DE112016006558T5 - A method of forming a CdTe thin film solar cell including a metal doping step and a system for performing the metal doping step - Google Patents

Abstract

The present application relates to a process for producing a CdTe solar cell, beginning with the provision of a semi-finished CdTe solar cell containing a CdTe that forms a first surface of the semi-finished CdTe solar cell. A metal layer is deposited on the first surface of the semifinished CdTe solar cell, and an aqueous solution comprising metal ions or metal-containing ions is deposited on the back of the semi-finished CdTe solar cell and later removed. Application and removal of the aqueous solution can be carried out before or after the application of the metal layer. Furthermore, the semi-finished CdTe solar cell is additionally illuminated, or on the half-finished CdTe solar cell, for a first period of time, in which the aqueous solution is present on the back of the semi-finished CdTe solar cell, or for a second period after removal of the CdTe solar cell aqueous solution and applied an external electrical energy before applying the metal layer.

Description

The present application relates to a method for producing a CdTe solar cell including a metal doping step and a system for carrying out this metal doping step.

In the prior art, a CdTe solar cell has the following structure: On a glass substrate, a layer of a transparent conducting oxide (TCO) is deposited as a front contact. The TCO layer may include a high-resistance buffer layer that helps to minimize the shunt effect in the solar cell. Then a layer of cadmium sulfide (CdS) and then a layer of cadmium telluride (CdTe) are deposited. Finally, a metal layer, for. Molybdenum, nickel vanadium, tantalum, titanium, tungsten, gold or any composition or compound comprising any of these elements applied to collect the charge carriers. This process is called superstrate configuration.

In order to achieve a high efficiency of the solar cell, a good ohmic contact between the CdTe layer and the metal layer should be established. For this, copper can be introduced into the CdTe layer at the interface to the metal layer. The copper may be provided on the CdTe layer as an elemental layer comprising only copper or as a dopant contained in another material or as an ion or part of a chemical compound. The copper may for example consist of a gas, for. B. by sputtering, or from an aqueous solution, eg. B. copper chloride or a copper salt are applied to the CdTe layer. After applying the copper on the CdTe layer, a temperature treatment can be carried out. In the prior art, any process for introducing copper into the CdTe layer is referred to as a copper doping step.

However, copper migrates very easily within the CdTe and can therefore degrade the properties of the CdTe solar cell over time. Therefore, it is very important to precisely control the amount and position of copper introduced into the CdTe layer in order to maintain good ohmic contact while reducing the risk of copper migration. This can be done, for example, by controlling the copper concentration in the aqueous solution or the duration for which an aqueous solution is provided on the CdTe layer or the heat balance of the temperature treatment step defined by the temperature and duration of this step. Unfortunately, some of these parameters can not be controlled as accurately as necessary.

It is an object of the present invention to provide a method of forming a CdTe thin film cell including a metal doping step, which method provides improved control of the amount and position of the metal ions introduced into the CdTe layer by the metal doping step. Another object is to provide a system suitable for carrying out this method.

The method according to the present application comprises the steps of providing a semi-finished CdTe solar cell, applying an aqueous solution comprising metal ions or metal-containing ions to a backside of the semi-finished CdTe solar cell, removing the aqueous solution from the back of the half-finished CdTe Solar cell and applying a metal layer on a first surface of the semi-finished CdTe solar cell to form a back contact. The semifinished CdTe solar cell contains at least a transparent substrate, a front contact layer, a CdS layer and a CdTe layer, wherein a surface of the CdTe layer opposite the transparent substrate forms the first surface of the semi-finished CdTe solar cell. The back side on which the aqueous solution is applied is either the first surface of the semi-finished CdTe solar cell or a first surface of the metal layer opposite to the transparent substrate. The semifinished CdTe solar cell may comprise further layers between the mentioned layers and one or more layers, for example the front contact layer, may also be formed as a layer sequence as known in the art. The front contact layer is usually transparent and is often implemented by a transparent conductive oxide (TCO). The CdS layer, the CdTe layer and the front contact layer or the layer sequence are formed by methods known in the art.

• - Eintauchen der halbfertigen CdTe-Solarzelle (oder der Rückseite der halbfertigen CdTe-Solarzelle) in die in einem Behälter befindliche wässrige Lösung,
• - Aufsprühen,
• - Schleuderbeschichten,
• - Walzbeschichten mit einer Schwammwalze usw.

The aqueous solution may be applied to the back of the semi-finished CdTe solar cell by methods known in the art, such as, but not limited to:

• Immersing the half-finished CdTe solar cell (or the back of the semi-finished CdTe solar cell) in the aqueous solution contained in a container,
• - spraying,
• - spin coating,
• - Roll coating with a sponge roller, etc.

