JP2024048407A - Performance evaluation device and performance evaluation method - Google Patents

Abstract

To quickly and contactlessly evaluate the performance of a solar cell that has a plurality of band gaps.SOLUTION: In a performance evaluation device 1, an irradiation unit 10 irradiates different irradiation areas on a solar cell with excitation light beams in a plurality of different wavelengths for causing a solar cell having a plurality of band gaps to emit photoluminescence light beams in a plurality of different wavelengths. An imaging unit 30 captures an image of the solar cell using the photoluminescence light beams in the plurality of different wavelengths emitted from the solar cell by excitation light beams in the plurality of different wavelengths, so as to acquire the captured image of the solar cell. An image processing unit 50 acquires information regarding the performance of the solar cell on the basis of the captured image.SELECTED DRAWING: Figure 1

Description

The present invention relates to a performance evaluation device and a performance evaluation method.

Technologies for evaluating the performance of solar cells are known. For example, Patent Document 1 discloses an inspection device for solar cell panels that uses electroluminescence (EL). Patent Document 2 discloses an inspection device for solar cell cells that uses photoluminescence (PL).

JP 2021-58043 A JP 2018-163059 A

When EL is used in the performance evaluation of the above-mentioned solar cells, the following problems arise.
(1) Evaluation is only possible after the solar cell has passed the final manufacturing process, which means that it takes time to identify defects that occur during the manufacturing process.
(2) In order to image the solar cell using EL, it is necessary to pass a current through the electrodes of the solar cell. Therefore, the solar cell may be damaged by contact with the probe, and the evaluation setup takes time. In particular, when materials with different crystal lattice sizes are used, the damage caused by the probe contact tends to spread widely.
(3) Imaging using EL lacks stability in the brightness of normal areas, which is disadvantageous in identifying defects through image processing.

In contrast, when using PL to evaluate the performance of solar cells, it can be applied even during the manufacturing process, and since it can be evaluated without contact, there is no issue of possible damage due to contact. However, because PL light is weak, it requires long periods of exposure.

In particular, when evaluating the performance of solar cells with multiple bandgaps, applying separate exposure times to PL light of multiple wavelengths corresponding to the multiple bandgaps hinders high-speed performance evaluation. Under these circumstances, there is a demand for high-speed, non-contact evaluation of the performance of solar cells with multiple bandgaps.

The present invention has been made to solve the above problems, and aims to provide a performance evaluation device that can quickly and non-contactly evaluate the performance of solar cells with multiple bandgaps.

In order to achieve the above object, a performance evaluation apparatus according to a first aspect of the present invention comprises:
an irradiation unit that irradiates different irradiation areas on a solar cell having a plurality of band gaps with excitation light of a plurality of different wavelength ranges to cause the solar cell to emit photoluminescence light of a plurality of different wavelengths;
an imaging unit that captures an image of the solar cell by imaging the solar cell using photoluminescence light of the multiple wavelengths emitted from the solar cell in response to excitation light of the multiple wavelength ranges; and
and an image processing unit that acquires information regarding the performance of the solar cell based on the captured image.

In order to achieve the above object, a performance evaluation method according to a second aspect of the present invention comprises:
An irradiation step of irradiating different irradiation areas on a solar cell having a plurality of band gaps with excitation light having a plurality of different wavelength ranges to emit photoluminescence light having a plurality of different wavelengths;
an imaging step of capturing an image of the solar cell by capturing an image of the solar cell using photoluminescence light of the multiple wavelengths emitted from the solar cell in response to excitation light of the multiple wavelength ranges;
and an image processing step of acquiring information regarding the performance of the solar cell based on the captured image.

The present invention allows the performance of solar cells with multiple bandgaps to be evaluated quickly and without contact.

1 is a schematic diagram showing an overall configuration of a performance evaluation device according to an embodiment; FIG. 2 is a diagram showing a cross section of an evaluation target in the embodiment. FIG. 2 is a diagram showing a configuration of an irradiation unit in the embodiment. 5A and 5B are diagrams illustrating an example of the relationship between the wavelength and the luminance intensity of excitation light and PL light in the embodiment. FIG. 2 is a diagram illustrating a configuration of an imaging unit in the embodiment. 5A and 5B are diagrams illustrating an example of a pre-sensor filter provided in an imaging unit in the embodiment. 11A and 11B are diagrams illustrating examples of wavelengths filtered by a pre-lens filter and a pre-sensor filter in an embodiment. 5A to 5C are diagrams illustrating examples of captured images captured by an imaging section in the embodiment. FIG. 2 is a block diagram showing a configuration of an image processing unit in the embodiment. 5A to 5C are diagrams showing a procedure for cutting out a target image from a captured image in an embodiment. 6A to 6C are diagrams illustrating a process of accumulating luminance values of a plurality of captured images in an embodiment. 1A, 1B, and 1C are diagrams showing examples of integrated images of a top cell, a middle cell, and a bottom cell in an embodiment, respectively, and FIG. 1D is a diagram showing an integrated image obtained by integrating the integrated images shown in 1A to 1C. 4 is a flowchart showing the flow of a performance evaluation process executed by the performance evaluation device according to the embodiment. 1A is a diagram showing a schematic diagram of a difference in the light-focusing position depending on the wavelength in a lens having chromatic aberration, and FIG. 1B is a diagram showing an example in which the light-focusing position is adjusted by a filter in front of the sensor in a modified example.

The following describes in detail an embodiment of the present invention with reference to the drawings. Note that the same or corresponding parts in the drawings are given the same reference numerals.

