Performance evaluation apparatus and performance evaluation method

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

Technical Field

[0001] The present invention relates to a performance evaluation apparatus and a performance evaluation method.

Background Art

[0002] Techniques for evaluating the performance of solar cells are known. For example, Patent Document 1 discloses an inspection apparatus for a solar cell panel using electroluminescence (EL). Further, Patent Document 2 discloses an inspection apparatus for a solar cell using photoluminescence (PL).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the performance evaluation of solar cells as described above, when using EL, there are the following problems. (1) It cannot be evaluated unless it is in the cell state after passing through the final manufacturing process of the solar cell. Therefore, the identification of defects occurring during the manufacturing process is delayed. (2) In order to image with EL, it is necessary to energize the electrodes of the solar cell. Therefore, there is a possibility that the solar cell may be damaged by probe contact, and furthermore, it takes time for the setup of the evaluation. In particular, when using materials with different crystal lattice sizes, the damage caused by probe contact tends to spread widely. (3) Imaging with EL lacks the luminance stability in the normal part, which is disadvantageous for defect identification by image processing.

[0005] In contrast, when using PL (photovoltaic) to evaluate the performance of solar cells, it can be applied even during the manufacturing process, and since the evaluation is non-contact, the issue of potential damage due to contact does not arise. However, because PL light is weak, it requires long exposure times.

[0006] In particular, when evaluating the performance of solar cells with multiple band gaps, applying individual exposure times to each of the multiple wavelengths of PL light corresponding to the multiple band gaps hinders high-speed performance evaluation. Under these circumstances, there is a need for high-speed, non-contact evaluation of the performance of solar cells with multiple band gaps.

[0007] This invention was made to solve the above-mentioned problems, and aims to provide a performance evaluation device, etc., that can evaluate the performance of solar cells having multiple band gaps quickly and non-contact. [Means for solving the problem]

[0008] To achieve the above objective, the performance evaluation apparatus according to the first aspect of the present invention is An irradiation unit that irradiates different irradiation areas on a solar cell having multiple band gaps with excitation light in multiple different wavelength ranges to emit photoluminescent light of multiple different wavelengths, Using the photoluminescence light of the plurality of wavelengths emitted from the solar cell by excitation light of the plurality of wavelengths at the same time The imaging unit acquires an image of the solar cell by imaging the solar cell, The system includes an image processing unit that acquires information regarding the performance of the solar cell based on the captured image. picture, The imaging unit is A single lens that simultaneously focuses the photoluminescent light of multiple wavelengths emitted from the solar cell, The system includes an image sensor that is sensitive to both visible light and infrared light and receives the photoluminescent light of multiple wavelengths focused by the lens. ru.

[0009] To achieve the above objective, the performance evaluation method according to the second aspect of the present invention is: For a solar cell having a plurality of band gaps, an irradiation step of irradiating excitation light in a plurality of different wavelength bands for emitting photoluminescence light of a plurality of different wavelengths to different irradiation areas on the solar cell; using the photoluminescence light of the plurality of wavelengths emitted from the solar cell by the excitation light in the plurality of wavelength bands at the same time an imaging step of obtaining an imaging image of the solar cell by imaging the solar cell; an image processing step of obtaining information regarding the performance of the solar cell based on the imaging image, and including fruit , In the imaging step, an image of the solar cell is acquired using a lens that simultaneously focuses the photoluminescent light of multiple wavelengths emitted from the solar cell, and an image sensor that is sensitive to both visible and infrared light and receives the photoluminescent light of multiple wavelengths focused by the lens. .

Advantages of the Invention

[0010] According to the present invention, the performance of a solar cell having a plurality of band gaps can be evaluated at high speed and non-contact.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic diagram showing the overall configuration of a performance evaluation apparatus according to an embodiment. [Figure 2] It is a diagram showing a cross section of an evaluation target in an embodiment. [Figure 3] It is a diagram showing the configuration of an irradiation unit in an embodiment. [Figure 4] It is a diagram showing an example of the relationship between the wavelength and the luminance intensity of excitation light and PL light in an embodiment. [Figure 5] It is a diagram showing the configuration of an imaging unit in an embodiment. [Figure 6] It is a diagram showing an example of a sensor pre-filter provided in the imaging unit in an embodiment. [Figure 7] It is a diagram showing an example of wavelengths filtered by a lens pre-filter and a sensor pre-filter in an embodiment. [Figure 8] It is a diagram showing an example of an imaging image captured by the imaging unit in an embodiment. [Figure 9]It is a block diagram showing the configuration of the image processing unit in the embodiment. [Figure 10] It is a diagram showing the procedure for cutting out the target image from the captured image in the embodiment. [Figure 11] It is a diagram for explaining the process of integrating the luminance values of a plurality of captured images in the embodiment. [Figure 12] (a), (b), and (c) are diagrams showing examples of integrated images of the top cell, middle cell, and bottom cell in the embodiment, respectively. (d) is a diagram showing an integrated image obtained by integrating the integrated images shown in (a) to (c). [Figure 13] It is a flowchart showing the flow of the performance evaluation process executed by the performance evaluation apparatus according to the embodiment. [Figure 14] (a) is a diagram schematically showing the difference in the wavelength of the condensing position in a lens with chromatic aberration. (b) is a diagram showing an example in which the condensing position is adjusted by a sensor front filter in a modification.

