Knowledges

Overview of Topcon photovoltaic module technology and advantages

TOPCon (Tunnel Oxide Passivated Contact) photovoltaic (PV) module technology represents the latest advancements in the solar industry for improving cell efficiency and reducing costs. The core of the TOPCon technology lies in its unique passivation contact structure, which effectively reduces carrier recombination at the cell surface, thereby enhancing the cell's conversion efficiency.

Technical Highlights

1. Passivation Contact Structure: TOPCon cells prepare a super-thin oxide silicon layer (1-2nm) on the back of the silicon wafer, followed by the deposition of a doped polycrystalline silicon layer. This structure not only provides excellent interface passivation but also forms a selective carrier transport channel, allowing majority carriers (electrons) to pass through while preventing minority carriers (holes) from recombining, thus significantly increasing the cell's open-circuit voltage (Voc) and fill factor (FF).

2. High Conversion Efficiency: The theoretical maximum efficiency of TOPCon cells is as high as 28.7%, significantly higher than the 24.5% of traditional P-type PERC cells. In practical applications, the mass production efficiency of TOPCon cells has exceeded 25%, with potential for further improvement.

3. Low Light-Induced Degradation (LID): N-type silicon wafers have a lower light-induced degradation, meaning that TOPCon modules can maintain a higher initial performance in actual use, reducing performance loss over the long term.

4. Optimized Temperature Coefficient: The temperature coefficient of TOPCon modules is better than that of PERC modules, which means that in high-temperature environments, the power generation loss of TOPCon modules is smaller, especially in tropical and desert regions where this advantage is particularly evident.

5. Compatibility: TOPCon technology can be compatible with existing PERC production lines, requiring only a few additional devices, such as boron diffusion and thin-film deposition equipment, without the need for backside opening and alignment, simplifying the production process.

Production Process

The production process of TOPCon cells mainly includes the following steps:

1. Silicon Wafer Preparation: First, N-type silicon wafers are used as the base material for the cell. N-type wafers have higher minority carrier lifetime and better weak light response.

2. Oxide Layer Deposition: A super-thin oxide silicon layer is deposited on the back of the silicon wafer. The thickness of this oxide silicon layer is usually between 1-2nm and is the key to achieving passivation contact.

3. Doped Polycrystalline Silicon Deposition: A doped polycrystalline silicon layer is deposited on the oxide layer. This polycrystalline silicon layer can be achieved through low-pressure chemical vapor deposition (LPCVD) or plasma-enhanced chemical vapor deposition (PECVD) technology.

4. Annealing Treatment: High-temperature annealing treatment is used to change the crystallinity of the polycrystalline silicon layer, thereby activating the passivation performance. This step is crucial for achieving low interface recombination and high cell efficiency.

5. Metallization: Metal grid lines and contact points are formed on the front and back of the cell to collect photo-generated carriers. The metallization process of TOPCon cells requires special attention to avoid damaging the passivation contact structure.

6. Testing and Sorting: After the cell manufacturing is complete, electrical performance tests are conducted to ensure that the cells meet the predetermined performance standards. The cells are then sorted according to performance parameters to meet the needs of different markets.

7. Module Assembly: The cells are assembled into modules, typically encapsulated with materials such as glass, EVA (ethylene-vinyl acetate copolymer), and backsheet to protect the cells and provide structural support.

Advantages and Challenges

The advantages of TOPCon technology lie in its high efficiency, low LID, and good temperature coefficient, all of which make TOPCon modules more efficient and have a longer lifespan in actual applications. However, TOPCon technology also faces cost challenges, especially in terms of initial equipment investment and production costs. With continuous technological advancements and cost reduction, it is expected that the cost of TOPCon cells will gradually decrease, enhancing their competitiveness in the photovoltaic market.

In summary, TOPCon technology is an important direction for the development of the photovoltaic industry. It improves the conversion efficiency of solar cells through technological innovation while maintaining compatibility with existing production lines, providing strong technical support for the sustainable development of the photovoltaic industry. With continuous technological progress and cost reduction, TOPCon photovoltaic modules are expected to dominate the photovoltaic market in the future.