Large-area photocurrent scanning imaging system

Abstract

The invention discloses a large-area photocurrent scanning imaging system, and belongs to the technical field of defect detection of solar cells and photoelectric detectors. The driving devices are connected to the two adjacent sides of the displacement plate, so that the displacement plate drives light spots on the surface of a sample through the reflecting mirror, the semi-transparent and semi-reflecting mirror and the objective lens to move in the X-axis direction or the Y-axis direction, two-dimensional scanning of the light spots is achieved, one-way scanning is adopted in the scanning mode, the resolution ratio is increased, and the detection precision is improved. The problem that leads need to be frequently welded on electrodes when different devices are measured in a sample table scanning mode is solved, and the problems that the scanning range is limited, images are distorted and a light path system is complex due to a galvanometer scanning mode are also solved; besides, by means of the semi-transparent semi-reflecting mirror, the camera and the Z-axis adjusting frame, light spots can be adjusted to be small enough, the spatial resolution of photocurrent scanning imaging is increased, the structure is simple, and operation is convenient.

Description

Technical Field

[0001] The invention belongs to the technical field of defect detection of solar cells and photoelectric detectors, and in particular relates to a large-area photocurrent scanning imaging system. Background Art

[0002] In recent years, driven by the demand for solar energy utilization and high-performance photoelectric detection, solar cells, photodetectors, and especially new low-dimensional material-based photodetectors have developed rapidly. Photoelectric performance testing and characterization is a key link in the development and application of optoelectronic devices, which directly affects the optimization and performance improvement of devices.

[0003] Photocurrent scanning imaging technology, as a non-destructive technology, can directly obtain the photoelectric response image of optoelectronic devices. This technology scans the sample and captures the distribution of local photocurrent, thereby revealing the device's defects, spatial uniformity, diffusion length, local efficiency and pn junction (including junction area, junction depth, leakage current location and other information). This information is of great significance for further optimizing the structure of the device and improving the photoelectric conversion efficiency, and has therefore received widespread attention in scientific research and industry.

[0004] There are two main common photocurrent scanning imaging methods: (1) The translation stage drives the sample to move in two dimensions. This method is to fix the sample electrodes on the translation stage by welding leads, and then drive the translation stage to move along the X and Y axes, thereby scanning the sample surface point by point. This method requires welding leads on the sample electrodes, which is not as convenient as probe connection, and the difference in solder joint resistance will also affect the performance comparison between different devices. (2) The scanning mirror drives the light spot to scan the sample in two dimensions. In this method, the sample is fixed and the probe can be directly used to connect the positive and negative electrodes of the device. The direction of the light beam is adjusted by the scanning mirror to scan the light spot in two dimensions on the sample surface. The scanning speed is high, but there are disadvantages such as limited image scanning range, image distortion caused by inconsistent XY scanning, and complex optical path system.

[0005] Therefore, there is an urgent need for a large-area photocurrent scanning imaging system to address the defects in the existing technology and provide an efficient and accurate imaging solution to meet the needs of defect detection and performance evaluation of large-area optoelectronic devices. Summary of the invention

[0006] The purpose of the present invention is to provide a large-area photocurrent scanning imaging system to solve the problems of slow measurement speed caused by welding leads on sample electrodes and limited scanning range, image distortion and complex optical path system caused by galvanometer scanning.

[0007] In order to achieve the above-mentioned purpose, the present invention provides the following technical solutions: a large-area photocurrent scanning imaging system, comprising a placement platform, a beam scanning device, a sample placement device and a probe device, wherein the beam scanning device comprises a reflector, a semi-transparent and semi-reflective mirror, an objective lens, a camera, a base plate, a displacement stage and a driving component, wherein: the displacement stage is slidably arranged on the placement platform, the base plate is fixedly mounted on the displacement stage, the reflector and the semi-transparent and semi-reflective mirror are fixedly mounted on the base plate, and the mirror surfaces of the two mirrors face each other, the camera is arranged above the semi-transparent and semi-reflective mirror, the objective lens is embedded in the base plate and is located below the semi-transparent and semi-reflective mirror, and the driving component has two groups, both of which are arranged on the placement platform and are respectively connected to two adjacent sides of the displacement stage to drive the displacement stage to move along the X-axis or Y-axis direction;

