The front surface of TOPCON cells has the same structure as conventional N-type solar cells. The main difference is that an ultra-thin layer of silicon oxide is prepared on the back of the cell, and then a layer of doped silicon is deposited. The two together form a passivated contact structure, which effectively reduces surface recombination and metal contact recombination.
The excellent passivation effect of ultrathin silicon oxide and heavily doped silicon films causes the energy bands on the silicon wafer surface to bend, thereby forming a field passivation effect. This greatly increases the probability of electron tunneling, reduces contact resistance, and ultimately improves conversion efficiency.
Advantages of TOPCon batteries
1. Passivation Advantages: Surface passivation performance mainly depends on chemical passivation and field passivation. Thermally grown SiO2 has excellent chemical passivation capabilities. Heavy doping in polycrystalline silicon can induce band bending in silicon, causing the aggregation of majority carriers and the depletion of minority carriers at the interface, reducing recombination and playing a field passivation role.
2. Advantages of Metal-Contact Composites: Metal-contact composites have become a bottleneck limiting the efficiency of conventional solar cells. In industrial applications, metallization typically involves screen printing followed by high-temperature sintering. During this process, the metal paste "etches" into poly-Si, creating "spiking" and disrupting the passivation contact structure, resulting in a higher J0c in the metal contact region compared to the passivation region. However, with p+ poly and n+ poly metal-contact composites, even with the "spiking" damaging the passivation contact structure, the metal composite efficiency is significantly lower than that of conventional emitter/back surface fields.
3. Advantages of metal contact resistivity: In addition to metal contact recombination, the metal-semiconductor contact resistivity (ρc) is also crucial to the device performance of crystalline silicon solar cells. Good ohmic contact between metal and semiconductor helps to reduce resistance loss and improve the fill factor.
