Patent Application
20090291231
1. Field of the Invention
The present invention refers to an apparatus for producing a solar cell module having an array of photovoltaic cells on a common substrate, the apparatus comprising at least one treating chamber for depositing a layer on a substrate and at least one patterning means for patterning the deposited layer. The present invention further refers to an appropriate method for producing a solar cell module.
2. Prior Art
Energy generation by photovoltaic processes are becoming more and more important; since fossil energy resources like crude oil or natural gas become more and more restricted. Accordingly, great efforts are made to improve solar cell technology.
A lot of different concepts exist with respect to the design of photovoltaic devices or solar cells. All of these concepts are based on a semiconductor junction where charge carriers generated by impinging light are separated so that they can be led away through terminals connected to the semiconductor junction.
The different designs of solar cells comprise single semiconductor junctions like p-n-junctions with a p-doped semiconductor and a n-doped semiconductor adjacent to each other as well as multiple semiconductor junctions like pin-structures or nip-structures. While in the past most solar cells were based on silicon substrates, where respective semiconductor junctions were formed, modern photovoltaic devices are based on the so-called thin film technology. This technology utilizes an insulating substrate, e.g. a glass substrate or a plastic foil, or a metallic substrate onto which different layers are deposited to form an appropriate photovoltaic device. For example, U.S. Pat. No. 6,168,968 B1 and U.S. Pat. No. 6,288,325 B1 describe methods of producing thin film solar cells, where metallic or glass substrates are coated with a front or a back electrode layer, several semiconductor layers of doped and un-doped amorphous or micro-crystalline silicon as well as an appropriate back or front contact layer, respectively. If a glass substrate is used, the front contact may be formed by a transparent conductive oxide TCO, for example formed by indium tin oxide ITO.
WO 2006/053129 A2 describes an apparatus and a method for manufacturing photovoltaic devices by which such layers like a conductive back layer, a p-type semiconductor layer, an n-type semiconductor layer and a transparent conductive front layer can be deposited continuously on a substrate.
Although, the method described in WO 2006/053129 A2 is efficient for producing a layer stack of a solar cell or a photovoltaic structure, the described process may be disadvantageous for an industrially produced solar cell module in terms of efficiency and throughput.
In order to generate a sufficient yield of the electric energy or power generated, it is known in prior art to produce a plurality of separated and independent photovoltaic devices on a common substrate to be connected serially. Such an array of serially connected photovoltaic devices on a common substrate allows combining the electric energy generated in each photovoltaic device in order to increase the output voltage of the solar cell module. For this purpose, it is already known to pattern or to structure the deposited layers of the photovoltaic device, as described in U.S. Pat. No. 6,168,968 B1, U.S. Pat. No. 6,288,325 B1 and U.S. Pat. No. 5,527,716 A. During patterning or structuring trenches are introduced into the deposited layers in order to produce single areas separated to each other. Accordingly, the separated and independent areas of the successively deposited layers form together single and independent photovoltaic devices which can be appropriately electrically connected to form a solar cell module having a high electrical output.
Patterning, which might also be designated as trenching, is most often performed by a laser beam which is scanned over the surface of the photovoltaic layer structure in order to remove one or more deposited layers and/or parts of the substrate along the movement path of the laser beam. Accordingly, this process is also designated as scribing.
Although, structuring and patterning lead to an improved solar cell module, it is detrimental that this makes the overall production process very laborious and complex.
It is therefore an object of the present invention to provide an apparatus as well as a method for producing a solar cell module which avoids the disadvantages of prior art. In particular, the inventive method as well as the inventive apparatus should ensure an efficient and simple process for producing a solar cell module having an array of independent photovoltaic devices on a common substrate while at the same time good quality of the solar cells and especially high output of electrical energy should be reached. Moreover, the apparatus for producing such a solar cell module should be easy to manufacture.
The above-mentioned objects of the present invention are achieved by an apparatus having the features of claim 1 as well as a method having the features of claim 14 or 15. Preferred embodiments are subject matter of the dependent claims.