Mode for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

[0013] Fig. 1 shows the overall configuration of a performance evaluation apparatus 1 according to an embodiment of the present invention. The performance evaluation apparatus 1 is an apparatus that acquires a photoluminescence image (PL image) by imaging a solar cell using photoluminescence light (PL light) and evaluates the performance of the solar cell based on the PL image.

[0014] Here, photoluminescence (hereinafter referred to as "PL") is luminescence caused by the irradiation of electromagnetic waves (light energy), and is a phenomenon in which light having a wavelength corresponding to the energy difference between the excited state and the ground state is emitted when electrons excited by irradiating a substance with light return to the ground state.

[0015] <Evaluation target 3> Evaluation target 3 is an object that will be evaluated for performance by performance evaluation device 1, and specifically, is a solar cell having multiple band gaps. An example of an evaluation target 3 is a solar cell in its cellular state. Note that the solar cell evaluation target 3 may be in a state after the final manufacturing process, or in an intermediate state during the manufacturing process.

[0016] Solar cells with multiple band gaps that are subject to evaluation 3 are, for example, multi-junction solar cells. Here, multi-junction solar cells are also called stacked, tandem, or multi-junction solar cells, and are solar cells formed by multiple pn junctions, etc., with the aim of absorbing light in multiple different wavelength ranges.

[0017] 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 composed of three semiconductor layers formed from raw materials mainly consisting of group 3 elements (e.g., gallium) and group 5 elements (e.g., arsenic).

[0018] As an example, as shown in Figure 2, the solar cell under evaluation 3 is a laminate having three layers: a top cell 3a, a middle cell 3b, and a bottom cell 3c. The top cell 3a, middle cell 3b, and bottom cell 3c are semiconductor layers formed from different materials and having different band gaps, in order to efficiently generate solar energy.

[0019] 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 band gaps. For example, the top cell 3a has an optical absorption edge of approximately 650 nm, emits PL light with a peak wavelength of approximately 650 nm and an emission width of approximately 80 nm. The middle cell 3b has an optical absorption edge of approximately 850 nm, emits PL light with a peak wavelength of approximately 850 nm and an emission width of approximately 100 nm. The bottom cell 3c has an optical absorption edge of approximately 1250 nm, emits PL light with a peak wavelength of approximately 1250 nm and an emission width of approximately 300 nm.

[0020] Thus, since the solar cell under evaluation 3 has multiple semiconductor layers with different band gaps, when PL is generated by irradiation with excitation light, it emits PL light of multiple different wavelengths. The performance evaluation device 1 acquires images of each layer of the solar cell simultaneously using such PL light of multiple wavelengths, thereby evaluating the performance of the multi-layer solar cell non-contact and at high speed.

[0021] Returning to Figure 1, the performance evaluation device 1 comprises a transport unit 5, an illumination unit 10, an imaging unit 30, and an image processing unit 50. The illumination unit 10 and the imaging unit 30 together can also be called the imaging device 2.

[0022] The transport unit 5 transports the evaluation object 3 along a predetermined transport path in a predetermined direction (the +X direction in the example of Figure 1) at a predetermined transport speed V. Hereinafter, the direction in which the evaluation object 3 is transported by the transport unit 5 is defined as the X direction, the width direction of the evaluation object 3 transported by the transport unit 5 is defined as the Y direction, and the vertical direction is defined as the Z direction.

[0023] <Irradiation area 10> The irradiation unit 10 is a unit that irradiates the evaluation target 3 with excitation light. The excitation light irradiated from the irradiation unit 10 is an electromagnetic wave that excites electrons in each layer of the evaluation target 3, namely the top cell 3a, middle cell 3b, and bottom cell 3c, causing each layer to emit PL light. The irradiation unit 10 irradiates the evaluation target 3, which is transported by the transport unit 5, with electromagnetic waves (also simply called "light") in the wavelength range from visible light to infrared light.

[0024] The irradiation unit 10 is positioned diagonally above the evaluation target 3, which is transported by the transport unit 5, and irradiates the evaluation target 3 with excitation light from diagonally above. Specifically, the irradiation unit 10 irradiates the evaluation target 3 with excitation light from a direction that is, for example, 20° to 60° inclined with respect to the Z direction, which is perpendicular to the surface of the evaluation target 3, which is transported in a predetermined direction (+X direction).

[0025] The irradiation unit 10 has multiple light sources for emitting PL light of different wavelengths onto the object to be evaluated 3. The irradiation unit 10 then irradiates different irradiation areas on the object to be evaluated 3 with excitation light of different wavelength ranges from the multiple light sources. Specifically, as shown in Figure 3, the irradiation unit 10 is equipped with 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.

[0026] The first light source 11 emits excitation light to generate 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 shorter than the optical absorption edge of the top cell 3a (i.e., at an energy higher than the optical absorption edge). As an example, the first light source 11 emits excitation light with a peak wavelength of approximately 440-480 nm.

[0027] The second light source 12 emits excitation light to generate PL in the middle cell 3b and irradiates the second irradiation area 15 on the transported evaluation object 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., at an energy higher than the optical absorption edge). As an example, the second light source 12 excites light with a peak wavelength of approximately 730-780 nm.

[0028] The third light source 13 emits excitation light to generate 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 shorter than the optical absorption edge of the bottom cell 3c (i.e., at an energy higher than the optical absorption edge). As an example, the third light source 13 emits excitation light with a peak wavelength of approximately 930-980 nm.

[0029] In this manner, the irradiation unit 10 simultaneously outputs excitation light in multiple wavelength ranges from three light sources 11 to 13 to generate PL for the top cell 3a, middle cell 3b, and bottom cell 3c, respectively, and irradiates three different irradiation areas 14 to 16 on the transported evaluation target 3.

[0030] The excitation light emitted from the three light sources 11-13 is output to the outside via a light guide member (not shown in the figure) and an internal filter within the light source. The light guide member guides the excitation light into a linear emission. Through the light guide member, the irradiation areas 14-16 to which the excitation light is irradiated are elongated in the width direction (Y direction) of the evaluation target 3 and become a narrow linear area in the transport direction (X direction).

[0031] The internal light source filter is an interference filter used to select 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 internal light source filter is set to a wavelength range (for example, about 25 nm) that is separate from the wavelength range of the PL light transmitted by the pre-sensor filter 33, which will be described later, so that the excitation light is not received by the image sensor 34 of the imaging unit 30.

[0032] Figure 4 shows the relationship between the wavelength and brightness intensity of the excitation light irradiated from the irradiation unit 10 to the evaluation target 3, and the PL light emitted from the evaluation target 3 in response to the excitation light. In Figure 4, the wavelength distribution of the excitation light irradiated to the top cell 3a, middle cell 3b, and bottom cell 3c is shown by solid lines, and the wavelength distribution of the PL light emitted in response to the excitation light is shown by dashed lines.

[0033] When excitation light is shone onto the top cell 3a from the first light source 11, electrons contained in the material of the top cell 3a are excited, generating PL (Plantless Light). As a result, the top cell 3a emits PL light with a wavelength longer than the wavelength of the shone excitation light. Similarly, when excitation light is shone onto the middle cell 3b from the second light source 12, PL is generated in the middle cell 3b, and when excitation light is shone onto the bottom cell 3c from the third light source 13, PL is generated 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 shone excitation light.

[0034] Note that the wavelength values ​​of the excitation light emitted from each light source 11-13 are merely examples. The wavelength of the excitation light must be selected to match the band gap of the solar cell being evaluated 3. Therefore, it is necessary to change the wavelength of the excitation light to appropriately generate PL in the evaluation target 3, depending on the evaluation target 3 being used.

[0035] <Imaging unit 30> Returning to Figure 1, the imaging unit 30 is a unit that acquires an image of the evaluation target 3 by imaging the evaluation target 3. The imaging unit 30 is positioned above the evaluation target 3, which is transported by the transport unit 5, and receives the PL light emitted from the evaluation target 3. As a result, the imaging unit 30 acquires an image (PL image) of the evaluation target 3 captured by the PL light.

[0036] As shown in Figure 5, the imaging unit 30 comprises a lens front filter 31, a lens 32, a sensor front filter 33, and an image sensor 34. Each of these components is positioned perpendicular to the surface of the evaluation target 3, which is transported by the transport unit 5, and images the evaluation target 3 from directly above.

[0037] In evaluation target 3, PL light is emitted from linear emission areas 17-19 corresponding to the irradiation areas 14-16 to which the excitation light is irradiated. The imaging unit 30 images the imaging area which includes all of the linear emission areas 17-19.

[0038] The front lens filter 31 is installed in front of the lens 32 and is an interference filter that prevents unwanted light from entering the lens 32. The front lens filter 31 blocks wavelength components shorter than a predetermined wavelength from 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, and are therefore blocked in front of the lens 32 by the front lens filter 31. Note that in Figure 5, the front lens filter 31 is positioned away from the lens 32. However, the front lens filter 31 is not limited to this; any filter installed in front of the lens 32 may be used, for example, a filter coated on the lower surface of the lens 32.

[0039] The lens 32 focuses PL light of multiple wavelengths emitted from the object under evaluation 3. The optical axis of the lens is perpendicular to the surface of the object under evaluation 3 being transported. The lens 32 simultaneously focuses the three wavelengths of PL light emitted from each of the three layers of the object under evaluation 3, which have passed through the pre-lens filter 31, and forms an image on the image sensor 34.

[0040] Lens 32 is designed to focus PL light of three wavelengths with a single lens, and is therefore well-corrected for chromatic aberration and distortion across the wavelength range from visible light to infrared light. For example, it is desirable that chromatic aberration and distortion be within ±0.01% in the wavelength range from 400 nm to 1600 nm. In this way, by using a lens specifically designed to correct chromatic aberration and distortion, lens 32 can image the PL light emitted from each layer of the evaluation target 3 at the same imaging distance.

[0041] The pre-sensor filter 33 is an interference filter installed between the lens 32 and the image sensor 34 to prevent unwanted light from entering the image sensor 34. The pre-sensor filter 33 has multiple individual filters in different regions, each corresponding one-to-one to multiple wavelengths of PL light emitted from the evaluation target 3. Each of the multiple individual filters transmits PL light of its corresponding wavelength among the multiple wavelengths.

[0042] Specifically, as shown in Figure 6, the sensor pre-filter 33 has three individual filters—a top cell filter 33a, a middle cell filter 33b, and a bottom cell filter 33c—divided into three regions, corresponding to the PL light emitted from the three layers of the evaluation target 3.

[0043] The top cell filter 33a individually transmits the PL light emitted from the top cell 3a and blocks other wavelength components. The middle cell filter 33b individually transmits the PL light emitted from the middle cell 3b and blocks other wavelength components. The bottom cell filter 33c individually transmits the PL light emitted from the bottom cell 3c 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 are reversed between the evaluation target 3 and the image sensor 34. Therefore, the correspondence between the three light-emitting areas 17-19 and the three individual filters in the sensor front filter 33 is reversed in the X direction. Specifically, the top cell filter 33a, which transmits PL light emitted from the -X side light emission area 17 on the evaluation target 3, is located on the +X side, while the bottom cell filter 33c, which transmits PL light emitted from the +X side light emission area 19 on the evaluation target 3, is located furthest to the -X side.

[0044] Figure 7 shows examples of wavelength ranges filtered by the lens filter 31 and the sensor filter 33. Light from the object under evaluation 3 towards the lens 32 is first blocked by the lens filter 31, where wavelength components below 600 nm (the darkly colored portion in Figure 7) are blocked before reaching the lens 32.

[0045] The light that has passed through the lens filter 31 then passes through the lens 32 and is filtered by the sensor filter 33 to include the wavelength range (lightly colored area in Figure 7) that contains the peak wavelength 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 sensor filter 33 is set to cover, for example, 50-90% of the intensity of the PL light spectrum, with respect to the corresponding peak wavelength of the PL light.

[0046] Returning to Figure 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 positioned at the light-gathering location of the lens 32. The image sensor 34 receives PL light of multiple wavelengths emitted from the object under evaluation 3, which has passed through the lens prefilter 31, lens 32, and sensor prefilter 33, and generates an image captured by the PL light (PL image).

[0047] More specifically, the image sensor 34 comprises an array of photodiodes and a readout circuit using CMOS (Complementary Metal Oxide Semiconductor). The photodiodes are, for example, compound semiconductors such as InGaAs (indium gallium arsenide). PL light incident on the image sensor 34 is photoelectrically converted by the photodiodes 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 the analog signal representing the 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.

[0048] By using an image sensor 34 that has sensitivity over a wide wavelength range, imaging can be performed with PL light of various wavelengths, making it possible to evaluate the performance of multiband solar cells formed from various materials.

[0049] Figure 8 shows an example of an image 70 captured by the imaging unit 30. The image 70 is an image captured using PL light of different wavelengths emitted simultaneously from three layers of the evaluation target 3. As mentioned above, the correspondence between the PL light emission position on the evaluation target 3 and the PL light reception position on the image sensor 34 is inverted in the X and Y directions. However, for ease of understanding, the XY coordinates in the image 70 shown in Figure 8 are set to match the XY coordinates on the evaluation target 3. The same applies to subsequent figures.

[0050] 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 the region captured when the image sensor 34 receives PL light emitted from the top cell 3a and transmitted through the top cell filter 33a. The second region 72 is the region captured when the image sensor 34 receives PL light emitted from the middle cell 3b and transmitted through the middle cell filter 33b. The third region 73 is the region captured when the image sensor 34 receives PL light emitted from the bottom cell 3c and transmitted through the bottom cell filter 33c.

[0051] In this way, PL light emitted from each layer of the evaluation target 3 is used to image each region separately. As a result, 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 parts of the captured image 70 corresponding to the linear light-emitting areas 17-19 (white parts in Figure 8) show brighter luminance values ​​(pixel values) compared to the other parts (colored parts in Figure 8). Thus, a single captured image 70 includes images from PL light emitted from the top cell 3a, middle cell 3b, and bottom cell 3c, respectively.

[0052] The imaging unit 30 acquires multiple images 70 by repeatedly acquiring such images 70 at predetermined time intervals Δt. More specifically, the imaging unit 30 acquires an image 70 each time the evaluation target 3 is transported by the transport unit 5 by a distance d corresponding to one pixel. For this purpose, the time interval Δt is set to the time obtained by dividing the distance d corresponding to one pixel by the transport speed V, "Δt = d / V". By repeatedly imaging at this time interval Δt, the imaging unit 30 can image the entire area of ​​the evaluation target 3 transported by the transport unit 5 from end to end with PL light of three different wavelengths.

[0053] <Image processing unit 50> Returning to Figure 1, the image processing unit 50 is a unit that acquires information regarding the performance of the solar cell, which is the subject of evaluation 3, based on the captured image 70 acquired by the imaging unit 30. Specifically, the image processing unit 50 is an information processing device such as a personal computer or a cloud server.

[0054] Here, information regarding the performance of the solar cell is, for example, information indicating the presence or absence of foreign matter, defects, etc., in the solar cell, or whether or not the solar cell meets a predetermined performance standard, or other information that directly indicates the performance of the solar cell. Alternatively, the information regarding the performance of the solar cell may be, for example, an image processed from the captured image 70 for the purpose of evaluating the performance of the solar cell, such as the integrated images 81-83 or the combined image 85 described later.

[0055] More specifically, as shown in Figure 9, the image processing unit 50 comprises a control unit 51, a storage unit 52, an input receiving unit 53, a display unit 54, and a communication unit 55.

[0056] The control unit 51 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU is a central processing unit that includes a microprocessor and performs various processes and calculations. In the control unit 51, the CPU reads the control program stored in the ROM and controls the operation of the entire image processing unit 50 while using the RAM as work memory. The control unit 51 may also include an image processing processor such as a DSP (Digital Signal Processor) or GPU (Graphics Processing Unit).

[0057] The storage unit 52 is a non-volatile memory such as flash memory or a hard disk. The storage unit 52 stores programs and data executed by the control unit 51, and data generated by the control unit 51.

[0058] The input receiving unit 53 is equipped with input devices such as a keyboard, mouse, and touch panel, and accepts user input.

[0059] The display unit 54 is equipped with 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 representing the evaluation results from the performance evaluation device 1.

[0060] The communication unit 55 is equipped with a communication interface for communicating with external devices to the image processing unit 50, which includes 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).

[0061] The control unit 51 functionally comprises a cutting unit 110, an accumulating unit 120, an integration unit 130, an evaluation unit 140, and an output unit 150. In the control unit 51, the CPU functions by reading a program stored in ROM into RAM, executing that program, and controlling it.

[0062] The cropping unit 110 extracts the target image from the captured image 70 captured by the imaging unit 30 to evaluate the performance of the evaluation target 3. Specifically, the cropping unit 110 uses the ROI (Region of Interest) function to extract the portion corresponding to the line-shaped light emission areas 17-19 from the captured image 70.

[0063] More specifically, as shown in Figure 10, the cropping unit 110 normalizes the brightness value of each pixel in the captured image 70 and then integrates it in the width direction (Y direction) of the evaluation target 3. This allows the cropping unit 110 to generate a one-dimensional brightness distribution in the transport direction (X direction) of the evaluation target 3. Then, from each of the three regions 71-73, the cropping unit 110 extracts a region with a width of W pixels (for example, 32 pixels) in the X direction, centered on the position where the brightness value peaks in the brightness distribution.

[0064] Specifically, the cropping unit 110 crops target images 74 to 76 from three regions 71 to 73 of the captured image 70. Each of the target images 74 to 76 has, for example, a length of 1024 pixels in the width direction (Y direction) of the evaluation target 3 and a length of 32 pixels in the transport direction (X direction).

[0065] The integration unit 120 generates an integrated image by integrating the brightness values ​​of pixels that are captured at the same position on the evaluation target 3 in multiple captured images 70 acquired by the imaging unit 30. By integrating the brightness values ​​in multiple captured images 70, the exposure time can be extended and fixed noise can be suppressed, which is advantageous for improving sensitivity in imaging using weak PL light.

[0066] The integration procedure by the integration unit 120 will be explained in more detail with reference to Figure 11. The integration unit 120 considers each of the target images 74 to 76 extracted from the multiple captured images 70 by the extraction unit 110 as a TDI (Time Delay Integration) sensor, and integrates the brightness values ​​in synchronization with the transport speed V of the evaluation target 3.

[0067] Here, each of the multiple captured images 70 is acquired at a predetermined time interval Δt, each time the object to be evaluated 3 is transported a distance of one pixel. Therefore, the same position on the object to be evaluated 3 is shifted by one pixel in the X direction across the multiple captured images 70. As a result, as shown in Figure 11, the pixels in the leftmost column (indicated by the dashed line) of the target images 74-76 acquired at time t are shifted to the second column from the left in the target images 74-76 acquired at time t+Δt, to the third column from the left in the target images 74-76 acquired at time t+Δt×2, and to the rightmost column in the target images 74-76 acquired at time t+Δt×(W-1).

[0068] The integration unit 120 shifts the brightness values ​​of each pixel in the W consecutive target images 74-76 by one pixel each, in accordance with the shift of the same position on the evaluation target 3 by one pixel in the transport direction, and then integrates them. As a result, the integration unit 120 generates integrated images 81-83, for example, as shown in Figures 12(a)-(c).

[0069] More specifically, when the position (x,y) on the evaluation target 3 is captured within the target image 74 for a time interval Δt × W from time t to time t + Δt × (W-1), the integration unit 120 calculates the sum of the brightness values ​​obtained in (1) to (W) below, "P(1,y) + P(2,y) + P(3,y) + ... + P(W,y)", as the brightness value of the position (x,y) in the integrated image 81. (1) The brightness value P(1,y) at position (1,y) in the target image 74 extracted from the captured image 70 at time t. (2) The brightness value P(2,y) at position (2,y) in the target image 74 extracted from the captured image 70 acquired at time t+Δt. (3) The brightness value P(3,y) at position (3,y) in the target image 74 extracted from the captured image 70 acquired at time t+Δt×2. ... (W) The brightness value P(W,y) at position (W,y) in the target image 74 extracted from the captured image 70 acquired at time t+Δt×(W-1).

[0070] The integration unit 120 calculates the luminance value of each position in the integrated image 81 by calculating the sum of these W luminance values ​​for all positions on the evaluation target 3. Similarly, for the target images 75 and 76 as well as the target image 74, the integration unit 120 calculates the luminance value of each position in the integrated images 82 and 83 by calculating the sum of the luminance values ​​obtained in (1) to (W) above for all positions on the evaluation target 3.

[0071] In this way, the integration unit 120 integrates the brightness values ​​of pixels that are imaged 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 integration unit 120 generates an integrated image 81 of the top cell 3a as shown in Figure 12(a) from the target image 74, an integrated image 82 of the middle cell 3b as shown in Figure 12(b) from the target image 75, and an integrated image 83 of the bottom cell 3c as shown in Figure 12(c) from the target image 76.

[0072] Returning to Figure 9, the integration unit 130 generates a combined image 85 by integrating the multiple combined images 81 to 83 generated by the integration unit 120. Specifically, the integration unit 130 generates a combined image 85 as shown in Figure 12(d) by adding up the brightness values ​​of the same coordinates in the three combined images 81 to 83 shown in Figures 12(a) to (c). The brightness value of each pixel in the combined image 85 is the sum of the brightness values ​​of the pixels at the same coordinates in the combined images 81 to 83.

[0073] The integration by the integration unit 130 brings together foreign objects X1 to X3, which were separately captured in the three integrated images 81 to 83, into a single integrated image 85. This makes it easier to determine whether the defect or foreign object contamination occurs in a single layer of the evaluation target 3 or across multiple layers.

[0074] In the performance evaluation device 1 according to this embodiment, three integrated images 81 to 83 are acquired by one lens 32 and one area sensor image sensor 34, resulting in high consistency in resolution and position among the multiple integrated images 81 to 83. Therefore, a highly accurate integrated image 85 can be generated.

[0075] Returning to Figure 9, the evaluation unit 140 evaluates the performance of the solar cell, which is the subject of evaluation 3, based on the integrated image 85 generated by the integration unit 130. Specifically, the evaluation unit 140 analyzes the brightness distribution of the integrated image 85 and converts the brightness distribution of the integrated image 85 into information indicating the performance of the solar cell, which is the subject of evaluation 3. Specifically, the information indicating the performance of the solar cell includes whether foreign matter is mixed in the solar cell, whether defects have occurred, and whether the solar cell meets predetermined performance standards.

[0076] For example, as shown in Figure 12(d), if 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. The evaluation unit 140 then identifies the type of each foreign object X1 to X3, such as whether it is a void or an impurity, based on its characteristic features such as shape and size.

[0077] Alternatively, even if there are no foreign objects X1 to X3 or defects in the object to be evaluated 3, the evaluation unit 140 may determine from the brightness distribution of the integrated image 85 whether the solar cell, which is the object to be evaluated 3, meets predetermined performance standards. By evaluating the performance of the solar cell based on the integrated image 85 in this way, it is possible to determine whether or not any abnormalities have occurred in the manufacturing process of the solar cell, which can lead to the manufacture of solar cells with higher performance.

[0078] The output unit 150 outputs the evaluation results from 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 results as audio, or output them to an external device via the communication unit 55.

[0079] The image processing unit 50 does not necessarily have to have the functions of the evaluation unit 140; an external device to the image processing unit 50 may have the functions of the evaluation unit 140. In that 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 perform the processing of the evaluation unit 140 described above based on the integrated image 85.

[0080] Next, referring to the flowchart shown in Figure 13, we will explain the flow of the performance evaluation process performed by the performance evaluation device 1.

[0081] When the performance evaluation process is started, the transport unit 5 transports the evaluation target 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 target 3 being transported by the transport unit 5 with excitation light in different wavelength ranges (step S2). Steps S1 and S2 are examples of the transport step and the irradiation step, respectively.

[0082] When excitation light is emitted by the irradiation unit 10, the imaging unit 30 uses the PL light emitted from each layer of the evaluation target 3 by the emitted excitation light to image the evaluation target 3 (step S3). As a result, the imaging unit 30 acquires, for example, the image 70 shown in Figure 8. More specifically, the imaging unit 30 acquires multiple image 70 by repeatedly imaging the transported evaluation target 3 at a fixed time interval Δt. Step S3 is an example of an imaging step.

[0083] Next, the image processing unit 50 analyzes each of the multiple captured images 70 acquired by the imaging unit 30 and obtains information regarding the performance of the evaluation target 3. Specifically, the image processing unit 50 functions as a cropping unit 110 and crops out target images 74 to 76 corresponding to the PL light emission areas 17 to 19 from each of the multiple captured images 70 (step S4).

[0084] When target images 74 to 76 are extracted, the image processing unit 50 functions as an integration unit 120 and integrates the brightness values ​​of pixels that were 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 integrated images 81 to 83, for example, as shown in Figures 12(a) to (c).

[0085] Once the integrated images 81-83 are generated, the image processing unit 50 functions as an integration unit 130 and integrates the integrated images 81-83 (step S6). As a result, the image processing unit 50 generates the integrated image 85 shown in Figure 12(d), for example.

[0086] Once the integrated image 85 is generated, the image processing unit 50 functions as an evaluation unit 140 and evaluates the performance of the object to be evaluated 3 by analyzing the integrated image 85 (step S7). Specifically, the image processing unit 50 determines whether foreign matter, defects, etc., are present in the object to be evaluated 3, or whether the object to be evaluated 3 meets predetermined performance standards as a solar cell.

[0087] Once the performance is evaluated, the image processing unit 50 functions as an output unit 150 and outputs the evaluation result from step S7 to the outside via display, sound, communication, etc. (step S8). This completes the performance evaluation process shown in Figure 13. Steps S4 to S8 are just one example of image processing steps.

[0088] As described above, the performance evaluation apparatus 1 according to this embodiment irradiates a solar cell having multiple band gaps, which is the object of evaluation 3, with excitation light in multiple different wavelength ranges to emit PL light of multiple different wavelengths, acquires an image 70 by imaging the solar cell using PL light of multiple wavelengths, and acquires information regarding the performance of the solar cell based on the image 70.

[0089] The performance evaluation apparatus 1 according to this embodiment utilizes photoluminescence (PL) instead of electroluminescence (EL), enabling non-contact evaluation. Therefore, there is no risk of damaging the object to be evaluated 3, and evaluation can be performed even in the middle of the manufacturing process, making it possible to identify defects that occur during the manufacturing process.

[0090] Furthermore, the performance evaluation device 1 according to this embodiment irradiates the evaluation target 3 with excitation light of multiple different wavelength ranges and simultaneously images all of the emission areas 17 to 19 that emit light due to the excitation light of multiple wavelength ranges, making it possible to image with PL light of multiple wavelengths in a single scan. This allows the evaluation target 3 to be evaluated at high speed, leading to a reduction in inspection time.

[0091] In particular, the performance evaluation apparatus 1 according to this embodiment uses a single imaging system consisting of a single lens capable of handling wavelengths from visible light to infrared light and a single image sensor 34 to image the evaluation target 3 with PL light of multiple wavelengths. Since there is no need to provide multiple imaging systems for imaging with PL light of multiple wavelengths, the size and cost of the apparatus can be reduced, leading to miniaturization and weight reduction of the apparatus.

[0092] Furthermore, the performance evaluation apparatus 1 according to this embodiment images the evaluation target 3 with PL light of multiple wavelengths using a single imaging system, thereby improving the consistency of resolution and position between images captured with PL light of multiple wavelengths. As a result, images captured with PL light of multiple wavelengths can be compared with high accuracy, improving the evaluation accuracy of the evaluation target 3.

[0093] Furthermore, the performance evaluation apparatus 1 according to this embodiment filters PL light of multiple wavelengths with a single sensor pre-filter 33, eliminating the need for a rotating mechanism such as a filter changer to change filters. Therefore, it is possible to suppress the adhesion of particles to the evaluation target 3 caused by the driving of a rotating mechanism, thereby reducing the effort required to clean particles that have adhered to the evaluation target 3 in subsequent processes.

[0094] (modified version) Although 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.

[0095] For example, in the above embodiment, the device under evaluation 3 was a multi-junction solar cell having three layers. However, the number of layers in the device under evaluation 3 is not limited to three; it may be two, four or more, or any number of layers. If the number of layers in the device under evaluation 3 is other than three, the number of light sources in the irradiation unit 10 and the number of filters in the sensor pre-filter 33 are also set to be the same as the number of layers in the device under evaluation 3, i.e., the number of wavelengths of PL light emitted from the device under evaluation 3, rather than three.

[0096] Alternatively, evaluation target 3 is a solar cell having multiple band gaps that emits PL light of multiple different wavelengths when irradiated with excitation light, and does not necessarily have to be clearly divided into multiple layers. For example, evaluation target 3 may be a so-called multiband solar cell in which multiple materials emitting PL light of different wavelengths are mixed within a single layer. Also, in the above embodiment, evaluation target 3 was a group 3-5 semiconductor solar cell, but it may also be a tandem solar cell combining perovskite and quantum dot cells.

[0097] 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 effect of the chromatic aberration of the lens 32 can be suppressed by adjusting the thickness of each individual filter in the sensor prefilter 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 sensor prefilter 33 in the optical axis direction (Z direction) of the lens 32 may differ from one another, depending on the wavelength of the PL light transmitted by each individual filter, under the condition that the lens 32 has chromatic aberration.

[0098] 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. Note that Figure 14(a) shows the case where a pre-sensor filter 33 is not provided between the lens 32 and the image sensor 34 for illustrative purposes. 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 are shifted in the Z direction.

[0099] In contrast, Figure 14(b) shows an example in which a pre-sensor filter 33 is installed between the lens 32 and the image sensor 34, and the focusing positions F1 to F3 for each wavelength are adjusted by making the thickness of the three individual filters in the pre-sensor filter 33 different. Note that Figure 14(b) shows only the three individual filters and the vicinity of the image sensor 34 for ease of understanding, and the lens 32 is omitted. Also, the dimensions do not necessarily match the actual dimensions.

[0100] In the example shown in Figure 14(b), the top cell filter 33a is made the thickest of the three individual filters, and the bottom cell filter 33c is made the thinnest. As a result, the focusing position F1 of the PL light emitted from the top cell 3a is adjusted to be further away from the lens 32, and the focusing position F3 of the PL light emitted from the bottom cell 3c is adjusted to be closer to the lens 32. Consequently, the Z-direction deviation of the focusing positions F1 to F3 of the PL emitted from each of the three cells can be reduced.

[0101] Thus, even if the chromatic aberration of the lens 32 is large, by creating a difference in thickness between the individual filters in the sensor front filter 33, the focal position of the PL light emitted from each of the three layers of the evaluation target 3 can be adjusted to be on the image sensor 34. Therefore, at the same imaging distance, the PL light emitted from each of the three layers of the evaluation target 3 can be imaged.

[0102] Note that the magnitude of chromatic aberration for each wavelength varies depending on the design of the lens 32 (including the design of the lens coating), so the difference in the thickness of the individual filters is not limited to the example shown in Figure 14(b). For example, depending on the design of the lens 32, the thickness of the top cell filter 33a may be made the thinnest and the thickness of the bottom cell filter 33c may be made the thickest among the three individual filters.

[0103] This invention allows for various embodiments and modifications without departing from the broad spirit and scope of the invention. Furthermore, the embodiments described above are for illustrative purposes only and do not limit the scope of the invention. In other words, the scope of the invention is indicated not by the embodiments, but by the claims. Various modifications made within the scope of the claims and the equivalent scope of the meaning of the invention are considered to be within the scope of this invention. [Explanation of symbols]

[0104] 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 Emission area, 30 Imaging unit, 31 Lens front filter, 32 Lens, 33 Sensor front filter, 33a Filter for top cell, 33b Filter for middle cell, 33c Filter for bottom cell, 34 Image sensor, 50 Image processing unit, 51 Control unit, 52 Storage unit, 53 Input reception unit, 54 Display unit, 55 Communication unit, 70 Captured image, 71-73 Area, 74-76 Target image, 81-83 Integrated image, 85 Integrated image, 110 Cropping unit, 120 Integration unit, 130 Integration unit, 140 Evaluation unit, 150 Output unit, F1-F3 Focusing position, X1~X3 Foreign matter

Claims

1. An irradiation unit that irradiates different irradiation areas on a solar cell having multiple band gaps with excitation light in multiple different wavelength ranges to emit photoluminescent light of multiple different wavelengths, An imaging unit acquires an image of the solar cell by simultaneously imaging the solar cell using photoluminescent light of multiple wavelengths emitted from the solar cell by excitation light of the multiple wavelength ranges, The system includes an image processing unit that acquires information regarding the performance of the solar cell based on the captured image, The imaging unit is A single lens that simultaneously focuses the photoluminescent light of multiple wavelengths emitted from the solar cell, The system includes an image sensor that is sensitive to both visible light and infrared light and receives the photoluminescent light of multiple wavelengths focused by the lens, Performance evaluation device.

2. The imaging unit further includes a pre-sensor filter between the lens and the image sensor. The sensor pre-filter has multiple individual filters, each corresponding one-to-one to the multiple wavelengths, for each region, each being an individual filter that transmits photoluminescent light of a corresponding wavelength among the multiple wavelengths. The performance evaluation apparatus according to claim 1.

3. The thickness of each of the aforementioned individual filters is different from one another, depending on the wavelength of the photoluminescent light transmitted through each individual filter, under the condition that the lens has chromatic aberration. The performance evaluation apparatus according to claim 2.

4. The imaging unit further includes a front lens filter in front of the lens. The lens front filter blocks wavelength components shorter than a predetermined wavelength from among the photoluminescent light of multiple wavelengths emitted from the solar cell. A performance evaluation apparatus according to any one of claims 1 to 3.

5. The irradiation unit irradiates the solar cell, which is being transported at a predetermined transport speed, with excitation light in the plurality of wavelength ranges. The imaging unit acquires multiple images by repeatedly imaging the solar cell being transported at the transport speed at predetermined time intervals using photoluminescent light of multiple wavelengths, The image processing unit generates an integrated image by accumulating the brightness values ​​of pixels that are captured at the same position on the solar cell in the plurality of captured images. A performance evaluation apparatus according to any one of claims 1 to 3.

6. The image processing unit generates the integrated image for each of the plurality of wavelengths, and generates a combined image by integrating the integrated images generated for each of the plurality of wavelengths. The performance evaluation apparatus according to claim 5.

7. An irradiation step in which excitation light in different wavelength ranges to emit photoluminescent light of different wavelengths to a solar cell having multiple band gaps is irradiated onto different irradiation areas on the solar cell, An imaging step to acquire an image of the solar cell by simultaneously imaging the solar cell using photoluminescent light of multiple wavelengths emitted from the solar cell by excitation light of the multiple wavelength ranges, The process includes an image processing step of obtaining information regarding the performance of the solar cell based on the captured image, In the imaging step, an image of the solar cell is acquired using a lens that simultaneously focuses the photoluminescent light of multiple wavelengths emitted from the solar cell, and an image sensor that is sensitive to both visible light and infrared light and receives the photoluminescent light of multiple wavelengths focused by the lens. Performance evaluation method.

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