Figure 1 shows the overall configuration of a performance evaluation device 1 according to an embodiment of the present invention. The performance evaluation device 1 is a device that captures an image of a solar cell using photoluminescence light (PL light), obtains a photoluminescence image (PL image), and evaluates the performance of the solar cell based on the PL image.

Here, photoluminescence (hereinafter referred to as "PL") is luminescence caused by irradiation with electromagnetic waves (light energy), and is a phenomenon in which electrons excited by irradiating a substance with light emit light of a wavelength corresponding to the energy difference between the excited state and the ground state when they return to the ground state.

<Evaluation target 3>
The evaluation object 3 is an object that is the subject of performance evaluation by the performance evaluation device 1, and specifically, is a solar cell having multiple bandgaps. One example of the solar cell that is the evaluation object 3 is a solar cell in a cell state. Note that the solar cell that is the evaluation object 3 may be in a state after having passed through the final manufacturing process, or in a state during the manufacturing process.

The solar cell with multiple bandgaps that is the evaluation target 3 is, for example, a multi-junction solar cell. Here, a multi-junction solar cell is also called a stacked type, tandem type, multi-junction type, or other solar cell, and is a solar cell formed by multiple p-n junctions, etc., for the purpose of absorbing light in multiple different wavelength ranges.

One example of a multi-junction solar cell is a group 3-5 (III-V) semiconductor solar cell. A group 3-5 semiconductor solar cell is a solar cell made up of three layers of semiconductors, formed from raw materials mainly consisting of group 3 elements (e.g. gallium) and group 5 elements (e.g. arsenic).

As an example, as shown in FIG. 2, the solar cell to be evaluated 3 is a laminate having three layers: a top cell 3a, a middle cell 3b, and a bottom cell 3c. The top cell 3a, the middle cell 3b, and the bottom cell 3c are each made of different materials so as to generate solar energy effectively, and are semiconductor layers having different bandgaps.

When irradiated with excitation light, the top cell 3a, middle cell 3b, and bottom cell 3c emit PL light of different wavelengths corresponding to their respective bandgaps. As an example, the top cell 3a has an optical absorption end of about 650 nm and emits PL light with a peak wavelength of about 650 nm and an emission width of about 80 nm. The middle cell 3b has an optical absorption end of about 850 nm and emits PL light with a peak wavelength of about 850 nm and an emission width of about 100 nm. The bottom cell 3c has an optical absorption end of about 1250 nm and emits PL light with a peak wavelength of about 1250 nm and an emission width of about 300 nm.

In this way, the solar cell to be evaluated 3 has multiple semiconductor layers with different bandgaps, and therefore emits PL light of multiple different wavelengths when PL occurs due to irradiation with excitation light. The performance evaluation device 1 uses such PL light of multiple wavelengths to simultaneously capture images of each layer of the solar cell, thereby evaluating the performance of the solar cell having multiple layers in a non-contact and high-speed manner.

Returning to FIG. 1, the performance evaluation device 1 includes a transport unit 5, an irradiation unit 10, an imaging unit 30, and an image processing unit 50. The irradiation unit 10 and the imaging unit 30 can be collectively referred to as the imaging device 2.

The conveying unit 5 conveys the evaluation object 3 along a predetermined conveying path in a predetermined direction (+X direction in the example of FIG. 1) at a predetermined conveying speed V. Hereinafter, the direction in which the evaluation object 3 is conveyed by the conveying unit 5 is defined as the X direction, the width direction of the evaluation object 3 conveyed by the conveying unit 5 is defined as the Y direction, and the vertical direction is defined as the Z direction.

<Irradiation unit 10>
The irradiation unit 10 is a unit that irradiates excitation light onto the evaluation object 3. The excitation light irradiated from the irradiation unit 10 is electromagnetic waves for exciting electrons in each layer of the top cell 3a, the middle cell 3b, and the bottom cell 3c in the evaluation object 3, causing each layer to emit PL light. The irradiation unit 10 irradiates the evaluation object 3 transported by the transport unit 5 with electromagnetic waves (also simply referred to as "light") in a wavelength range from visible light to infrared light.

The irradiation unit 10 is disposed diagonally above the evaluation object 3 being transported by the transport unit 5, and irradiates the evaluation object 3 with excitation light from diagonally above. Specifically, the irradiation unit 10 irradiates the excitation light from a direction tilted, for example, by 20° to 60° with respect to the Z direction, which is the perpendicular direction to the surface of the evaluation object 3 being transported in a predetermined direction (+X direction).

The irradiation unit 10 has multiple light sources for emitting PL light of multiple different wavelengths toward the evaluation object 3. The irradiation unit 10 then irradiates different irradiation areas on the evaluation object 3 with excitation light of multiple different wavelength ranges from the multiple light sources. Specifically, as shown in FIG. 3, the irradiation unit 10 has three light sources 11 to 13. The three light sources 11 to 13 are LED (Light Emitting Diode) light sources that emit excitation light of different wavelength ranges.

The first light source 11 emits excitation light for generating PL in the top cell 3a, and irradiates the first irradiation area 14 on the transported evaluation object 3. Specifically, the first light source 11 outputs excitation light having a peak wavelength at a wavelength shorter than the optical absorption edge of the top cell 3a (i.e., energy higher than the optical absorption edge). As an example, the first light source 11 emits excitation light with a peak wavelength of approximately 440 to 480 nm.

The second light source 12 emits excitation light for generating PL in the middle cell 3b, and irradiates the second irradiation area 15 on the transported evaluation target 3. Specifically, the second light source 12 outputs excitation light having a peak wavelength at a wavelength shorter than the optical absorption edge of the middle cell 3b (i.e., energy higher than the optical absorption edge). As an example, the second light source 12 emits excitation light with a peak wavelength of approximately 730 to 780 nm.

The third light source 13 emits excitation light for generating PL in the bottom cell 3c, and irradiates the third irradiation area 16 on the transported evaluation object 3. Specifically, the third light source 13 outputs excitation light having a peak wavelength at a wavelength shorter than the optical absorption edge of the bottom cell 3c (i.e., energy higher than the optical absorption edge). As an example, the third light source 13 emits excitation light with a peak wavelength of approximately 930 to 980 nm.

In this way, the irradiation unit 10 simultaneously outputs excitation light in multiple wavelength ranges from the three light sources 11 to 13 to generate PL in the top cell 3a, middle cell 3b, and bottom cell 3c, respectively, and irradiates three different irradiation areas 14 to 16 on the evaluation object 3 being transported.

The excitation light emitted from the three light sources 11 to 13 is output to the outside via a light-guiding member and a filter within the light source (not shown). The light-guiding member guides the excitation light into a line-shaped emitted light. By passing through the light-guiding member, the irradiation areas 14 to 16 onto which the excitation light is irradiated extend long in the width direction (Y direction) of the evaluation object 3, and become a thin line-shaped area in the transport direction (X direction).

The in-light source filter is an interference filter for selecting the wavelength range of the excitation light emitted from each of the three light sources 11 to 13. The wavelength range of the excitation light transmitted by the in-light source filter is set to a wavelength range separated (for example, by about 25 nm) from the wavelength range of the PL light transmitted by the pre-sensor filter 33 described below so that the excitation light is not received by the image sensor 34 of the imaging unit 30.

Figure 4 shows the relationship between the wavelength and luminance intensity of the excitation light irradiated from the irradiation unit 10 to the evaluation object 3, and the PL light emitted from the evaluation object 3 in response to the excitation light. In Figure 4, the wavelength distribution of the excitation light irradiated to each of the top cell 3a, middle cell 3b, and bottom cell 3c is shown by a solid line, and the wavelength distribution of the PL light emitted in response to the excitation light is shown by a dashed line.

When the top cell 3a is irradiated with excitation light from the first light source 11, electrons contained in the material of the top cell 3a are excited, generating PL. As a result, the top cell 3a emits PL light with a wavelength longer than the wavelength of the irradiated excitation light. Similarly, when the middle cell 3b is irradiated with excitation light from the second light source 12, PL occurs in the middle cell 3b, and when the bottom cell 3c is irradiated with excitation light from the third light source 13, PL occurs in the bottom cell 3c. As a result, the middle cell 3b and the bottom cell 3c emit PL light with a wavelength longer than the wavelength of the irradiated excitation light.

Note that the wavelength values of the excitation light emitted from each light source 11 to 13 are merely examples. The wavelength of the excitation light must be selected to match the band gap of the solar cell to be evaluated 3. Therefore, depending on the evaluation object 3 being used, it is necessary to change the wavelength of the excitation light so that PL is appropriately generated in the evaluation object 3.

<Imaging unit 30>
1 , the imaging unit 30 is a unit that captures an image of the evaluation target 3 by capturing an image of the evaluation target 3. The imaging unit 30 is disposed above the evaluation target 3 transported by the transport unit 5, and receives PL light emitted from the evaluation target 3. In this way, the imaging unit 30 captures an image (PL image) of the evaluation target 3 captured with PL light.

As shown in FIG. 5, the imaging unit 30 includes a pre-lens filter 31, one lens 32, a pre-sensor filter 33, and one image sensor 34. These components are arranged facing perpendicularly to the surface of the evaluation object 3 being transported by the transport unit 5, and capture an image of the evaluation object 3 from directly above.

Here, in the evaluation object 3, the PL light is emitted from linear light-emitting areas 17-19 corresponding to the irradiation areas 14-16 irradiated with the excitation light. The imaging unit 30 captures an imaging area including all of the linear light-emitting areas 17-19.

The pre-lens filter 31 is an interference filter that is installed in front of the lens 32 and prevents unnecessary light from entering the lens 32. The pre-lens filter 31 blocks wavelength components shorter than a predetermined wavelength among the multiple wavelengths of PL light emitted from the evaluation target 3. The predetermined wavelength is a wavelength shorter than any of the wavelengths of the PL light, and is set to, for example, 600 nm. Such short wavelength components shorter than 600 nm become large noise components, so they are blocked by the pre-lens filter 31 in front of the lens 32. In FIG. 5, the pre-lens filter 31 is located at a position away from the lens 32. However, the pre-lens filter 31 is not limited to this, and may be, for example, a coating on the lower surface of the lens 32 as long as it is installed in front of the lens 32.

The lens 32 collects PL light of multiple wavelengths emitted from the evaluation object 3. The optical axis of the lens is perpendicular to the surface of the evaluation object 3 being transported. The lens 32 simultaneously collects PL light of three wavelengths that are emitted from each of the three layers of the evaluation object 3 and transmitted through the pre-lens filter 31, and forms an image on the image sensor 34.

Lens 32 is designed to collect PL light of three wavelengths using a single lens, and chromatic aberration and curvature aberration are sufficiently corrected in the wavelength range from visible light to infrared light. For example, it is desirable that chromatic aberration and curvature aberration are within ±0.01% in the wavelength range from 400 nm to 1600 nm. In this way, by using a lens specialized for chromatic aberration and curvature aberration as lens 32, it is possible to image the PL light emitted from each layer of evaluation target 3 at the same imaging distance.

The pre-sensor filter 33 is an interference filter installed between the lens 32 and the image sensor 34 to prevent unnecessary light from entering the image sensor 34. The pre-sensor filter 33 has a number of individual filters for each region that correspond one-to-one to the multiple wavelengths of the PL light emitted from the evaluation object 3. Each of the multiple individual filters transmits the PL light of the corresponding wavelength among the multiple wavelengths.

Specifically, as shown in FIG. 6, the pre-sensor filter 33 has three individual filters, a top cell filter 33a, a middle cell filter 33b, and a bottom cell filter 33c, which are separated into three regions to correspond to the PL light emitted from the three layers of the evaluation object 3.

The top cell filter 33a transmits the PL light emitted from the top cell 3a individually and blocks other wavelength components. The middle cell filter 33b transmits the PL light emitted from the middle cell 3b individually and blocks other wavelength components. The bottom cell filter 33c transmits the PL light emitted from the bottom cell 3c individually and blocks other wavelength components. Since the PL light emitted from each of the three light-emitting areas 17-19 is collected by a single lens 32, the positions in the X and Y directions on the evaluation object 3 and on the image sensor 34 are reversed. Therefore, the correspondence between the three light-emitting areas 17-19 and the three individual filters in the pre-sensor filter 33 is reversed in the X direction. Specifically, the top cell filter 33a, which transmits PL light emitted from the light emitting area 17 on the -X side of the evaluation object 3, is located on the +X side, and the bottom cell filter 33c, which transmits PL light emitted from the light emitting area 19 on the +X side of the evaluation object 3, is located closest to the -X side.

Figure 7 shows an example of the wavelength range filtered by the pre-lens filter 31 and the pre-sensor filter 33. Light traveling from the evaluation object 3 toward the lens 32 is first blocked by the pre-lens filter 31 in front of the lens 32, with wavelength components of 600 nm or less (the darkly colored parts in Figure 7).

The light transmitted through the pre-lens filter 31 passes through the lens 32 and is then filtered by the pre-sensor filter 33 into a wavelength range (lightly colored areas in FIG. 7) that includes the peak wavelengths of the PL light emitted from each of the three layers in the evaluation target 3. The wavelength range filtered by each individual filter in the pre-sensor filter 33 is set to cover, for example, 50-90% of the intensity of the PL light spectrum, based on the peak wavelength of the corresponding PL light.

Returning to FIG. 5, the image sensor 34 is a single area sensor that is sensitive to both visible light and infrared light (for example, in the wavelength range of 400 to 1600 nm). The image sensor 34 is disposed at the light collection position by the lens 32. The image sensor 34 receives PL light of multiple wavelengths that is emitted from the evaluation object 3 and passes through the pre-lens filter 31, the lens 32, and the pre-sensor filter 33, and generates an image captured by the PL light (PL image).

More specifically, the image sensor 34 includes photodiodes arranged in an array and a readout circuit using a complementary metal oxide semiconductor (CMOS). One example of the photodiode is InGaAs (indium gallium arsenide), which is a compound semiconductor. The PL light incident on the image sensor 34 is photoelectrically converted by the photodiode and read out as a signal by a readout circuit (not shown). The readout circuit includes, for example, an A/D (Analog/Digital) converter that converts an analog signal representing an image captured by the image sensor 34 into digital data. The signal read out by the image sensor 34 is output to the image processing unit 50.

By using an image sensor 34 that has sensitivity over such a wide wavelength range, images can be captured using PL light of various wavelengths, making it possible to evaluate the performance of multi-band solar cells made of various materials.

Figure 8 shows an example of an image 70 captured by the imaging unit 30. The captured image 70 is an image captured simultaneously using PL light of different wavelengths emitted from three layers of the evaluation object 3. As described above, the correspondence between the emission position of the PL light on the evaluation object 3 and the reception position of the PL light on the image sensor 34 is inverted in the X and Y directions. However, to make it easier to understand, the X and Y coordinates in the captured image 70 shown in Figure 8 are made to match the X and Y coordinates on the evaluation object 3. The same applies to the subsequent figures.

Specifically, the captured image 70 is divided into three regions 71 to 73 corresponding to the top cell filter 33a, the middle cell filter 33b, and the bottom cell filter 33c, respectively. The first region 71 is an area captured by the image sensor 34 receiving PL light emitted from the top cell 3a and transmitted through the top cell filter 33a. The second region 72 is an area captured by the image sensor 34 receiving PL light emitted from the middle cell 3b and transmitted through the middle cell filter 33b. The third region 73 is an area captured by the image sensor 34 receiving PL light emitted from the bottom cell 3c and transmitted through the bottom cell filter 33c.

In this way, images are taken by region using the PL light emitted from each layer of the evaluation target 3, so that a linear light-emitting area 17 is imaged in the first region 71, a linear light-emitting area 18 is imaged in the second region 72, and a linear light-emitting area 19 is imaged in the third region 73. The portions of the captured image 70 that correspond to the linear light-emitting areas 17-19 (white portions in FIG. 8) exhibit brighter luminance values (pixel values) than the other portions (colored portions in FIG. 8). In this way, one captured image 70 contains images using the PL light emitted from each of the top cell 3a, middle cell 3b, and bottom cell 3c.

The imaging unit 30 acquires multiple captured images 70 by repeatedly acquiring such captured images 70 at a predetermined time interval Δt. More specifically, the imaging unit 30 acquires an captured image 70 each time the evaluation object 3 is transported by the transport unit 5 a distance d equivalent to one pixel. For this reason, the time interval Δt is set to "Δt = d/V", which is the distance d equivalent to one pixel divided by the transport speed V. By repeatedly capturing images at time intervals Δt in this manner, the imaging unit 30 can capture an image of the entire area from one end of the evaluation object 3 transported by the transport unit 5 with PL light of three different wavelengths.

<Image Processing Unit 50>
Returning to Fig. 1, the image processing unit 50 is a unit that acquires information on the performance of the solar cell that is the evaluation target 3, based on the captured image 70 acquired by the imaging unit 30. The image processing unit 50 is specifically an information processing device such as a personal computer or a cloud server.

Here, the information regarding the performance of the solar cell is, for example, information regarding the presence or absence of foreign matter, defects, etc. in the solar cell, or information that directly indicates the performance of the solar cell, such as whether the solar cell meets a predetermined performance standard. Alternatively, the information regarding the performance of the solar cell may be an image processed from the captured image 70 for the purpose of evaluating the performance of the solar cell, such as the integrated images 81 to 83 or integrated image 85 described below.

More specifically, as shown in FIG. 9, the image processing unit 50 includes a control unit 51, a memory unit 52, an input receiving unit 53, a display unit 54, and a communication unit 55.

The control unit 51 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU includes a microprocessor and is a central processing unit that executes various processes and calculations. In the control unit 51, the CPU reads out a control program stored in the ROM and controls the operation of the entire image processing unit 50 while using the RAM as a work memory. The control unit 51 may also include a processor for image processing, such as a DSP (Digital Signal Processor) or a GPU (Graphics Processing Unit).

The storage unit 52 is a non-volatile memory such as a flash memory or a hard disk. The storage unit 52 stores the programs and data executed by the control unit 51, and the data generated by the control unit 51.

The input reception unit 53 is equipped with input devices such as a keyboard, mouse, and touch panel, and receives operational input from the user.

The display unit 54 includes a display device such as a liquid crystal display or an organic EL (Electro Luminescence) display, and displays various images under the control of the control unit 51. For example, the display unit 54 displays an image showing the evaluation results obtained by the performance evaluation device 1.

The communication unit 55 has a communication interface for communicating with devices external to the image processing unit 50, including the imaging unit 30. For example, the communication unit 55 communicates with external devices in accordance with well-known communication standards such as LAN (Local Area Network) and USB (Universal Serial Bus).

The control unit 51 functionally comprises a cutout unit 110, an integration unit 120, an integration unit 130, an evaluation unit 140, and an output unit 150. In the control unit 51, the CPU reads out a program stored in the ROM into the RAM, and executes and controls the program, thereby functioning as each of these units.

The cutout unit 110 cuts out a target image for evaluating the performance of the evaluation target 3 from the captured image 70 captured by the imaging unit 30. Specifically, the cutout unit 110 uses a region of interest (ROI) function to cut out a portion of the captured image 70 that corresponds to the linear light-emitting areas 17 to 19.

More specifically, as shown in FIG. 10, the cutout unit 110 normalizes the luminance value of each pixel in the captured image 70 and then integrates it in the width direction (Y direction) of the evaluation object 3. In this way, the cutout unit 110 generates a one-dimensional luminance distribution in the transport direction (X direction) of the evaluation object 3. Then, from each of the three regions 71 to 73, the cutout unit 110 cuts out a region having a width of W pixels (e.g., 32 pixels) in the X direction, centered on the position where the luminance value peaks in the luminance distribution.

Specifically, the cutout unit 110 cuts out the target images 74 to 76 from the three regions 71 to 73 of the captured image 70. Each of the target images 74 to 76 has a length of 1024 pixels in the width direction (Y direction) of the evaluation object 3, and a length of 32 pixels in the transport direction (X direction), for example.

The accumulator 120 generates an accumulated image by accumulating the luminance values of pixels in the multiple captured images 70 acquired by the imaging unit 30 that capture the same position on the evaluation target 3. Accumulating the luminance values in the multiple captured images 70 makes it possible to lengthen the exposure time and suppress fixed noise, which is advantageous in improving sensitivity in imaging using weak PL light.

The accumulation procedure performed by the accumulation unit 120 will be described in more detail with reference to FIG. 11. The accumulation unit 120 regards each of the target images 74 to 76 cut out from the multiple captured images 70 by the cutout unit 110 as a TDI (Time Delay Integration) sensor, and accumulates the brightness values while synchronizing with the transport speed V of the evaluation target 3.

Here, each of the multiple captured images 70 is acquired at a predetermined time interval Δt, each time the evaluation target 3 is transported a distance of one pixel, so that the same position on the evaluation target 3 shifts by one pixel in the X direction between the multiple captured images 70. Therefore, as shown in FIG. 11, the pixel in the leftmost column (the column indicated by the dashed line) in the target images 74-76 acquired at time t shifts to the second column from the left in the target images 74-76 acquired at time t+Δt, shifts to the third column from the left in the target images 74-76 acquired at time t+Δt×2, and shifts to the rightmost column in the target images 74-76 acquired at time t+Δt×(W-1).

The accumulator 120 accumulates the luminance values of each pixel of the W chronologically consecutive target images 74-76 by shifting them by one pixel at a time in accordance with the shifting of the same position on the evaluation target 3 by one pixel in the transport direction. In this way, the accumulator 120 generates accumulated images 81-83, for example, as shown in Figures 12(a)-(c).

More specifically, when a position (x, y) on the evaluation object 3 is captured within the target image 74 over a time period Δt×W from time t to time t+Δt×(W-1), the accumulation unit 120 calculates the sum of the luminance values obtained from (1) to (W) below, "P(1, y)+P(2, y)+P(3, y)+...+P(W, y)", as the luminance value of the position (x, y) in the accumulated image 81.
(1) A luminance value P(1, y) of a position (1, y) in a target image 74 cut out from a captured image 70 acquired at a time t
(2) The luminance value P(2, y) of the position (2, y) in the target image 74 cut out from the captured image 70 acquired at time t+Δt
(3) The luminance value P(3, y) of the position (3, y) in the target image 74 cut out from the captured image 70 acquired at time t + Δt × 2
...
(W) Brightness value P(W, y) of position (W, y) in the target image 74 cut out from the captured image 70 acquired at time t+Δt×(W−1)

The accumulator 120 calculates the sum of these W brightness values for all positions on the evaluation target 3, thereby calculating the brightness value of each position of the accumulated image 81. The accumulator 120 calculates the sum of the brightness values obtained in (1) to (W) above for not only the target image 74 but also the target images 75 and 76 in the same way, thereby calculating the brightness value of each position of the accumulated images 82 and 83.

In this way, the integrating unit 120 integrates the luminance values of pixels captured at the same position on the evaluation target 3 for each of the multiple wavelengths of PL light emitted from the evaluation target 3. As a result, the integrating unit 120 generates an integrated image 81 of the top cell 3a as shown in FIG. 12(a) from the target image 74, an integrated image 82 of the middle cell 3b as shown in FIG. 12(b) from the target image 75, and an integrated image 83 of the bottom cell 3c as shown in FIG. 12(c) from the target image 76.

Returning to FIG. 9, the integration unit 130 generates an integrated image 85 by integrating the multiple integrated images 81-83 generated by the accumulation unit 120. Specifically, the integration unit 130 generates an integrated image 85 as shown in FIG. 12(d) by adding together the luminance values of the pixels at the same coordinates in the three integrated images 81-83 shown in FIGS. 12(a)-(c). The luminance value of each pixel in the integrated image 85 is the sum of the luminance values of the pixels at the same coordinates in the integrated images 81-83.

Through integration by the integration unit 130, foreign objects X1 to X3 captured separately in the three integrated images 81 to 83 are contained within a single integrated image 85. This makes it easier to check whether a defect or foreign object is present in a single layer of the evaluation object 3 or across multiple layers.

In the performance evaluation device 1 according to this embodiment, the three integrated images 81 to 83 are acquired using one lens 32 and one image sensor 34, which is an area sensor, so there is high consistency in resolution and position between the multiple integrated images 81 to 83. As a result, a highly accurate integrated image 85 can be generated.

Returning to FIG. 9, the evaluation unit 140 evaluates the performance of the solar cell, which is the evaluation target 3, based on the integrated image 85 generated by the integration unit 130. Specifically, the evaluation unit 140 analyzes the luminance distribution of the integrated image 85 and converts the luminance distribution of the integrated image 85 into information indicating the performance of the solar cell, which is the evaluation target 3. Specifically, the information indicating the performance of the solar cell is whether the solar cell contains foreign matter, whether a defect has occurred, whether the solar cell meets predetermined performance standards, etc.

For example, as shown in FIG. 12(d), when foreign objects X1 to X3 are captured in the integrated image 85, the evaluation unit 140 detects that the evaluation target 3 contains foreign objects X1 to X3. Then, the evaluation unit 140 identifies the type of each of the foreign objects X1 to X3, such as whether it is a void or an impurity, based on the feature quantities such as the shape and size of each of the foreign objects X1 to X3.

Alternatively, even if the evaluation object 3 does not have any foreign bodies X1 to X3 or defects, the evaluation unit 140 may determine whether the solar cell, which is the evaluation object 3, satisfies a predetermined performance standard from the luminance distribution of the integrated image 85. By evaluating the performance of the solar cell based on the integrated image 85 in this way, it is possible to determine whether any abnormality has occurred in the solar cell manufacturing process, which can lead to the manufacturing of solar cells with higher performance.

The output unit 150 outputs the evaluation result by the evaluation unit 140. For example, the output unit 150 displays an image representing the evaluation result of the evaluation target 3 on the display unit 54 and notifies the user. Alternatively, the output unit 150 may output the evaluation result by voice, or may output the evaluation result to an external device via the communication unit 55.

The image processing unit 50 may not have the functionality of the evaluation unit 140, and a device external to the image processing unit 50 may have the functionality of the evaluation unit 140. In this case, the output unit 150 outputs the integrated image 85 generated by the integration unit 130 to the external device via the communication unit 55. The external device may then execute the processing of the evaluation unit 140 described above based on the integrated image 85.

Next, the flow of the performance evaluation process executed by the performance evaluation device 1 will be described with reference to the flowchart shown in FIG.

When the performance evaluation process starts, the transport unit 5 transports the evaluation object 3 along a predetermined transport path at a constant transport speed V (step S1). Then, the irradiation unit 10 turns on the three light sources 11 to 13 and irradiates the evaluation object 3 transported by the transport unit 5 with excitation light in different wavelength ranges (step S2). Steps S1 and S2 are examples of a transport step and an irradiation step, respectively.

When the excitation light is irradiated by the irradiation unit 10, the imaging unit 30 images the evaluation object 3 using PL light emitted from each layer of the evaluation object 3 by the irradiated excitation light (step S3). As a result, the imaging unit 30 acquires an image 70, for example, as shown in FIG. 8. More specifically, the imaging unit 30 acquires multiple images 70 by repeatedly imaging the evaluation object 3 being transported at a constant time interval Δt. Step S3 is an example of an imaging step.

Next, the image processing unit 50 analyzes each of the multiple captured images 70 acquired by the imaging unit 30, and acquires information regarding the performance of the evaluation target 3. Specifically, the image processing unit 50 functions as a cutout unit 110, and cuts out target images 74-76 corresponding to the PL light emission areas 17-19 from each of the multiple captured images 70 acquired (step S4).

After cutting out the target images 74 to 76, the image processing unit 50 functions as an accumulating unit 120 and accumulates the luminance values of pixels captured at the same position on the evaluation target 3 for each of the target images 74 to 76 (step S5). As a result, the image processing unit 50 generates accumulated images 81 to 83, for example, as shown in Figures 12(a) to (c).

After generating the integrated images 81 to 83, the image processing unit 50 functions as the integration unit 130 and integrates the integrated images 81 to 83 (step S6). As a result, the image processing unit 50 generates, for example, the integrated image 85 shown in FIG. 12(d).

When the integrated image 85 is generated, the image processing unit 50 functions as the evaluation unit 140 and evaluates the performance of the evaluation object 3 by analyzing the integrated image 85 (step S7). Specifically, the image processing unit 50 determines whether the evaluation object 3 contains foreign matter, defects, etc., or whether the evaluation object 3 satisfies a predetermined performance standard as a solar cell.

After evaluating the performance, the image processing unit 50 functions as the output unit 150 and outputs the evaluation result in step S7 to the outside by display, sound, communication, etc. (step S8). This ends the performance evaluation process shown in FIG. 13. Note that steps S4 to S8 are an example of image processing steps.

As described above, the performance evaluation device 1 according to this embodiment irradiates the solar cell having multiple bandgaps to be evaluated 3 with excitation light in multiple different wavelength ranges to cause the solar cell to emit PL light of multiple different wavelengths, captures an image 70 by imaging the solar cell using the PL light of multiple wavelengths, and obtains information regarding the performance of the solar cell based on the captured image 70.

The performance evaluation device 1 according to this embodiment uses photoluminescence (PL) instead of electroluminescence (EL), making it possible to perform evaluation without contact. This means that there is no risk of damaging the evaluation target 3, and evaluation is possible even during the manufacturing process, making it possible to identify defects that occur during the manufacturing process.

Furthermore, the performance evaluation device 1 according to this embodiment irradiates the evaluation object 3 with excitation light in multiple different wavelength ranges and simultaneously images all of the light-emitting areas 17-19 that emit light due to the excitation light in multiple wavelength ranges, making it possible to image using PL light of multiple wavelengths in a single scan. This allows the evaluation object 3 to be evaluated quickly, leading to a reduction in inspection time.

In particular, the performance evaluation device 1 according to this embodiment captures an image of the evaluation target 3 using PL light of multiple wavelengths with a single imaging system consisting of a single lens capable of handling wavelength ranges from visible light to infrared light and a single image sensor 34. Since there is no need to provide multiple imaging systems for capturing images using PL light of multiple wavelengths, the size and cost of the device can be reduced, leading to a smaller and lighter device.

In addition, the performance evaluation device 1 according to this embodiment uses a single imaging system to capture images of the evaluation target 3 using PL light of multiple wavelengths, improving the consistency of resolution and position between images captured using PL light of multiple wavelengths. This allows images captured using PL light of multiple wavelengths to be compared with high accuracy, improving the accuracy of evaluation of the evaluation target 3.

In addition, the performance evaluation device 1 according to this embodiment filters PL light of multiple wavelengths using a single pre-sensor filter 33, so there is no need for a rotation mechanism such as a filter changer to change the filter. This makes it possible to prevent particles from adhering to the evaluation object 3 due to the operation of the rotation mechanism, thereby reducing the effort required to clean particles adhering to the evaluation object 3 in a subsequent process.

(Modification)
Although the embodiments of the present invention have been described above, it is possible to combine the embodiments, or to modify or omit the embodiments as appropriate.

For example, in the above embodiment, the evaluation object 3 was a multi-junction solar cell having three layers. However, the number of layers of the evaluation object 3 is not limited to three, and may be two, or four or more. If the number of layers in the evaluation object 3 is other than three, the number of light sources in the irradiation unit 10 and the number of filters in the pre-sensor filter 33 are also not three, but are set to the same as the number of layers in the evaluation object 3, i.e., the number of wavelengths of the PL light emitted from the evaluation object 3.

Alternatively, the evaluation object 3 may be a solar cell with multiple bandgaps that emits PL light of multiple different wavelengths when irradiated with excitation light, and may not be clearly divided into multiple layers. For example, the evaluation object 3 may be a so-called multi-band solar cell in which multiple materials that emit PL light of different wavelengths are mixed in one layer. Also, in the above embodiment, the evaluation object 3 was a Group 3-5 semiconductor solar cell, but it may also be a tandem solar cell that combines a perovskite and a quantum dot cell.

In the above embodiment, a lens 32 was used in which chromatic aberration was sufficiently corrected in the wavelength range from visible light to infrared light. However, even if the chromatic aberration of the lens 32 is large, the influence of the chromatic aberration of the lens 32 can be suppressed by adjusting the thickness of each individual filter in the pre-sensor filter 33. Specifically, the thickness of each of the multiple individual filters (top cell filter 33a, middle cell filter 33b, and bottom cell filter 33c) in the pre-sensor filter 33 in the optical axis direction (Z direction) of the lens 32 may be different from each other according to the wavelength of the PL light transmitted by each individual filter, provided that the lens 32 has chromatic aberration.

Specifically, Figure 14(a) shows the difference in focusing positions F1 to F3 when PL light of different wavelengths is focused by a lens 32 with chromatic aberration. For the sake of explanation, Figure 14(a) shows a case where a pre-sensor filter 33 is not provided between the lens 32 and the image sensor 34. As shown in Figure 14(a), when the lens 32 has chromatic aberration, the focal length changes depending on the wavelength of the PL light, so the focusing positions F1 to F3 of the PL light shift in the Z direction.

In contrast to this, FIG. 14(b) shows an example in which a pre-sensor filter 33 is placed between the lens 32 and the image sensor 34, and the thicknesses of three individual filters in the pre-sensor filter 33 are made different, thereby adjusting the focusing positions F1 to F3 for each wavelength. Note that, for ease of understanding, FIG. 14(b) only shows the three individual filters and the vicinity of the image sensor 34, and the lens 32 is omitted. Also, the dimensions do not necessarily match the actual dimensions.

In the example of FIG. 14(b), of the three individual filters, the filter 33a for the top cell is made the thickest, and the filter 33c for the bottom cell is made the thinnest. This allows the focusing position F1 of the PL light emitted from the top cell 3a to be adjusted farther away from the lens 32, and the focusing position F3 of the PL light emitted from the bottom cell 3c to be adjusted closer to the lens 32. As a result, it is possible to reduce the deviation in the Z direction of the focusing positions F1 to F3 of the PL light emitted from each of the three cells.

In this way, even if the chromatic aberration of the lens 32 is large, by providing a difference in thickness between the individual filters in the pre-sensor filter 33, the focal positions of the PL light emitted from each of the three layers of the evaluation object 3 can be adjusted on the image sensor 34. Therefore, the PL light emitted from each of the three layers of the evaluation object 3 can be imaged at the same imaging distance.

The magnitude of chromatic aberration for each wavelength varies depending on the design of the lens 32 (including the design of the coating of the lens 32), so the difference in thickness of the individual filters is not limited to the example shown in FIG. 14(b). For example, depending on the design of the lens 32, the thickness of the top cell filter 33a of the three individual filters may be the thinnest, and the bottom cell filter 33c may be the thickest.

The present invention allows for various embodiments and modifications without departing from the broad spirit and scope of the present invention. Furthermore, the above-described embodiments are intended to explain the present invention and do not limit the scope of the present invention. In other words, the scope of the present invention is indicated by the claims, not the embodiments. Various modifications made within the scope of the claims and within the scope of the meaning of the invention equivalent thereto are considered to be within the scope of the present invention.

1 Performance evaluation device, 2 Imaging device, 3 Evaluation target, 3a Top cell, 3b Middle cell, 3c Bottom cell, 5 Transport unit, 10 Irradiation unit, 11-13 Light source, 14-16 Irradiation area, 17-19 Light emission area, 30 Imaging unit, 31 Lens front filter, 32 Lens, 33 Sensor front filter, 33a Top cell filter, 33b Middle cell filter, 33c Bottom cell filter, 34 Image sensor, 50 Image processing unit, 51 Control unit, 52 Memory unit, 53 Input reception unit, 54 Display unit, 55 Communication unit, 70 Captured image, 71-73 Area, 74-76 Target image, 81-83 Accumulated image, 85 Integrated image, 110 Cutout unit, 120 Accumulation unit, 130 Integration unit, 140 Evaluation unit, 150 Output unit, F1-F3 Light collection position, X1 to X3 Foreign matter

Claims (8)

an irradiation unit that irradiates different irradiation areas on a solar cell having a plurality of band gaps with excitation light of a plurality of different wavelength ranges to cause the solar cell to emit photoluminescence light of a plurality of different wavelengths;
an imaging unit that captures an image of the solar cell by imaging the solar cell using photoluminescence light of the multiple wavelengths emitted from the solar cell in response to excitation light of the multiple wavelength ranges; and
and an image processing unit that acquires information regarding the performance of the solar cell based on the captured image.
Performance evaluation device. The imaging unit includes:
a lens that collects the photoluminescence light of the multiple wavelengths emitted from the solar cell;
an image sensor having sensitivity to both visible light and infrared light, the image sensor receiving the photoluminescence light of the multiple wavelengths collected by the lens;
The performance evaluation device according to claim 1 . the imaging unit further includes a pre-sensor filter between the lens and the image sensor;
The pre-sensor filter has a plurality of individual filters for each region, each of which is an individual filter that transmits photoluminescence light of a corresponding wavelength among the plurality of wavelengths, the individual filters corresponding to the plurality of wavelengths in a one-to-one relationship.
The performance evaluation device according to claim 2 . the thicknesses of the individual filters are different from one another depending on the wavelength of the photoluminescence light transmitted through each individual filter under the condition that the lens has chromatic aberration;
The performance evaluation device according to claim 3 . The imaging unit further includes a pre-lens filter in front of the lens,
The pre-lens filter blocks wavelength components shorter than a predetermined wavelength among the photoluminescence light of the plurality of wavelengths emitted from the solar cell.
The performance evaluation device according to claim 2 . The irradiation unit irradiates the solar cell transported at a predetermined transport speed with excitation light in the plurality of wavelength ranges,
the imaging unit repeatedly images the solar cell transported at the transport speed at a predetermined time interval using the photoluminescence light of the plurality of wavelengths, thereby obtaining a plurality of captured images;
the image processing unit generates an integrated image by integrating luminance values of pixels in the plurality of captured images in which the same position on the solar cell is captured.
The performance evaluation device according to claim 1 . the image processing unit generates the integrated image for each of the plurality of wavelengths, and generates an integrated image by integrating the integrated images generated for each of the plurality of wavelengths.
The performance evaluation device according to claim 6. An irradiation step of irradiating different irradiation areas on a solar cell having a plurality of band gaps with excitation light having a plurality of different wavelength ranges to emit photoluminescence light having a plurality of different wavelengths;
an imaging step of capturing an image of the solar cell by capturing an image of the solar cell using photoluminescence light of the multiple wavelengths emitted from the solar cell in response to excitation light of the multiple wavelength ranges;
and an image processing step of acquiring information regarding performance of the solar cell based on the captured image.
Performance evaluation method.

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