Method for improving the ohmic contact behavior between contact grid and emitter layer of silicon solar cells

Abstract

The present invention relates to a method for improving the ohmic contact behavior between a contact grid and an emitter layer of a silicon solar cell, the method comprising the steps of: biasing and illuminating the silicon solar cell while applying a current of 200 A / cm2 to the treatment section; 2 ~20,000A / cm 2 The object of the present invention is to provide an improved method for improving the ohmic contact behavior between the contact grid and the emitter layer of a silicon solar cell, which comprises carrying out a measurement step before and / or after the treatment step, in which the solar-facing side of the silicon solar cell is illuminated and biased to induce a treatment current flow with a current density of 1 mA / cm. 2 ~500mA / cm 2 and the current intensity of said measured current flow is sensed using an ammeter and assigned to each measuring section and stored.

Description

[Technical Field]

[0001] The present invention relates to a method for improving the ohmic contact behavior between a contact grid and an emitter layer of a silicon solar cell, the method comprising applying, in one processing step by means of a voltage source and a contact device connected thereto, a voltage between the contact grid and the back contact of the silicon solar cell, in a direction opposite to the forward direction of the silicon solar cell and having a value lower than the breakdown voltage of the silicon solar cell, and when said voltage is applied, directing a point light source onto the solar side of the silicon solar cell, thereby illuminating process treatment sections of sub-areas of the solar side, thus inducing a process current flow to each sub-area, said process current flow being 200 A / cm2 for the treatment section. 2 ~20,000A / cm 2 and acts on the sub-area for 10 ns to 10 ms. [Background technology]

[0002] During the manufacturing process of crystalline silicon solar cells, a metal paste is screen-printed in the form of a contact grid onto the front side of the silicon nitride dielectric coating. After applying the metal paste, a tempering step is performed at 800–900°C to contact the emitter layer of the silicon solar cell underneath the silicon nitride layer. During this step, the silver in the metal paste diffuses from the silicon nitride layer into the emitter layer via the glass frit contained in the metal paste. Process control during the tempering step is crucial to contact formation. With proper process control, the transition between the contact grid and the emitter layer is characterized by low contact resistance. Inadequate process control typically results in high contact resistance. For example, if the tempering temperature is too low, the metal paste will not sufficiently diffuse through the silicon nitride layer, resulting in only a small contact area between the contact grid and the emitter layer and high contact resistance. High contact resistance significantly reduces the efficiency of the solar cell, preventing it from being incorporated into a solar module and resulting in a rejection.

[0003] Patent document 1 discloses a method for improving the ohmic contact behavior between the contact grid and the emitter layer of a silicon solar cell. In the method, in a processing step, the silicon solar cell is electrically biased in the reverse direction of its forward bias and scanned with a point light source. In the process, a current of 200 A / cm is applied to each illuminated sub-area of the solar cell. 2 ~20,000A / cm 2 This generates a process current flow with a current density of the order of 1000 s. A point light source is guided onto the solar cell so that the process current flow acts on a sub-area for a period of 10 ns to 10 ms. This current flow, caused by the interaction of the illumination with the voltage opposite to the forward direction of the silicon solar cell, improves the ohmic contact behavior between the contact grid and the emitter layer of the silicon solar cell.

[0004] However, a disadvantage is that the solar cell must be electrically characterized after application of the method to quantify the improvement in ohmic contact behavior achieved by the method. Such characterization can include, for example, measuring the current-voltage characteristics of the solar cell under irradiation with a sun simulator. In this case, the improvement in contact behavior can be derived from the series resistance of the silicon solar cell, which is determined from the current-voltage curve. However, measuring the solar cell before and after application of the known method requires time for the overall processing of the solar cell. Furthermore, application of the method to improve ohmic contact behavior can result in damage to some solar cells. This is because, for example, different parameters (e.g., shorter exposure time to current flow) can be applied to some subareas of these solar cells compared to the rest of the solar cells. Since the ohmic contact behavior between the contact grid and the emitter layer of a silicon solar cell can also vary locally, applying the known method essentially involves corresponding parameter changes. While such local variations in parameters can be established using the known method, the regions of the silicon solar cell where corresponding local variations in parameters are required when applying the known method are unknown. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] German Patent Application Publication No. 102018001057 Summary of the Invention [Problem to be solved by the invention]

