DE102011104020A1 - Process for producing a contact layer of a solar module and solar module produced in this way - Google Patents

Abstract

The invention relates to a method for producing a contact layer of a solar module, wherein the material of the contact layer for forming a surface is arranged on a carrier substrate. The method is characterized in that a gradient is formed in the contact layer and increase along the gradient of the electrical resistance and the transmission in the same direction of the surface. A solar module manufactured in this way is disclosed.

Description

The invention relates to a method for producing a contact layer of a solar module and a solar module produced in this way.

State of the art

A known method to realize an integrated series connection of a large-area thin-film solar module is in 1 roughly schematically shown in cross section for a silicon based module.

First, a contact layer, for. B. a transparent conductive layer 2 , z. B. ZnO or SnO ₂ on a transparent substrate 1 as carrier material, see 1b , As a carrier substrate z. As glass or foil used. A typical process temperature for applying a ZnO layer by sputtering is 300 ° C.

Subsequently, the P1 lines are laser ablated at room temperature. In this case, parallel to each other arranged first trenches 5 made over the length of the module ( 1c ).

Hereinafter, the term "over the length of the module" is used in such a way that is meant structuring, which runs in the depth of the leaf level of the figures. The characteristic of solar modules lines are formed. In supervision of the finished solar module, the lines are visible, see 1h ,

Thereafter, an absorber layer system of semiconductor layers is applied, for. B. an a-Si / μc tandem solar cell (see 1d ). This will be the first trenches 5 filled. A typical process temperature for the deposition of silicon layers by PECVD method is 100-250 ° C.

Then the P2 lines are again formed by ablation. Parallel to the first trenches are the second trenches 6 made in 1 always to the right of the first ditches.

This is followed by a second contact layer 4 as back contact on the semiconductor layers 3 applied, z. A ZnO / Ag contact, see 1f , Here are the second trenches 6 filled. A typical process temperature for applying a ZnO / Ag back contact by sputtering is the room temperature.

Subsequently, the P3 lines are again made with a laser, see 1g , This will be third trenches 7 parallel and formed in the picture always to the right of the first and second trenches. So there are the same number of trenches 5 . 6 and 7 , Thus, the series connection of the cell A to the cell B and that of the cell B to the cell C and so on is completed.

When using the 1a - 1g explained interconnection method is after the deposition of the first contact layer 2 (Front contact, TCO), and after the deposition of the semiconductor layers 3 and after the deposition of the second contact layer 3 (Back contact) in each case a separation of the layers during the P1-P3 structuring z. B. performed by laser ablation. The trenches or lines of the P1 structuring are thus each produced parallel to one another over the length of the solar module. Laterally offset, the trenches or lines of the P2 structuring and the P3 structuring along the length of the solar module are likewise written parallel to each other.

For laser ablation of the TCO as the first electrical contact layer (front contact), a different laser is generally used than for the semiconductor layers or for the second electrical contact layer, the back contact. This requires a laser with a wavelength at which the TCO material is absorbent.

Incidentally, it is known that the material ZnO is etchable as a material of the first contact layer in acid or in alkali. An etching takes place regularly before the arrangement of the semiconductor layers 3 , At the same time, the surface of ZnO becomes 2 with a wet-chemical etching process z. B. roughened with hydrochloric acid. An anisotropic layer removal of ZnO occurs.

The roughening of the ZnO layer is important to ensure better light coupling and light scattering of the trapped light back into the semiconductor layers.

From the publication Lu et al. ( Hui Lu, Yaoquan Tu, Xian Lin, Bin Fang, Duanbin Luo, Aatto Laaksonen (2010). Effects of laser irradiation on the structure and optical properties of ZnO thin films. Materials Letters 64, 2072-2075 ) it is known that ZnO films can be changed in their optical and structural properties by laser treatment. The grain size as a measure of the crystal property is selectively increased by the laser treatment and increases the optical band gap of the material.

Processes for the production and series connection of thin-film solar modules are known in which deviating from 1 First, several of the layers are sequentially deposited and then the P1-P3 structures are written.