The aqueous solution may be a solution of a metal salt, for example CuCl ₂ , CuSO ₄ , Cu (NO ₃ ) ₂ , SbCl ₃ , AsCl ₃ , AgCl or any other Compound comprising metal-containing complexes. In the solution, the metal is in the form of metal ions or bound in electrically charged complexes, ie ions containing metal. The aqueous solution contains the metal in a concentration in the range between 0.05 mmol / l and 10 mmol / l. As a result, ions of a metal such as copper (Cu), antimony (Sb), silver (Ag) or arsenic (As) are introduced into the CdTe layer, or in other words: the CdTe layer is doped with metal ions.

The aqueous solution may be obtained from the backside of the semi-finished CdTe solar cell by removing the semi-finished CdTe solar cell from the aqueous solution in a container and / or by blowing, rinsing with a cleaning solution, drying or a combination thereof, or by other means known in the art Technique known methods are removed.

The step of depositing a metal layer on the first surface of the semi-finished CdTe solar cell is known in the art and may include depositing a layer of molybdenum, nickel vanadium, gold, tantalum, tungsten, alloys of molybdenum, tantalum, titanium, and tungsten, Compounds comprising molybdenum or tungsten or other materials or depositing combinations or layer sequences of various of these materials using sputtering, evaporation / sublimation or chemical vapor deposition or any other suitable deposition technique. In addition, the step of depositing a metal layer may also include forming an additional layer of another material such as ZnTe, Cu ₂ O, Cu ₂ Te, CuTe, or other metal telluride compounds between the first surface of the semi-finished CdTe solar cell and the metal layer also known from the prior art.

According to the present application, the semi-finished CdTe solar cell is additionally illuminated and / or to the semi-finished CdTe solar cell, an electrical energy is applied by the solar cell is electrically connected to an electrical power supply. As a result, an additional electric field is formed over the semi-finished CdTe solar cell. This step of additionally lighting and / or applying an electrical energy may be for a first period of time in which the aqueous solution is present on the back of the semi-finished CdTe solar cell and / or for a second period of time after performing the step of Removing the aqueous solution from the back of the semi-finished CdTe solar cell and before the step of applying a metal layer on the first surface are performed. The first period may be the entire time between the beginning of the step of applying an aqueous solution and the end of the step of removing the aqueous solution, i. H. the entire time that the aqueous solution is at least partially present on the backside of the semi-finished CdTe solar cell, or only part of that time. The second period may be the entire time between the end of the step of removing the aqueous solution and the beginning of the step of applying a metal layer, i. H. the entire time between these two steps, or just part of that time.

1. 1. Bereitstellen der halbfertigen CdTe-Solarzelle, Aufbringen einer wässrigen Lösung, zusätzliches Beleuchten und/oder Anlegen einer elektrischen Energie, Entfernen der wässrigen Lösung und Aufbringen einer Metallschicht;
2. 2. Bereitstellen der halbfertigen CdTe-Solarzelle, Aufbringen einer Metallschicht, Aufbringen einer wässrigen Lösung, zusätzliches Beleuchten und/oder Anlegen einer elektrischen Energie und Entfernen der wässrigen Lösung;
3. 3. Bereitstellen der halbfertigen CdTe-Solarzelle, Aufbringen einer wässrigen Lösung, Entfernen der wässrigen Lösung, zusätzliches Beleuchten und/oder Anlegen einer elektrischen Energie und Aufbringen einer Metallschicht;
4. 4. Bereitstellen der halbfertigen CdTe-Solarzelle, Aufbringen einer wässrigen Lösung, zusätzliches Beleuchten und/oder Anlegen einer elektrischen Energie, Entfernen der wässrigen Lösung, zusätzliches Beleuchten und/oder Anlegen einer elektrischen Energie und Aufbringen einer Metallschicht.

Therefore, there are four possible process flows according to the present application, wherein the steps are performed in the mentioned sequence and wherein only the step of additionally illuminating and / or applying an electrical energy with the steps of applying an aqueous solution and removing the aqueous solution in the first, the second and the first part of the fourth process flow may overlap:

1. 1. providing the semi-finished CdTe solar cell, applying an aqueous solution, additionally illuminating and / or applying an electrical energy, removing the aqueous solution and applying a metal layer;
2. 2. providing the semi-finished CdTe solar cell, applying a metal layer, applying an aqueous solution, additionally illuminating and / or applying an electrical energy and removing the aqueous solution;
3. 3. providing the semi-finished CdTe solar cell, applying an aqueous solution, removing the aqueous solution, additionally illuminating and / or applying an electrical energy and applying a metal layer;
4. 4. Provision of the semi-finished CdTe solar cell, application of an aqueous solution, additional illumination and / or application of electrical energy, removal of the aqueous solution, additional illumination and / or application of electrical energy and application of a metal layer.