[0006] The object of the present invention is to improve a method for improving the ohmic contact behavior between the contact grid and the emitter layer of a silicon solar cell. In particular, it should be possible to quantify the improvement achieved by the method while it is being carried out. Furthermore, damage caused by the application of unfavorable process parameters should be detected during the process. [Means for solving the problem]

[0007] This object is achieved according to the invention by a method for improving the ohmic contact behavior between the contact grid and the emitter layer of a silicon solar cell having the characteristics of claim 1. Advantageous embodiments are set out in claims 2 to 20.

[0008] In a process known per se, a silicon solar cell is first prepared, which comprises an emitter layer, a contact grid, and a back contact. In one process step, a voltage, opposite to the forward direction of the silicon solar cell, is applied between the contact grid and the back contact by means of a contact device and a voltage source, the voltage being lower than the breakdown voltage of the silicon solar cell. When this voltage is applied, a point light source is then guided onto the solar side of the silicon solar cell, thereby illuminating treatment sections of subareas on the solar side, thus inducing a treatment current flow in each subarea, the treatment current flow being 200 A / cm2 through the treatment section. 2 ~20,000A / cm 2The current density is set to 10 ns to 10 ms and acts on the sub-area.

[0009] According to the invention, before and / or after the treatment step, a measuring step is carried out, in which a voltage is applied between the contact grid and the back contact using a voltage source and a contact device, and when the voltage is applied, a measurement section of a sub-area on the sun-facing side of the silicon solar cell is illuminated with a point light source, while the voltage and illumination intensity are set so as to induce a measurement current flow in each sub-area, the measurement current flow being 1 mA / cm2 through the measurement section. 2 ~500mA / cm 2 The measured current flow at a given voltage and illumination intensity is sensed using an ammeter and assigned to a respective measurement section and stored.

[0010] The current intensity measured in each measurement section can be used for further processing, such as process monitoring, process control, or quality control. Areas with good ohmic contact between the contact grid and the emitter layer, or areas with low local short-circuit currents, contrast with areas with high current intensities and poor ohmic contact. Because the current intensities are assigned to each measurement section and / or processing section and stored, spatially resolved information about the electrical properties of the silicon solar cell is available. This spatially resolved information can be used as a control parameter for a processing step. During the processing step, the illumination intensity of the point light source, and / or the exposure time to illumination, and / or the forward and reverse voltage levels of the silicon solar cell can be adjusted during illumination to affect the processing current flow.

[0011] Depending on the desired measurement information, the voltage applied in the measurement step is directed in the opposite direction to the forward direction of the silicon solar cell and has a value lower than the breakdown voltage of the silicon solar cell, or the voltage applied in the measurement step is directed in the forward direction of the silicon solar cell.

[0012] In a further embodiment of the method according to the invention, the respective process current flows are also sensed using an ammeter and assigned to the respective process section during the process step for at least some of the illuminated process sections and stored. The sensing of the intensity of the measured current flow and the sensing of the intensity of the process current flow can be performed relative to one another in any way. For example, it is possible that a measurement step is performed only before the process step, with no process current sensed during the process step and no further measurement step performed after the process step. It is also possible that the process current flow is sensed only during the process step, with no measurement step performed before or after the process step. It is also possible that measurement steps are performed before and after the process step and the process current flow is sensed during the process step, or that the measured current flow is sensed only during the measurement steps before and after the process step without any process current sensed during the process step.

[0013] The sensed and stored process current flow values may then be used for further process operations, for example for process monitoring, process control or quality control.

[0014] In the method according to the invention, the intensity of the measurement current flow is detected in the measuring step at a given voltage and a given illumination intensity. It is generally known that electrical measurements can also be performed by detecting a constant current and a respective voltage, and therefore the measuring step of the method according to the invention can also be performed in such a way that a constant current flow is specified and the respective voltage is sensed using a voltmeter and assigned and stored in the respective measurement or processing section. Therefore, both measurement forms can be considered equivalent for the purposes of the present invention.

