JP7626644B2 - Solar cell inspection method, solar cell manufacturing method, and solar cell inspection device - Google Patents

Description

The present invention relates to a solar cell inspection method, a solar cell manufacturing method, and a solar cell inspection device.

Solar cells are widely used, but there are many cases where aesthetics are required for solar cells. If there are fine scratches on the surface of a solar cell, the aesthetics may be marred by light reflection, etc. On the surface of a solar cell, fine irregularities called texture are often formed to improve the light incidence rate. Small scratches on the surface of a solar cell with texture formed on its surface cannot be easily identified by image processing of visible light images taken of the surface of the solar cell.

A method is known for inspecting defects in solar cells by irradiating the solar cell with light to excite carriers and photographing the light (photoluminescence) emitted when the carriers recombine (see, for example, Patent Document 1). In normal photoluminescence images, scratches inside the solar cell also appear as reduced brightness, making it impossible to distinguish between surface scratches that affect the aesthetic appearance and internal scratches that do not affect the aesthetic appearance.

JP 2017-219458 A

In view of the current situation as described above, the present invention aims to provide a solar cell inspection method and solar cell inspection device that can accurately detect scratches on the surface of a solar cell, as well as a solar cell manufacturing method that can produce solar cells with excellent aesthetic appearance.

A solar cell inspection method according to one aspect of the present invention includes a step of taking a short-wavelength photoluminescence image of photoluminescence by irradiating a solar cell with short-wavelength measurement light having a wavelength equal to or less than half the band gap of the solar cell, and a step of detecting scratches on the light-receiving surface of the solar cell based on the short-wavelength photoluminescence image.

The above-mentioned solar cell inspection method may further include a step of capturing a long-wavelength photoluminescence image of photoluminescence by irradiating the solar cell with long-wavelength measurement light having a wavelength closer to the band gap than the short-wavelength measurement light, and in the step of detecting the flaw, the short-wavelength photoluminescence image may be compared with the long-wavelength photoluminescence image to detect the flaw on the light-receiving surface.

In the solar cell inspection method described above, the illuminance of the short wavelength measurement light and the illuminance of the long wavelength measurement light may be made different.

A solar cell manufacturing method according to one aspect of the present invention includes a step of performing the solar cell inspection method described above, and a step of selecting the solar cells based on the inspection results of the solar cell inspection method.

A solar cell inspection device according to one aspect of the present invention is a solar cell inspection device that inspects the light receiving surface of a solar cell for scratches, and includes a short-wavelength light source that irradiates the solar cell with short-wavelength measurement light of a first wavelength, a long-wavelength light source that irradiates the solar cell with long-wavelength measurement light of a second wavelength longer than the first wavelength, an imaging unit that captures a photoluminescence image of the solar cell immediately after it is irradiated with the short-wavelength measurement light or the long-wavelength measurement light, and an image processing unit that detects scratches on the light receiving surface of the solar cell by image processing the photoluminescence image captured by the imaging unit.

The present invention makes it possible to accurately detect scratches on the surface of solar cells.

1 is a schematic diagram showing a configuration of a solar cell inspection device according to an embodiment of the present invention. 1 is a flowchart showing the steps of a solar cell inspection method according to an embodiment of the present invention. 1 is a flowchart showing the steps of a solar cell manufacturing method according to one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the configuration of a solar cell inspection device 1 according to one embodiment of the present invention.

The solar cell inspection device 1 is a device that detects scratches on the light receiving surface of a solar cell S. The solar cell inspection device 1 includes a transport device 10 that transports the solar cell S, a short-wavelength light source 20 that irradiates the solar cell S with short-wavelength measurement light of a first wavelength, a long-wavelength light source 30 that irradiates the solar cell S with long-wavelength measurement light of a second wavelength longer than the first wavelength, an imaging unit 40 that captures a photoluminescence image of the solar cell S immediately after it is irradiated with the short-wavelength measurement light or the long-wavelength measurement light, an imaging control unit 50 that controls the transport device 10, the short-wavelength light source 20, the long-wavelength light source 30, and the imaging unit 40, and an image processing unit 60 that detects scratches on the light receiving surface of the solar cell S by image processing the photoluminescence image captured by the imaging unit 40.