According to the present invention, it is suggested to carry out the patterning or structuring of a photovoltaic layer structure by laser treatment, maser (microwave amplification by stimulated emission of radiation) treatment, ultrasonic treatment, mechanical cutting or milling or a similar treatment under technical vacuum conditions so that this process step can be integrated into a vacuum apparatus for depositing layers for a photovoltaic layer structure. Accordingly, the patterning step is performed in a treating or vacuum chamber.
The patterning step can be carried out in the same treating chamber in which one or several deposition steps are performed. For example, such a treating chamber may provide different support positions for a substrate to be treated, in which different treating steps may be performed. While such a design is suitable for stationary treatment of the substrate, i.e. the substrate is stationary during single treating steps and/or during several or between successive treating steps, a separate treating chamber for carrying out the patterning step is preferable for continuous or dynamic treatment of the substrate which means that the substrate is moved during a single treatment step and/or between single treatment steps. A separate treating chamber for only carrying out the patterning step is also useful for stationary treatment in order to avoid contamination problems.
The present invention is particularly beneficial with respect to a continuously working apparatus where different treating chambers and the corresponding treating steps are passed one after the other by the substrate to be treated. Such a continuously working apparatus as well as the corresponding method are very advantageous with respect to reduced handling times for the substrate and the improved efficiency and throughput due to reduced locking processes and correspondingly reduced times for evacuation and filling the treating chambers with gas and/or cooling and heating of the substrates.
Thus, an apparatus according to the present invention may be equipped with transporting means for transporting a substrate from a first treating chamber for depositing a layer to a second treating chamber for patterning the deposited layer as well as for moving the substrate through the first and second treating chambers.
Such transporting means may be designed such that a common transport path through the first and second treating chambers or the whole apparatus is provided for, on which the substrate carriers supporting the substrate during movement through the apparatus can be moved in every conceivable manner. For example, sliding movement of the substrate carriers along rails as well as contactless movement achieved by magnetic forces of the substrate carriers may be used. The transporting means may be designed such that continuous movement and/or a stepwise movement can be performed. Moreover, buffer chambers or the like may be provided for.
Accordingly, the substrate carrier for the substrate may be used during the whole movement of the substrate through the apparatus, i.e. the movement through all the different treating chambers of the apparatus. The first treating chamber for depositing a layer as well as the second treating chamber for patterning the layer deposited in the first treating chamber are accordingly disposed such that the substrate can be moved from the first treating chamber to the second treating chamber without leaving the vacuum atmosphere of the apparatus or the treating chambers, respectively. Especially, the first and second treating chambers may be disposed adjacent to each other. Particularly, no time-consuming lock-in and lock-out processes have to be carried out for moving the substrate from the first treating chamber to the second treating chamber. Accordingly, effort with respect to lock-in and lock-out devices can be saved.
According to the simple and effective design of the present invention, a transfer opening may be present in the chamber walls of adjacent treating chambers to allow simple transfer from the substrate from one treating chamber to the other.
Through this common opening of adjacent treating chambers the common transport path may extend.
Due to the design of the very close arrangement of neighbouring treating chambers, the apparatus can be simplified by using common vacuum means for producing technical vacuum conditions in adjacent treating chambers, like the first treating chamber for depositing a layer and the second treating chamber for patterning the layer. Moreover, means for pressure adjustment between the first and the second treating chamber may be provided for, like additional openings, which at the end would allow providing only vacuum means at one of two adjacent treating chambers.
Since for a photovoltaic layer structure several layers have to be deposited, the apparatus may comprise several first treating chambers for depositing different layers and several second treating chambers for patterning these layers. The first and second treating chambers may be disposed alternately in-line. The number of pairs of first and successive second treating chambers may be in a range of one to twenty.
Instead of a sequence of pairs of first and second treating chambers it is also conceivable to design the apparatus such that several first treating chambers are disposed one after the other adjacent to each other with only one second treating chamber at the end of the series of first treating chambers. This is possible, if the patterning can be carried out for more than one layer in a single process step so that several layers deposited one after the other can be removed by a single patterning step.