[0015] The method according to the invention is likewise not limited to storing the current intensities of the measured or processed current flows assigned to each measurement or processing section. This storage can also be carried out in converted form, for example, as a current density, where the respective current intensities are related, for example, to the area of the measurement section. Alternatively, for example, the current intensities can be stored as resistance values related to the applied voltage.

[0016] The voltage source and contact device in the measurement step can be the same as those used in the processing step. This has the advantage that no additional contact device is required. However, the invention is not limited to this. In principle, a different contact device and / or a different voltage source can also be used to sense the measurement current flow than those used to sense the processing current. With regard to the point light source, it is of course advantageous to use the same point light source in both the processing step and the measurement step, but the invention is not limited to this and in principle, different point light sources can also be used.

[0017] Sensing the processed current flow and / or the measured current flow offers the possibility of using the sensed current flow as an indicator of the quality of the ohmic contact behavior between the contact grid and the emitter layer. For constant illumination and applied voltage, subareas with good ohmic contact behavior between the contact grid and the emitter layer will have a stronger measured current flow than subareas with poor ohmic contact behavior. By providing a measurement step prior to the processing step, subareas with poor ohmic contact can be identified. Correction parameters for these areas, for example, the reverse voltage of the silicon solar cell and the illumination intensity of the point light source, can be applied during the processing step. Alternatively, only subareas with poor ohmic contact behavior can be processed during the processing step, while subareas that already exhibit good ohmic contact behavior can be omitted from the processing step.

[0018] Sensing the measured current flow after a processing step can be used as a quality characteristic for further processing of silicon solar cells, for example in a solar module.

[0019] By sensing the measured current flow both before and after a processing step, it is possible to determine in a spatially resolved manner the improvement in ohmic contact behavior achieved by the processing step. This improvement in ohmic contact behavior is manifested as an increase in the measured current flow, given constant voltage and illumination intensity parameters. Again, this allows for the identification of subareas that have not yet reached the target value for good ohmic contact behavior between the contact grid and the emitter layer, and therefore allows further processing steps to be limited to these subareas in a targeted manner.

[0020] Furthermore, the process current flow measured and locally allocated during a process step can also be used to set the parameters of the process step itself, for example, the current intensity allocated to a process section can be used as a control parameter to set the illumination intensity of a point light source and / or the exposure time to illumination and / or the forward and reverse voltage levels of a silicon solar cell during illumination of a subsequent process section in the same process step.

[0021] It is also advantageous if, during a processing step, a first current intensity followed by a second current intensity is sensed using an ammeter while one of the processing sections is illuminated, and both current intensities are assigned to and stored in the processing section. These two current intensities can then be used to calculate a current intensity gradient for each processing section, which can be used as a measure of the improvement in ohmic contact behavior resulting from the processing step. Again, the current intensity gradient can be used within the processing step to control parameters of the subsequent processing section, or can be used entirely for the subsequent processing step.

[0022] In addition to sensing the intensity of the measurement or processing current flow during illumination, the reverse current of the silicon solar cell can also be sensed during previous and / or subsequent measurement and / or processing steps, even without illuminating the silicon solar cell, and assigned to and stored in the respective processing or measurement section. The reverse current value is suitable for assessing possible damage to the silicon solar cell due to the application of processing steps with unfavorable parameters. The reverse current is assessed using a reference value, which is compared with a reverse current value obtained, for example, from an electrical characterization (e.g., recording a current-voltage curve) of the silicon solar cell prior to the application of the method of the present invention. For example, if the reverse current measured when applying the method of the present invention is greater than the reverse current value obtained from the prior electrical characterization, this can indicate damage to the silicon solar cell due to unfavorable parameters during the application of the remediation method. Such damage can be, for example, the creation of a short circuit in the silicon solar cell, which can be identified from an increase in the reverse current of the silicon solar cell.

[0023] In addition to using a reverse current value generated from a previous electrical characterization, the reference value can also be a reverse current sensed in a measurement step prior to the processing step, or the reverse current can be measured in the processing step before illuminating at least a portion of the processing section.