[0008] The sample placement device comprises a two-dimensional sample stage and a Z-axis adjustment frame, wherein the Z-axis adjustment frame is arranged below the placement platform, and the two-dimensional sample stage is rotatably connected to the Z-axis adjustment frame for placing the sample;

[0009] The probe device includes two three-axis adjustable displacement platforms, a probe connecting rod and a probe, wherein the two three-axis adjustable displacement platforms are symmetrically arranged on both sides of the two-dimensional sample stage, one end of the probe connecting rod is connected to the execution end of the three-axis adjustable displacement platform, and the probe is installed at the other end of the probe connecting rod and abuts against the positive pole or negative pole of the sample.

[0010] In a further embodiment, the driving assembly includes a stepper motor and a lead screw, the stepper motor is mounted on the placement platform, the lead screw is connected to the output end of the stepper motor, and is connected to the moving platform through a nut in the lead screw, so as to realize the linear motion of the moving platform, provide power for the light beam scanning, and determine the path of the light beam scanning.

[0011] In a further embodiment, a shell is installed on the outer periphery of the bottom plate, a plurality of first pillars are installed on the bottom plate, a base is installed on the first pillars, the camera is fixedly mounted on the base, and the first pillars do not block the mirror surfaces of the reflector and the semi-transparent and semi-reflective mirror, the shell protects the light beam scanning device from external influences, the base provides a mounting carrier for the camera, and the first pillars do not affect the reflection path of the light beam.

[0012] In a further embodiment, a through hole is opened on the bottom plate for installing the objective lens, and the objective lens is located above the two-dimensional sample stage for focusing the light spot on the sample placed on the two-dimensional sample stage.

[0013] In a further embodiment, a plurality of second pillars are installed on the lower surface of the placement platform, and the Z-axis adjustment frame is slidably installed on one of the second pillars to achieve the up and down movement of the two-dimensional sample stage.

[0014] In a further embodiment, a plurality of third pillars are arranged below the three-axis adjustable displacement platform, a support plate is mounted on the third pillars, and the three-axis adjustable displacement platform is fixedly mounted on the support plate, providing a mounting carrier for the three-axis adjustable displacement platform.

[0015] In a further embodiment, a data acquisition system and a control system are also included. The data acquisition system includes positive and negative wires and a source meter. One end of the positive and negative wires are respectively connected to two probes, and the other end is connected to the source meter, which is used to measure the photocurrent data of the sample and transmit, display and store it; the control system is electrically connected to the driving component to control the scanning path of the light beam scanning device.

[0016] In a further embodiment, the control system controls the driving component so that the light spot generated in the light beam scanning device performs light beam scanning in a unidirectional scanning manner, and during the scanning imaging process, the light spot sets the displacement distance and step length along the X-axis direction to move unidirectionally, and scans step by step. After reaching the set end point, the light spot returns to the starting position along the X-axis, and at this time the Y-axis takes one step, and the light spot continues to scan unidirectionally along the X-axis, and the cycle is repeated.

[0017] Beneficial effects: In the present invention, a driving device is connected to two adjacent sides of the displacement plate, so that the displacement plate drives the light spot on the sample surface through the reflector, the semi-transparent and semi-reflective mirror and the objective lens to move along the X-axis or Y-axis direction, thereby realizing two-dimensional scanning of the light spot. The scanning method adopts unidirectional scanning, which improves the resolution and avoids the problem of frequent welding of leads on electrodes when measuring different devices caused by the sample stage scanning method, and also avoids the problems of limited scanning range, image distortion and complex optical path system caused by the galvanometer scanning method. In addition, through the semi-transparent and semi-reflective mirror, the camera, and the Z-axis adjustment frame, the light spot can be adjusted to be small enough, thereby increasing the spatial resolution of photocurrent scanning imaging, and the structure is simple and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the hardware structure of the photocurrent scanning imaging system.