Furthermore, variations of the design of successive first and second treating chambers may be applied at the end of the apparatus, since a final patterning step may be carried out under normal atmospheric pressure, since at the end of the apparatus one lock-out process has to be carried out anyway. Accordingly, the last patterning step can be carried out under normal atmospheric pressure.
Furthermore, the apparatus may comprise a third treating chamber or several third treating chambers for carrying out a cleaning step, especially after the patterning step. During this cleaning step particles generated during removing of material in the patterning step, which are only loosely adhered to the surface of the substrate, can be removed in order to avoid detrimental effects on the subsequent deposited layers and the photovoltaic device. Accordingly, after each second treating chamber for laser patterning the substrate a third treating chamber for carrying out the cleaning step may be arranged.
This third treating chamber for cleaning the substrate may be disposed along the transport path of the substrate similar to the first and second treating chamber so as to form a row of first, second and third treating chambers. Such a design may be especially useful when the cleaning step in the third treating chamber is also carried out under vacuum conditions.
Alternatively, the third treating chamber can be disposed offset of the transport path of the substrate through the first and second treating chambers. Such a design may be used, if the treating step is not carried out under vacuum conditions, but under normal atmospheric conditions so that in this case additional lock-in and lock-out processes have to be carried out. This can be done very efficiently, if the third treating chamber is not in-line with the first and the second treating chambers, since this place at the transport path may be used for a lock-in and a lock-out chamber.
If the third treating chamber is located in-line with respect to the first and the second treating chambers along the transport path of the substrate through the apparatus, the treating chamber may be designed similar to the first and second treating chambers.
Especially, the whole apparatus may comprise a plurality of identical modules which can be combined with each other and individually equipped according to the specific requirements of the apparatus.
One module may comprise one or several treating chambers, for example a pair of first and second treating chambers or a triple of first, second and third treating chambers.
The treating chambers may be equipped according to the methods and processes which are to be carried out in the treating chambers. For example, deposition of the different layers may be performed by chemical or physical vapor deposition processes CVD or PVD, especially low pressure chemical vapor deposition LPCVD, plasma enhanced chemical vapor deposition PECVD, cathode evaporation also designated as sputtering or reactive cathode evaporation (reactive sputtering).
The second treating chamber, wherein the laser patterning step is carried out, may be equipped with a corresponding device inside the treating chamber or outside of the treating chamber, for example in case a laser is used as patterning means. When the laser device is disposed outside the treating chamber, the treating chamber may comprise a transparent window for the laser irradiation in order to allow the laser beam to be directed onto the substrate to be laser treated.
If the laser or any other patterning means is arranged inside the treating chamber, vacuum feed throughs for supply lines may be provided for.
The cleaning processes carried out in the third treating chamber may comprise different cleaning methods or combinations thereof including fluid cleaning, chemical cleaning, electrostatic cleaning, blow cleaning and suction cleaning. However, some of the cleaning processes may only be carried out under normal atmospheric pressure conditions, while others also can be used under vacuum conditions. For example, electrostatic cleaning using electronic forces for attracting charged particles can also be used in vacuum as blow cleaning or suction cleaning. Blow cleaning uses a stream of inert gas to blow away particles from the surface of the substrate while suction cleaning utilizes suction means to attract particles. Especially, blow cleaning and suction cleaning may be used in combination. Fluid cleaning or chemical cleaning are preferably used under normal atmospheric pressure conditions, since the liquids used during this cleaning process may negatively affect vacuum atmosphere.
At the end of the manufacturing process of a solar cell module the solar cell is encapsulated so that the apparatus may also comprise an encapsulating unit. However, this process may be carried out under normal atmospheric pressure so that no vacuum chamber is necessary for this process.
Further advantageous, features and characteristics of the present invention will become apparent from the following description of preferred embodiments of the present invention with respect to the accompanying drawings. The drawings show in a pure schematic way in
The apparatus 1 comprises 16 chambers which are disposed one after the other along the transport path 2. Accordingly, during operation the substrates to be treated in the apparatus 1 are moved through the chambers 5 to 20 successively.
