01. Background Introduction
HJT cells, or heterojunction cells, are a type of solar cell with a special structure. They are characterized by depositing an amorphous silicon thin film on crystalline silicon to form a PN heterojunction.
HJT battery structure:
The main processes for producing HJT photovoltaic cells include:
Sorting, pre-cleaning, texturing and cleaning, PECVD coating, PVD coating, impurity removal, screen printing, curing and testing sorting, etc.
Getter process
A P-source layer is formed on the surface of the silicon wafer by means of tubular diffusion or chain coating of P-source. The silicon wafer is then subjected to high-temperature treatment at 700~800°C. After high-temperature diffusion, a PSG and P-heavy doped layer is formed on the surface of the silicon wafer. Under the influence of high temperature and impurity concentration gradient, the metal impurities in the silicon wafer extend to the surface. Through subsequent cleaning processes, this impurity layer can be removed, thereby improving the quality of the silicon wafer.
Advantages of gettering
Raw material cost reduction
This can reduce the requirements for silicon raw material procurement for HJT batteries, thereby reducing silicon costs.
High efficiency
It can improve the efficiency of HJT cells. Googling can reduce minority carrier recombination centers in silicon wafers, increase the open-circuit voltage of cells, and improve the photoelectric conversion efficiency of cells by more than 0.15%.
economic
It can improve the economics of HJT cells. By improving efficiency, the cost of silicon per watt can be reduced. In the cell module segment, the cost of non-silicon components, except for equipment investment, will be reduced. It is estimated that the introduction of gettering process can reduce the cost of HJT modules by about 0.6 cents/W.
02. Equipment Introduction
HJT sanitary suction equipment:
The HJT getter equipment performs a gettering process on silicon wafers with impurities to reduce the impurity content on the surface of the wafers, and then the processed wafers flow into the next process.
The HJT getter device consists of 13 steps:
Entering the flower basket track
The AGV transports a full basket (loaded with silicon wafers that need to be put into the getter process) to the track docking point. After the AGV docks with the getter equipment, the full basket flows into the upper layer of the basket track.
robotic arm gripping I
The robotic arm grabs a full flower basket from the upper flower basket track and places it on the transplanting unit, while simultaneously reading the flower basket's RFID and uploading the information to the MES system.
Transplanting I
The transplanting unit transports the flower basket to the suction cup pick-up point, where the silicon wafer is pushed out by the lifting and lateral movement of the top teeth for the suction cup to pick up.
Suction cup suction I
Two suction cups pick up the unprocessed silicon wafers from the basket and place them in quartz boats on the left and right sides. After loading the silicon wafers, the quartz boats are moved to different positions.
Grab I
The XZ gripper picks up the quartz boat from the boat tray and places it onto the docking host track.
Enter host
The quartz boat is transferred from the docking host to the main unit via the track.
Host getter
The host machine performs gettering on the silicon wafers inside the quartz boat.
Outgoing host
The docking host track receives the quartz boats sent by the host and reads the boat number. The temporary storage platform is used to store excess quartz boats.
Grab II
The XZ gripper will grab the quartz boat on the docking host track or temporary storage platform and place it onto the boat tray.
Suction Cup Extraction II
The suction cups extract the processed silicon wafers from the quartz boat and place them into the basket, while the top teeth lift up to receive the silicon wafers lowered by the suction cups.
Transplanting II
After the flower basket is filled with silicon wafers, the transplanting unit transports the full flower basket to the robotic arm's gripping position.
robotic gripper II
The robotic arm grabs the full flower basket and moves it to the lower flower basket track.
Flower basket track
The flower basket track transports the finished full flower baskets to the track docking point, where AVG receives the flower baskets and prepares them for the next process.
03. Technological Challenges
Difficulty A
The overall solution requires the use of multiple devices, each supporting different communication protocols, resulting in complex wiring.
Solution:
The system utilizes the Hechuan HCQ5P series controller, which supports multiple protocols including EtherCAT, Ethernet/IP, OPC UA, Modbus TCP, and Modbus RTU. Its rich interface options allow for flexible compatibility with field devices. Connecting to servo devices via the EtherCAT bus protocol reduces cabling and ensures more stable and efficient communication.
Difficulty B
Based on actual production needs, the HJT getter solution needs to switch between single loading mode, single unloading mode, or loading/unloading mode according to the signal sent by the main unit.
Solution:
Hechuan HJT getter solution has three modes:
Single-load mode: The main unit sends an empty quartz boat, and the transfer unit and XZ gripper move to load the unprocessed silicon wafer onto the quartz boat;
Single unloading mode: The main unit sends a full quartz boat, and the transfer unit and XZ gripper move to place the gotted silicon wafers into the basket;
Loading and unloading mode: Loading unprocessed silicon wafers and unloading processed silicon wafers are performed alternately.
The three modes automatically switch based on production signals, and customers can also manually switch modes on the HMI. After a successful mode switch, some request signals are automatically cleared, allowing the equipment to accurately switch to the new mode without stopping the machine.
04. Hechuan Plan
Topology graph
Performance metrics:
1. Getter efficiency of raw silicon wafers: 10000pcs/h
Advantages of the solution:
Reliable and stable
The system utilizes a complete control solution from Hechuan, consisting of an HCQ5P controller, Q-series modules, X5FB-series servo motors, and X2-series servo motors. It offers stable and efficient communication, high precision, and low error. The HCQ5P device features a rich array of interfaces, supports multiple protocols, and can connect to third-party devices through these interfaces.
High efficiency
The Hechuan HJT impurity suction solution is divided into two sides, A and B, which saves the waiting time generated during quartz boat scheduling and greatly improves the efficiency of single loading, single unloading and loading and unloading modes.
Cost saving
The HCQ5P communicates with the AGV, automating the flow of flower baskets and saving manpower.