[0019] Figure 2 The front view of the hardware structure of the photocurrent scanning imaging system.

[0020] Figure 3 It is a structural schematic diagram of the light beam scanning device.

[0021] Figure 4 Schematic diagram of the internal optical path and beam movement direction of the beam scanning component.

[0022] Figure 5 This is a surface photocurrent scanning image of the silicon photovoltaic cell in Example 1.

[0023] Figure 6 This is the photocurrent image of the silicon photovoltaic cell in Example 2, the surface of which is covered with the printing paper with the word "South" printed in small 5-size font.

[0024] Figure 7 The surface of the embodiment 3 is covered with grating strips and the scanning range is 0.2×0.2 mm 2 , Photocurrent image of a silicon photocell with a step size of 5 μm.

[0025] Figure 8 The surface of the embodiment 4 is covered with grating strips and the scanning range is 0.1×0.1 mm 2 , Photocurrent image of a silicon photocell with a step size of 2.5μm.

[0026] Fig. 9 This is the photocurrent scanning image of the Cu2ZnSnS4 solar cell in Example 5.

[0027] Figure numerals: 1. reflector; 2. camera; 3. base; 4. first pillar; 5. housing; 6. drive assembly; 7. placement platform; 8. second pillar; 9. three-axis adjustment displacement stage; 10. probe connecting rod; 11. probe; 12. support plate; 13. third pillar; 14. two-dimensional sample stage; 15. Z-axis adjustment frame; 16. objective lens; 17. displacement stage; 18. stepping motor; 19. semi-transparent and semi-reflective mirror; 20. bottom plate. DETAILED DESCRIPTION

[0028] In the following description, a large number of specific details are provided to provide a more thorough understanding of the present invention. However, it is apparent to those skilled in the art that the present invention can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present invention, some technical features well known in the art are not described.

[0029] See also Figures 1 to 3 The present application provides a large-area photocurrent scanning imaging system, hereinafter referred to as the system. The system includes a placement platform 7, a beam scanning device, a sample placement device, a probe device, a data acquisition system and a control system.

[0030] See also Figure 3The light beam scanning device includes a reflector 1, a semi-transparent and semi-reflective mirror 19, an objective lens 16, a camera 2, a base plate 20, a displacement stage 17 and a driving component 6. The displacement stage 17 is slidably arranged on the placement platform 7, and the base plate 20 is fixedly installed on the displacement stage 17. The reflector 1 and the semi-transparent and semi-reflective mirror 19 are fixedly installed on the base plate 20, and the mirror surfaces of the two are facing each other, respectively used for light beam reflection and light splitting. The camera 2 is arranged above the semi-transparent and semi-reflective mirror 19 for capturing the scanned image. The objective lens 16 is embedded in the base plate 20 and is located below the semi-transparent and semi-reflective mirror 19 for adjusting the light beam into a light spot for focusing. The driving component 6 has two groups, both of which are arranged on the placement platform 7 and are respectively connected to the adjacent two sides of the displacement stage 17, so as to drive the displacement stage 17 to move along the X-axis or Y-axis direction to achieve precise movement.

[0031] Specifically, the driving assembly 6 includes a stepper motor 18 and a lead screw. The stepper motor 18 is installed on the placement platform 7. The lead screw is connected to the output end of the stepper motor 18 and is connected to the moving platform through a nut in the lead screw. It is used to realize the linear motion of the moving platform, provide power for the light beam scanning, and determine the path of the light beam scanning.

