflection between the housing and electrically active regions of the solar cell according to the invention is close to 0, but at least <5%.

In one possible embodiment of the solar cell according to the invention, the crystalline silicon substrate is n-doped silicon and the at least one SiO _x , SiN _y and / or SiC _z layer is p-doped. The deposition of in-situ doped layers proved to be simpler in the case of p-doping than the deposition of n-doped layers. Therefore, initially solar cells with n-doped silicon and p-doped amorphous layer were realized. In conventional homojunction silicon solar cells, however, a p-doped silicon substrate is preferred. It can therefore not be ruled out that preference is also given to heterojunction solar cells in the course of the development of p-doped substrates and n-doped amorphous layers deposited thereon.

In a preferred embodiment of the solar cell according to the invention, the at least one SiO _x , SiN _y and / or SiC _z layer is contacted, and on the at least one SiO _x , SiN _y and / or SiC _z layer and the contacts a layer sequence of ethyl vinyl acetate and glass provided. The layer resistances of the amorphous doped SiO _x , SiN _y and / or SiC _z layer are too high to dissipate the charge carriers generated in the solar cell to an edge of the solar cell. Therefore, electrodes are provided on the solar cell, which take over the power line over long distances. The at least one amorphous doped layer only takes over the conduction of the charge carriers up to the contacts of the electrodes. On the front side of the solar cell, for which the irradiation with light is provided, consisting of finger and bus lines metal structures are common, sometimes also large-area electrodes of transparent conductive oxides, such as ITO, are used. On the back of the solar cells, whole-area electrodes are often provided, which in the case of metals also act as a reflector, which reflects light which penetrates the solar cell back into the solar cell. In the construction of solar cell modules, it has proven to be favorable to einzulaminieren the solar cell in ethyl vinyl acetate and connect by lamination with a glass sheet. In improved versions, the glass is additionally anti-reflective. In this case, the optical properties of the at least one amorphous doped layer must be partially adapted to the anti-reflection of the glass.

In another aspect of the present invention, the object is achieved by a method of the aforementioned type, in which at least one SiO _x , SiN _y and / or SiC _z layer is deposited as at least one amorphous doped layer, wherein in the layer deposition the refractive index of the SiO _x , SiN _y and / or SiC _z layer is modulated by adjusting the factor x, y and / or z, where x ≠ 2, y ≠ 4/3 and z ≠ 1, and thereby to a Value is set between 2 and 3; the conductivity of the at least one SiO _x , SiN _y and / or SiC _z layer is adjusted by doping this layer between 50 Ω / □ and 500 Ω / □; and the at least one SiO _x , SiN _y and / or SiC _z layer having a layer thickness of 50 nm to 300 nm is deposited.

In this method, during the deposition of an amorphous doped layer containing silicon in each case, the proportion of oxygen, nitrogen and / or carbon in the layer is modulated so that the layer, if its optical properties are described with a single-layer model, has a refractive index between 2 and 3. The refractive index is thus smaller than that of silicon, and the layer is more transparent than a silicon layer. Due to the greater transparency of the amorphous doped layer, incident sunlight penetrates to a greater extent into deep areas of the solar cell. By high silicon content and an additional doping sufficient conductivity of the layer and a functioning pn junction is produced. By setting a suitable layer thickness and a suitable refractive index, an optimized reflection reduction is realized with the deposition of the amorphous doped layer.

The layer deposition also takes place in such a way that a required passivation of the Solar cell is reached. The passivation is achieved, for example, by deposition conditions in which sufficient amounts of hydrogen are incorporated into the layer. The amorphous structure of the layer is ensured by sufficiently low processing temperatures at which crystallization of the amorphous doped layer is avoided.

In an advantageous development of the method according to the invention, at least one amorphous intrinsic layer is provided between the crystalline silicon substrate and the at least one SiO _x , SiN _y and / or SiC _z layer. As a pn junction as sharp and trouble-free atomic structure is desirable. In a coating of a substrate, which was exposed to contact with air, an ideal interface structure can not be achieved. For example, by chemically or physically bound to the surface adsorbates impurities are introduced into the interface, and for example, by an ion bombardment during the deposition of a layer takes place a fusion of atoms at the interface instead. By depositing a thin, undoped amorphous layer prior to deposition of the doped amorphous layer, an improved pn junction is produced in effect.

The amorphous intrinsic layer is often deposited as an amorphous undoped silicon layer. Since the substrate is a silicon substrate, a silicon layer is preferably also produced as a suitable coating.