Solar modules are generally produced with the aim of providing the most homogeneous layer properties in terms of layer thickness and layer properties or layer quality over the entire coated surface. This applies independently for the contact layers as front and back contact as well as for the absorber layers (semiconductor layers). Unwanted inhomogeneities and deviations from standard parameters such as the thickness of the layers in themselves lead to increased electrical and / or optical losses of the solar module.

The P1-P3 structures are written to reduce the current density in a large area solar panel. The solar module is therefore subdivided into smaller sub-cells, strips A, B, C, D and so on. The cell strips are all the same size and are interconnected in series. 1g shows a schematic representation of a series-connected solar module.

2 shows a simplified schematic representation of a silicon thin-film solar module. The arrows in the module indicate the direction of current flow during operation of the solar module via the four series-connected cell strips A-D by arrows. The solar module consists of the carrier glass 21 , a first contact layer 22 , the so-called transparent front contact (TCO), the silicon (semiconductor) layers 23 with the absorber layer system and the back contact 24 , The layer properties are distributed very homogeneously over the cell fringe surface A, B, C and D as desired, and the individual cell fringes A, B, C, D and so on are made identical in their properties such as width and so on.

The efficiency of a single solar module with a p-i-n structure or with an n-i-p structure of the semiconductor layers, that is without a tandem arrangement, is still comparatively low despite great efforts.

Disadvantageously, none of the methods known from the prior art have been able to provide a solar module with improved efficiency.

Task and solution of the invention

The object of the invention is to provide a method for producing a solar module with high efficiency. Another object of the invention is to provide the solar module as such.

The object is achieved by a method according to claim 1 and by the module according to the independent claim. Advantageous embodiments emerge from the respective back claims.

Description of the invention

On a carrier substrate, a first contact layer is uniformly arranged over the entire surface. The contact is used in the finished solar module as a front contact or as a back contact. Both are possible.

As a substrate is in particular a glass, a plastic film, or a metal with an insulating layer into consideration. The material of the first electrical contact layer has a good conductivity. ZnO: Al, ZnO: Ag, ZnO: B, ZnO: Ga, SnO ₂ : F, ITO, or TiO ₂ and alloys such as. B. ZnMgO in question. Furthermore, metals can be used.

The aluminum-doped zinc oxide (ZnO: Al) is particularly advantageously used, since this is particularly easy to treat.

The substrate is also considered to be a structure comprising a carrier substrate with a contact layer applied thereon and semiconductor layers arranged thereon, onto which a contact layer according to the invention is then arranged.

The surface of the carrier substrate is z. B. to 10 × 10 cm ² . The deposited contact layer is slightly smaller because the edge of the substrate should be left free.

The object of the invention is achieved by the method for producing the contact layer of the solar module on the carrier substrate and in particular the deposition of a front contact layer.

The contact layer has a first order region per se. A first-order region is defined as a planar arrangement in a homogeneous, uniformly deposited material of the contact layer on the carrier substrate, such. B. a uniformly deposited aluminum-doped zinc oxide layer (ZnO: Al).

Deviating from the prior art, the contact layer on the carrier substrate has location-dependent layer properties with respect to the electrical resistance and the transmission in the area. The material of the contact layer is arranged to form a surface on the carrier substrate. Possible coating methods for the contact layer are sputtering, vapor deposition and PECVD methods and other deposition methods.

The thickness of the contact layer is preferably between 100 and 1000 nm. According to the invention, the contact layer is arranged in such a way that a gradient is formed in the contact layer in the first-order region. Along the gradient, the electrical resistance and the transmission increase in the same direction of the surface of the contact layer. The gradient thus preferably runs in the area. It is conceivable to form this also in the depth of the contact layer according to the invention.

The gradient is preferably stripe-shaped in the contact layer, that is to say over a plurality of strips. The gradient is produced in the direction of an expected decreasing current density on the contact layer so that the electrical resistance and the transmission of the contact layer in the finished solar module increase with decreasing current density.