[0032] As a preferred embodiment, a shell 5 is installed on the outer periphery of the base plate 20 to protect the light beam scanning device from external influences and improve the stability of the light beam scanning; a plurality of first pillars 4 are installed on the base plate 20, a base 3 is installed on the first pillars 4, and the camera 2 is fixedly installed on the base 3 to provide a mounting carrier for the camera 2, and the first pillars 4 do not block the mirror surfaces of the reflector 1 and the semi-transparent and semi-reflective mirror 19, and will not affect the reflection path of the light beam.

[0033] Continue reading Figure 1 and Figure 2 The sample placement device includes a two-dimensional sample stage 14 and a Z-axis adjustment frame 15. The Z-axis adjustment frame 15 is arranged below the placement platform 7. The two-dimensional sample stage 14 is rotatably connected to the Z-axis adjustment frame 15 for placing samples and providing two-dimensional movement. Specifically, a plurality of second pillars 8 are installed on the lower surface of the placement platform 7. The Z-axis adjustment frame 15 is slidably installed on a second pillar 8 for realizing the up and down movement of the two-dimensional sample stage 14, so as to facilitate the adjustment of the size of the light spot.

[0034] As a preferred embodiment, a through hole is provided on the base plate 20 for installing the objective lens 16 , and the objective lens 16 is located above the two-dimensional sample stage 14 for focusing the light spot on the sample placed on the two-dimensional sample stage 14 .

[0035] The probe 11 device includes two three-axis adjustment displacement tables 9, a probe connecting rod 10 and a probe 11, wherein the two three-axis adjustment displacement tables 9 are symmetrically arranged on both sides of the two-dimensional sample stage 14 for accurately adjusting the position of the probe 11, one end of the probe connecting rod 10 is connected to the execution end of the three-axis adjustment displacement table 9, and the probe 11 is installed at the other end of the probe connecting rod 10 and abuts against the positive or negative pole of the sample for contacting the sample and performing current scanning.

[0036] Specifically, a plurality of third pillars 13 are arranged below the three-axis adjustable displacement platform 9 , a support plate 12 is mounted on the third pillars 13 , and the three-axis adjustable displacement platform 9 is fixedly mounted on the support plate 12 , providing a mounting carrier for the three-axis adjustable displacement platform 9 .

[0037] The data acquisition system includes positive and negative wires and a source meter. One end of the positive and negative wires are respectively connected to two probes 11, and the other end is connected to the source meter, which is used to measure the photocurrent data of the sample and transmit, display and store it; the control system is electrically connected to the driving component 6, which is used to control the scanning path of the light beam scanning device.

[0038] Specifically, the control system controls the driving component 6 so that the light spot generated in the light beam scanning device performs light beam scanning in a unidirectional scanning manner, and in the scanning imaging process, the light spot sets the displacement distance and step length along the X-axis direction to move unidirectionally, and scans step by step. After reaching the set end point, the light spot returns to the starting position along the X-axis, and at this time the Y-axis takes one step, and the light spot continues to scan unidirectionally along the X-axis, and the cycle is repeated.

[0039] The specific working principle is as follows: Figure 4 , the laser is incident on the reflector 1, and reflected to the semi-transparent mirror 19, and focused on the sample through the objective lens 16. At the same time, the size of the light spot is photographed by the camera 2. By adjusting the Z-axis adjustment frame 15, the distance between the sample surface and the objective lens 16 is changed to change the size of the light spot to achieve the best focusing state. The control system controls the stepper motor 18 to drive the translation stage 17 to drive the reflector 1 and the semi-transparent mirror 19 to move linearly along the X-axis direction or the Y-axis direction to achieve two-dimensional scanning of the light spot. During the light spot scanning process, the photocurrent data of the sample is transmitted to the data acquisition system through the probe 11 connection, and the current data and the corresponding sample position are displayed and stored in real time in the form of images.

[0040] Embodiment 1, as Figure 5 As shown, the system is used to measure the surface image of silicon photovoltaic cells, which can clearly show the "mountain" electrode structure of silicon photovoltaic cells, proving that the present invention can be used for 11×11mm 2 Area photocurrent scanning imaging.