The transport device 10 may be configured, for example, by a belt conveyor. The transport device 10 positions the solar cell S at a position where the solar cell S can be irradiated with short-wavelength measurement light and long-wavelength measurement light by the short-wavelength light source 20 and long-wavelength light source 30 and a photoluminescence image can be captured by the imaging unit 40. The transport device 10 may have a sensor or the like that confirms the position of the solar cell S.

The short-wavelength light source 20 irradiates the solar cell S with short-wavelength measurement light having a wavelength less than half the band gap. Note that, while the unit of band gap is usually energy [eV], the unit of wavelength is length [nm], so although they are different dimensions, the photon energy E [eV] of light with a wavelength λ [nm] can be expressed as E [eV] = h·c/λ using Planck's constant h and the speed of light c [m/s]. In other words, the short-wavelength light source 20 irradiates short-wavelength measurement light with a wavelength in which the photon energy is less than half the band gap.

Short-wavelength measurement light, which has such a short wavelength, is absorbed near the light-receiving surface of the solar cell S and does not reach deep inside. For this reason, when short-wavelength measurement light is irradiated, carriers are generated only in the low-depth region near the light-receiving surface, so the amount of movement in the surface direction inside the solar cell S until the carriers recombine is small. Therefore, in the photoluminescence image, the reduction in carriers caused by scratches on the light-receiving surface of the solar cell S is not diluted by the surrounding carriers and appears as a clear decrease in brightness.

The lower limit of the wavelength of the short-wavelength measurement light is preferably 10% of the band gap of the solar cell S, more preferably 20%. On the other hand, the upper limit of the wavelength of the short-wavelength measurement light is preferably 50% of the band gap of the solar cell S, more preferably 40%. By setting the wavelength of the short-wavelength measurement light to the lower limit or more, it is possible to prevent the short-wavelength light source 20 from becoming unnecessarily expensive. In addition, by setting the wavelength of the short-wavelength measurement light to the upper limit or less, it is possible to prevent the short-wavelength measurement light from exciting carriers deep inside the solar cell S, so that only scratches on the light-receiving surface of the solar cell S can be selectively detected. Note that the wavelength of the measurement light does not need to be determined according to the band gap value of each solar cell S, and can be selected according to a representative value such as a design value or an average value.

The long-wavelength light source 30 irradiates the solar cell S with long-wavelength measurement light having a wavelength closer to the band gap of the solar cell S than the short-wavelength measurement light. The lower limit of the wavelength of the long-wavelength measurement light is preferably 75% of the band gap of the solar cell S, and more preferably 80%. On the other hand, the upper limit of the wavelength of the long-wavelength measurement light is preferably 90% of the band gap of the solar cell S, and more preferably 95%. By setting the wavelength of the long-wavelength measurement light to the lower limit or more, it is easy to check for a decrease in the brightness of photoluminescence due to defects other than scratches on the light-receiving surface of the solar cell S. In addition, by setting the wavelength of the long-wavelength measurement light to the upper limit or less, the output required of the long-wavelength light source 30 to generate sufficient carriers can be suppressed.

The long-wavelength measurement light may have a different illuminance from the short-wavelength measurement light. By making the illuminance of the long-wavelength measurement light and the short-wavelength measurement light different at the light-receiving surface of the solar cell S, the difference in photoluminescence intensity caused by the difference in carrier generation efficiency, carrier lifetime, etc. between the short-wavelength measurement light and the long-wavelength measurement light can be compensated for, making it easier to perform image analysis by the image processing unit 60.

The imaging unit 40 captures photoluminescence, which is light emitted when carriers excited by short-wavelength measurement light or long-wavelength measurement light recombine and return to the ground state in the solar cell S, and obtains a photoluminescence image that shows the brightness of the photoluminescence for each two-dimensional position on the solar cell S. The imaging unit 40 may be configured to have a two-dimensional imaging element such as a CCD or CMOS.

The imaging control unit 50 controls the operation timing of the transport device 10, the short-wavelength light source 20, the long-wavelength light source 30, and the imaging unit 40 so that, in synchronization with the transport device 10, the short-wavelength light source 20 irradiates short-wavelength light and the imaging unit 40 captures a photoluminescence image (short-wavelength photoluminescence image), and the long-wavelength light source 30 irradiates long-wavelength light and the imaging unit 40 captures a photoluminescence image (long-wavelength photoluminescence image).

The imaging control unit 50 can be realized, for example, by having a computer device equipped with a memory, a CPU, an input/output interface, etc. execute an appropriate control program.