The first chamber 5 is a lock chamber which allows locking in the substrates to be treated into the apparatus 1. Since the whole apparatus 1 is operated with technical vacuum conditions inside the chambers 6 to 19, the substrates have to run through a lock chamber 5 at the inlet as well as the outlet (lock chamber 20) to be brought from the normal atmospheric pressure outside the apparatus 1 to the near vacuum conditions inside the apparatus 1 and vice versa.
In proximate neighbourhood to the lock-in chamber 5 a first treating chamber 6 is provided for. The treating chamber 6 is designed such so as to allow a deposition of a transparent conductive oxide layer onto the substrate which is preferably a glass substrate. The transparent conducive oxide TCO may be deposited by a sputtering process, especially a reactive sputtering process or Low Pressure Chemical Vapour Deposition LPCVD, so that the treating chamber 6 is equipped with a cathode evaporation device.
The TCO layer deposited in the treating chamber 6 may be an aluminium doped zinc oxide layer, a fluorine doped tin oxide (F—SnO), indium doped tin oxide (ITO) or a similar layer used in photovoltaic industry for making the front contact.
The apparatus 1 is designed to handle large-area substrates in order to produce big-sized solar cell modules. In order to achieve a high electrical output from the solar cell module, such large-area solar cell modules are made of an array of single photovoltaic cells being arranged in rows and columns adjacent to each other on the module. In order to produce such a plurality of separated photovoltaic cells, the layers deposited to form a photovoltaic structure are patterned or structured in order to form trenches in the respective layers so as to separate specific areas forming single photovoltaic cells. Accordingly, this process is also designated as trenching.
Consequently, the apparatus 1 comprises a second treating chamber 7 following successively the first treating chamber 6 along the transport path 2. Accordingly, the first treating chamber and the second treating chamber 7 have a common sidewall 21 with an opening (not shown) through which the substrate is moved along the transport path.
The patterning step in the treating chamber 7 is carried out by a laser process. A laser having a focused laser beam may scan over the surface of the substrate or the layer deposited in the treating chamber 6, respectively, in order to cut a trench into said layer. Accordingly, this process is also designated as scribing a pattern or structure into a surface of the substrate. Instead of moving the laser beam over the surface to be treated the substrate may be moved with respect to the fixed laser beam or combined movement may be carried out. Such a relative movement can also be applied to other patterning methods like mechanical patterning or maser patterning.
During the patterning step in treating chamber 7 the particles removed by laser cutting may be blown away by a blowing gas stream of inert gas directed onto the surface of the substrate to be treated and/or sucked off from the surface of the substrate by suction means. For this purpose, nozzles for blowing inert gas onto the substrate as well as to suck off a surface area of the substrate may also be moved over the surface of the substrate similar to the laser beam. In addition, other cleaning processes may be simultaneously carried out during the patterning step. For example, electrostatic cleaning may be used. For this process, the substrate carrier as well as the substrate are set to a specific electric potential in order to charge the particles removed by the laser beam. Spaced apart from the substrate counter electrodes may be provided to electrically attract the charged particles and thereby remove the loose particles from the substrate.
Alternatively or in addition to the cleaning during the patterning step, a third treating chamber 8 for carrying out a cleaning step may be provided. While the embodiment shown in
If a cleaning chamber 8 as in the embodiment shown in
The next treating chamber 9 being also closely attached to the treating chamber 8 again is a treating chamber of the first type. Accordingly, in the treating chamber 9 a deposition process is carried out. The treating chamber 9 is a CVD chamber wherein a chemical vapor deposition of a first semiconductor layer is carried out. Accordingly, treating chamber 10 is again a treating chamber of the second type in which the layer deposited in the CVD chamber 9 is patterned by a laser treatment. After the laser chamber 10 again a cleaning chamber 11 is disposed as seen in the transport direction of the transport path 2.