[0041] The specific steps are as follows:

[0042] Step 1: Solder metal wires to the positive and negative pins of the silicon photovoltaic cell and connect them to the source meter. Set the driver subdivision number to 1600 (the lead screw lead of the translation stage 17 is 0.5 mm).

[0043] Step 2: Turn on the control system of the photocurrent scanning system, the stepper motor 18 drives the optical scanning component to initialize, and inputs parameters such as bias voltage on the source meter.

[0044] Step 3: Move the two-dimensional sample stage 14 to move the sample to a suitable position below the light spot.

[0045] Step 4: Adjust the distance between the sample and the objective lens 16, use the camera 2 to shoot the spot size in real time, and adjust the spot to the minimum.

[0046] Step 5: Make voltage-current and time-current measurements to ensure circuit continuity.

[0047] Step 6: Set the step distance of the X-axis and Y-axis to 11mm and the step length to 0.22mm, and start scanning in a unidirectional scanning mode. During the scanning process, the intensity map is used to display the current intensity of each position coordinate in real time, and the current data of each coordinate position is stored in real time.

[0048] Step 7: Scanning is finished, and the measurement is ended, or according to the tested photocurrent intensity value, an area of ​​interest can be selected for more detailed scanning.

[0049] Embodiment 2, as Figure 6 As shown, the difference from Example 1 is that the area between the silicon photovoltaic cell electrodes is covered with a "South" printed on paper with a size 5 font, and the step distance of the X and Y axes is 3 mm and the step length is 0.075 mm. Figure 6 The photocurrent results obtained by scanning clearly show the word "South".

[0050] Embodiment 3, as Figure 7 As shown, the difference from Example 1 is that the area between the silicon photovoltaic cell electrodes is covered with 360 LPI grating strips, and the step distance of the X and Y axes is 0.2 mm and the step length is 5 μm. Figure 7 The photocurrent results obtained by scanning clearly show the grating structure, and the repetition period between the lines is 70μm, which is consistent with the theoretical value of 70.6μm.

[0051] Embodiment 4, as Figure 8 As shown, the difference from Example 1 is that the area between the silicon photovoltaic cell electrodes is covered with 360 LPI grating strips, and the step distance of the X and Y axes is 0.1 mm and the step length is 2.5 μm. Figure 8 The photocurrent results obtained by scanning clearly show the grating structure, proving that the spatial resolution of the system can reach 2.5μm.

[0052] Embodiment 5, as Fig. 9 As shown, the difference from Example 1 is that the Cu2ZnSnS4 solar cell is placed on the sample stage, and the step distance of the X and Y axes is 2 mm and the step length is 0.05 mm. Fig. 9 The photocurrent results obtained by scanning show that a dark area of ​​current appears in the upper right part of the battery, and a bright spot with larger current appears in the lower right corner, proving that the Cu2ZnSnS4 battery has many defects.

[0053] Compared with the prior art, the present invention realizes two-dimensional scanning of the light beam by using a light beam scanning device, realizes light spot focusing by using a semi-transparent and semi-reflective mirror 19 and a camera 2, and realizes large-area, high-spatial-resolution photocurrent scanning in combination with a unidirectional scanning method. It avoids the problem of frequently welding leads on the sample electrode when measuring different devices caused by the sample stage scanning method, and also avoids the problems of limited scanning range, image distortion and complex optical path system caused by the galvanometer scanning method. The system structure of the present invention is simple and easy to operate.