The fourth case is a combination of the first case and the third case. In the first case, the third case, and the fourth case, the back side of the semi-finished CdTe solar cell to which the aqueous solution is applied is formed by a surface of the CdTe layer which is the first surface of the semi-finished CdTe solar cell. In the second case, the back side of the semi-finished CdTe solar cell to which the aqueous solution is applied is formed by the first surface of the metal layer.

The additional electric field over the half-finished CdTe solar cell, which through the additional illumination or the supplied electrical energy is superimposed on the irrelevant electric field formed by the pn junction between the CdS layer and the CdTe layer. "Superimposed" means that the additional electric field either enhances or counteracts the inherent electric field. In the case of additional illumination or contacting of the front contact layer with a negative pole of the power supply, more metal ions or positively charged metal-containing complexes migrate within the CdTe layer toward the CdS layer than without the additional illumination or external supply of electrical energy , In the case of contacting the front contact layer with a positive pole of the power supply, the migration of metal ions or positively charged metal-containing complexes within the CdTe layer toward the CdS layer is reduced compared to the case without the external supply of electrical energy. Therefore, the amount and location of metal ions introduced through a metal doping step within the CdTe layer can be more precisely controlled as compared to the prior art copper treatment step which involves controlling only the copper concentration in the aqueous solution or the duration of the copper concentration Copper treatment step can be influenced.

Therefore, the metal doping step according to the present application comprises the following three sub-steps: applying an aqueous solution comprising metal ions or metal-containing ions to the back of the semi-finished CdTe solar cell, removing the aqueous solution from the back of the semi-finished CdTe solar cell, and additional Illuminating and / or electrically connecting the semi-finished CdTe solar cell to an electrical power supply for a first period or a second period, each sub-step being performed at a defined location within the entire process flow.

"Additional illumination" means illumination that is higher than illumination due to the light present during the prior art copper treatment step. In the prior art, this step is usually not performed in a darkroom but under normal production conditions, including ordinary lighting conditions. In addition to these lighting conditions, the "additional lighting" is provided by a special lighting unit and provides additional light with an illuminance in the range of 5,000 to 200,000 lx.

The light with which the semi-finished CdTe solar cell is additionally illuminated has a wavelength in the absorption range of the CdTe solar cell, and preferably in the range between 300 to 900 nm.

When the semi-finished CdTe solar cell is electrically connected to an electrical power supply, this electrical power supply provides an additional electric field over the semi-finished CdTe solar cell. The additional electric field may be provided between the aqueous solution and the front contact layer of the semi-finished CdTe solar cell, or between ground and the front contact layer, if the aqueous solution is not present on the backside of the semi-finished CdTe solar cell. For example, the front contact layer of the semi-finished CdTe solar cell may be electrically conductively connected to a first contact of the electrical power supply and the aqueous solution may be electrically connected to a second contact of the electrical power supply. Nevertheless, it is also possible to contact only the front contact layer and leave the aqueous solution unconnected, i. H. floating, or connecting them to the earth. The additional electric field may result in an electric current flowing through the semi-finished CdTe solar cell having an absolute value greater than zero and less than or equal to twice the short-circuit current of the CdTe solar cell. That is, the electric current may be positive or negative as compared with the short-circuit current.

Only one of the measures, additional lighting and electrical power supply may be performed as a single measure, or both may be performed separately in succession in any order or simultaneously. If both measures are taken, exposure to light, i. H. the amount of energy, the additional lighting and / or the electrical energy are reduced, compared to the case where only one measure is performed.

The first period or the second period in which one or both measures are carried out is preferably in the range between 5 s (seconds) to 30 min (minutes). The duration of the first period or the second period depends on the luminance and / or the electrical energy or the metal concentration within the aqueous solution and the desired distribution of the metal within the semifinished CdTe solar cell.

Moreover, the temperature of the semi-finished CdTe solar cell is controlled to be in the range between 25 ° C and 80 ° during the first period, that is, while one or both of the mentioned measures are performed and the aqueous solution is present on the back side C is. If the step of additional lighting and / or applying electrical energy, after the aqueous solution has already been removed, the temperature of the semi-finished CdTe solar cell is controlled to be in the range between 25 ° C and 225 ° C during the second period. The temperature of the semi-finished CdTe solar cell is another parameter for controlling the distribution of the introduced metal within the semi-finished CdTe solar cell. To achieve a desired temperature, the semi-finished CdTe solar cell may be heated or cooled, or sequentially heated and cooled, in any order during the first period or the second period.

