TW201528540A - Solar cell production method and solar cell treatment method - Google Patents

Abstract

The invention relates to a solar cell production process and to a solar cell treatment process. The solar cell production process has a heat-treatment step, in which a substrate (1) is exposed to a heat-treatment temperature profile (51, 52), wherein the heat-treatment temperature profile (51, 52) lies in a heat-treatment range between a lower range limit of approximately 400 degrees Celsius (DEG C) and an upper range limit of approximately 700 DEG C over a heat-treatment time of at least 3 seconds.

Description

Solar cell manufacturing method and solar cell processing method

The present invention relates to a method of fabricating a solar cell and a method of processing a solar cell.

In the current solar cell structure, attenuation may occur, a phenomenon that is reflected in a sudden sharp drop in power or efficiency of the solar cell. In general, solar cells are subject to performance degradation during operation. Changes in operating parameters of the battery, such as the light intensity of the solar cell power supply and the operating temperature of the solar cell, determine whether the solar cell has occurred. Performance degradation plays an important role. The attenuation of solar cell performance is also triggered during the operation of the solar cell.

Recently, it has been found that the Recombination-active defect may be the cause of the deterioration of the performance of the solar cell, and the defect of the composite is caused by the incident light being irradiated into the interior of the crucible. This phenomenon of solar cell performance degradation due to light irradiation is also referred to as LID-light induced degradation, which occurs because a boron-oxygen complex is formed in the crystal volume. The above effects can be prevented by using a germanium wafer having a low boron content and a low oxygen content in the production of solar cells according to a known method.

However, even if a solar cell is manufactured using a germanium wafer having less boron and oxygen content as a raw material, there is still a phenomenon in which battery performance is attenuated, and more specifically, a solar cell design has appeared and continues to have an attenuation effect, and it is impossible to The degree of interpretation based on the above-described boron oxide effect. In addition to the boron-oxygen decay effect (boron oxygen decay or LID) that is now being understood in the industry, there is another attenuation effect, such as the 2012 27th European Photovoltaic Solar Conference and Exhibition (EUPVSEC). This conclusion can be drawn from the article "Light Induced Degradation of Rear Passicated mc-Si Solar Cells" by K. Ramspeck et al. The article explains that polycrystalline tantalum solar cells (mc-Si solar cells) designed with surface passivated PERC (PERC-passivated emitter and backside cells) produce a photoinduced attenuation that cannot be explained by previous boron-oxygen models. By reducing the oxygen content, the boron oxide decay effect in polycrystalline germanium solar cells is relatively small. However, here there is an attenuation effect that may significantly exceed the known boron-oxygen decay. The above article indicates that when the light irradiation intensity is 400 watts per square meter (W/m ² ) and the battery temperature is 75 ° C, the efficiency attenuation value is 5-6% (relative).

SUMMARY OF THE INVENTION An object of the present invention is to provide a solar cell manufacturing method by which a solar cell having a lower degree of attenuation or no late decay at all can be produced in a reliable manner. In addition, the present invention also provides a method for processing a solar cell, which, after the above treatment, can reduce the sensitivity of the battery to attenuation in a subsequent operation step or can eliminate an increase in a method step in the solar cell manufacturing step. The sensitivity of solar cells to battery decay phenomena.

According to the present invention, the above object is achieved by a solar cell manufacturing method according to claim 1 and a solar cell processing method according to claim 12 of the patent application. Other improvements of the invention will be described in the scope of the appended claims.

In this context, in order to distinguish the performance degradation associated with the present invention from the performance attenuation mechanism involved in LID photoinduced attenuation, in the following sections of the article, eLID is used to represent the performance degradation to be described herein. This name means an enhanced photoinduced attenuation effect (eLID-enhanced light induced degradation). Standard solar cells also exhibit enhanced photo-induced attenuation, but solar cells made of polycrystalline semiconductors have a high probability of enhanced photo-induced attenuation. The solar cells made of the above-mentioned polycrystalline semiconductors have a relatively low oxygen content. The sensitivity of LID photoinduced attenuation is also relatively low. Newer solar cells developed in recent times show higher eLID sensitivity, such as PERC-structured solar cells or other surface-passivated solar cells, especially those that use solar cells to fire laser equipment (LFC). The contact-connection solar cells achieved by laser fired contacts are very prone to eLID.