[0054] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A large-area photocurrent scanning imaging system, comprising a placement platform (7), a beam scanning device, a sample placement device and a probe device, characterized in that: The light beam scanning device comprises a reflector (1), a semi-transparent and semi-reflective mirror (19), an objective lens (16), a camera (2), a base plate (20), a displacement stage (17) and a driving component (6), wherein: the displacement stage (17) is slidably arranged on the placement platform (7), the base plate (20) is fixedly mounted on the displacement stage (17), the reflector (1) and the semi-transparent and semi-reflective mirror (19) are fixedly mounted on the base plate (20), and the mirror surfaces of the two mirrors face each other, the camera (2) is arranged above the semi-transparent and semi-reflective mirror (19), the objective lens (16) is embedded in the base plate (20) and is located below the semi-transparent and semi-reflective mirror (19), and the driving component (6) is provided with two groups, both of which are arranged on the placement platform (7) and are respectively connected to two adjacent sides of the displacement stage (17) to drive the displacement stage (17) to move along the X-axis or Y-axis direction; The sample placement device comprises a two-dimensional sample stage (14) and a Z-axis adjustment frame (15), wherein the Z-axis adjustment frame (15) is arranged below the placement platform (7), and the two-dimensional sample stage (14) is rotatably connected to the Z-axis adjustment frame (15) for placing samples; The probe device comprises two three-axis adjustable displacement platforms (9), a probe connecting rod (10) and a probe (11), wherein the two three-axis adjustable displacement platforms (9) are symmetrically arranged on both sides of the two-dimensional sample platform (14), one end of the probe connecting rod (10) is connected to the execution end of the three-axis adjustable displacement platform (9), and the probe (11) is installed at the other end of the probe connecting rod (10) and contacts the positive electrode or the negative electrode of the sample.

2. A large-area photocurrent scanning imaging system according to claim 1, characterized in that: The driving assembly (6) comprises a stepper motor (18) and a lead screw, wherein the stepper motor (18) is mounted on the placement platform (7), the lead screw is connected to the output end of the stepper motor (18), and is connected to the moving platform via a nut in the lead screw, so as to realize the linear motion of the moving platform.

3. A large-area photocurrent scanning imaging system according to claim 1, characterized in that: A housing (5) is installed on the outer periphery of the bottom plate (20), a plurality of first pillars (4) are installed on the bottom plate (20), a base (3) is installed on the first pillars (4), the camera (2) is fixedly installed on the base (3), and the first pillars (4) do not block the mirror surfaces of the reflector (1) and the semi-transparent and semi-reflective mirror (19).

4. A large-area photocurrent scanning imaging system according to claim 1, characterized in that: The bottom plate (20) is provided with a through hole for installing the objective lens (16), and the objective lens (16) is located above the two-dimensional sample stage (14) and is used to focus a light spot on a sample placed on the two-dimensional sample stage (14).

5. A large-area photocurrent scanning imaging system according to claim 1, characterized in that: A plurality of second pillars (8) are installed on the lower surface of the placement platform (7), and the Z-axis adjustment frame (15) is slidably installed on one of the second pillars (8) to realize the up and down movement of the two-dimensional sample stage (14).

6. A large-area photocurrent scanning imaging system according to claim 1, characterized in that: A plurality of third pillars (13) are arranged below the three-axis adjustable displacement platform (9), a support plate (12) is mounted on the third pillars (13), and the three-axis adjustable displacement platform (9) is fixedly mounted on the support plate (12).

7. A large area photocurrent scanning imaging system according to claim 1, characterized in that: It also includes a data acquisition system and a control system. The data acquisition system includes positive and negative electrode wires and a source meter. One end of the positive and negative electrode wires are respectively connected to two probes (11), and the other end is connected to the source meter, which is used to measure the photocurrent data of the sample and transmit, display and store it; the control system is electrically connected to the driving component (6) and is used to control the scanning path of the light beam scanning device.

8. A large area photocurrent scanning imaging system according to claim 7, characterized in that: The control system controls the driving component (6) so that the light spot generated in the light beam scanning device performs light beam scanning in a unidirectional scanning manner, and in the scanning imaging process, the light spot moves unidirectionally along the X-axis direction with a set displacement distance and step length, and performs step-by-step scanning. After reaching the set end point, the light spot returns to the starting position along the X-axis, and at this time, the Y-axis steps one step, and the light spot continues to perform unidirectional step-by-step scanning along the X-axis, and the cycle is repeated.

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