[0024] In an advantageous embodiment, the deviation of the reverse current from the respective reference reverse current can likewise be used as a control parameter for setting the illumination intensity and / or the exposure time to illumination and / or the forward and reverse voltage levels of the silicon solar cells during illumination of at least a part of the processing section. Similarly, by defining a threshold value for the reverse current after a processing step and / or defining a threshold value for the change in the reverse current resulting from a processing step, rejection criteria for silicon solar cells can also be created, which allows the corresponding silicon solar cells to be withdrawn from further processing and, for example, to be prevented from being installed in a solar module.

[0025] If a reverse current is detected in the measurement or processing step, a voltage opposite to the forward direction and having a value lower than the breakdown voltage of the silicon solar cell can also be changed. In this way, a reverse current is defined for each given voltage, assigned to the respective measurement section or processing section, and stored. By changing the voltage opposite to the forward direction, the type of damage to the silicon solar cell can be identified, and therefore, for example, damage in the form of cracks in the silicon solar cell can be distinguished from damage due to increased charge carrier recombination.

[0026] In a further embodiment of the method, during the treatment and / or measurement steps, the proportion of illumination reflected by the solar side of the silicon solar cell during illumination of at least a part of the treatment or measurement section is measured and assigned to the respective section and stored, thus allowing changes in optical properties due to the treatment steps to also be determined.

[0027] Advantageously, the wavelength of the optical radiation emitted by the point light source is changed during illumination of the measurement section in the measurement step and / or during illumination of the treatment section in the treatment step, and the current intensity for this optical radiation is also sensed in the measurement step and / or treatment step and assigned to the respective section and stored. DETAILED DESCRIPTION OF THE INVENTION

[0028] Advantageously, the same ammeter can be used to sense the current intensity of the measurement current flow and / or the process current flow and / or the reverse current. However, the invention is not limited to this. Different measurement meters can also be used depending on the measurement range. For example, if the current intensity of the process current and the current intensity of the reverse current are orders of magnitude different, it may therefore be advantageous to use two ammeters optimized for the respective ranges. [Example]

[0029] Different exemplary embodiments of the present invention are described below.

[0030] First Exemplary Embodiment In a method for improving the ohmic contact behavior between a contact grid and an emitter layer of a silicon solar cell according to the present invention, a silicon solar cell having an emitter layer, a contact grid, and a back contact is first prepared. This may be, for example, a polycrystalline silicon solar cell having dimensions of 15.7 cm x 15.7 cm, which may be placed on a processing table. Next, a contact device electrically connects the contact grid to one pole of a voltage source and the back contact to the other pole of the voltage source. The contact device may, for example, comprise a spring contact pin that is located on the contact grid and back contact of the silicon solar cell and is connected to the voltage source via a cable connection.

[0031] In the first measurement step, a voltage source is used to apply a voltage directed in the forward direction of the silicon solar cell between the contact grid and the back contact via the contact device. When this voltage is applied, individual measurement sections of the subarea on the solar cell's solar-facing side are illuminated using a point light source, such as a laser or a focused white light source. As a result of the illumination, a measurement current flow is induced in each subarea, and this measurement current flow is 1 mA / cm2 for the measurement section. 2 ~500mA / cm 2 The applied voltage and illumination intensity of the point light source are set so that the current density of the silicon solar cell is 1 / 2. The illumination of each measurement section is achieved by directing light emitted by the point light source from measurement section to measurement section, with the applied voltage and illumination intensity of the point light source being kept constant. The current flow to the silicon solar cell is then measured for each measurement section using an ammeter and a contact device, and the sensed current intensity of each measured current flow is assigned to each measurement section and stored. The assignment of the measured current intensity to each measurement section is performed, for example, by storing each current intensity together with the position coordinates of that measurement section on the solar-facing side of the silicon solar cell.

[0032] In the treatment step following the first measurement step, a voltage lower than the breakdown voltage of the silicon solar cell is applied by a voltage source and a contact device in the forward and reverse directions of the silicon solar cell. When this voltage is applied, the point light source already used in the measurement step is guided onto the solar surface of the silicon solar cell, illuminating in the process a treatment section of a sub-area of the solar surface. As a result of the illumination, a current flow is induced in each sub-area. This current flow is 200 A / cm2 through the section. 2 ~20,000A / cm 2 The current density is 0.01 s, and the exposure time is 10 ms to 10 ns. The current intensity and exposure time are set within this parameter window via the speed of movement of the point light source relative to the silicon solar cell, the irradiance of the point light source, and the forward and reverse voltage levels of the silicon solar cell (but lower than the breakdown voltage). As a result of this processing step, the ohmic contact behavior between the contact fingers and the emitter layer of the silicon solar cell is significantly improved, especially in areas that had a high contact resistance between the contact grid and the emitter layer before the processing step.