The invention is based on the knowledge that the sensitivity of the solar cell described in this article to the aforementioned attenuation, i.e. the eLID sensitivity of the solar cell, depends to a large extent on the production parameters in the solar cell manufacturing step. The inventors have discovered that such battery performance degradation phenomena are associated with another battery performance attenuation mechanism that is different from the attenuation mechanisms in the now known boron-oxygen decay effects. In addition, the inventors have successfully designed a method that significantly reduces or even completely avoids eLID sensitivity.

The sensitivity of eLID and the sensitivity of LID have similar properties, that is, when the solar cell is irradiated with light or current flows through the solar cell, battery performance degradation is likely to occur. Although the term "photoinduced" is used in both LID and eLID, in practice, when a current flows through a solar cell, that is, a voltage is applied across the solar cell, and a high voltage is generated between different positions of the solar cell. The voltage flowing to a low voltage current may also cause too The performance of the solar battery is attenuated. The light intensity or current density required to produce attenuation depends on the operating temperature, lighting or power-on time, and other operating parameters and production parameters of the solar cell.

When eLID type battery performance degradation occurs, solar cell efficiency will drop by a few percentage points, for example, by at least 3%, 5%, 7%, 9% or more. This efficiency decay is usually accompanied by a decrease in carrier lifetime, which is at least half or even an order of magnitude decrease. For example, the carrier lifetime may be shortened from a few hundred microseconds to tens of microseconds. Carrier lifetime measurements on the substrate are made prior to substrate contact or metallization.

An important aspect of the invention is based on the discovery that there is a manufacturing step in the manufacturing step of the solar cell that can induce eLID sensitivity in the finished product of the solar cell, that is, the eLID sensitivity of the solar cell can be increased. In general, in the solar cell manufacturing process flow, the firing process or the firing step is a particularly critical step, that is, the above-mentioned decisive step that affects its eLID sensitivity. To effect metallization of the metallized paste, a layer of metallized paste is applied to the surface of the substrate such that after undergoing a firing step, the metallized paste forms a metallized layer. The above firing step is very likely to cause eLID sensitivity in future solar cells. Until now, it has not been possible to find out which effect led to eLID. It is now known that when LID-type performance degradation occurs, the mechanism of battery performance degradation is the formation of a boron-oxygen complex in a solar cell. When an eLID occurs, a mechanism in which a plurality of different battery performance attenuations may exist simultaneously is at work.

As can be understood from the above description, a heat treatment step can be provided to reduce the tendency of the eLID sensitivity to increase in one manufacturing step. In other words, after the substrate undergoes a manufacturing step that results in an increase in eLID sensitivity, the semi-finished product is subjected to a heat treatment step such that its eLID sensitivity is eliminated to some extent. To this end, in the heat treatment step, The substrate is subjected to a heat treatment temperature profile. The heat treatment temperature profile needs to be set such that the substrate is placed in an environment that reaches a temperature range for a heat treatment time of at least 3 seconds, the temperature range having a lower limit of about 400 ° C and an upper range of about 700 ° C. Likewise, the heat treatment temperature profile described above can also be employed in the processing steps for a finished solar cell. In this context, all of the heat treatment temperature profiles mentioned in the solar cell manufacturing steps are applicable to the solar cell processing step and vice versa.

The eLID sensitivity can also be eliminated when the substrate or solar cell product is placed at a certain temperature for a heat treatment period and the above temperature is within the heat treatment temperature range. In a preferred treatment scheme, the heat treatment time is at least 3, 4, 5, 7 or 9 seconds. Preferably, the lower limit of the heat treatment temperature range is 400 ° C, 420 ° C, 450 ° C or 480 ° C. Preferably, the upper limit of the heat treatment temperature is 550 ° C, 600 ° C, 650 ° C or 700 ° C.