Chambers 12 to 14 and 15 to 18 form also triples of chambers like the chambers 9 to 11 comprising a deposition chamber 5, 15 and a laser chamber 13, 16 for trenching the layer deposited before as well as cleaning chambers 14, 17 to remove waste particles of the surface of the substrate.
The deposition chambers 9, 12 and 15 are used to deposite semiconductor layers by chemical vapor deposition CVD or especially plasma enhanced chemical vapor deposition PECVD in order to form a photovoltaic structure. Semiconductor layers deposited in the chambers 9, 12, 15 may be p-doped, n-doped or intrinsic silicon layers, especially hydrogenated silicon layers of amorphous or micro-crystalline type in order to form pin- or nip-structures. However, other types of photovoltaic structures formed of other layer structures or any other suitable semiconductor material, for example semiconductors formed by elements of the groups III/V of the periodic table, are also conceivable. Accordingly, the numbers of deposition chambers as well as successive patterning chambers and cleaning chambers of the apparatus may be adapted to the specific requirements.
For this reason, it is advantageous to design the apparatus 1 as a combination of a plurality of modules, one or more chambers forming one module. Thus, the apparatus 1 can be designed specifically with respect to the solar cell module to be produced by combining the appropriate number of modules. In this respect it is also advantageous to use identical modules or chambers, respectively, as a basic component of the apparatus 1. Such a basic component or chamber can be equipped with the appropriate devices and means so as to form a treating chamber of a first type, a second type or a third type, i.e. a deposition chamber, a patterning chamber or a cleaning chamber.
After the sequence of the chambers for deposition of layers and patterning as well as cleaning of the semiconductor layers (chambers 9 to 17), a further treating chamber of the first type is disposed adjacent to the cleaning chamber 17. The treating chamber 18 serves for producing a back contact layer, which might be a metallic layer, like aluminum.
Subsequent to the treating chamber 18 a treating chamber 19 for patterning of the back contact is provided for.
At the end of the apparatus 1 a lock out chamber 20 is disposed in order to remove the treated substrate or the produced solar cell module from the apparatus 1 by bringing it to the normal atmospheric pressure outside the apparatus 1 without destroying the vacuum conditions being present inside the apparatus 1.
As may be understood from the foregoing description, the whole apparatus 1 comprising treating chambers 6 to 19 is operated under technical vacuum conditions. Accordingly, means for producing such a vacuum (not shown) are provided for. Although, almost the same vacuum conditions may be present during operation in at least some of the treating chambers 6 to 19 of the apparatus 1, the single chambers 6 to 19 are separated by sidewalls 21 in order to enable a module concept and to avoid influences from one treating process carried out in one chamber to another treating process carried out in an adjacent chamber. For this purpose, lock means like shutters or valves or the like may be provided at the openings or transitions between the chambers 6 to 19. However, due to the fact that all different treating processes like deposition process, patterning process and cleaning process are carried out under technical vacuum conditions, it is not necessary to perform time-consuming lock-in and lock-out processes. Accordingly, it is neither necessary to provide additional lock-in and lock-out means which require additional expensive devices and space.
However, some processes are carried out under different vacuum conditions, like CVD processes at pressures in the range of 1 to 10 hPa and sputter processes at pressures in the area of 5*10−3 hPa. Accordingly, between treating chambers in which such different processes are carried out means for dealing with such pressure differences and/or gas separation means for separating different gas atmospheres have to be provided for. Thus, slit valves or lock-valves may be arranged between treating chambers in which different pressures and/or different gas atmospheres are present during processing of the substrates.
Moreover, buffer chambers (not shown) may be disposed in the apparatus to allow adapting of processing speed in different chambers or parts of the apparatus to each other. Accordingly, buffer chambers may be used to speed down or accelerate the substrates in the continuously working apparatus. In addition, buffer chambers may allow operation of parts of the apparatus for a while during breakdown of other parts to thereby improve efficiency of the apparatus.