[0033] After the processing step, a second measurement step similar to the first measurement step is performed. Again, the current intensity of the measured current flow is preferably sensed using the same voltage and illumination intensity parameters as during the first measurement step and is assigned to and stored for each measurement section. Thus, for each measurement section, there is a value for the intensity of the measured current flow before the processing step and a value for the intensity of the measured current flow after the processing step. Thus, the change in each measured current value provides a spatially resolved quantification of the improvement in the ohmic contact behavior between the contact grid and the emitter layer. The calculated change from the measured current flow can also be assigned to and stored for each measurement section. The silicon solar cell can then be subjected to a further processing step depending on the results (change in the intensity of the measured current flow). In this further processing step, for example, only processing sections whose corresponding measurement sections have not yet reached a specified change in the measured current flow and / or a specified target value for the measured current flow in the measurement step are processed.

[0034] The voltage applied in the measurement step may be in a direction opposite to the forward direction of the silicon solar cell and may have a value lower than the breakdown voltage of the silicon solar cell, or the voltage applied in the measurement step may be in the forward direction of the silicon solar cell.

[0035] Second Exemplary Embodiment The measurement step is performed similarly to the first exemplary embodiment. However, in the treatment step, the parameters of the forward and reverse voltages and the illumination intensity of the point light source are adjusted based on the current intensity of the measured current flow sensed in the first measurement step. Areas with low current intensities of the measured current flow in the first measurement step are processed in the treatment step with a higher treatment current flow and / or a longer exposure time to the treatment current flow than areas already exhibiting high current intensities of the measured current flow. The increase in treatment current flow can be achieved via an increase in the forward and reverse voltages and / or an increase in the illumination intensity of the point light source. The increase in exposure time to the treatment current flow is controlled via the dwell time of the point light source over each treatment section.

[0036] Third Exemplary Embodiment Again, the measured current flow is sensed during illumination of the measurement section in the measurement step, and the processing step is performed accordingly. Furthermore, in a second measurement step, before and / or after illumination of at least a first portion of the measurement section, the solar-facing side of the silicon solar cell is left unilluminated, and a voltage reverse to the forward direction, having a value lower than the breakdown voltage of the silicon solar cell, is applied between the contact grid and the back contact via the contact device using a voltage source. When the voltage is applied, a reverse current of the silicon solar cell is sensed using an ammeter. This reverse current is assigned to each measurement section and stored. This reverse current can be used as a characteristic value of damage caused to the silicon solar cell during the processing step. For this purpose, the determined reverse current of the measured measurement section is compared with a reference reverse current obtained from an electrical characterization of the silicon solar cell prior to the method. This electrical characterization can include, for example, a current-voltage curve in determining solar cell efficiency, which is typically performed during the manufacturing process of the silicon solar cell. Advantageously, the reverse current is measured before or after illumination of all measurement sections in the measurement step.

[0037] The change in the reverse current determined in the second measurement step relative to the previously determined reference reverse current is used as an indicator of damage to the silicon solar cell due to the processing step. If the reverse current of the silicon solar cell increases after the processing step, it can be determined that damage to the silicon solar cell has occurred due to the processing step.

[0038] (Fourth Exemplary Embodiment) The method proceeds similarly to the third exemplary embodiment. However, in contrast, a reference reverse current is generated in a first measurement step. As in the second measurement step, before and / or after illuminating at least a first portion of the measurement section, the solar-facing side of the silicon solar cell is left unilluminated, and an ammeter is used to sense the reverse current of the silicon solar cell when a voltage is applied. The change in the reverse current sensed in the second measurement step relative to the reverse current sensed in the first measurement step is then used as an indicator of damage caused to the silicon solar cell by the treatment step.

