During cell production, the thermal diffusion process often affects numerous factors in the performance of TOPCon solar cells, resulting in changes in cell performance. In order to scientifically evaluate the degree of influence of the thermal diffusion process on the performance of TOPCon solar cells

Thermal diffusion and its effect on TOPCon performance factors

The thermal diffusion process is an important step in the preparation of TOPCon solar cells, which is mainly used to form doped regions on the surface of silicon wafers, so as to achieve the formation of P-N junctions and selective collection of carriers. There are two main types of thermal diffusion processes: displacement diffusion and interstitial diffusion. Alternate diffusion refers to the position of impurity atoms replacing silicon atoms to form a doped region; Interstitial diffusion refers to impurity atoms filling the voids in the silicon lattice, forming a doped area.

Effect on the passivation effect of the TOPCon interface

The thermal diffusion process will affect the interfacial density of the silicon wafer surface, thus affecting the interfacial passivation effect. The lower the density of states at the interface, the better the interface passivation, the less carrier recombination, and the higher the open-circuit voltage. In general, alternate diffusion is more beneficial than interstitial diffusion to reduce the interfacial density of states because it reduces lattice distortion and vacancy defects. Therefore, in TOPCon solar cells, a better interface passivation effect can be obtained by using the substitution diffusion process.

Effect on selective collection of TOPCon carriers

The thermal diffusion process affects the selective collection of carriers on the surface of the wafer, which affects the fill factor and short-circuit current. The higher the carrier selective collection capability, the higher the fill factor and short-circuit current. In the thermal diffusion process, cell manufacturers usually use interstitial diffusion for preparation, because interstitial diffusion is easier to achieve process stability and controllability than relocation-based diffusion. The reaction rate and doping concentration of interstitial diffusion are more simple and linear as a function of temperature. Therefore, in TOPCon solar cells, the interstitial diffusion process can be used to achieve higher process stability and controllability.

Impact on TOPCon process stability and controllability

The thermal diffusion process is affected by a variety of factors such as temperature, time, pressure, atmosphere, etc., which affects the stability and controllability of the process. The more stable and controllable the process, the more uniform and reliable the battery performance will be. When using the two diffusion types for thermal diffusion processes, it is important to understand that interstitial diffusion is easier to achieve process stability and controllability than relocation-based diffusion, because the reaction rate and doping concentration of interstitial diffusion are more simple and linear in relation to temperature.