A large-area photocurrent scanning imaging system

Abstract

The application discloses a large-area photocurrent scanning imaging system and belongs to the technical field of defect detection of solar cells and photodetectors. In the application, driving devices are connected to two adjacent sides of a displacement plate, the displacement plate drives a light spot on the surface of a sample to move along the X-axis or Y-axis direction through a reflecting mirror, a half-transmitting and half-reflecting mirror and an objective lens, two-dimensional scanning of the light spot is realized, the scanning mode is one-way scanning, the resolution is improved, the problem that different devices need to be frequently welded with lead wires on electrodes during measurement caused by the sample stage scanning mode is avoided, and the problems of limited scanning range, image distortion and complex optical path system caused by the galvanometer scanning mode are avoided. In addition, the half-transmitting and half-reflecting mirror, the camera and the Z-axis adjusting frame are combined, the light spot can be adjusted to be small enough, the spatial resolution of the photocurrent scanning imaging is increased, and the structure is simple and the operation is convenient.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of defect detection of solar cells and photodetectors, and particularly relates to a large-area photocurrent scanning imaging system. BACKGROUND

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

[0003] As a non-destructive technology, photocurrent scanning imaging technology can directly obtain the photodetection response image of a photodetector. This technology reveals the defects, spatial uniformity, diffusion length, local efficiency, and p-n junction (including junction area, junction depth, and leakage current position) of the device by scanning the sample and capturing the local photocurrent distribution. These information is of great significance for further optimizing the structure of the device and improving the photovoltaic conversion efficiency, and thus has attracted widespread attention in the scientific research and industrial fields.

[0004] The current common photocurrent scanning imaging methods mainly include two types: (1) a displacement table is used to drive the sample to move in two dimensions. In this method, the electrode of the sample is welded with a lead, the displacement table is driven to move along the X and Y axes, and thus the sample surface is scanned point by point. This method needs to weld a lead on the electrode of the sample, which is not as convenient as the probe connection, and the difference in the resistance of the welding points will also affect the performance comparison between different devices. (2) a scanning mirror is used to drive the light spot to scan the sample in two dimensions. In this method, the sample is fixed, the positive and negative electrodes of the device can be directly connected by using a probe, the direction of the light beam is adjusted by the scanning mirror, and the light spot is scanned 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 system.

[0005] Therefore, there is an urgent need for a large-area photocurrent scanning imaging system to solve the defects in the prior art, provide an efficient and accurate imaging scheme, and meet the defect detection and performance evaluation requirements of large-area photodetectors. SUMMARY

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

[0007] In order to achieve the above object, the present application provides the following technical scheme: a large-area photocurrent scanning imaging system, comprising a placing platform, a light beam scanning device, a sample placing device and a probe device, the light beam scanning device comprising a mirror, a half-mirror, an objective lens, a camera, a base plate, a displacement table and a driving assembly, wherein: the displacement table is slidingly arranged on the placing platform, the base plate is fixedly installed on the displacement table, the mirror and the half-mirror are fixedly installed on the base plate, and the mirror surfaces of the two are opposite to each other, the camera is arranged above the half-mirror, the objective lens is embedded in the base plate and located below the half-mirror, the driving assembly is provided with two groups, which are arranged on the placing platform and connected with the adjacent two sides of the displacement table respectively, so as to drive the displacement table to move along the X-axis or Y-axis direction;

[0008] The sample placing device comprises a two-dimensional sample table and a Z-axis adjusting frame, the Z-axis adjusting frame is arranged below the placing platform, and the two-dimensional sample table is rotationally connected with the Z-axis adjusting frame and used for placing a sample.

[0009] The probe device comprises two three-axis adjusting displacement tables, a probe connecting rod and a probe, wherein the two three-axis adjusting displacement tables are symmetrically arranged on the two sides of the two-dimensional sample table, one end of the probe connecting rod is connected with the execution end of the three-axis adjusting displacement table, and the probe is installed at the other end of the probe connecting rod and abuts against the positive electrode or negative electrode of the sample.