As a result, a person skilled in the art now has a large number of parameters that he or she can control to achieve a desired distribution of metal within the semi-finished CdTe solar cell: the luminance of the additional illumination, the electrical energy generated by the electrical energy supply during the first period or the second period, the concentration of the metal within the aqueous solution, and the duration of the presence of the aqueous solution on the back side. Thus, overdoping the semi-finished CdTe solar cell with the metal, i. H. introducing a quantity of metal higher than that required to form a good ohmic contact and reducing the consequent degradation of the finished CdTe solar cell as the process window for the metal doping step increases.

The method of the present application may include further steps such as a temperature treatment step or a conditioning step that includes illuminating and / or providing electrical energy to the CdTe solar cell, or a combination of these steps. However, these steps, which are known in the art, are performed at least after the step of depositing a metal layer on the first surface of the semi-finished CdTe solar cell to form a backside contact and without the presence of the aqueous solution.

According to the present application, a system for performing a metal doping step of a semi-finished CdTe solar cell comprises a first unit for applying an aqueous solution comprising metal ions or metal-containing ions on a back side of a semi-finished CdTe solar cell, a second unit for removing the aqueous Solution from the back of the semi-finished CdTe solar cell and a lighting unit. The semi-finished CdTe solar cell contains at least a transparent substrate, a front contact layer, a CdS layer and a CdTe layer, wherein the back of the semi-finished CdTe solar cell is a surface of the semi-finished CdTe solar cell opposite the transparent layer. In particular, the semifinished CdTe solar cell may comprise a transparent substrate, a front contact layer, a CdS layer, and a CdTe layer, the back side being formed by a surface of the CdTe layer, or the semifinished CdTe solar cell may be a transparent substrate, a front contact layer , a CdS layer, a CdTe layer and a metal layer, the back side being formed by a surface of the metal layer. The illumination unit is capable of additionally illuminating the semi-finished CdTe solar cell for a first period of time while the aqueous solution is present on the back of the semi-finished CdTe solar cell.

The lighting unit may be combined with the first unit and / or the second unit such that all combined units perform their function at least part of their respective process time simultaneously. For example, if the first unit comprises a container containing the aqueous solution and a component for immersing the semi-finished CdTe solar cell in the aqueous solution, the illumination unit may be arranged such that the light generated thereby will cause the semi-finished CdTe solar cell to have at least one Part of the time illuminated, in which the semi-finished CdTe solar cell is immersed in the aqueous solution. Nevertheless, it is possible for the first unit and the lighting unit or the second unit and the lighting unit to perform their functions sequentially even though they are combined. "Combination of the first unit and / or the second unit and the lighting unit" means that a process area of the lighting unit overlaps at least partially with the first unit and / or with the second unit. "Process area" means the spatial area in which light generated by the lighting unit acts on the semi-finished CdTe solar cell. In one embodiment, the first unit and the lighting unit are arranged in one unit.

However, it is also possible for the lighting unit to be spatially separated from the first unit and / or the second unit, so that the lighting unit is arranged in a run-on sequence of units after the first unit and before the second unit. The run order of units describes the order of the units in which they are used. A spatial arrangement of the units in a production hall may differ from the sequence of execution of the units. While the semi-finished CdTe solar cell is within the process area of the lighting unit, the aqueous solution is at least partially on The first surface of the semi-finished CdTe solar cell is present. For example, the first unit could comprise or include a container containing the aqueous solution and a component for immersing the semi-finished CdTe solar cell in the aqueous solution or it could comprise a nozzle unit for spraying the aqueous solution onto the back of the semi-finished CdTe solar cell could comprise a roller unit for roll coating the aqueous solution onto the back of the semi-finished CdTe solar cell. In all cases, the process area of the lighting unit is spatially separated from the first unit. Therefore, the first unit stops its work, ie, by removing the half-finished CdTe solar cell from the container containing the aqueous solution, or stopping the aqueous solution to be sprayed or roll coated on the back of the semi-finished CdTe solar cell, and then the semifinished CdTe solar cell transported from the first unit to the process area of the lighting unit and illuminated there. In this case, the illumination unit is designed so that the aqueous solution remains on the back of the semi-finished CdTe solar cell during illumination. For example, the lighting unit has a holder that holds the semi-finished CdTe solar cell so that the back surface is kept horizontal, and that the lateral distribution of the aqueous solution over the lateral dimensions of the back side compared to that from the first unit for applying the aqueous Solution results, not changed. Subsequently, the semi-finished CdTe solar cell is transported from the lighting unit to the second unit, where the aqueous solution is removed from the back of the semi-finished CdTe solar cell.