The image processing unit 60 uses image processing techniques to detect scratches on the light receiving surface of the solar cell S based on the short wavelength photoluminescence image captured by the imaging unit 40, preferably by comparing the short wavelength photoluminescence image with the long wavelength photoluminescence image.

The image processing unit 60 can be realized by executing an appropriate image processing program on a computer device similar to the imaging control unit 50. The image processing unit 60 may be realized by the same computer device as the imaging control unit 50. The imaging control unit 50 and the image processing unit 60 are classified according to their functions, and do not have to be clearly distinguishable according to their physical configuration and program configuration.

Scratches on the light receiving surface of the solar cell S cause a change in brightness in the photoluminescence image. Typically, scratches on the light receiving surface result in a decrease in the brightness of the photoluminescence image as a whole, so the image processing unit 60 can be configured to detect areas of low brightness in the short wavelength photoluminescence image as areas containing scratches. Since even minute scratches appear with a relatively large change in brightness in short wavelength photoluminescence, scratches on the light receiving surface of the solar cell S can be detected more easily and accurately than by capturing an ordinary visible light image.

When the solar cell S produces uniform photoluminescence over the entire surface, the image processing unit 60 may extract areas whose brightness differs from other areas. Also, when the photoluminescence is patterned due to the structure of the solar cell S, the image processing unit 60 may extract areas whose brightness differs greatly from a reference photoluminescence image captured of an undamaged solar cell S.

The image processing unit 60 may also compare the short-wavelength photoluminescence image with the long-wavelength photoluminescence image, and detect areas in which the short-wavelength photoluminescence image has a lower brightness than the long-wavelength photoluminescence image as areas with scratches. The brightness of the photoluminescence decreases not only in areas where there are scratches on the light-receiving surface, but also in areas where there are defects deep inside or on the back surface. The sensitivity of the brightness reduction to defects in the long-wavelength photoluminescence image is approximately uniform in the thickness direction of the solar cell S, but the sensitivity of the brightness reduction to defects in the short-wavelength photoluminescence image is greater on the light-receiving surface side and smaller on the back surface side, as described above. For this reason, areas where the brightness reduction in the short-wavelength photoluminescence image is greater than that in the long-wavelength photoluminescence image can be determined to have a defect, i.e., a scratch, on the light-receiving surface of the solar cell S.

The image processing unit 60 may also estimate the photoelectric conversion efficiency of the solar cell S using at least one of the short-wavelength photoluminescence image and the long-wavelength photoluminescence image. When the illuminance of the short-wavelength measurement light and the long-wavelength measurement light differs, an estimate of the photoelectric conversion efficiency at each illuminance can be calculated from the short-wavelength photoluminescence image and the long-wavelength photoluminescence image, thereby deriving a function that represents the relationship between illuminance and photoelectric conversion efficiency, making it possible to estimate the photoelectric conversion efficiency at any illuminance.

As shown in FIG. 2, one embodiment of the solar cell inspection method according to the present invention, which can be performed using the solar cell inspection device 1, includes a step of obtaining a short-wavelength photoluminescence image of the photoluminescence by irradiating the solar cell S with short-wavelength measurement light having a wavelength equal to or less than half the band gap of the solar cell (step S01: short-wavelength photographing step), a step of photographing a long-wavelength photoluminescence image of the photoluminescence by irradiating the solar cell S with long-wavelength measurement light having a wavelength closer to the band gap than the short-wavelength measurement light (step S02: long-wavelength photographing step), and a step of detecting scratches on the light-receiving surface of the solar cell S based on the short-wavelength photoluminescence image and the long-wavelength photoluminescence image (step S03: scratch detection step).

In the short-wavelength photographing process of step S01, the short-wavelength light source 20 irradiates the solar cell S with short-wavelength measurement light, and the imaging unit 40 photographs a short-wavelength photoluminescence image.

In the long-wavelength photographing process of step S02, the long-wavelength light source 30 irradiates the solar cell S with long-wavelength measurement light, and the imaging unit 40 captures a long-wavelength photoluminescence image. The order of the long-wavelength photographing process and the short-wavelength photographing process may be reversed.

In the scratch detection process of step S03, the image processing unit 60 processes the short-wavelength photoluminescence image and the long-wavelength photoluminescence image to extract areas of reduced brightness in the short-wavelength photoluminescence image.