[0010] In a further embodiment, the driving assembly comprises a stepping motor and a lead screw, the stepping motor is installed on the placing platform, the lead screw is connected with the output end of the stepping motor, and the displacement table is connected with the lead screw through a nut in the lead screw, so as to realize the linear motion of the displacement table, provide power for the light beam scanning and determine the path of the light beam scanning.

[0011] In a further embodiment, an outer shell is installed on the outer periphery of the base plate, a plurality of first support columns are installed on the base plate, a base is installed on the first support column, the camera is fixedly installed on the base, and the first support column does not block the mirror surfaces of the mirror and the half-mirror, the outer shell protects the light beam scanning device from external influences, the base provides an installation carrier for the camera, and the first support column does not affect the reflection path of the light beam.

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

[0013] In a further embodiment, a plurality of second support columns are installed on the lower surface of the placing platform, the Z-axis adjusting frame is slidingly installed on one of the second support columns, and the up-down movement of the two-dimensional sample table is realized.

[0014] In further embodiments, a plurality of third support columns are arranged below the three-axis adjustment displacement table, a support plate is mounted on the third support columns, and the three-axis adjustment displacement table is fixedly mounted on the support plate to provide a mounting carrier for the three-axis adjustment displacement table.

[0015] In further embodiments, a data acquisition system and a control system are further included, the data acquisition system includes positive and negative electrode leads and a source table, one end of the positive and negative electrode leads is respectively connected to two probes, and the other end is connected to the source table, for measuring, transmitting, realizing and storing the photocurrent data of the sample; and the control system is electrically connected with the driving assembly to control the scanning path of the light beam scanning device.

[0016] In further embodiments, the control system controls the driving assembly to generate a light spot in the light beam scanning device to perform light beam scanning in a unidirectional scanning manner, and in the scanning imaging process, the light spot moves in a unidirectional manner along the X-axis direction with a set displacement distance and step length, gradually step scans, and after reaching the set end point, the light spot returns to the starting position along the X-axis, at which time the Y-axis step is further, and the light spot continues to step scan in a unidirectional manner along the X-axis, and the process is repeated in sequence.

[0017] Beneficial effects: In the present application, the driving device is connected to the two adjacent sides of the displacement plate, so that the displacement plate drives the light spot on the sample surface through the reflecting mirror, the half-mirror and the objective lens to move along the X-axis or Y-axis direction, realizing two-dimensional scanning of the light spot, and the scanning mode adopts unidirectional scanning, which improves the resolution, avoids the problem of frequent welding of lead wires on the electrode for measuring different devices caused by the scanning mode of the sample table, and also avoids the problems of limited scanning range, image distortion and complex optical system caused by the galvanometer scanning mode. In addition, through the half-mirror, the camera and the Z-axis adjusting frame, the light spot can be adjusted to be small enough, increasing the spatial resolution of the photocurrent scanning imaging, and the structure is simple and the operation is convenient. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 It is a structural schematic diagram of the hardware structure of the photocurrent scanning imaging system.

[0019] Figure 2 It is a 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 It is a schematic diagram of the internal optical path and light beam movement direction of the light beam scanning assembly.

[0022] Figure 5 It is a surface photocurrent scanning image of a silicon photocell in embodiment 1.

[0023] Figure 6 Photocurrent image of a silicon photocell with the surface covered with a printed paper of small five font printed "South" word in Example 2.

[0024] Figure 7 Photocurrent image of a silicon photocell with the surface covered with grating bars and scanning range of 0.2 x 0.2 mm 2 , step of 5 μm in Example 3.

[0025] Figure 8 Photocurrent image of a silicon photocell with the surface covered with grating bars and scanning range of 0.1 x 0.1 mm 2 , step of 2.5 μm in Example 4.

[0026] Figure 9 Photocurrent scanning image of a Cu2ZnSnS4 solar cell in Example 5.