In a preferred embodiment of the present invention, the heat treatment step includes a temperature rising phase and/or a temperature decreasing phase, wherein the substrate undergoes a heat treatment temperature profile in the heat treatment step, and the maximum gradient is in the temperature rising phase of the heat treatment step and/or a temperature drop phase. 100 sec (K/s), 70K/s, 50K/s, 40K/s or 30K/s. In a preferred heat treatment scheme, the maximum gradient in the temperature rise phase of the heat treatment step is 100 gram per second (K/s), 70 K/s, 50 K/s, 40 K/s or 30 K/s, and the cooling step of the heat treatment step The maximum internal gradient is 100 gram per second (K/s), 70K/s, 50K/s, 40K/s or 30K/s. This refers to the absolute value of the maximum gradient, especially in the step of cooling, the value of which is negative.

By changing the temperature of the substrate or finished solar cell within a certain temperature range for a certain period of time, the eLID sensitivity of the solar cell can be greatly reduced or completely eliminated. It is also possible to change the spatial position of the component to be processed so that the temperature of the component to be processed is The heat treatment is used to replace the temperature of the substrate or the finished solar cell in a certain period of time, for example, by moving the substrate or the finished solar cell from one position in the space to another at a different temperature to achieve heat treatment of the part.

In particular, it can be stated that the base/finished solar cell can be subjected to the entire heat treatment step of the component by a continuous heating furnace.

During the heat treatment, the substrate or finished solar cell can be heated to a maximum allowable heating temperature greater than 400 ° C, 430 ° C, 450 ° C, 470 ° C, 500 ° C or 550 ° C.

In a preferred embodiment of the present invention, in the step of manufacturing the solar cell, the substrate is coated by a firing step, a heating step of a firing step, or a cooling step of a firing step by the above treatment. A metallized layer is formed on the metallized paste on the surface of the substrate. The firing step may be a step leading to eLID sensitivity of the solar cell, depending on the method parameters in this step. That is, the manufactured solar cell has a higher eLID sensitivity because of the above-described firing step, or simply because of the temperature rising phase in the firing step or simply because of the cooling phase in the firing step. In this case, if the relevant component is subjected to a heat treatment step after the firing step is completed, so that the eLID sensitivity of the solar cell is eliminated, it is advantageous to improve the performance of the solar cell.

If a step of the solar manufacturing process includes a firing step and includes a temperature rising phase therein, it is preferred to integrate the heat treating step into a cooling stage during a firing step. For example, when setting the processing temperature of the firing step, a plateau (Plateau) may be set on the temperature profile of the firing step to achieve the heat treatment step, that is, after the temperature of the firing process reaches the maximum temperature, the Temperature for a while.

According to a preferred embodiment of the invention, the substrate or solar energy is in the heat treatment stage The battery is illuminated by light and/or energized on a substrate or solar cell. Illuminating or energizing the substrate or solar cell may facilitate the solar cell to eliminate its eLID sensitivity, or for viewing the substrate and solar cell during the heat treatment step.

According to a preferred embodiment of the invention, the substrate is made of monocrystalline, polycrystalline or multicrystalline semiconductor. The substrate is preferably made of tantalum.

The invention relates to a solar cell manufacturing scheme which is advantageous for realizing the design requirements of a solar cell. The substrate is covered with a passivation layer having a surface passivation function on one or both sides. The passivation layer may preferably be disposed on a surface coated with a metal paste to produce a slurry metallization substrate. In this case, a laser firing contact treatment step (LFC) may be additionally provided before or after the firing step. The passivation layer is preferably, in particular, an aluminum oxide layer, an aluminum oxynitride layer, a tantalum oxide layer and/or a tantalum nitride layer. In practical applications, there are also a plurality of passivation layers which can be disposed to overlap each other, for example, one of the chemical passivation layers and one passivation layer having field effect passivation characteristics.