Furthermore, as shown in FIG. 3, one embodiment of the solar cell manufacturing method according to the present invention includes a step of forming a solar cell S (step S11: solar cell formation step), a step of performing the solar cell inspection method of FIG. 2 (step S12: solar cell inspection step), a step of selecting solar cells based on the inspection results of the solar cell inspection method (step S13: solar cell selection step), and a step of manufacturing the selected solar cells (step S14: solar cell manufacturing step).

In step S11, the solar cell formation process, the solar cell S is formed by a known method. For example, the solar cell S is obtained by forming a photoelectric conversion structure by stacking semiconductor layers having different conductivity types on the front and back of a semiconductor substrate.

In the solar cell inspection process of step S12, the above-mentioned solar cell inspection method is used to extract areas that are thought to be scratches on the light receiving surface of the solar cell S.

In the solar cell sorting process in step S13, the solar cells S are sorted based on the inspection results of the solar cell inspection process. For example, the solar cells S may be ranked or sorted based on the area, major axis, etc. of the area that is believed to be a detected scratch, or defective products may be identified and removed.

In the solar cell manufacturing process in step S14, the selected solar cells S are manufactured into a product. Manufacturing here includes not only further processing the solar cells S and incorporating the solar cells S into electronic devices to turn them into final products, but also arranging the solar cells S on a specified tray, packaging, or labeling them to make them ready to be handed over to those who will use them as intermediate products.

The solar cell manufacturing method of FIG. 3, which includes the above steps, can accurately detect scratches on the surface of the solar cell S using the solar cell inspection method of FIG. 2 in the solar cell inspection step, making it possible to manufacture solar cells S with excellent aesthetics.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-mentioned embodiments, and various modifications and variations are possible. For example, the present invention does not require the capture of long-wavelength photoluminescence images. In other words, the solar cell inspection method of the present invention may detect scratches on the light-receiving surface of a solar cell based only on short-wavelength photoluminescence images, and the solar cell inspection device of the present invention may not have a long-wavelength light source. Also, in the solar cell inspection device of the present invention, a transport device is not required, and the device may be one that positions solar cells using a robot or the like.

Reference Signs List 1 Solar cell inspection device 10 Conveying device 20 Short wavelength light source 30 Long wavelength light source 40 Imaging unit 50 Photography control unit 60 Image processing unit S Solar cell

Claims (3)

A step of taking a short-wavelength photoluminescence image of photoluminescence by irradiating the solar cell with short-wavelength measurement light having a wavelength equal to or less than half the wavelength corresponding to the band gap of the solar cell;
a step of capturing a long-wavelength photoluminescence image of photoluminescence by irradiating the solar cell with long-wavelength measurement light having an illuminance different from that of the short-wavelength measurement light and a wavelength closer to the wavelength corresponding to the band gap than the short-wavelength measurement light;
detecting flaws on the light receiving surface of the solar cell by comparing the short wavelength photoluminescence image with the long wavelength photoluminescence image ;
calculating an estimated value of photoelectric conversion efficiency at each illuminance from the short-wavelength photoluminescence image and the long-wavelength photoluminescence image, and deriving a function representing a relationship between illuminance and photoelectric conversion efficiency;
A solar cell inspection method comprising: A step of carrying out the solar cell inspection method according to claim 1 ;
sorting the solar cells based on an inspection result of the solar cell inspection method;
A solar cell manufacturing method comprising: A solar cell inspection device for inspecting a light receiving surface of a solar cell for scratches, comprising:
a short wavelength light source that irradiates the solar cell with a short wavelength measurement light having a first wavelength;
a long-wavelength light source that irradiates the solar cell with long-wavelength measurement light having a second wavelength that is longer than the first wavelength;
an imaging unit that captures a short-wavelength photoluminescence image of the solar cell immediately after the short-wavelength measurement light is irradiated and a long-wavelength photoluminescence image of the solar cell immediately after the long-wavelength measurement light is irradiated ;
an image processing unit that performs image processing on the short wavelength photoluminescence image and the long wavelength photoluminescence image captured by the imaging unit , detects scratches on the light receiving surface of the solar cell by comparing the short wavelength photoluminescence image with the long wavelength photoluminescence image , and calculates an estimate of photoelectric conversion efficiency at each illuminance from the short wavelength photoluminescence image and the long wavelength photoluminescence image to derive a function that represents the relationship between illuminance and photoelectric conversion efficiency ;
A solar cell inspection device comprising:

Images