[0027] Figures; 1, mirror; 2, camera; 3, base; 4, first pillar; 5, housing; 6, driving assembly; 7, placing platform; 8, second pillar; 9, three-axis adjusting displacement stage; 10, probe connecting rod; 11, probe; 12, support plate; 13, third pillar; 14, two-dimensional sample stage; 15, Z-axis adjusting frame; 16, objective lens; 17, displacement stage; 18, stepping motor; 19, half-transmission half-reflection mirror; 20, base plate. DETAILED DESCRIPTION

[0028] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the application. However, it will be apparent to one skilled in the art that the application can be practiced without one or more of these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the application.

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

[0030] Referring to Figure 3The light beam scanning device comprises a mirror 1, a half-mirror 19, an objective lens 16, a camera 2, a base plate 20, a displacement table 17 and a driving assembly 6. The displacement table 17 is slidingly arranged on the placing platform 7. The base plate 20 is fixedly arranged on the displacement table 17. The mirror 1 and the half-mirror 19 are fixedly arranged on the base plate 20, and the mirror surfaces of the mirror 1 and the half-mirror 19 face each other and are respectively used for reflecting and splitting the light beam. The camera 2 is arranged above the half-mirror 19 and is used for capturing a scanning image. The objective lens 16 is embedded in the base plate 20 and is located below the half-mirror 19 and is used for adjusting the light beam into a light spot and converging the light spot. The driving assembly 6 comprises two groups, which are arranged on the placing platform 7 and are respectively connected with the adjacent two sides of the displacement table 17, so as to drive the displacement table 17 to move along the X-axis or Y-axis direction and realize accurate movement.

[0031] Specifically, the driving assembly 6 comprises a stepping motor 18 and a lead screw. The stepping motor 18 is arranged on the placing platform 7. The lead screw is connected with the output end of the stepping motor 18 and is connected with the displacement table 17 through a nut in the lead screw, so as to realize the linear movement of the displacement table 17, provide power for the light beam scanning and determine the path of the light beam scanning.

[0032] As a preferred mode, the outer periphery of the base plate 20 is provided with an outer shell 5, which is used for protecting the light beam scanning device from the influence of the outside world and improving the stability of the light beam scanning. A plurality of first struts 4 are arranged on the base plate 20. A base 3 is arranged on the first struts 4. The camera 2 is fixedly arranged on the base 3 and is used for providing an installation carrier for the camera 2. The first struts 4 do not block the mirror surfaces of the mirror 1 and the half-mirror 19 and do not affect the reflection path of the light beam.

[0033] Continuously referring to Figure 1 and Figure 2 The sample placing device comprises a two-dimensional sample table 14 and a Z-axis adjusting frame 15. The Z-axis adjusting frame 15 is arranged below the placing platform 7. The two-dimensional sample table 14 is rotationally connected with the Z-axis adjusting frame 15 and is used for placing a sample and providing two-dimensional movement. Specifically, the lower surface of the placing platform 7 is provided with a plurality of second struts 8. The Z-axis adjusting frame 15 is slidingly arranged on one second strut 8 and is used for realizing the up-down movement of the two-dimensional sample table 14 and facilitating the adjustment of the size of the light spot.

[0034] As a preferred mode, the base plate 20 is provided with a through hole, which is used for arranging the objective lens 16. The objective lens 16 is located above the two-dimensional sample table 14 and is used for focusing the light spot on the sample placed on the two-dimensional sample table 14.

[0035] The probe 11 device comprises 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 two sides of a two-dimensional sample table 14 and are used for accurately adjusting the position of the probe 11, one end of the probe connecting rod 10 is connected with an 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 electrode or the negative electrode of the sample, so as to contact the sample and perform current scanning.

[0036] Specifically, a plurality of third support columns 13 are arranged below the three-axis adjustment displacement table 9, a support plate 12 is installed on the third support columns 13, and the three-axis adjustment displacement table 9 is fixedly installed on the support plate 12, so as to provide an installation carrier for the three-axis adjustment displacement table 9.