The at least one amorphous intrinsic layer is advantageously deposited with a layer thickness between 5 nm and 15 nm. The intrinsic layer should be made as thin as possible, so that it unfolds no adverse effects. Layer thicknesses between 5 and 15 nm have proven to be optimal.

In a variant of the method, an amorphous intrinsic layer is deposited only on the side of the solar cell facing the sunlight, in other embodiments of the method both sides of the crystalline silicon substrate are coated with an amorphous intrinsic layer. In the case of a symmetrical coating of the substrate on both sides, the layer stresses of the front and rear side coating are compensated and the substrate is not or only slightly warped as a result of the coating. For example, to reduce the risk of fracture of solar cells during their production, it is advantageous to coat the solar cells as symmetrically as possible on the front and back and, inter alia, to deposit an amorphous intrinsic layer on both sides of the substrate. A two-sided coating can often be produced as a simultaneous front and back coating in a coating chamber, so that there are only a small additional cost to the two-sided coating over the single-sided coating.

In a preferred option of the method according to the invention, the factor x, y, and / or z of the at least one SiO _x , SiN _y and / or SiC _z layer is changed in the layer deposition with the layer thickness, so that the at least one SiO _x - , SiN _y and / or SiC _z layer has refractive indexes which have been changed over their layer thickness. The refractive index of the amorphous doped layer should be set to a target value. This is possible by changing the composition of the layer. For adjusting the desired optical properties, therefore, the refractive index is changed with the layer thickness, which is achieved by adjusting suitable oxygen, nitrogen and / or carbon contents in the layer.

In an equally favorable variation of the method according to the invention, the factor x, y and / or z of the at least one SiO _x , SiN _y and / or SiC _z layer is changed in the layer deposition with the layer thickness such that the at least one SiO _x -, SiN _y - and / or SiC _z layer on its side facing the crystalline silicon substrate side has a higher refractive index than at its opposite surface. On the outer surfaces of the solar cell, especially on the side of the solar cell facing the sunlight, a low refractive index and a high transparency is desirable so that as little light as possible reflects and as much light as possible is transmitted to the pn junction of the solar cell. Therefore, a low refractive index is set at this side of the amorphous doped layer. In some embodiments of the method according to the invention, a similar layer is produced on the side of the solar cell facing away from the sun for reasons of symmetry.

In an analogous manner, in an advantageous variant of the method according to the invention, the doping of the at least one SiO _x , SiN _y and / or SiC _z layer is changed in the layer deposition with the layer thickness, so that the at least one SiO _x -, SiN _y - and / SiC _z layer has changed over their layer thickness changed conductivities.

In the production of the amorphous doped layer as large as possible conductivities are to be produced. In particular, this requirement exists where the amorphous doped layer is involved in the formation of the heterojunction pn junction. At least on this side of the layer, the production of a high conductivity is required in order to achieve a functioning of the solar cell. On On the other side of the amorphous doped layer, lower conductivity is partially acceptable. Among other things, since the conductivity strongly depends on the doping, the part of the layer which requires a high conductivity is preferably also highly doped.

In a preferred embodiment of the method according to the invention, the thickness and the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer are set so selected during the deposition thereof that the reflection of the solar cell in a wavelength range of the incident light of 600 nm to 700 nm <5%. The antireflection property of the amorphous doped layer is optimized in this case to the wavelength range between 600 nm and 700 nm, whereby the entire available spectral range is used optimally by the solar cell.

In other special applications of the method according to the invention, the thickness of the at least one SiO _x , SiN _y and / or SiC _z layer is optimized to a different wavelength. One reason for this can be, for example, the implementation of a specific architectural color desire to the appearance of the solar cell.

In a further embodiment of the method according to the invention, the at least one SiO _x , SiN _y and / or SiC _z layer is contacted, and on the at least one SiO _x , SiN _y and / or SiC _z layer and their contacts a layer sequence of ethyl vinyl acetate and glass provided. By contacting the amorphous doped layer or provided on both sides of the solar cell amorphous doped layers, a good electrical connection of the solar cell is achieved. By forming a stacked structure of glass, ethyl-vinyl-acetate and solar cell, a long-term stable hermetically sealed housing for the solar cell is formed. The enclosure of the solar cell with ethyl vinyl acetate and glass is not only advantageous on the solar facing front of the solar cell, but also on its back. A favorable property of glass is its resistance to aggressive atmospheric constituents, such. B. ammonia.