The illumination unit is suitable for illuminating the semi-finished CdTe solar cell with a light having a wavelength in the absorption range of the CdTe solar cell, and preferably with light having a wavelength in the range between 300 to 900 nm.

In a particular embodiment, the system further comprises a third unit for controlling a temperature of the semi-finished CdTe solar cell to be in the range between 25 ° C and 80 ° C during the first period. The third unit may comprise a heater or a cooling device or a combination thereof, depending on the desired temperature of the semi-finished CdTe solar cell.

For example, the lighting unit and the third unit may be combined in a tempered tunnel containing one or a plurality of light-generating lamps. This tunnel may be arranged in a run order of units after the first unit that applies the aqueous solution to the backside of a semi-finished CdTe solar cell, for example, by spraying or roll coating, and before the second unit.

• 1A bis 1C zeigen schematisch beispielhafte Prozessabläufe des Verfahrens gemäß der vorliegenden Anmeldung.
• 2 zeigt schematisch eine erste Ausführungsform des Systems gemäß der vorliegenden Anmeldung, wobei die erste Einheit und die Beleuchtungseinheit miteinander kombiniert sind.
• 3 zeigt schematisch eine zweite Ausführungsform des Systems gemäß der vorliegenden Anmeldung, wobei die erste Einheit und die Beleuchtungseinheit getrennt voneinander sind.

In addition to the lighting unit, the system may include an electrical power supply and a contact device for connecting the front contact layer of the semi-finished CdTe solar cell to the electrical power supply during the first period of time. The electrical power supply is capable of forming an additional electric field across the semi-finished CdTe solar cell when connected to the half-finished CdTe solar cell.

• 1A to 1C schematically show exemplary process flows of the method according to the present application.
• 2 schematically shows a first embodiment of the system according to the present application, wherein the first unit and the lighting unit are combined.
• 3 schematically shows a second embodiment of the system according to the present application, wherein the first unit and the lighting unit are separated from each other.

The method and system according to the invention are explained below in exemplary embodiments, wherein the figures are not intended to imply a limitation of the embodiments shown.

1A shows a first exemplary process flow of the method according to the present application. At the beginning, in one step S110 a semi-finished CdTe solar cell provided with a first surface as described above. In a next step S120, an aqueous solution comprising metal ions as described above is applied to the first surface, ie, to a surface of the CdTe layer. The aqueous solution is at least partially present on the first surface of the semi-finished CdTe solar cell until completely removed from the first surface in a step S140, ie, in a period of aqueous presence with t _A referred to as. The time from the beginning of step S120 to the end of step S140 is the time of the metal doping step performed by t _D which in this example is equal to the period t _A is. Over a first period t ₁ During the time t _A the semi-finished CdTe solar cell is additionally illuminated (step S131 ) and / or electrical energy is applied to the semi-finished CdTe solar cell (step S132 ). That is, one or both steps S131 and S132 can be done. If both steps are performed, the steps may S131 and S132 be performed simultaneously or partially overlapping or completely separated in time. That is, the periods t ₃₁ and t ₃₂ in which step S131 and step S132 may be the same or may differ from each other and may be completely or partially overlapping or completely separated from each other on the timescale. However, the entire period, ie the sum of all time periods, is in at least one of the steps S131 and step S132 is carried out in 1A shown first period t ₁ , The steps S131 and or S132 can with step S120 and / or with step S140 overlap. After that step S140 a metal layer is deposited on the first surface of the semi-finished CdTe solar cell (step S150 ). The combination of the entirety of the steps S120 . S131 . S132 and S140 is called Metalldotierungsschritt according to the present application.

In 1B a second exemplary process flow of the method according to the present application is shown schematically. step S210 corresponds to step S110 from 1A , Then in the next step S220 a metal layer is deposited on the first surface of the semi-finished CdTe solar cell. As a result, the semi-finished CdTe solar cell has a backside formed by the metal layer. Subsequently, an aqueous solution comprising metal ions as described above is applied to the back surface, ie, to a surface of the metal layer (step S230 ). The aqueous solution is at least partially present on the backside of the semi-finished CdTe solar cell until it is in one step S250 is completely removed from the back, ie in a period of aqueous presence, with t _A referred to as. The time from the beginning of step S230 until the end of step S250 is the time of the metal doping step that goes through t _D is designated, which in turn equals the period t _A is. Over a first period t ₁ During the time t _A the semi-finished CdTe solar cell is additionally illuminated (step S241 ) and / or electrical energy is applied to the semi-finished CdTe solar cell (step S242 ). That is, one or both steps S241 and S242 can be done. If both steps are performed, the steps may S241 and S242 be performed simultaneously or partially overlapping or completely separated in time. That is, the periods t ₄₁ and ₄₂ in which step S241 and step S242 may be the same or they may be different from each other and may be completely or partially overlapping or completely separated on the timescale. However, the entire period, ie the sum of all time periods, is in at least one of the steps S241 and step S242 is carried out in 1B shown first period t ₁ , As with respect to the first exemplary process flow in FIG 1A can describe the steps S241 and or S242 with step S230 and / or with step S250 overlap. The combination of the entirety of the steps S230 . S241 . S242 and S250 is called Metalldotierungsschritt according to the present application.