Only in cases, where cleaning of the surface after the patterning step is crucial, a second type of a cleaning chamber or a second kind of arrangement of a cleaning chamber, respectively, may be chosen. An example is shown in
The part of the apparatus 100 shown in
Further, apparatus 100 comprises a deposition chamber 109 and a patterning chamber 110. Contrary to the embodiment of
The chambers 8, 9, 10, 11, 12 and 13 are separated by chamber walls which comprise transfer openings for the substrates to be moved along the transport path 2. In
The treating chamber 9 shown in
In order to achieve technical vacuum conditions a vacuum pump 38 which is serving for the adjacent chambers 9 and 10 is provided. The vacuum pump 38 is connected to the chambers 9 and 10 by conducting pipes 39 and 40. Instead of a common conduction pipe for adjacent chambers, like chamber 9 and 10, each chamber may have a separate vacuum pump as shown with the vacuum pump 44 and the conduction pipe 45 for the chamber 11.
After depositing a semiconductor layer 51 in the treating chamber 9 the substrate 26 is moved to the chamber 10 wherein a patterning or structuring of the layer 51 is performed. For this purpose, a laser device 41 is disposed outside the vacuum chamber 10. The laser device 41 produces a focused laser beam 42 which is directed to the surface of the substrate 26 or the layer 51, respectively. For this purpose, a window 43 being transparent for the laser light produced by the laser device 41 is disposed in the respective sidewall of the chamber 10.
The laser light beam 42 is moved over the surface of the substrate 26 in order to produce trenches 49 shown for the substrate 26 disposed in the chamber 11. By the trenches 49 the layer 51 is divided into separate areas to form separate photovoltaic cells on a common substrate 26.
The chamber 11 serves for cleaning of the substrate 26 as well as of the trenches 49 and the layer areas 48 produced in the preceding chambers 9 and 10. The cleaning process performed in the cleaning chamber 11 is an electrostatic cleaning. The substrate carrier 25 is connected to an electrical voltage source 46 so that the substrate carrier as well as the substrate 26 and all particles adhered to the surface of the substrate 26 are set to a first potential. The counter electrode 47 which is also connected to the power supply 46 is set to a second potential opposite to the first potential so that the particles electrically charged are attracted to the counter electrode 47. Accordingly, the surface of the substrate 26 is cleaned.
Although, the deposition chamber 9, the patterning chamber 10 and the cleaning chamber 11 are described with respect to specific processes, it is clear for a man skilled in the art that other processes suitable for producing appropriate photovoltaic cells or solar cell modules may be performed in correspondingly equipped treating chambers.
A further embodiment of the present invention is shown with respect to
After patterning of the transparent conductive oxide layer or front contact layer a second coating chamber 205 for depositing the absorber layers or solar cell structure is provided for. Instead of one second coating chamber 205 as shown in
The apparatus 200 of
As can be seen from
The embodiment of
When a metallic substrate is used, the layer sequence which has to be deposited is different to the layer sequence deposited on isolating, transparent substrates. For metallic substrates first of all an isolating layer may be deposited onto which a conductive layer as back contact may be coated. On the back contact the absorber layers or a layer stack for generating a photovoltaic device is provided for. The closing layer is a front contact formed from transparent conductive material like transparent conductive oxide. In addition to the transparent conductive oxide a contact structure made by screen printing may be applied.
In case of a transparent substrate, a patterning of the deposited layers can be carried out from both sides of the substrate, while for non-transparent substrates a patterning is carried out from the side where the layers are deposited. Accordingly, the laser or other suitable means for patterning may be arranged at different positions within the vacuum chamber with respect to the substrate.
Although, the present invention is described in detail with respect to the embodiments, it is evident for a man skilled in the art, that the invention is not restricted to these embodiments, but modifications and amendments are possible, with respect to a different combination of all the features disclosed in the specification or by omitting one of the features of the embodiments without leaving the scope of the present invention which is defined by the attached claims. In particular, the present invention comprises all possible combinations of all claims, even if single claims are only referred to other single claims.
The invention is especially defined by the following features:
