TW201316522A - Solar cell inspection method and apparatus thereof - Google Patents

Abstract

A solar cell inspection method is disclosed and includes: charging a diffusion capacitance of a solar cell; after charging the diffusion capacitance, discharging the diffusion capacitance; and detecting light emitted by the solar cell during the discharging step.

Description

Solar cell detection method and related device

The invention relates to a solar cell detecting method and related device, in particular to a solar cell detecting method and related device using a physical phenomenon of electroluminescence (EL).

Since solar cells are a relatively clean source of electricity, it is generally expected that their penetration rate will continue to rise in the foreseeable future.

However, the manufacturing process of solar cells is quite complicated, and it will inevitably lead to some defects on the battery, such as micro cracks or other defects, which often affect the photoelectric conversion efficiency and battery life of the battery, and reduce the quality of the battery. .

Therefore, manufacturers of solar cells are committed to improving production techniques to reduce the occurrence of defects. In addition, manufacturers must test the manufactured solar cells before shipment to ensure battery quality, reduce future warranty and maintenance costs, and increase user satisfaction.

The minority carrier diffusion length and the minority carrier lifetime are two important parameters of the solar cell. The relationship between these two parameters is: DL=(D*τ) ^1/2 . That is, τ = DL ² /D, where DL is the diffusion length, D is the diffusion coefficient (diffusion coefficient or diffusivity), and τ is the life cycle. If some points on the solar cell have a relatively low diffusion length DL, the quality of these points is poor, and there may be defects that cannot be observed with the naked eye. In addition to the fact that the current may not be normally contributed, the risk of future breakage of these points is relatively Higher. Therefore, detecting the diffusion length of each point on the solar cell is one way to judge the quality of the battery.

Electron beam induced current (EBIC) and laser beam induced current (LBIC) can be applied to detect changes in the diffusion length of each point of the solar cell to determine the battery. quality. However, such detection methods are costly, slow in detection, and large in size, so they are not suitable for practical applications. In addition, other solar cell detection methods based on electroluminescence (EL) cannot detect a small change in the diffusion length, so there is a problem that the discrimination is too low.

In view of this, solar cell detection methods and devices having relatively high discrimination, simpler architecture, and lower detection cost are very valuable to the solar cell industry.

The present specification provides an embodiment of a solar cell detecting method, comprising the steps of: charging a diffusion capacitance of a solar cell; discharging a diffusion capacitor after charging the diffusion capacitor; and sensing light emitted by the solar cell in the discharging step.

The present specification provides an embodiment of a method for detecting a solar cell, comprising the steps of: applying a forward DC bias to the solar cell; applying a reverse DC bias to the solar cell after applying the forward DC bias; and sensing the solar energy The light emitted by the battery during the period in which the reverse DC bias is applied.

The present specification provides an embodiment of a solar cell detecting device, including a charging and discharging module and a light sensing module. The charge and discharge module is used to charge and discharge the diffusion capacitance of the solar cell. The light sensing module is used to sense the light emitted by the solar cell when the charge and discharge module discharges the capacitance.

Compared with the detection method based on the electron beam induced current or the laser beam induced current, the above embodiment has low cost, fast detection speed, small detection machine volume, and high detection discrimination, so it is more suitable for practical applications. . Compared with other detection methods based on electroluminescence, the above embodiments can achieve higher discrimination, so that defects in the solar cell can be detected more accurately.

Please refer to FIG. 1 , which is a schematic diagram of an embodiment of a solar cell detecting device 1 of the present invention. The detecting device 100 is used for detecting a solar cell 180. The solar cell 180 may be a single solar cell unit or a solar cell module composed of a plurality of solar cells. Equivalently, the solar cell 180 includes a diffusion capacitance C _D indicated by a broken line and other equivalent elements (eg, equivalent resistance) not shown in the drawing. The detecting device 100 includes a charging and discharging module 120 and a light sensing module 140. The charge and discharge module 120 is used to charge and discharge the diffusion capacitor C _D of the solar cell 180 first. The light sensing module 140 is configured to sense the light emitted by the solar cell 180 when the charging and discharging module 120 discharges the diffusion capacitance C _D .

FIG. 2 is a schematic diagram of an embodiment of the charging and discharging module 120 of FIG. The charging and discharging module 120 of the embodiment includes a logic control stage 125 and a bridge 130. The bridge circuit 130 includes switches 132, 134, 136, and 138. The four switches may be The transistor, wherein switches 132 and 138 form a first set of switches, switches 134 and 136 form a second set of switches.

The voltage V _DD is the DC supply voltage accepted by the charge and discharge module 120. The positive output terminal (+) and the negative output terminal (-) of the bridge circuit 130 in FIG. 2 are the positive output terminal (+) and the negative output terminal (-) of the charging and discharging module 120 of FIG. 1, respectively. The logic controller 125 is configured to turn on the first set of switches 132 and 138 and open the second set of switches 134 and 136 such that the first set of switches 132 and 138 apply a forward DC bias V _F to the solar cell 180 to charge the diffusion capacitor C _D The second set of switches 134 and 136 are turned on and the first set of switches 132 and 138 are turned off such that the second set of switches 134 and 136 apply a reverse DC bias voltage V _R to the solar cell 180 to discharge the diffusion capacitance C _D . In addition to controlling the four switches, the logic controller 125 can also be used to control the operation of the light sensing module 140 of FIG. 1, for example, to control the shutter opening and closing of the light sensing module 140.

The light sensing module 140 can be a camera that senses the amount of light emitted by the solar cell 180 during an exposure period that is equivalent to the integration of the luminous intensity of the solar cell 180 with the exposure period. The light sensing module 140 can transmit the image of the sensed solar cell 180 to a judging unit (not shown) in the back end, and the judging unit judges whether there is a defect on the solar cell 180 according to the image.

3 is a timing diagram showing an embodiment of a solar cell detecting method of the present invention for detecting the aforementioned solar cell 180. The timing diagram of Figure 3 is also an example of the operation of the apparatus of Figure 1. Although the apparatus shown in FIG. 1 and the method shown in FIG. 3 can exist independently, and do not constitute each other's constraints, for the convenience of description, the following two figures will be combined to introduce the same in FIG. The operation of each component and the various steps in Figure 3.

First, in step 320, the charge and discharge module 120 charges the diffusion capacitor C _D . As shown, the present embodiment employs a method of applying a forward DC bias voltage V _F to the solar cell 180 to allow a forward DC current to flow through the solar cell 180. On the solar cell 180, the minority carrier lifetime is equal to a point of τ _n , and the forward DC current is I _F . In theory, the length of time in this step needs to be equal to or longer than τ _n , and the diffusion capacitance of the point will accumulate the amount of charge of I _F *τ _n before the end of the step.

Next, in step 340, the charge and discharge module 120 discharges the diffusion capacitor C _D . As shown, the present embodiment employs a method of applying a reverse DC bias voltage V _R to the solar cell 180 to allow a reverse direct current that gradually returns to zero to flow through the solar cell 180. In theory, this step will gradually reduce the diffusion capacitance of the life cycle equal to a point of τ _n from the original I _F * τ _n to zero.

In step 360, the light sensing module 140 senses the light emitted by the solar cell 180 when the charging and discharging module 120 discharges the diffusion capacitance C _D . Ideally, the step 360 and the step 340 should start synchronously. However, if the start time of the step 360 is earlier than the start time of the step 340, then in step 360, the light sensing module 140 additionally senses the solar cell 180 in the step. A portion of the light emitted by 320.

In step 320, solar cell 180 will illuminate stably based on the principle of electroluminescence. Light emission intensity of each point approximately proportional to the length of the diffusion point DL _n, and the light emission time length is approximately equal to the length of the applied forward bias voltage V _F of the current time. If the light sensing module 140 senses the amount of light emitted by the solar cell 180 in the whole or part of the period of step 320, the amount of light emitted by each point is approximately proportional to the diffusion length DL _n of the point. However, since the difference in the diffusion length between the normal point and the abnormal point on the solar cell 180 may not be large, the difference in the amount of luminescence of the solar cell 180 at different points when performing step 320 is not too large, in other words, only the aforementioned proportional relationship It may not be sufficient to clearly identify changes in the diffusion length of each point of the solar cell 180.

In step 340, solar cell 180 will briefly illuminate based on the principles of electroluminescence and minority carrier storage time. The light intensity gradually decreasing at each point is approximately proportional to the diffusion length DL _n of the point. Further, as shown by the following formula, the time length t _{s of} each point of illumination is approximately the square of the diffusion length DL _n of the point. In direct proportion. Therefore, if the light sensing module 140 senses the total amount of light emitted by the solar cell 180 in step 340, the total amount of light emitted by each point is proportional to the product of the intensity of the point and the time of the light, in other words, each point. The total amount of luminescence is approximately proportional to the cube of the diffusion length DL _n of the point. At this time, the difference in the amount of luminescence between the normal point and the abnormal point on the solar cell 180 is large. In other words, such a cubic relationship can greatly enhance the discrimination of the diffusion length of each point of the solar cell 180.

In combination with the above two paragraphs, the period in which step 360 overlaps with step 320 (if there is overlap) brings the ordinary discriminating degree of the above embodiment, and the period in which step 360 overlaps with step 340 brings the higher discrimination to the above embodiment. degree. Regardless of the overlap of these three steps, the above embodiments should achieve a higher degree of discrimination than conventional detection devices/methods.

The image of the solar cell 180 obtained in the above embodiment can be used as a target for detecting the solar cell 180. If the brightness of some points in the image is relatively low or below a preset threshold, it means that the diffusion length of the darker points is shorter and may be where the defect lies. If the solar cell 180 is a newly manufactured product, the manufacturer may need to identify the battery cells including the dark spots on the entire solar cell 180 or the solar cell 180 as defective; if the solar cell 180 is already in use The maintenance personnel may need to replace the entire solar cell 180 or the solar cell 180 with the darker cells.

The following is a related formula derivation, where τ _n is the minority carrier lifetime of a certain point of the solar cell 180, C is the equivalent diffusion capacitance of the point, Q is the amount of charge in the diffusion capacitor C at this point, and i is the flow The current at this point, R is the equivalent series resistance at that point, V _C is the voltage across the diffusion capacitor C, I _F is the forward current flowing through the point in step 320, and I _R flows through the instant at which step 340 begins. The reverse current of the point.

First of all, ......(1)

In step 340, the following expression is also established.

Bring the above formula back to equation (1), the following formula can be derived in order

Since Q(0)=I _F *τ _n and Q(t _s )=0, it can be further derived:

Choosing the appropriate R value makes R*C much larger than τ _n , then the above formula can be rewritten as:

It can be known from the above equation that the illuminating time t _{s at} this point is approximately proportional to the minority carrier lifetime τ _{n at} that point. And since τ _n = DL _n ² /D, the illuminating time t _s of the point is approximately proportional to the square of the diffusion length DL _n of the point.

For the light sensing module 140, the sensed image intensity Iv is proportional to the exposure time in addition to the light intensity, and can be expressed as:

Where DL _n = (D * τ _n ) ^1/2 , and since t _s is proportional to τ _n , therefore:

Compared with the conventional conventional detection method, the image intensity Iv is only proportional to τ _n ^1/2 , so the method of the present invention can greatly increase the contrast of the sensed image.

Referring back to FIG. 3, if the above embodiment is to have a better degree of discrimination, the time point at which step 360 starts should be equal to or earlier than the time point at which step 340 begins, and the time overlap between step 360 and step 320 is shorter. Preferably, and the length of time t _{R of} step 340 should be no less than the maximum possible time of illumination time t _s on solar cell 180. Of course, in determining the timing of the three steps, the speed limits of the charging and discharging module 120 and the light sensing module 140 are also taken into consideration.

In the current common solar cells, the minority carrier life cycle is on the order of 0.001 seconds or less, and usually not higher than 0.005 seconds. Therefore, in the above embodiment, the time length t _{F of} step 320 and step 340 The length of time t _{R is} shorter than 0.005 seconds, and this arrangement can shorten the time required for detection.

As mentioned in the previous paragraph, the frequency of change of the voltage shown in Figure 3 is at least 100 Hz, which is higher than 60 Hz of general AC power. In addition, the voltage shown in FIG. 3 varies between the forward DC bias voltage V _F and the reverse DC bias voltage V _R . This square wave waveform is different from the sine wave waveform of a general alternating current power. If the voltage change shown in Fig. 3 is replaced by a general alternating current, the degree of discrimination obtained by the sinusoidal waveform of the alternating current and the too slow frequency will be greatly reduced, and the time required for the detection will be prolonged.

If it is desired to extend the sensing time of step 360, Figure 3 can be modified to Figure 4. In FIG. 4, steps 320 and 340 are alternately performed more than once, and the sensing time of step 360 is longer than one cycle of steps 320 and 340. In order to increase the degree of discrimination of the detection, the time length t _F of each step 320 in FIG. 4 may be shorter than the time length t _{R of} each step 340, and the time that the step 360 overlaps with each step 340 is greater than the total time of the step 360. The better.

In order to improve the discrimination and reliability of the detection, when the solar cell is detected by using the apparatus or method of the present invention, appropriate environmental control such as temperature, humidity, and the like can be appropriately controlled.

Compared with the detection method based on the electron beam induced current or the laser beam induced current, the above embodiment has low cost, fast detection speed, small detection machine volume, and high detection discrimination, so it is more suitable for practical applications. . Compared with other detection methods based on electroluminescence, the above embodiments can achieve higher discrimination, so that defects in the solar cell can be detected more accurately.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

100. . . Testing device

120. . . Charge and discharge module

125. . . Logic controller

130. . . Bridge circuit

132, 134, 136, 138. . . switch

140. . . Light sensing module

180. . . Solar battery

C _D . . . Diffusion capacitor

1 is a schematic view of an embodiment of a solar cell detecting device of the present invention.

FIG. 2 is a schematic diagram of an embodiment of the charging and discharging module of FIG. 1. FIG.

3 is a timing diagram of an embodiment of a method for detecting a solar cell of the present invention.

4 is a timing diagram of another embodiment of a solar cell detecting method of the present invention.

Claims (10)

A solar cell detecting method includes: charging a diffusion capacitor of a solar cell; discharging the diffusion capacitor after charging the diffusion capacitor; and sensing light emitted by the solar cell in the discharging step. The solar cell detecting method of claim 1, wherein the discharging step comprises: applying a reverse DC bias to the solar cell to discharge the diffusion capacitor. The solar cell detecting method of claim 1, wherein the charging step comprises: applying a forward DC bias to the solar cell to charge the diffusion capacitor; and the discharging step comprises: applying a reverse direction to the solar cell A DC bias is applied to discharge the diffusion capacitor. The solar cell detecting method according to claim 1 or 2 or 3, wherein the charging step has a length of time shorter than a length of time of the discharging step. The solar cell detecting method according to claim 1 or 2 or 3, wherein the charging step and the discharging step are each shorter than 0.005 seconds. A method for detecting a solar cell, comprising: applying a forward DC bias to a solar cell; applying a reverse DC bias to the solar cell after applying the forward DC bias; and sensing that the solar cell is being The light emitted during the period of the reverse DC bias is applied. The solar cell detecting method according to claim 6, wherein the step of applying the forward DC bias is shorter than the length of the step of applying the reverse DC bias. The solar cell detecting method according to claim 6 or 7, wherein the length of the step of applying the forward DC bias and the step of applying the reverse DC bias are both shorter than 0.005 seconds. A solar cell detecting device comprises: a charging and discharging module for charging and discharging a diffusion capacitor of a solar cell; and a light sensing module for sensing the discharging capacitance of the charging and discharging module The light emitted by the solar cell. The solar cell detecting device of claim 9, wherein the charging and discharging module comprises: a logic controller; and a bridge circuit comprising a first group of switches and a second for coupling to the solar cell a group switch; wherein the logic controller is configured to turn on the first group of switches and open the second group of switches to cause the first group of switches to charge the diffusion capacitor, or turn on the second group of switches and open the first group of switches to The second set of switches is caused to discharge the diffusion capacitor.