A third exemplary process flow of the method according to the present application is with reference to 1C shown. step S310 corresponds to step S110 from 1A and step S210 from 1B , Then, an aqueous solution comprising metal ions as described above is applied to the first surface, that is, to a surface of the CdTe layer (step S320 ). The aqueous solution is at least partially present on the first surface of the CdTe ready solar cell until it is in one step S330 is completely removed from the first surface, ie in a period of aqueous presence with t _A referred to as. After that step S330 becomes the semi-finished CdTe solar cell over a second period of time t ₂ during an interim period t _i between step S330 and one step S350 in which a metal layer is applied on the first surface, additionally illuminated (step S341 ) and / or electrical energy is applied to the semi-finished CdTe solar cell (step S342 ). That is, one or both steps S341 and S342 can be done. If both steps are performed, the steps may S341 and S342 be performed simultaneously or partially overlapping or completely separated in time. That is, the periods t ₄₁ and ₄₂ in which step S341 and step S342 may be the same, or they may be different and may overlap completely or partially, or be completely separated on the timescale. However, the entire period, ie the sum of all periods, is in at least one of the steps S341 and step S342 is carried out in 1C shown second period t ₂ , The combination of the entirety of the steps S320 . S330 . S341 and S342 is called Metalldotierungsschritt according to the present application.

In 2 schematically is a first embodiment ( 100 ) of the system according to the present invention. The system ( 100 ) comprises a first unit ( 110 ), a second unit ( 120 ), a lighting unit ( 130 ) and an electrical energy supply ( 140 ). The first unit ( 110 ) is suitable to prepare an aqueous solution ( 20 ) as described above on a back side ( 11 ) of a half-finished CdTe solar cell ( 10 ). The back surface may be a surface of the CdTe layer or it may be a surface of a metal layer serving as a back contact layer. This includes the first unit ( 110 ) a container ( 111 ), in which the aqueous solution ( 20 ), and one Component ( 112 ) for immersing the half-finished CdTe solar cell ( 10 ) into the aqueous solution ( 20 ). The component ( 112 ) can be, for example, a holder with a clamp attached to the half-finished CdTe solar cell ( 10 ) is attached. The aqueous solution ( 30 ) can be replaced by a third unit ( 150 ) so that the aqueous solution ( 20 ) has a temperature between 25 ° C and below 100 ° C (below the boiling point of the aqueous solution). As a result, the semi-finished CdTe solar cell ( 10 ) preferably a temperature between 25 ° C and 80 ° C, when in the aqueous solution ( 20 ) is dipped. In addition, an electrode ( 113 ), which are also in the aqueous solution ( 20 ) is dipped. When the electrical power supply ( 140 ) by a contact device, for example, electrical conductors ( 141 ), with one side electrically conductive with a front contact layer of the half-finished CdTe solar cell ( 10 ) and with its other side with the electrode ( 113 ) is formed between the first electrode ( 113 ) and the aqueous solution ( 20 ) on one side and the front contact layer of the semi-finished CdTe solar cell ( 10 ) on the other side an electric field. This allows the movement of metal ions or ions containing charged metal within the aqueous solution ( 20 ) and / or within the semi-finished CdTe solar cell ( 10 ) to be controlled. Furthermore, a lighting unit ( 130 ), for example a halogen lamp having an illuminance of 100,000 Ix, with the first unit ( 110 ), so that the illumination unit ( 130 ) the semi-finished CdTe solar cell ( 10 ) while immersing in the aqueous solution ( 20 ) is immersed. After removing the half-finished CdTe solar cell ( 10 ) from the aqueous solution ( 20 ), the semi-finished CdTe solar cell ( 20 ) to the second unit ( 120 ) (which is shown by the arrow). The second unit ( 120 ), which is known from the prior art, comprises, for example, a flushing device ( 121 ) and a drying device ( 122 ) containing the aqueous solution ( 20 ) or remnants thereof from the back ( 11 ) of the half-finished CdTe solar cell ( 10 ) remove.