The passivation layer is suitable for use as a back passivation layer and/or as a front passivation layer, wherein an aluminum oxide layer, an aluminum oxynitride layer and/or aluminum oxide, aluminum oxynitride, hafnium oxynitride and/or nitride are often used. The stack of tantalum is particularly suitable as a back passivation layer, and a layer composed of tantalum oxynitride or tantalum nitride is suitable as a front passivation layer and/or an antireflection layer.

The invention will be explained by way of examples with reference to the accompanying drawings in which: Figures 1a) to e) are schematic views of the steps of the invention relating to the method of manufacturing a solar cell; Figure 2 is a graph of heat treatment temperature; and Figure 3 is an integration Temperature profile during the firing step of the heat treatment step.

The different steps in the flow of the solar cell manufacturing process are shown from Figures 1 a) to e). In particular, it can be seen from this schematic that a heat treatment step has elapsed after the component has obtained the functional layer. As shown in Fig. 1a), a substrate 1 is first provided. As shown in Figure 1 b), a functional layer 2 is formed on the substrate. In the example given by the present invention, the functional layer may be, for example, a metallization layer, a passivation layer, a doped layer or the like, or it is also possible to provide a plurality of layers of the above functional layers on one component. In the subsequent step, the substrate 1 coated with the functional layer 2 is passed through the continuous heating furnace 3, and the heat treatment step is completed in the above step.

The temperature in the continuous heating furnace 3 shown in the drawing is different, and the description can be simplified to divide the temperature in the furnace into three temperature zones, namely, 31, 32, and 33. The substrate 1 first enters the inlet region 30, and then enters the continuous heating furnace 3, leaving the continuous heating furnace 3 after the substrate 1 passes through the outlet region 34. In the above step, the substrate 1 passes through all three temperature regions 31, 32, 33. In the first temperature zone 31, the substrate 1 is heated and heated. That is to say, the substrate 1 also undergoes a temperature rising phase of the heat treatment high temperature treatment during this period. In the second temperature range 32, the temperature of the substrate 1 reaches the maximum temperature or the highest limit temperature. Then, in the step of the substrate 1 by the third temperature region of the continuous heating furnace 3, the substrate 1 undergoes a cooling stage of heat treatment.

It can be seen in Figure 1c) that the substrate 1 enters the continuous furnace 3 and passes through the first temperature zone 31. After that, as shown in Figure 1d), the substrate 1 enters the second temperature zone 32. Here, the temperature of the substrate reaches the highest temperature throughout the processing step. After that, as shown in Fig. 1e), the substrate 1 enters the third temperature zone and its temperature begins to drop, and then the substrate 1 exits the continuous furnace 3 through the outlet zone 34.

As shown in FIG. 2, since the substrate 1 is to pass through the continuous heating furnace 3, Body 1 undergoes a temperature change process. In the temperature diagram, the time change along the X-axis direction and the temperature change along the Y-axis direction. As can be seen from the figure, the heat treatment temperature profile 51 is composed of a temperature rising phase 51a and a temperature decreasing phase 51b. Since the step of conforming to the heat treatment temperature profile 51 has been experienced, the eLID sensitivity that may be present in the solar cell may be reduced or completely eliminated. For this reason, the maximum gradient during the temperature rising phase 51a and/or the cooling phase 51b cannot exceed about 100 K/s.

Figure 3 is another schematic diagram in which a temperature change process curve 4 in the firing process step is involved. The temperature change process curve 4 includes a firing process step heating stage 4a and a firing process step cooling stage 4b. Here, the temperature change curve of the firing process step temperature rising phase 4a and the firing process step cooling phase 4b may be a conventionally used temperature profile. In this case, if the temperature change of the firing treatment step is changed in accordance with the temperature change curve 4, it is likely to cause an increase in the sensitivity of the manufactured solar cell eLID. In order to avoid the above situation, it is necessary to introduce a heat treatment step which is integrated in the step of the cooling stage 4b of the firing step. In other words, the temperature of the substrate 1 is maintained within a certain temperature range during the heat treatment time, that is, higher than the lower limit temperature and lower than the upper limit temperature, so that the substrate 1 is subjected to heat treatment in the cooling stage 4b in the firing treatment step. . In the example shown in Fig. 3, the heat treatment temperature profile 52 of another heat treatment step having another cooling stage 52b constitutes a plateau period in the cooling stage 4b of the firing treatment stage.