Preferred embodiments of the present invention, their structure, function and advantages will be explained in more detail below with reference to figures, wherein

1 schematically shows an embodiment of a solar cell according to the invention in cross-section through its layer structure;

2 schematically shows the reflection of a solar cell of the prior art; and

3 schematically shows the reflection of an embodiment of a solar cell according to the invention.

1 schematically shows a section of the cross section of a solar cell according to the invention 1 , The solar cell 1 has a heterojunction pn junction 2 on between a crystalline silicon substrate 3 and at least one amorphous doped layer 5 is trained. In the illustrated embodiment, the crystalline silicon substrate is 3 n-doped and the amorphous doped layer 5 is p-doped. Between the at least one amorphous doped layer 5 and the crystalline silicon substrate 3 is an amorphous intrinsic, so undoped, layer 6 intended. The intrinsic layer 6 is an auxiliary layer that in practice has the pn junction between the silicon substrate 3 and the layer 5 is formed, improved.

The at least one amorphous doped layer 5 lies on the front side of the crystalline silicon substrate 3 and the solar cell 1 , From this side is the collapse of sunlight into the solar cell 1 and in the crystalline silicon substrate 3 intended. On the back of the crystalline silicon substrate 3 It has proven to be advantageous to provide an at least partially particularly highly doped back coating. This backside coating results in the space charge zone from the pn junction to the backside of the crystalline silicon substrate 3 is extended and the charge carrier transport by appropriate electric field gradient up to the back of the solar cell 1 works well. In the solar cell exemplified 1 For example, the backside coating consists of an amorphous intrinsic layer 7 and a highly n-doped layer 8th , In other embodiments, not shown, of the solar cell according to the invention, it is also possible to use a p-doped silicon substrate and a highly p-doped backside coating.

The layer thickness of the intrinsic layers 6 and 7 are chosen the same size, as are the layer thicknesses of the amorphous p-doped layer 5 and the amorphous highly n-doped layer 8th about the same size. By such a symmetric layer structure with respect to the crystalline silicon substrate 3 the forces are from layer stresses on the silicon substrate 3 compensated. The silicon substrate 3 is little warped and the risk of breakage for the silicon substrate 3 is minimized.

The electrodes of the solar cell 1 exist on the front of the contacts 11 which are metallic silver conductors in the case shown. The contacts 11 on the front of the solar cell 1 For example, they are screen-printed from silver pastes by a process similar to that of US Pat the method used in conventional homojunction silicon solar cells.

In the solar cell 1 is the backside electrode of an ITO layer 14 and an aluminum layer 15 educated. The ITO layer works 14 as a diffusion barrier against the penetration of aluminum atoms, which are p-dopants, from the aluminum layer 15 in the back of the n-doped silicon substrate 3 or one of the amorphous silicon layers 7 or 8th on the back of the silicon substrate 3 ,

The housing of the solar cell 1 has a glass on both the front and the back 13 . 17 on. An optical and mechanical connection between the glass panes 13 and 17 is through the EVA layers 12 and 16 achieved, with which the central components of the solar cell 1 be laminated and the glass panes 13 and 17 on the inner parts of the solar cell 1 be attached.

2 schematically shows the reflection of a solar cell 1 from the prior art, as for example from the document WO2009 / 078672 A2 is known, in a wavelength range between 300 nm and 1100 nm. The known solar cell uses an indium tin oxide (ITO) layer as an antireflection layer. The ITO layer has a high transparency for light and at the same time this layer is electrically conductive. However, the electrical conductivity of the ITO layer is not large enough to use the ITO layer alone as an electrode. For this reason, low-resistance metal lines in the form of contacts are additionally used to derive the charge carriers collected in the ITO layer. The layer thickness of the ITO layer is set at 80 nm, for example, so that the optical layer thickness equal to the product of the mechanical layer thickness and the refractive index is equal to one quarter of the design wavelength. The design wavelength is around 650 nm. At this wavelength, the best antireflectance or the lowest reflection is achieved. For complete antireflection of the silicon substrate used for light incident from a glass pane and an EVA layer, the antireflection coating, which in the illustrated embodiment is the ITO layer, requires a refractive index of 2.3. By contrast, ITO has a refractive index of 1.88 and is therefore not optimally suited for antireflection coating. This is in the diagram in 2 Recognizable that the reflection in the reflection minimum at the design wavelength is not 0 but> 3%. This results in a corresponding loss of efficiency of at least 3% compared to a hypothetical optimal antireflection layer. This disadvantage was accepted in the prior art, since no electrically conductive layers with a refractive index of 2.3 were available.

