Abstract
The effects of residual C on cell properties are investigated from the view point of thermal budget in the n-type bifacial cell processes. Implied Voc obtained from wafers with same Oi concentration depend on the thermal budgets decreases as the Cs concentration increases. The Voc values vary depending on the wafer with different growth cooling rate. To analyze the effect of thermal budget correspond to solar cell fabrication process, CZ wafers with almost the same Oi concentrations are prepared. One of the wafers with relatively high residual Cs concentration shows the longer lifetime than the initial value after the 950 oC annealing step. On the other hand, the lifetime of a wafer with relatively low Cs concentration dramatically decreased by the same process due to the O segregation. These results suggest that it is important to choose appropriate wafer specification, starting with feedstock material, for increasing the solar cell efficiency.
Highlights
For the crystalline silicon (Si) solar cell industry, it is required to reduce the production cost and increase the conversion efficiency
The effect of oxygen and carbon impurities on solar cell properties were investigated by applying a thermal budget during the n-type bifacial solar cell structure processes
These results indicated that other factors, in addition to Oi and Cs concentrations, determined the lifetime degradation due to the thermal budget corresponding to the cell fabrication processes
Summary
For the crystalline silicon (Si) solar cell industry, it is required to reduce the production cost and increase the conversion efficiency. Si wafers grown by the Czochralski process (CZ wafer) are widely used, because a relatively high conversion efficiency can be obtained with low cost. These wafers show a large amount of residual oxygen (Oi), which exists as interstitial incorporated during the crystal growth. Some of these Oi precipitate as silicon dioxide (SiO2) due to the high temperature processes during the cell fabrication. Those defects act as recombination centers, which decreases the short circuit current (Isc) and the open circuit voltage (Voc) in solar cell performances.[20,21,22] it is important to prevent this degradation of solar cell properties inducted by the precipitation during the cell fabrication
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