[0039] Fifth Exemplary Embodiment In addition to or as an alternative to sensing the measured current flow and / or reverse current in the measurement step, the actual current intensity of the process current flow is also sensed for at least some of the illuminated process sections in the process step, assigned to each process section, and stored. The current intensity is sensed at the end of the exposure time to the current flow for each subarea. The sensed process current for each process section is used as a measure of the improvement in ohmic contact behavior between the contact grid and the emitter layer achieved by the process step. When the process sections are processed using the same parameters of the reverse voltage of the silicon solar cell and the illumination intensity of the point light source, areas with better ohmic contact between the contact grid and the emitter layer are manifested by a higher current intensity at the end of the respective process section. The sensed and stored process current for each process section can be used, for example, as a quality characteristic for further processing of the silicon solar cell. Similarly, the sensed and stored process current can also be used to perform further process steps, in which case, for example, areas with low measured process currents are processed again in further process steps with parameters changed in a targeted manner. In this case, the parameters that are changed are again the illumination intensity of the point light source and / or the exposure time to the illumination and / or the forward and reverse voltage levels of the silicon solar cell.

[0040] Sixth Exemplary Embodiment In contrast to the fourth exemplary embodiment, if no measurement step is performed before the processing step, a reference reverse current can also be determined in the processing step for comparison with the reverse current determined in the second measurement step, such that in the processing step, before illumination of the processing section, the solar side of the silicon solar cell is left unilluminated, and the reverse current is sensed when forward and reverse voltages are applied to the silicon solar cell.

[0041] Seventh Exemplary Embodiment In contrast to the above-described exemplary embodiment, only during the processing step can both the reference reverse current and the reverse current after processing of the processing section be measured. Therefore, during the processing step, before illuminating the first portion of the processing section, the solar-facing side of the silicon solar cell is left unilluminated, and the reverse current is sensed when forward and reverse voltages are applied. The first portion of the processing section is then gradually illuminated. When the illumination of the first portion of the processing section is terminated, the solar-facing side of the silicon solar cell is again left unilluminated, and the reverse current is sensed again. The value of the reverse current sensed before illuminating the first portion of the processing section is then used as a reference value for the reverse current sensed after illuminating the first portion of the processing section.

[0042] In a processing step, a point light source is used to scan the sun-facing side of a silicon solar cell, for example, line by line, during processing of the processing sections, sequentially illuminating the processing sections lying along each line. After each line, the point light source is turned off or guided away from the sun-facing side of the solar cell beyond the edge of the on-state silicon solar cell, leaving the sun-facing side of the solar cell completely unilluminated, and a reverse current can be detected when a voltage in the opposite direction to the forward direction is applied. In either case, the reverse current detected after illumination of one line is used as a reference reverse current for the reverse current that occurs after illumination of subsequent lines. In this way, any damage to the silicon solar cell can be assigned to the processing of a specific line (or processing section).

[0043] Eighth Exemplary Embodiment The processing is performed similarly to the seventh exemplary embodiment. Furthermore, the change in reverse current occurring before and after the illumination of a line is used as a control parameter for setting parameters (illumination intensity of the point light source, exposure time to illumination, forward and reverse voltage levels) for the illumination of subsequent lines in the processing step. For example, if an increase in reverse current is detected, the parameters (e.g., exposure time to illumination) for the illumination of subsequent lines are changed so as to avoid further increase in reverse current.

[0044] In all the above exemplary embodiments, in a further embodiment, during the sensing of the reverse current in the measurement or processing step, the voltage in the direction opposite to the forward direction can also be changed, provided that this voltage still has a value lower than the breakdown voltage of the silicon solar cell. Thus, the reverse current is defined for a given voltage and assigned to the respective measurement or processing section and stored.

[0045] Ninth Exemplary Embodiment The process current flow of the process section sensed during a process step (see the fifth exemplary embodiment) is used to control the parameters for the process of the subsequent process section. The control is performed in such a way that the process current flow sensed during the process of the process section is compared with a reference value. If the sensed process current flow is, for example, lower than this reference value, this may be an indication that the improvement in the ohmic contact behavior between the contact grid and the emitter layer is still insufficient. Therefore, in the subsequent process section, the parameters for the illumination of this process section are adjusted accordingly.