This disadvantage is inventively eliminated in that the at least one amorphous doped layer 5 at least one SiO _x , SiN _y and / or SiC _z layer modulated by adjusting the factor x, y and / or z in the layer deposition in its refractive index 5 is. The at least one SiO _x , SiN _y and / or SiC _z layer 5 is in the in 1 illustrated training, for example, a hydrogen-containing silicon layer with oxygen and carbon fractions.

At the interface between the at least one SiO _x , SiN _y and / or SiC _z layer 5 and the amphora intrinsic layer 6 where the pn junction to the crystalline silicon substrate 3 is formed, has the at least one SiO _x , SiN _y and / or SiC _z layer 5 a low oxygen content (x <1) and a high boron doping. This results in a conductivity required for the formation of the pn junction. On the other hand, the at least one SiO _x , SiN _y and / or SiC _z layer 5 by the oxygen content itself at the interface with the amorphous intrinsic layer 6 an increased transparency compared to a pure amorphous silicon layer. This side of the SiO _x , SiN _y and / or SiC _z layer 5 is also the crystalline silicon substrate 3 facing side 51 this layer.

Due to the high silicon and the low oxygen content of the crystalline silicon substrate 3 facing side 51 the at least one SiO _x , SiN _y and / or SiC _z layer 5 For example, this side has a refractive index that is greater than the target refractive index, which is the optical design of the at least one SiO _x , SiN _y and / or SiC _z layer 5 can be reached. In order to achieve the target refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer, the outer surface becomes 52 the at least one SiO _x , SiN _y and / or SiC _z layer 5 having a refractive index smaller than the target refractive index. In the illustrated embodiment, this is achieved in that the oxygen content is increased.

To set the desired refractive index and the desired electrical properties, not only the oxygen content in the at least one SiO _x , SiN _y and / or SiC _z layer is suitable 5 but also with nitrogen and carbon contents, desired effects can be achieved. Other embodiments have in the at least one SiO _x , SiN _y and / or SiC _z layer 5 instead of or in addition to the modulated oxygen content modulated nitrogen and / or carbon on.

The refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer 5 is in the illustrated Embodiment adjusted to a resulting value of 2.3 and the layer thickness to 65 nm. This results in a minimized reflection behavior of the solar cell 1 in the wavelength range between 600 nm and 700 nm and a high electrical efficiency of the solar cell 1 when irradiated with sunlight.

The at least one SiO _x , SiN _y and / or SiC _z layer 5 also has a high electrical conductivity between 50 Ω / ☐ and 500 Ω / ☐, whereby the layer 5 also acts as an electrical conductor, which in the at least one SiO _x , SiN _y and / or SiC _z layer 5 collected charge carriers to the contacts 11 hinleitet.

The oxygen, nitrogen and / or carbon content in the at least one SiO _x , SiN _y and / or SiC _z layer 5 also hinder crystallization in this layer, so that it has a better temperature resistance than an amorphous silicon layer.

3 schematically shows the reflection in the 1 illustrated solar cell according to the invention 1 , to the light through the glass 13 falls. Due to the optimized refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer 5 For example, the reflection in the wavelength range between 600 nm and 700 nm is minimized to values near zero. As a result, the solar cell according to the invention 1 in addition to a simplified structure and an increased efficiency.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• WO 2009/078672 A2 [0006, 0048]

Claims (24)

