As a highly efficient solar cell technology with higher conversion efficiency and lower energy costs, photovoltaic TOPCon solar cells have received widespread attention. The development of production technology and the promotion of large-scale production have gradually reduced the cost of TOPCon solar cells, and will have obvious competitive advantages in the future market. Millennial Solar closely follows the development needs of users and the industry, proposes high-efficiency TOPCon cell research and development solutions, and develops the In-Line Thin Film Thickness Tester, which uses leading micro-nano film optical measurement technology to achieve an ultra-wide measurement range of 20nm-2000nm and 0.5 nm's ultra-high repeatability accuracy enables fast and automatic 5-point synchronous scanning of samples.

Principle of light injection annealing process

Efficient solar cells require good interface passivation and one-dimensional longitudinal transport as much as possible to maximize Voc and FF. Passivating contacts is one of the ways to achieve this function. Passivation silicon oxide between the poly-Si and Si substrate interface of the contact cell plays a very critical role in passivation. Silicon oxide reduces the interface state density between the Si substrate and poly-Si through chemical passivation. In heavily doped poly-Si, the concentration of majority carriers is much higher than that of minority carriers, which not only reduces the probability of electron-hole recombination, but also increases the conductivity to form selective contact of majority carriers. In the selective contact area, majority carrier transmission leads to resistance loss, while a small amount of minority carriers migrate to the metal contact area, causing recombination loss. The former corresponds to the contact resistance ρc, while the latter corresponds to the interface recombination current J0.

TOPCon solar cell structure

The process flow of the light injection annealing furnace: automatic loading (cell) → heating area (infrared lamp heating) → lighting area (LED light) → cooling → automatic unloading. Light injection annealing furnace process steps: the first step is to raise the temperature to activate the H atoms in the silicon nitride passivation film through the temperature rise; the second step is to control the valence state of the atoms through illumination so that they can be in the P+ emitter and N-type substrate and recombination center (Defects) combine to form a non-complex center. Finally, a good passivation effect is achieved and the purpose of improving Voc and FF is achieved.

 Effect of light injection annealing process on the electrical properties of N-TOPCon cells

Cells with the same efficiency level were used to compare the changes in various electrical performance parameters after the light injection annealing process.

Comparison of efficiency enhancement at different peak temperatures and light intensity during LED illumination

The process flow of the light injection annealing furnace: automatic loading (cell) → heating area (infrared lamp heating) → lighting area (LED light) → cooling → automatic unloading. Light injection annealing furnace process steps: the first step is to raise the temperature to activate the H atoms in the silicon nitride passivation film through the temperature rise; the second step is to control the valence state of the atoms through illumination so that they can be in the P+ emitter and N-type substrate and recombination center (Defects) combine to form a non-complex center. Finally, a good passivation effect is achieved and the purpose of improving Voc and FF is achieved.

Effect of light injection annealing process on the electrical properties of N-TOPCon cells

Cells with the same efficiency level were used to compare the changes in various electrical performance parameters after the light injection annealing process.

Monitoring passivation of symmetrical structures with different poly thicknesses before and after light injection

It can be seen from the figure that when the poly thickness of the back passivation layer is less than 150nm, the passivation performance is lost after the light injection annealing process; when the thickness is greater than or equal to 150nm, the passivation performance remains unchanged. As the poly thickness of the back passivation layer increases, the parasitic light absorption of the polysilicon layer will increase, reducing the light utilization efficiency. Therefore, the thickness of the passivation layer poly needs to comprehensively consider both parasitic absorption and passivation performance.

Effects of different light injection annealing processes on passivation properties of thin poly-Si

Take poly-Si double-sided symmetric structure test pieces with the same thickness and use different light injection annealing processes. Verify the effect of different light injection annealing processes on the passivation performance of thin poly-Si thickness cells. It can be seen from the figure that adjusting the light injection annealing temperature and light intensity does not improve the passivation performance of the thin poly passivation layer.

Passivation monitoring of 90nm thickness poly-Si symmetric structure before and after different light injection processes

In-Line Thin Film Thickness Tester

E-mail: market@millennialsolar.com

In-Line Thin Film Thickness Tester Poly5000 is specially designed for photovoltaic process monitoring. It can quickly and automatically scan the sample at 5 points simultaneously to obtain film thickness distribution information at different locations of the sample. The measurement size can be customized according to the size of the customer's sample.

● Effective spectral range 320nm~2400nm

● Fast, automatic 5-point synchronous scanning

● Repeatability accuracy <0.5nm

●Super wide measurement range 20nm~2000nm

●Online monitoring and detection to achieve zero fragmentation rate

● Realize automatic inspection of the entire production line, greatly saving inspection time

TOPCon solar cells use advanced processes and materials to improve the cell's conversion efficiency. High efficiency is one of the important goals of the photovoltaic industry, and cost reduction is one of the key factors driving this technology to compete in the market. TOPCon cell technology is still in the development stage, and new processes and improved materials are constantly being developed. Millennial Solar is committed to working with customers to improve the performance and competitiveness of TOPCon solar cells, and will continue to promote the development of the photovoltaic market through technological progress and innovation.