1‧‧‧ base

2‧‧‧ functional layer

3‧‧‧Continuous heating furnace

30‧‧‧ Entrance area

31‧‧‧First temperature zone

32‧‧‧Second temperature zone

33‧‧‧ Third temperature zone

34‧‧‧Export area

4‧‧‧temperature curve of the firing step

4a‧‧‧The warming phase of the firing step

4b‧‧‧The cooling phase of the firing step

51‧‧‧ Heat treatment temperature curve

51a‧‧‧ warming phase

51b‧‧‧ cooling stage

52‧‧‧ Another heat treatment temperature curve

52b‧‧‧ another cooling stage

4‧‧‧temperature curve of the firing step

4a‧‧‧The warming phase of the firing step

4b‧‧‧The cooling phase of the firing step

52‧‧‧ Another heat treatment temperature curve

52b‧‧‧ another cooling stage

Claims (12)

A solar cell manufacturing method having a heat treatment step in which a substrate (1) is exposed to a heat treatment temperature profile (51, 52), wherein the heat treatment temperature profile (51, 52) is within a heat treatment range during a heat treatment time of at least 3 seconds The lower limit of the range of the heat treatment range is about 400 ° C and the upper limit of the range is about 700 ° C. The solar cell manufacturing method according to claim 1, wherein the lower limit of the range is 400 ° C, 420 ° C, 450 ° C or 480 ° C and/or the upper limit of the range is 550 ° C, 600 ° C, 650 ° C or 700. °C. The solar cell manufacturing method according to claim 1 or 2, wherein the heat treatment step has a temperature rising phase (51a) and/or a temperature lowering phase (51b, 52b), wherein a temperature rising phase (51a) of the heat treatment step During the and/or and/or cooling stages (51b, 52b), the heat treatment temperature profile (51, 52) of the substrate has a maximum gradient of 100 gram per second (K/s), 70 K/s, 50 K/s. Or 30K/s. The method for producing a solar cell according to any one of the preceding claims, characterized in that the firing step, the heating step of the firing step of the firing step, or the cooling step of the firing step of the firing step, by the above treatment, The metallized slurry coated on the surface of the substrate forms a metallized layer. According to the solar cell manufacturing method of claim 4, in the specific example of the heating step of the firing step, the heat treatment step is integrated in the cooling step of the firing step of the firing step. A method of manufacturing a solar cell according to any one of the preceding claims, wherein the substrate is irradiated with light or energized during the heat treatment step. A method of manufacturing a solar cell according to any one of the preceding claims, wherein the base system is composed of a single crystal semiconductor or a polycrystalline semiconductor. A method of manufacturing a solar cell according to any one of the preceding claims, characterized in that one or both sides of the substrate are covered with a passivation layer having surface passivation properties. The method for fabricating a solar cell according to claim 8 is characterized in that the back passivation layer is made of alumina, aluminum oxynitride and/or by aluminum oxide, aluminum oxynitride, yttrium oxynitride and/or nitriding. The laminate made by 矽. The solar cell manufacturing method according to claim 8 or 9, wherein the front passivation layer is made of hafnium oxynitride or hafnium nitride. A method of manufacturing a solar cell according to any one of the preceding claims, characterized in that the antireflection coating is made of hafnium oxynitride or tantalum nitride. A solar cell processing method, wherein a solar cell is exposed to a heat treatment temperature profile (51, 52), wherein the heat treatment temperature profile (51, 52) is within a heat treatment range for a heat treatment range of at least 3 seconds, a lower limit of the range of the heat treatment range It is about 400 ° C and the upper limit of the range is about 700 ° C.