3 schematically shows a second embodiment ( 200 ) of the system according to the present invention. The system ( 200 ) comprises a first unit ( 210 ), a second unit ( 220 ) and a lighting unit ( 230 ). The first unit ( 210 ) comprises a nozzle arrangement or a nozzle device ( 211 ) through a fluid line ( 213 ) with a container ( 212 ), which is an aqueous solution ( 20 ) as described above. The aqueous solution ( 20 ) is passed through the nozzle device ( 211 ) on the back ( 11 ) of a half-finished CdTe solar cell ( 10 ) (as indicated by the dashed arrows). The back surface may be a surface of the CdTe layer or it may be a surface of a metal layer serving as a back contact layer. The semi-finished CdTe solar cell ( 10 ) is placed on a holder ( 214 ), which may be rotatable. After application of the aqueous solution ( 20 ) on the back side ( 11 ) of the half-finished CdTe solar cell ( 10 ), the semi-finished CdTe solar cell ( 10 ) with the one on the back ( 11 ) aqueous solution to a tempered tunnel ( 240 ), in which the lighting unit ( 230 ) is mounted. The lighting unit ( 230 ) is a lamp assembly that provides light having a wavelength of 300 to 800 nm and an illuminance of 30,000 to 200,000 Ix. While the semi-finished CdTe solar cell ( 10 ) on a tempered holder ( 241 ) within the temperature-controlled tunnel ( 240 ) illuminates the illumination unit ( 230 ) the semi-finished CdTe solar cell ( 10 ) over a first period. Therefore, the first unit ( 210 ) and the lighting unit ( 230 ) in the illustrated second embodiment ( 200 ) of the system are separated. To the semi-finished CdTe solar cell ( 10 ) while maintaining the lighting at a desired temperature, is within the tempered tunnel ( 240 ) a third unit ( 250 ), for example a cooling device, mounted. After illuminating the half-finished CdTe solar cell ( 10 ), the semi-finished CdTe solar cell ( 10 ) from the tempered tunnel ( 250 ) to the second unit ( 220 ), which may comprise the same or different devices as with respect to 2 described.

In the in 2 and 3 shown examples is the lighting unit ( 130 . 230 ) arranged so that that of the lighting unit ( 130 . 230 ) emitted light on the back ( 11 ) of the half-finished CdTe solar cell ( 10 ) falls. However, this is only an exemplary arrangement of the illumination unit that could be used if the back of the semi-finished CdTe solar cell is the first surface of the semi-finished CdTe solar cell, ie, a surface of the CdTe layer. If a metal layer has already been deposited on the CdTe layer such that the back side of the semi-finished CdTe solar cell is a surface of the metal layer, the illumination unit should be located within the system for performing a metal doping step such that the light emitted by the illumination unit is directed to the solar side of the metal semi-finished CdTe solar cell, ie on the transparent substrate falls. Regardless, the half-finished CdTe solar cell can always be illuminated on the sunny side.

The embodiments of the invention described in the foregoing description are examples given for illustrative purposes only, and the invention is by no means limited thereto. Any modification, variation, equivalent arrangement, and combinations of embodiments should be considered as included within the scope of the invention.

10

halbfertige CdTe-Solarzelle

11

Rückseite der halbfertigen CdTe-Solarzelle

20

wässrige Lösung

100, 200

System zum Durchführen eines Metalldotierungsschritts

110, 210

erste Einheit

111,212

Behälter

112

Komponente zum Eintauchen

113

Elektrode

120, 220

zweite Einheit

121

Spülvorrichtung

122

Trocknungsvorrichtung

130, 230

Beleuchtungseinheit

140

elektrische Stromversorgung

141

elektrischer Leiter

211

Düsenvorrichtung

213

Fluidleitung

214

Halter

240

temperierter Tunnel

241

temperierter Halter

150, 250

dritte Einheit

t₁

erster Zeitraum

t₂

zweiter Zeitraum

t_A

Zeitraum für die wässrige Gegenwart

t_D

Zeitraum für den Metalldotierungsschritt

t_I

Zwischenzeitraum

t₃₁, t₄₁

Zeitraum für zusätzliche Beleuchtung

t₃₂, t₄₂

Zeitraum zum Anlegen von elektrischer Energie

references

10

semi-finished CdTe solar cell

11

Back of the semi-finished CdTe solar cell

20

aqueous solution

100, 200

System for performing a metal doping step

110, 210

first unit

111.212

container

112

Component for immersion

113

electrode

120, 220

second unit

121

flushing

122

drying device

130, 230

lighting unit

140

electrical power supply

141

electrical conductor

211

nozzle device

213

fluid line

214

holder

240

tempered tunnel

241

tempered holder

150, 250

third unit

t ₁

first period

t ₂

second period

t _A

Period of aqueous presence

t _D

Period for the metal doping step

t _i

Intermediate Period

t _31, t ₄₁

Period for additional lighting

t ₃₂ , t ₄₂

Period for applying electrical energy

Claims (15)