The term "strip" preferably comprises a shape having a greater extension in length in the XY plane (Cartesian) of the layer than in the width, see the comments on 1g in terms of the definitions of length and width. Deviations from the strip form are permitted, provided that a greater length than width is formed. Meandering areas can also form a strip shape. With these second-order cell strips, in contrast to the separate first-order regions, as indicated for the prior art, means contacting regions or strips of the contact layer according to the invention. The contact layer is deposited over the surface and then, preferably by laser treatment, the gradient is formed in the layer, without the material being removed. Thus, this measure is fundamentally different from laser ablation to form the prior art strips of the prior art in which the material of the layer is ablated and removed, and trenches are formed between the first order regions.

The regions of second order can also be produced during the deposition, in which the material of the contact layer has different conductivities directly next to one another. This is achieved by using targets with different concentrations of conductive dopant atoms.

These regions or second order stripes are formed in the superordinate structure, that is to say in the regions or first order stripes as indicated for the prior art (cf. 1 ), educated. The transmittance and the resistance increase uniformly in the same direction of the area along the gradient, that is, from a second order area to the second order second area and so on, until the end is reached in the first order area.

In the context of the invention it was recognized that in silicon thin film solar modules with a highly conductive back contact, z. B. with ZnO: Al and silver as the back contact, the resistance of the contact layers as a whole largely by the resistance of the transparent conductive front contact z. B. with ZnO: Al is formed as a front contact. The transparent conductive front contact is thus preferably made of a so-called TCO (transparent conductive oxide) material such. B. ZnO: Al executed. In these material combinations, the properties of transmission and conductivity compete. If a TCO layer with less electrical resistance (higher conductivity) to be produced, for. B. by increasing the layer thickness or by increasing the concentration of the free charge carriers in the material, so reduces the transmission. Conversely, higher transmission of the TCO layer as a front contact can be achieved by increasing the electrical resistance, e.g. B. by a smaller layer thickness or by reducing the concentration of the free charge carriers. It was recognized in this connection that ZnO: Al layers with higher charge carrier concentration show lower transmission. This effect is particularly evident in the near infrared (NIR) spectral range> 800 nm wavelength.

It is also possible to arrange both contact layers, that is to say the front contact and the back contact with the gradient according to the invention, on the substrate, in particular if there are two TCO contact layers as the front and rear contact layers.

The TCO layer as a contact layer on the carrier substrate must therefore be optimized in terms of its ability to conduct the electric current and in terms of its transmission in the finished solar module, since an increase in the transmission results in an increase in the photocurrent.

It has been recognized that in the prior art modules, a non-homogeneous current density distribution is regularly dissipated from a self-homogeneous TCO layer as the front contact layer.

Therefore, by the formation of the Gra invention according to the invention, a local adaptation of the contact layer to the current density distribution via a local variation of the sheet resistance and thus made on the current density distribution in order to achieve in this way to a reduction of optical and / or electrical losses.

The gradient of the parameters according to the invention is formed in a first alternative by laser treatment.

Preferably, the gradient is formed by increasing the energy input during the laser treatment in the surface of the contact layer. A high energy input can be set, for example, by a long treatment time during a slow guidance of the laser and / or by a higher power. It is advantageously effected that the resistance and the transmission are increased with increasing energy input. The electrical conductivity, however, decreases.

With varying parameters during the laser treatment, the gradient in the first-order regions with respect to the electrical resistance and the transmission of the contact layer is advantageously produced. Thus, the laser power may be between 0 and 5 watts to form second order contacting regions in a first order region. Alternatively, to generate the gradient, the speed at which the laser is guided laterally over the surface of the contact layer can be varied. Thus, the laser speed can be adjusted between 0.1 to 15 mm · s ^-1 within a first order range to produce the gradient. This depends largely on the choice of the laser. A person skilled in the art will select the laser according to availability and adjust the parameters.

In a further alternative, the gradient in the contact layer is produced by temporally successive sputtering of targets with differently conductive material. For this purpose, a relative movement between the carrier substrate is carried out with a mask arranged thereon and the target. Particularly advantageously, the targets are changed during the relative movement. This increases the speed of the process. Advantageously, targets should be sputtered with a target doping amount between 0.2 and 1% in the relative movement. Then advantageously results in the desired conductivity, or the desired electrical resistance and thus transmission.

It is conceivable in a further embodiment of the invention that the gradient is formed by different layer thickness in the adjoining second-order regions. Then, the contact layer is arranged in a wedge shape over the surface on the carrier substrate.

With said alternatives, second order contacting regions are formed in a first order region of the contact layer. The second order resistance is preferably from 5 ohms to 30 ohms. Deviations are of course possible, as long as the transmission and the electrical resistance are changed within the scope of the invention. Thus, in the first order region comprising the second order regions, there also results a gradient from about 7 ohms to about 25 ohms from one end to the opposite end of the region.

In the case of a laser treatment, the second order region is effected with a resistance of about 5 ohms without treatment of the layer with the laser. The range of, for example, 25-30 ohms is achieved by laser treatment at low speed or high power. The interposed regions are provided by conditions adapted thereto for the laser treatment.

In the case of sputtering of targets with different aluminum concentrations in the zinc oxide z. For example, over a width B of the first-order region, targets having a concentration of aluminum of 0.1-2% target doping amount are used.

The solar module produced in this way is characterized in that at least one contact layer of the module in the direction of decreasing current density has the gradient with increasing electrical resistance and transmission. Accordingly, the conductivity decreases.

In the deposited (front) contact layer, no structures are initially contained after the full-surface arrangement (first-order region). The contact layer can be repeated, z. B. linear, are ablated, so that a plurality of first order arranged in parallel, in particular strip-shaped areas, are formed in the contact layer, as exemplified in the 1h are shown. This corresponds to the P1 structuring to form multiple first order regions as known in the art. Several areas of first order, z. B. stripes are identical to each other. They are parallel to each other on the carrier substrate before and form the basis for forming strip-shaped photovoltaic elements. This arrangement is advantageous in order to reduce the current density in the later large-area solar module. For this purpose, the solar module is subdivided into smaller sub-cells, strips A, B, C, D and so on. The cell strips are all the same size and are connected in series with the strips of the contact arranged on the other side of the semiconductor layers later in the process. The method is preferably also characterized in that a plurality of first-order cell regions, which are parallel to one another and spatially separated from each other by first trenches, are formed in the contact layer with corresponding gradients. Each of these areas has the desired gradient. Between the first-order regions, the material of the carrier substrate is exposed.

On the contact layer according to the invention, the active semiconductor layers are arranged over the whole area. As semiconductor layers, the layers for an a-Si: H-μc-Si: H tandem solar cell or any other layer sequence as they are commonly used in the solar cell industry. In particular, p-i-n or p-i-n-p-i-n layers or n-i-p or n-i-p-n-i-p layers are deposited. The invention is not limited in this sense.

Possible semiconductor layer systems are amorphous, microcrystalline, polycrystalline silicon, silicon germanium, silicon carbon, SiO ₂ , Si ₃ N ₄ , SiO x, SiON, CdTe and CIGS. It is also possible to arrange simple pin diodes made of a-Si or μc-Si or else pin-pin tandem structures of a-Si / a-Si or also a-Si / μc-Si and the respective alloys of silicon with germanium or carbon.

The P1 structures can be formed before or after the formation of the gradients according to the invention. The P1 structures can also be formed after the arrangement of the semiconductor layers and even after the arrangement of a further contact layer on the semiconductor layers. P2 and P3 structures and trenches are then formed parallel to the first trenches. This is the series connection of the strip-shaped photovoltaic elements.

Then, adjacent to and laterally offset from the first trenches of the first P1 structuring, second trenches are formed by a second P2 structuring. All second trenches are formed in parallel in the same orientation to the first trenches. In the second trenches, the surface of the contact layer according to the invention must be exposed, since the series connection of adjacent elements takes place here. The second trenches are preferably formed closely adjacent and parallel to the first trenches. With closely adjacent few are covered by distances of the parallel trenches to each other.

The second contact layer, z. As silver, aluminum or a combination of ZnO: Al and silver, is deposited on the semiconductor layers and in the second trenches. In the second trench, the electrical contact is advantageously used for series connection of adjacent strip-shaped elements. Possible coating methods for the second electrical contact layer are sputtering vapor deposition and PECVD method. The second electrical contact layer is not torn by the first trenches. Due to the second trenches, the desired contacts for series connection of the second electrical contact layer a first strip-shaped element, for. B. an element A, to a first electrical contact layer of a thereto adjacent second strip-shaped element, for. B. an element B, and so forth formed.

In parallel and closely adjacent and laterally offset from the first and the second trenches, respectively, third trenches are formed by a third structuring P3 corresponding to the number of first and second trenches. The third trenches further electrically separate the adjacent strip-shaped elements A, B, C and 50 from each other.

The first, second and / or third trenches for separating the strip-shaped elements are produced in particular by laser ablation.

The first trenches are produced by ablation of the first contact layer and subsequent wet chemical etching. For the laser process z. As a laser of wavelength 1064 nm used. This laser ablates only the semiconductor layers.

The second trenches are created by ablation of the semiconductor layers. For this purpose, a laser of wavelength 532 is usually used.

The third trenches are typically generated by simultaneous ablation of the semiconductor layers and the second electrical contact layer. For this purpose, a laser of wavelength 532 nm is also used.

All ablation steps can be through the substrate.

The module according to the invention accordingly has a plurality of adjacent strip-shaped elements. Each strip-shaped element has a layer sequence of carrier substrate, a first contact layer according to the invention on the substrate, the active semiconductor layers on the first electrical contact layer and second contact layer arranged thereon. For series connection, the second electrical contact layer of a strip-shaped element, for. B. element A, except for the first electrical contact layer of a thereto adjacent strip-shaped photovoltaic element, for. B. element B arranged. The module is characterized in that in each case gradients are present in the first electrical contact layer, in which the electrical resistance and the transmission of the contact layer increase.

In the direction of decreasing current density of the contact layer according to the invention, the transmission and thus the electrical resistance in the first order range are always increased. This measure alone causes the electrical and optical losses to be lower than in the prior art and thus the efficiency of the solar module is increased, by about 0.5% relative.

Special description part

Furthermore, the invention will be described in more detail with reference to exemplary embodiments and the attached figures, without this being intended to limit the invention.

Show it:

1 : Preparation and series connection of strip-shaped photovoltaic elements according to the prior art. 1a -G: cut; 1h : At sight.

2 : Current flow in the series-connected solar module according to the prior art. The strip-shaped photovoltaic elements A-D each correspond to four first-order regions.

3 : a) Enlargement to a first order area 2 , b) current flow in the first order (cell stripe C).

4 : a) Current flow in the strip-shaped photovoltaic element, for example element C, as the first-order region. b) section with increasing transmission and electrical resistance along the gradient in layer 42 the contact layer according to the invention.

5 - 6 : Schematic representation of the increase in laser treatment and thus the increase in transmission and electrical resistance (arrow J). The conductivity decreases along the gradient.

7 : Dependence of absorption on the wavelength of differently treated second order regions.

8th : Mask structure for the deposition of the contact layer.

1 shows schematically the manufacturing process of the prior art, as presented in the introduction.

In 2 a simplified schematic representation of a silicon thin film solar module is given. The arrows in the module indicate the direction of the current flow.

In the context of the invention, it was recognized that the current density distribution in the contact layers of a thin-film solar module or a cell strip is actually not homogeneous, in particular in the case of a perfectly homogeneous layer deposition, see 3 , It was recognized that, in principle, in a so-called homogeneous deposition, a position-dependent current density results over the cell stripe width.

The following properties actually occur per cell strip A-D. In 2 is in the cell strips A-D actually given a current density distribution, as exemplified in the clipping for cell stripe C in 3 is shown.

3a shows by way of example the strip-shaped photovoltaic element C from the 2 in magnification. 3 schematically shows approximately the circle of the section of the 2 , In fact, in the strip-shaped photovoltaic element C does not occur a homogeneous current density distribution, as previously suspected. In fact, the in 3b shown current density distribution. In the right part, high electrical losses occur due to the high current density. In the left part of the cell too low transmission of the TCO leads to high optical losses.

Therefore, a production method modified according to the invention for producing the contact layer on the carrier substrate was used as follows.

First embodiment

A 10 × 10 cm ² glass substrate 1 (Corning, Eagle XG) Is Annealed by Sputtering with Aluminum-Doped Zinc Oxide (ZnO: Al) 2 coated, which serves the solar cell as a front electrode. The carrier substrate 1 is here with the exception of its edge over the entire surface with the first contact layer 2 coated. The substrate temperature during the coating process is about 300 ° C. The first contact layer 2 is about 800 nm thick. It is homogeneous in terms of thickness, resistance and transmission and so on on the carrier substrate 1 arranged. After cooling the coated substrate 1 at room temperature, the layer sequence is etched for 30 seconds in dilute hydrochloric acid (0.5% wt). This etching step serves to roughen the layer and improves the optical properties of the layer.

The result is in the 1b shown. So far, the method of the prior art is known.

1. Inventive adaptation of a front contact layer (FIG. 4)

Using the example of a transparent conductive front contact 42 the further procedure is explained. 4 shows the schematic representation of the cell strip C of 2 in a silicon thin-film solar module according to the invention. In the direction of the arrow, ie in the direction of decreasing local current density in the TCO layer 42 (compare 3b ), the material is advantageously made less conductive, that is, the electrical resistance of the layer 42 via position X increases towards the left. The electrical resistance increases and so does the transmission. For the sake of simplicity, a linear trend for the sheet resistance is indicated here (solid lines).

For a prior art module with homogeneous resistance of the TCO layer 2 . 22 over the cell stripe width (cf. , bottom, dashed line) there is an optimal combination of TCO- Sheet resistance and cell stripe width. On the basis of such an optimized module, a reduction in the optical and electrical losses of the layer can be achieved if the areas of the front contact 42 , which have a comparatively high current density can be improved in their conductivity. These are in 4 schematically the areas to the right of the center M. The areas of the front contact 42 , which are to have a comparatively low current density to be reduced in their conductivity. These are the areas of the contact layer 42 left of center, see also 3b , It is important that an increase of the transmission occurs simultaneously with the reduction of the conductivity. This is the case with the typical materials of the front contact, in particular in the near infrared spectral range. Consequently, the resulting solar module according to the invention compared to the prior art has reduced electrical and optical losses and thus a higher efficiency.

5 shows the applicability of the method described above using the example of an adapted front contact made of sputtered and wet-chemically etched ZnO: Al. The gradient of the ZnO: Al properties is shown by laser annealing produced by the thick arrow. The laser enters the energy J The first-order cell stripe C (see 2 ) is thereby irradiated in sections to generate second-order regions with laser light. Irradiation and the absorption properties of the irradiated TCO material cause local heating of the material. As a result, the properties of ZnO: Al: It tends to be less conductive in laser annealing, that is, the resistance and at the same time increase the transmission.

Shown is the ZnO: Al surface before the deposition of the silicon semiconductor layers and the back contact. There are distinguished n strip-shaped areas, which have experienced a different treatment intensity. In the direction of the arrow, the treatment intensity increases so that a decrease in the conductivity is achieved with an increase in the transmission in the strip-shaped regions. The direction of the current flow is opposite to the direction of the arrow. The n regions have a gradient which is designed in such a way that the electrical and optical losses in the first-order cell stripe are minimal.

A module on a 10 × 10 cm ² glass substrate was practically implemented, in which every second of a total of 16 first-order cell strips was subdivided into n = 5 second-order strip-shaped regions. 6 shows the schematic representation of the front ZnO 42 in supervision even before the later deposition of silicon 43 ,

The front ZnO 42 is prepared in the following manner: A 10 × 10 cm ² glass substrate (Corning, Eagle XG) is coated by sputtering with aluminum-doped zinc oxide (ZnO: Al), which is the solar cell as a front electrode 42 serves. The excitation frequency is 13.56 MHz in a VISS 300 deposition system from Von Ardenne Anlagentechnik (VAAT). A ceramic target with 1% (wt) alumina content (Al ₂ O ₃ ) in ZnO was chosen. The substrate temperature is 300 ° C at a discharge power of 1.5 kW. The argon deposition pressure is 0.1 Pa. The layer thickness of the layer after deposition is about 800 nm. After cooling the coated substrate to room temperature, the future first-order cell strips A, B, C, D and so on were defined by using ZnO: Al layer by laser ablation 42 was locally removed, so that electrically isolated from each other, strip-shaped ZnO: Al first-order regions remained. Subsequently, the sample was subjected to a wet-chemical etching process in 0.5% (weight percent) hydrochloric acid for 50 seconds. In this case, about 150 nm are removed and the surface of the ZnO: Al layer is roughened. The etching was carried out at 25 ° C.