[0046] (Tenth Exemplary Embodiment) In contrast to the fifth exemplary embodiment, in which the current intensity of the treatment current flow is sensed at the end of the exposure time of each subarea to the current flow in each case, in this case, a first current intensity is sensed first, and a second current intensity is subsequently sensed using an ammeter for each treatment section during its illumination, and both current intensities are assigned to the treatment section and stored. The change (gradient) of the current intensity is used as an indicator of improvement in the ohmic contact behavior between the contact grid and the emitter layer. An increase in current intensity during illumination of a treatment section indicates improved ohmic contact behavior. A small or no increase in current intensity indicates only a small or no improvement in ohmic contact behavior. Therefore, the change in current intensity during illumination of a treatment section is used to control parameters of at least one subsequent treatment section (illumination intensity of the point light source, exposure time to illumination, forward and reverse voltage level). In addition to being used as a control parameter, the gradient of the current intensity is also assigned to each treatment section and stored.

[0047] In all enumerated exemplary embodiments, in the processing step and / or the measuring step, the proportion of illumination reflected by the solar-facing side of the silicon solar cell is optionally measured during illumination of at least a portion of the processing section or the measuring section and assigned to the respective section and stored. Furthermore, during sensing of the reflected proportion, the wavelength of the optical radiation emitted by the point light source is optionally changed, and the reflected proportion is sensed at a predetermined wavelength and assigned to the respective section and stored. The wavelength of the optical radiation emitted by the point light source is also optionally changed during sensing of the intensity of the measured current flow and / or the processed current flow, and in this case, the intensity of the measured current flow and / or the processed current flow is again sensed for the respective specified wavelength and assigned to the respective section and stored.

Claims

1. A method for improving the ohmic contact behavior between a contact grid and an emitter layer of a silicon solar cell, comprising: a treatment step, using a voltage source and a contact device connected thereto, applying a voltage having a value lower than the breakdown voltage of the silicon solar cell between the contact grid and a back contact of the silicon solar cell in a forward direction and a reverse direction of the silicon solar cell; when the voltage is applied, a point light source is guided above the solar surface side of the silicon solar cell, and the point light source is moved so as to direct light emitted by the point light source to each treatment section of a subarea of the solar surface side, thereby sequentially illuminating each treatment section of the subarea of the solar surface side, thereby guiding a treatment current flow to each subarea, and the treatment current flow is 200 A / cm2 to the treatment section. ２ ~20,000A / cm ２ and acting on the sub-areas for a time period between 10 ns and 10 ms, and performing a measuring step before and / or after the treating step, wherein in the measuring step, a voltage is applied between the contact grid and the back contact using the voltage source and the contact device, and when the voltage is applied, each measurement section of the sub-area on the sun-face side of the silicon solar cell is illuminated with a point light source that is moved to direct light emitted by the point light source to each measurement section of the sub-area on the sun-face side, thereby inducing a measurement current flow in each sub-area, and the measurement current flow is 1 mA / cm for the measurement section. ２ ~500mA / cm ２ wherein the current intensities of the measured current flows are sensed using an ammeter, assigned to each of the measurement sections and stored, and the stored current intensities are used as an indicator of the quality of the ohmic contact behavior between the contact grid and the emitter layer.

2. 2. The method of claim 1, wherein during the treatment step for at least some of the illuminated treatment sections, the current intensity of the treatment current flow is sensed using an ammeter and assigned to each of the treatment sections and stored.

3. 3. The method according to claim 1, wherein the voltage applied in the measurement step is in a direction opposite to the forward direction of the silicon solar cell, and has a value lower than the breakdown voltage of the silicon solar cell, or the voltage applied in the measurement step is in a direction in the forward direction of the silicon solar cell.

4. 4. The method according to claim 1, wherein the current intensity of the measurement current flow assigned to a measurement section in the measurement step is used as a control parameter in the processing step following the measurement step for setting the illumination intensity of the point light source and / or the exposure time to illumination and / or the forward and reverse voltage levels of the silicon solar cell during illumination of at least one of the processing sections.