[0037] The data acquisition system comprises positive and negative electrode leads and a source table, one end of the positive and negative electrode leads is respectively connected with the two probes 11, the other end is connected with the source table, and the source table is used for measuring, transmitting, realizing and storing the photocurrent data of the sample; the control system is electrically connected with the driving assembly 6 and is used for controlling the scanning path of the light beam scanning device.

[0038] Specifically, the control system controls the driving assembly 6, so that the light spot generated in the light beam scanning device performs light beam scanning in a unidirectional scanning mode, and in the scanning imaging process, the light spot moves in a unidirectional mode along the X-axis direction with a set displacement distance and a step length, gradually performs step-by-step scanning, after reaching a set end point, the light spot returns to the starting position along the X-axis, at this time, the Y-axis step is further increased, and the light spot continues to perform step-by-step scanning in a unidirectional mode along the X-axis, and the process is sequentially cycled.

[0039] The specific working principle is as follows: refer to Figure 4 , the laser is incident on the reflecting mirror 1 and is reflected to the half-transmission half-reflection mirror 19, is focused on the sample through the objective lens 16, the size of the light spot is photographed by using the camera 2, the distance between the sample surface and the objective lens 16 is changed to change the size of the light spot by adjusting the Z-axis adjusting frame 15, so as to achieve the best focusing state. The control system controls the stepping motor 18, so as to drive the displacement table 17 to drive the reflecting mirror 1 and the half-transmission half-reflection mirror 19 to move in a straight line along the X-axis direction or the Y-axis direction, so as to realize two-dimensional scanning of the light spot, in the light spot scanning process, the photocurrent data of the sample are transmitted to the data acquisition system through the probe 11, and the current data and the corresponding sample position are displayed and stored in the form of images in real time.

[0040] In example 1, as shown in Figure 5 , the system is used for measuring the surface image of a silicon photocell, and the "mountain" shaped electrode structure of the silicon photocell can be clearly displayed, which proves that the present application can be used for photocurrent scanning imaging of a 11*11mm 2 area.

[0041] The specific operation steps are as follows:

[0042] Step 1: Solder metal wires on the positive and negative electrode pins of the silicon photocell, and connect to the source table, set the driver subdivision to 1600 (displacement table 17 screw lead is 0.5 mm).

[0043] Step 2: Turn on the control system of the photocurrent scanning system, and initialize the optical scanning assembly driven by the stepper motor 18, and input the bias voltage and other parameters on the source table.

[0044] Step 3: Move the two-dimensional sample table 14 to move the sample to the appropriate position under the light spot.

[0045] Step 4: Adjust the distance between the sample and the objective lens 16, and use the camera 2 to take real-time photos of the light spot size, and adjust the light spot to the smallest.

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

[0047] Step 6: Set the step distance of the X and Y axes to 11 mm and the step length to 0.22 mm, and start scanning in a one-way scanning mode. During scanning, use the intensity map to display the current intensity of each coordinate in real time, and store the current data of each coordinate in real time.

[0048] Step 7: Scan is complete, end measurement, or according to the photocurrent intensity value tested, select the area of interest for more detailed scanning.

[0049] Example 2, as shown in Figure 6 the difference from Example 1 is that the area between the silicon photocell electrodes is covered with a "South" printed paper printed with small five-point 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 "South" word.

[0050] Example 3, as shown in Figure 7 the difference from Example 1 is that the area between the silicon photocell electrodes is covered with a 360 LPI grating bar, 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 repeating period between the lines is 70 μm, which is consistent with the theoretical value of 70.6 μm.

[0051] Example 4, as shown in Figure 8 the difference from Example 1 is that the area between the silicon photocell electrodes is covered with a 360 LPI grating bar, 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 2.5 μm.

[0052] Example 5, as Figure 9 shown, differs from Example 1 in 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 size is 0.05 mm. Figure 9 For the obtained photocurrent results, a dark region of current appears in the right upper part of the cell, and a bright region of current appears in the right lower corner, proving that the Cu2ZnSnS4 cell has many defects.

