Analysis of the Bowing Phenomenon for Thin c-Si Solar Cells using Partially Processed c-Si Solar Cells

Abstract

The silicon wafers for solar cells on which the paste is deposited experience a bowing phenomenon. The thickness of commonly used c-Si wafers is 180 μm or more. When fabricating c-Si solar cells with this wafer thickness, the bowing value is 3 mm or less and the problem does not occur. However, for the thin c-Si solar cells which are being studied recently, the output reduction due to failure during manufacture and cracking are attributed to bowing. In generally, it is known that the bowing phenomenon arises mainly from the paste applied to the back side electrode of c-Si solar cells and the effects of SiNx (silicon nitride) and the paste on the front side are not considered significant. The bowing phenomenon is caused by a difference in the coefficient of expansion between heterogeneous materials, there is the effect of bowing on the front electrode and ARC. In this paper, a partially processed c-Si solar cell was fabricated and a bowing phenomenon variation according to the wafer thicknesses was confirmed. As a result of the experiment, the measured bow value after the firing process suggests that the paste on the front-side indicates a direction different from that of the back-side paste. The bow value increases when Al paste is deposited on SiNx. The fabricated c-Si solar cell was analyzed on basis of the correlation between the bowing phenomenon of the materials and the c-Si wafer using Stoney’s equation, which is capable of analyzing the relationship between bowing and stress. As a result, the bowing phenomenon of the c-Si solar cell estimated through the experiment that the back side electrode is the important element, but also the front electrode and ARC influence the bowing phenomenon when fabricating c-Si solar cells using thin c-Si wafers.