Solar cell ( 1 ) with a heterojunction pn junction ( 2 ) sandwiched between a crystalline silicon substrate ( 3 ) of a first conductivity type and at least one amorphous doped layer of a second conductivity type, characterized in that the at least one amorphous doped layer comprises at least one SiO _x - modulated by adjusting the factor x, y and / or z in the layer deposition in its refractive index SiN _y and / or SiC _z layer ( 5 ) with x ≠ 2, y ≠ 4/3 and z ≠ 1; wherein the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) between 2 and 3, the conductivity of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) between 50 Ω / □ and 500 Ω / □ and the layer thickness of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is between 50 nm and 300 nm. Solar cell according to claim 1, characterized in that the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is between 2.1 and 2.5. Solar cell according to claim 1 or 2, characterized in that the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) Is 2.3. Solar cell according to at least one of the preceding claims, characterized in that between the crystalline silicon substrate ( 3 ) and the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) at least one amorphous intrinsic layer ( 6 ) is provided. Solar cell according to claim 4, characterized in that the amorphous intrinsic layer ( 6 ) is an amorphous undoped silicon layer. Solar cell according to claim 4 or 5, characterized in that the at least one amorphous intrinsic layer ( 6 ) has a layer thickness of 5 nm to 15 nm. Solar cell according to at least one of the preceding claims, characterized in that the factor x, y and / or z of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is changed with the layer thickness, so that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) has different refractive indices over its layer thickness. Solar cell according to claim 7, characterized in that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) on its crystalline silicon substrate ( 3 ) facing side ( 51 ) has a higher refractive index than at its opposite surface ( 52 ) having. Solar cell according to at least one of the preceding claims, characterized in that the doping of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is changed with the layer thickness, so that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) has changed conductivities over its layer thickness. Solar cell according to claim 9, characterized in that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) on its crystalline silicon substrate ( 3 ) facing side ( 51 ) has a higher conductivity than at its opposite surface ( 52 ) having. Solar cell according to at least one of the preceding claims, characterized in that the thickness and the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is selected so that the reflection of the solar cell ( 1 ) in a wavelength range of the incident light of 600 nm to 700 nm <5%. Solar cell according to at least one of the preceding claims, characterized in that the crystalline silicon substrate ( 3 ) n-doped silicon and the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is p-doped. Solar cell according to at least one of the preceding claims, characterized in that the at least one SiO _x -, SiN _y - and / or SiC _z layer ( 5 ), and on the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) and the contacts ( 11 ) a layer sequence of ethyl vinyl acetate ( 12 . 16 ) and glass ( 13 . 17 ) is provided. Method for producing a solar cell ( 1 ) with a heterojunction pn junction ( 2 ), wherein to form the pn junction on a crystalline silicon substrate ( 3 ) of a first conductivity type at least one amorphous doped layer of a second conductivity type is formed, characterized in that as at least one amorphous doped layer at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ), wherein in the layer deposition the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is modulated by setting the factor x, y and / or z, where x ≠ 2, y ≠ 4/3 and z ≠ 1, while setting it to a value between 2 and 3; the conductivity of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is adjusted by doping this layer between 50 Ω / □ and 500 Ω / □; and the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is deposited with a layer thickness of 50 nm to 300 nm. Method according to claim 14, characterized in that between the crystalline silicon substrate ( 3 ) and the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) at least one amorphous intrinsic layer ( 6 ) is provided. Process according to claim 15, characterized in that as an amorphous intrinsic layer ( 6 ) depositing an amorphous undoped silicon layer. Method according to claim 15 or 16, characterized in that the at least one amorphous intrinsic layer ( 6 ) is deposited with a layer thickness of 5 nm to 15 nm. Method according to at least one of claims 14 to 17, characterized in that the factor x, y and / or z of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is changed in the layer deposition with the layer thickness, so that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) has different refractive indices over its layer thickness. Method according to claim 18, characterized in that the factor x, y and / or z of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is changed in the layer deposition with the layer thickness such that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) on its crystalline silicon substrate ( 3 ) facing side ( 51 ) has a larger refractive index than at its opposite surface ( 52 ) having. A method according to any one of claims 14 to 19, characterized in that the doping of the at least one SiO _x -, SiN _y - and / or SiC _z layer ( 5 ) is changed in the layer deposition with the layer thickness, so that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) has changed conductivities over its layer thickness. Process according to Claim 20, characterized in that the doping of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is changed in the layer deposition with the layer thickness such that the at least one SiO _x , SiN _y and / or SiC _z layer at its the crystalline silicon substrate ( 3 ) facing side ( 51 ) has a higher conductivity than at its opposite surface ( 52 ) having. Method according to at least one of claims 14 to 21, characterized in that the thickness and the refractive index of the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) are set in their deposition so selected that the reflection of the solar cell ( 1 ) in a wavelength range of the incident light of 600 nm to 700 nm <5%. Method according to at least one of claims 14 to 22, characterized in that as a crystalline silicon substrate ( 3 ) n-doped silicon is used and the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) is p-doped. Method according to at least one of claims 14 to 23, characterized in that the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ), and on the at least one SiO _x , SiN _y and / or SiC _z layer ( 5 ) and the contacts ( 11 ) a layer sequence of ethyl vinyl acetate ( 12 . 16 ) and glass ( 13 . 17 ) is provided.

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