In the current photovoltaic industry, as the photoelectric conversion efficiency of solar cells continues to improve, traditional screen printing technology faces many challenges, especially in terms of accuracy and line uniformity. In response to these challenges, advanced automated image measurement technology has become the key to improving production efficiency and product quality. As an outstanding representative of this technology, Vision Measuring Machine VMM Pro has a high-resolution camera-based measurement system that can quickly and accurately measure various parts and many other advanced functions, greatly optimizing the screen printing process.

Improvement of photovoltaic cell screen printing process using automated vision measurement technology

The latest research shows that screen printing performance can be significantly improved by optimizing paste formula and finger design combined with advanced automated vision measurement technology. In an experiment, cell with side length of 125mm × 125mm and line width of 165mm was used, paste with excellent performance was selected and the positive electrode finger was redesigned to match the resistance requirements. The improved finger design has improved both the short-circuit current (ISC) and open-circuit voltage (UOC). The conversion efficiency of the tested cell reached 17.58%, which is about 0.3 percentage points higher than the standard process.

Schematic diagram of screen printing principle

Therefore, optimizing the paste and finger in the screen printing process can achieve an overall improvement in the efficiency of monocrystalline silicon solar cells. At the same time, timely adjustment of process parameters can reduce the occurrence of failures and ensure the stability of the printing process and product consistency. Vision Measuring Machine VMM PRO is equipped with a variety of geometric measurement functions and calculator functions, which can calculate various complex formulas and automatically output the results to reports. Its fast and accurate image focusing function allows one focusing to be completed in just 1 second, greatly improving measurement efficiency and accuracy.

Solar cell surface defect detection method based on finger detection

In recent years, visual machine-based surface defect detection of solar cells has been the main development trend. Existing technologies establish various types of mathematical models based on the characteristics of defects, such as gradient features, clustering algorithms, Frequency domain analysis and matrix decomposition, etc. However, these methods all have the problem of insufficient generalization ability, that is, they are only suitable for the detection of certain types of defects. For example, detection methods based on gradient features and clustering algorithms are suitable for crack type defect detection. Detection methods based on frequency domain analysis and matrix decomposition are more suitable for strip and partition-dispersed defect detection.

Schematic diagram of solar cell structure

In contrast, the newly invented solar cell surface defect detection technology based on finger detection can meet different types of defect detection. First, the cell surface image is preprocessed through image scaling and median filtering; Secondly, a finger detection method is used to delete the busbar and fingers in the cell surface image; Subsequently, a processing method that combines superpixel segmentation and adaptive thresholding is used to detect defective areas in the finger-free image, and the initial detection result map is obtained; Finally, the initial detection result map is post-processed through image scaling to obtain the final detection result map.

Calculate the grayscale sum of each row and column of the preprocessed image

Among them, (x, y) represents the grayscale value of the pixel in the xth row and yth column of the image, SHx represents the grayscale sum of all pixels in the xth row of the image, detects the position of the busbar and finger, and represents the grayscale value of all pixels in the yth column of the image. Grayscale sum, k, g represent the number of rows and columns of the image.

This invention of deleting busbar and finger not only has lower requirements for the collection quality of solar cell surface images, but also has faster detection speed and finger processing while maintaining a high detection accuracy, which is beneficial to improving the quality of monocrystalline silicon solar cells. Quality inspection efficiency and factory qualification rate are of great significance. Most finger detection instruments can only detect the parameters of the finger within a single coordinate area during measurement, resulting in limited measurement data and difficulty in quickly and effectively calculating the silver paste coverage of the cell. In contrast, the Vision Measuring Machine produced by Millennial Solar has an exclusive metal coverage measurement. The Mview software equipped with this function can automatically measure the silver paste area of the entire cell with one click, thereby helping manufacturers evaluate the cost of solar cells to achieve the effect of cost reduction and growth!

Vision Measuring Machine

E-mail: market@millennialsolar.com

Vision Measuring Machine is used to detect the image, 2D plane, finger width, printing effect, etc. of photovoltaic stencils. The equipment is equipped with a measurement system based on a high-resolution camera, which can quickly and accurately measure various parts.

● LED light source to realize a variety of lighting methods

● Focus repeatability can reach 0.002mm~0.003mm

●LED optical system, display resolution up to 0.0001mm

●One-click document and data visualization function software

Vision Measuring Machine VMM PRO not only optimizes the accuracy and efficiency of screen printing, but also enables automated measurement technology to monitor and adjust key parameters in the printing process in real time, improving the overall performance of the cell. In this way, it not only stabilizes the production quality, but also adds a guarantee to the market competitiveness of solar cells. VMM PRO's technological innovation and application results prove its key role in promoting the progress of the photovoltaic industry.