Effect of Silicon Thickness on Performance of Polycrystalline Silicon Solar Cells

In order to further reduce the cost of polysilicon solar cells, the effect of the thickness of the silicon wafer on the short-circuit current density, open-circuit voltage and efficiency of the polysilicon solar cells was investigated. It can be seen that under the premise that the performance of the polycrystalline silicon solar cell is not changed or increased, the thickness of the silicon wafer can be reduced to 200 um. If the thickness continues to be reduced, the performance of the battery will decrease.

1. Improving the photoelectric conversion efficiency and reducing the cost of solar cells is the main research direction of solar cells. Thin-film solar cells can significantly reduce the amount of materials used, which is the most effective means to reduce the cost of solar cells. Polycrystalline silicon solar cells account for about half of the world's solar cell market. Therefore, under the premise of ensuring the performance of the solar cell is unchanged or even increased, reducing the thickness of the silicon wafer of the polycrystalline silicon solar cell has important significance for reducing the cost of the photovoltaic energy.

2. Effects of Silicon Thickness on Short-Circuit Current Jsc One of the problems to face when using thinner polysilicon wafers is surface composite and base material quality. It has been experimentally confirmed that when SiNx is used as the front surface passivation layer and Al is used as the back surface field (BSF), when the thickness of the polysilicon wafer is greater than 200 μm, Jsc and the wafer thickness are independent of each other, and only the wafer thickness is less than 200 μm. Only decrease with the thickness. BSF can hinder the movement of the photogenerated minority to the back surface, reduce the back surface recombination, and facilitate the collection of carriers at the p/n junction. When the thickness is low, the absorption of the incident light by the substrate is reduced. At this time, the effect of BSF on the short-circuit current density of the solar cell is more pronounced. SiNx as a front surface passivation layer can reduce surface recombination and improve the quality of the base material. However, when the wafer thickness is very low, very low energy photons will pass through the wafer and cannot be absorbed, and Jsc will tend to decrease.

3. Effect of silicon wafer thickness on open circuit voltage Voc When using AL-BSF on the backside of a polysilicon solar cell, if the wafer thickness is greater than 200um, the open circuit voltage Voc is independent of the wafer thickness. The saturation current Jo of a silicon solar cell depends on the effective recombination speed.

4. Effect of Wafer Thickness Efficiency When the silicon wafer thickness is greater than 200 μm, the efficiency of the polysilicon solar cell using AL-BSF is independent of the wafer thickness. For silicon wafers less than 200um in thickness, the efficiency of the solar cell with high base quality will decrease as the thickness decreases. For solar cells with low base quality, the efficiency is still constant.

5. Conclusions In the standard industry, the 200um wafer thickness is the starting point for the reduction of the performance of polysilicon solar cells. When the thickness of the polysilicon wafer is less than 200 μm, the main electrical parameters of the polycrystalline silicon solar cell begin to decrease. When reducing wafer thickness to reduce photovoltaic costs, effective surface passivation methods are used to reduce surface recombination and improve base quality.