A process for producing a CdTe solar cell, comprising the steps of: a) providing a semifinished CdTe solar cell comprising at least one transparent substrate, a front contact layer, a CdS layer and a CdTe layer, wherein one surface of the CdTe layer is opposite to the transparent one Substrate forms a first surface of the semi-finished CdTe solar cell, b) applying an aqueous solution comprising metal ions or metal-containing ions to a backside of the semi-finished CdTe solar cell, c) removing the aqueous solution from the backside of the semi-finished CdTe solar cell d) applying a metal layer to the first surface of the semi-finished CdTe solar cell, and e) additionally illuminating the semi-finished CdTe solar cell and / or applying electrical energy to the semi-finished CdTe solar cell by electrically connecting it to an electrical power supply wherein the back of the semi-finished CdTe solar cell, e Neither the first surface of the semi-finished CdTe solar cell or a first surface of the metal layer facing the transparent substrate is characterized in that step e) for a first period of time in which the aqueous solution on the back of the semi-finished CdTe solar cell is present, and / or for a second period after step c) and before step d) is performed. Method according to Claim 1 characterized in that steps b) and c) are performed prior to step d), the backside being the first surface of the semi-finished CdTe solar cell, and step e) for the first time period in which the aqueous solution on the backside of the half-finished CdTe Solar cell is present, is performed. Method according to Claim 1 characterized in that steps b) and c) are performed after step d), the backside is the first surface of the metal layer, and step e) for the first time period in which the aqueous solution is present on the backside of the semi-finished CdTe solar cell is, is performed. Method according to Claim 1 characterized in that steps b) and c) are performed before step d), the back side is the first surface of the semi-finished CdTe solar cell, and step e) is performed for the second period after step c) and before step d). Method according to Claim 1 , characterized in that the light with which the semi-finished CdTe solar cell is additionally illuminated has a wavelength in the absorption range of the CdTe solar cell. Method according to Claim 5 , characterized in that the wavelength of the light is in the range of 300 to 900 nm. Method according to Claim 1 , characterized in that the electrical power supply provides an electrical current that flows through the semi-finished CdTe solar cell and has an absolute value greater than zero and less than or equal to twice the short-circuit current of the CdTe solar cell. Method according to Claim 1 , characterized in that the first period or the second period is in a range between 5 s to 30 min. Method according to the Claims 2 or 3 Characterized in that a temperature of the semi-finished CdTe solar cell is controlled to be during the first period in the range between 25 ° C and 80 ° C. Method according to Claim 4 , characterized in that a temperature of the semi-finished CdTe solar cell is controlled to be in the range between 25 ° C and 225 ° C during the second period. A system for performing a metal doping step of a semi-finished CdTe solar cell, the system comprising: a first unit for applying an aqueous solution comprising metal ions or metal-containing ions to a back side of a semi-finished CdTe solar cell containing at least one transparent substrate, a front contact layer, a CdS layer and a CdTe layer, wherein the Back of the semi-finished CdTe solar cell is a surface of the semi-finished CdTe solar cell opposite the transparent substrate, a second unit for removing the aqueous solution from the back of the semi-finished CdTe solar cell, and a lighting unit capable of additionally illuminating the semi-finished CdTe solar cell for a first period of time while the aqueous solution applied by the first unit to the semi-finished CdTe solar cell is present on the back of the semi-finished CdTe solar cell. System after Claim 11 Characterized in that the lighting unit is adapted to illuminate the semi-finished CdTe solar cell with light having a wavelength in the absorption range of the CdTe solar cell. System after Claim 12 , characterized in that the wavelength of the light is in the range of 300 to 900 nm. System after Claim 11 , further comprising a third unit for controlling a temperature of the semi-finished CdTe solar cell to be in the range between 25 ° C and 80 ° C during the first period. System after Claim 11 , further comprising an electrical power supply and a contact device for connecting the half-finished CdTe solar cell to the electrical power supply, wherein the electrical power supply is adapted to form an additional electric field over the half-finished CdTe solar cell during the first period of time, when combined with the semi-finished CdTe solar cell is connected.

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