5. 5. The method according to claim 1, wherein a change is determined from the current intensity of one of the measurement sections sensed in the measurement step prior to the processing step and the current intensity of the one measurement section sensed in the measurement step following the processing step, and the change is assigned to each of the measurement sections and stored.

6. 6. The method according to claim 5, characterized in that the change in the current intensity assigned to the measurement section is used as a control parameter of a further processing step for setting the illumination intensity of the point light source and / or the exposure time to illumination and / or the forward and reverse voltage levels of the silicon solar cell during illumination of at least one of the processing sections.

7. 7. The method according to claim 1, wherein the current intensity assigned to a processing section is used in said processing step as a control parameter for setting the illumination intensity of the point light source and / or the exposure time to illumination and / or the forward and reverse voltage levels of the silicon solar cell during illumination of a subsequent processing section of said processing step.

8. 8. The method according to claim 1, wherein in the processing step, a first current intensity followed by a second current intensity is sensed using the ammeter during illumination of one of the processing sections, and both current intensities are assigned to and stored in the processing sections.

9. 9. The method of claim 8, wherein a current intensity gradient is determined from the first current intensity and the second current intensity and is assigned and stored in the processing section.

10. 10. The method of claim 9, wherein the current intensity gradient assigned to the processing section in the processing step is used as a control parameter for setting the illumination intensity and / or the exposure time to illumination and / or the forward and reverse voltage levels of the silicon solar cell during illumination of a subsequent processing section in the processing step.

11. 11. The method according to claim 1, wherein in the treatment step, before and / or after illuminating at least a first part of the treatment section, the sun-facing side of the silicon solar cell is not illuminated and a reverse current of the silicon solar cell is sensed using the ammeter.

12. 11. The method according to claim 1, wherein in the measuring step, before and / or after illuminating at least a first portion of the measurement section, the solar-facing side of the silicon solar cell is not illuminated, and a voltage having a value lower than the withstand voltage of the silicon solar cell is applied between the contact grid and the back contact using the voltage source via the contact device in a reverse direction to the forward direction, and in this process, a reverse current of the silicon solar cell is sensed using the ammeter, assigned to the measurement section, and stored.

13. 12. The method according to claim 11, characterized in that the reverse current is compared with a reference reverse current and a deviation of the reverse current from the reference reverse current is used as a control parameter for setting the illumination intensity and / or the exposure time to illumination and / or the forward and reverse voltage levels of the silicon solar cell during illumination of the further part of the treatment section on the sun-face side of the silicon solar cell.

14. 14. The method of claim 13, wherein the reference reverse current is obtained from an electrical characterization of the silicon solar cell prior to the method.

15. 14. The method of claim 13, wherein the reverse current sensed in the processing step prior to illuminating the first portion of the processing section is used as a reference reverse current for the reverse current sensed subsequently in the first portion of the processing section.

16. 14. The method of claim 13, wherein the reference reverse current used in the processing step for a processing section is the reverse current determined in the measuring step for a measurement section preceding the processing step.

17. 17. The method according to claim 11, wherein in the measuring step and / or the processing step for sensing the reverse current, the voltage is changed in the forward and reverse directions to have a value lower than the breakdown voltage of the silicon solar cell.

18. 18. The method according to any one of claims 1 to 17, characterized in that in the processing step and / or the measuring step, during illumination of at least a part of the processing section or the measuring section, the proportion of illumination reflected by the solar facing side of the silicon solar cell is measured and assigned to the respective processing section or the measuring section and stored.

19. 19. The method according to claim 18, characterized in that in the processing step and / or the measuring step, during illumination of at least a part of the processing section or the measuring section, the wavelength of the optical radiation emitted by the point light source is changed, and the proportion of illumination at said wavelength that is reflected by the solar facing side of the silicon solar cell is measured and assigned to the respective processing section or measuring section and stored.

20. 20. The method according to any one of claims 1 to 19, characterized in that the wavelength of the optical radiation emitted by the point light source is changed in the measuring step and / or the processing step, and the current intensity is also sensed for this optical radiation in the measuring step and / or the processing step and assigned to and stored in the respective processing section or measuring section.

21. 21. The method according to any one of claims 1 to 20, characterized in that the ammeter is connected to the contact device or to a further contact device which is connected to the contact grid and the back contact of the silicon solar cell.