This was followed by the laser annealing according to the invention of every second successive cell strip. In this case, each treated cell strip was subdivided into five second-order strip-shaped regions in order to produce the gradient according to the invention. A schematic representation of a graded cell strip in a plan view in front of the silicon deposition shows 6 ,

The five areas, labeled 1-5, differ in the intensity of their respective laser treatment and thus in their electrical resistance and transmission. Starting from area 1, the intensity of the laser treatment increases. Area 2 is treated very strongly and area 5 is treated the most with laser radiation. The absolute energy input in J per area serves as a measure.

The goal is the formation of a gradient of the properties transmission and resistance of ZnO: Al. Table 1 shows examples of the laser parameters used and their effects on the sputtered, etched ZnO: Al layers. Second order area laser power frequency speed line offset sheet resistance 5 5W cw 2.5 mm / s 25 μm 23.6 ohms 4 5 W cw 5 mm / s 25 μm 18.8 ohms 3 5 W cw 10 mm / s 25 μm 14.5 ohms 2 5 W cw 15 mm / s 25 μm 10.3 ohms 1 untreated - - - 7 ohms Table 1: cw = continous wave; Laser parameters for the treatment of the ranges 1-5 and the effects on the sheet resistance and the transmission of an 800 nm thick rf-sputtered and then wet-chemically etched ZnO: Al layer.

On the thus designed transparent front contact 42 was then the solar module made of microcrystalline silicon 43 arranged. The absorber layer thickness was about 1 μm. The back contact 44 consisted of 80 nm ZnO and 200 nm silver. It was found that the graded cell strips have on average about 7% higher efficiency than the cell strips without corresponding gradients.

7 shows the effects on the transmission or absorption as a graph. The laser treatment also influences the optical properties of the TCO 42 , The spot diameter of the laser was about 600 μm in diameter during the treatment. A laser from Rofin, type Powerline 10E was used. Shown is the absorption of the layer 42 as a function of wavelength. With increasing laser treatment, carried out by low pass speed, the absorption is reduced, especially in the long-wave range and thus increases the transmission.

Second embodiment (FIG. 8):

A 10 × 10 cm ² glass substrate (Corning, Eagle XG) was coated by sputtering with aluminum-doped zinc oxide (ZnO: Al), which serves as the front electrode of the solar cell according to the invention. Here, first, a mask with 16 strip-shaped recesses 91.1 - 91.16 placed in front of the substrate. The recesses of the mask have a size of 1.76 × 80 mm ² and a distance of 5 mm from each other.

Then a first layer is sputtered. For each recess, a second-order strip-shaped region of ZnO: Al forms on the substrate. Then the mask becomes 91 in the direction along the short side of the first layer, see arrow, laterally offset. The mask is offset by 1.66 mm. It is then applied parallel to the first layer, a second layer. The first layer and the second layer thus have an overlap area of 0.1 mm along their long side. Thereafter, the mask is offset laterally in the same direction by 1.66 mm and deposited another layer. The layers 1-3 define 16 first-order stripes with three second-order regions at the end.

Dimensions: The first-order stripes have z. B. a total width of 5 mm. Then the second order areas each have a width of 1.66 mm. The length of the strip-shaped elements amount to z. B. 8 cm.