[0053] Compared with the prior art, the present application realizes two-dimensional scanning of the light beam by using a light beam scanning device, realizes focusing of the light spot by using a half-transmission half-reflection mirror 19 and a camera 2, and realizes large-area and high spatial resolution photocurrent scanning in combination with a one-way scanning mode. The present application not only avoids the problem of frequent welding of lead wires on the sample electrode for measuring different devices caused by the sample stage scanning mode, but also avoids the problems of limited scanning range, image distortion and complex optical system caused by the galvanometer scanning mode. The present application has simple system structure and is easy to operate.

[0054] As described above, although the present application has been shown and described with reference to specific preferred embodiments, it is to be understood that such is by way of illustration and not of limitation. Various changes and modifications can be made therein without departing from the spirit and scope of the present application 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 beam scanning device includes a reflector (1), a semi-transparent mirror (19), an objective lens (16), a camera (2), a base plate (20), a displacement stage (17), and a drive assembly (6), wherein: the displacement stage (17) is slidably disposed on the placement platform (7), the base plate (20) is fixedly installed on the displacement stage (17), the reflector (1) and the semi-transparent mirror (19) are fixedly installed on the base plate (20), and their mirror surfaces face each other, the camera (2) is disposed above the semi-transparent mirror (19), the objective lens (16) is embedded in the base plate (20) and located below the semi-transparent mirror (19), and the drive assembly (6) has two sets, both disposed on the placement platform (7), and respectively connected to the adjacent two sides of the displacement stage (17), driving the displacement stage (17) to move along the X-axis or Y-axis direction; 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 located below the placement platform (7). The two-dimensional sample stage (14) is rotatably connected to the Z-axis adjustment frame (15) for placing samples. The probe device includes two triaxial adjustment displacement stages (9), a probe connecting rod (10), and a probe (11). The two triaxial adjustment displacement stages (9) are symmetrically arranged on both sides of the two-dimensional sample stage (14). One end of the probe connecting rod (10) is connected to the execution end of the triaxial adjustment displacement stage (9). The probe (11) is installed at the other end of the probe connecting rod (10) and abuts against the positive or negative electrode of the sample. The large-area photocurrent scanning imaging system 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 is connected to two probes (11) respectively, and the other end is connected to the source meter. It 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 beam scanning device. The control system controls the drive component (6) to make the light spot generated in the beam scanning device perform beam scanning in a unidirectional scanning manner. During the scanning imaging process, the light spot moves unidirectionally along the X-axis with a set displacement distance and step size, and scans step by step. After reaching the set endpoint, the light spot returns to the starting position along the X-axis. At this time, the Y-axis takes a step, and the light spot continues to scan unidirectionally along the X-axis, and so on.

2. The large-area photocurrent scanning imaging system according to claim 1, characterized in that, The drive assembly (6) includes a stepper motor (18) and a lead screw. 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 displacement stage (17) through a nut in the lead screw, so as to realize the linear motion of the displacement stage (17).

3. The large-area photocurrent scanning imaging system according to claim 1, characterized in that, The outer periphery of the base plate (20) is fitted with a shell (5), and a plurality of first pillars (4) are mounted on the base plate (20). A base (3) is mounted on the first pillar (4). The camera (2) is fixedly mounted on the base (3), and the first pillars (4) do not obstruct the mirror surface of the reflector (1) and the semi-transparent mirror (19).

4. The large-area photocurrent scanning imaging system according to claim 1, characterized in that, The base plate (20) has a through hole for mounting the objective lens (16), and the objective lens (16) is located above the two-dimensional sample stage (14) for focusing the light spot onto the sample placed on the two-dimensional sample stage (14).

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

6. The large-area photocurrent scanning imaging system according to claim 1, characterized in that, Multiple third pillars (13) are provided below the three-axis adjustable displacement stage (9), and a support plate (12) is installed on the third pillar (13). The three-axis adjustable displacement stage (9) is fixedly installed on the support plate (12).

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