Possible deposition conditions for the layers 1-3 are shown in Table 2. Table 2: Areas 1 to 3 and the effects on sheet resistance and transmission at 1000 nm wavelength of an 800 nm thick rf-sputtered ZnO: Al layer. layer thickness substrate temperature Targetdotiermenge Transmission at 1000 nm sheet resistance 1 800 nm 300 ° C 1% 82 3.4 ohms 2 800 nm 375 ° C 0.5% 88 6.5 ohms 3 800 nm 400 ° C 0.2% 90 19.2 ohms

Basically, it is conceivable for both embodiments, each of the layers involved and also several simultaneously, z. B. also the back contact, an intermediate reflector, the doped layers (p or n), antireflection layers, etc. to provide with a gradient according to the invention, which leads to a reduction in losses or to save material graded layer or other layer.

Of course, the method according to the embodiments can be combined with each other for the arrangement of the different layers.

The deposition of the semiconductor layers and / or the second contact can also be done as for 1 , the prior art described.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited non-patent literature

• Hui Lu, Yaoquan Tu, Xian Lin, Bin Fang, Duanbin Luo, Aatto Laaksonen (2010). Effects of laser irradiation on the structure and optical properties of ZnO thin films. Materials Letters 64, 2072-2075 [0014]

Claims (14)

A method for producing a solar module, wherein the material of the contact layer is arranged on a substrate for forming a surface, characterized in that at least one gradient is formed in the contact layer during the manufacture of the solar module and in the gradient of the electrical resistance and the transmission in the same Increase direction of the surface of the contact layer. Method according to the preceding claim, characterized in that a plurality of gradients are formed in the contact layer, in which the electrical resistance and the transmission increase in the same direction of the surface of the contact layer. A method according to claim 1 or 2, characterized in that the gradient is formed with a laser treatment. Method according to the preceding claim, characterized in that for generating the gradient of the electrical resistance and the transmission of the contact layer, the laser power is varied. Method according to one of the preceding two claims, characterized in that, for generating the gradient, the speed with which the laser is guided laterally over the surface of the contact layer is varied. Method according to one of the preceding claims, characterized in that the gradient in the contact layer is produced by temporally successive sputtering of targets with differently conductive material. A method according to the preceding claim, characterized in that for this purpose a relative movement between the substrate is carried out with a mask arranged thereon and the target. Method according to the preceding claim, characterized by changing the target during the relative movement. Method according to one of the preceding three claims, characterized by sputtering of targets with a concentration of 0.2 to 2% in the target. Method according to one of the preceding claims, characterized in that a plurality of mutually parallel and spatially separated by first trenches cell strips are formed in the contact layer, each having a gradient, and in the gradient of the electrical resistance and the transmission in the same direction of the surface of the Increase contact layer. Method according to the preceding claim, in which further steps are carried out for the formation and series connection of strip-shaped photovoltaic elements: a) a semiconductor layer system is arranged on the cell strip of the contact layer, b) a plurality of second trenches arranged parallel to the first trenches are formed in the semiconductor layer system and the surface of the contact layer is exposed therein, c) a second contact layer is arranged on the semiconductor layer system, so that in the second trenches a contact is formed from the second electrical contact layer of a first strip-shaped element (A) to a first electrical contact layer of an adjacent second strip-shaped element (B), d) adjacent and laterally offset from the first and second trenches are respectively formed third trenches in the second electrical contact layer, the adjacent strip-shaped elements (A, B, C) separated from each other. Method according to one of the preceding claims, characterized in that both contact layers of the solar module have at least one gradient, and increase in the gradient of the electrical resistance and the transmission in the same direction of the surface of the contact layer. Solar module, comprising a substrate on which the material of a contact layer for forming a surface is arranged, characterized in that the contact layer has a gradient and increase along the gradient of the electrical resistance and the transmission in the same direction of the surface. Solar module having a plurality of adjacent strip-shaped, photovoltaic elements, wherein each photovoltaic element on a carrier substrate has a layer sequence comprising a first contact layer, active semiconductor layers and disposed thereon second contact layer, and for series connection, the second contact layer of a photovoltaic element (A) except for the first electrical contact layer of a photovoltaic element (B) adjacent thereto is arranged, characterized in that each first contact layer and / or second contact layer of the elements has a gradient and increase along the gradient of the electrical resistance and the transmission in the same direction of the surface.

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