Numerical simulation of bowing phenomenon in ultra-thin crystalline silicon solar cells

Abstract

In order to reduce the cost per watt of photovoltaic power generation, reducing the thickness of the crystalline silicon solar cell is a promising strategy. However, with a thinner silicon wafer, the bowing depth induced by two distinctive thermal expansion rates between the silicon substrate and the aluminum layer in the rear side grows exponentially. Excessive bowing can cause damage such as breakage and microcracks to the silicon wafer, eventually resulting in ruining the cell. The detail understanding of the bow phenomenon is undoubtedly significant in thin crystalline silicon solar cell fabrication. In this study, we worked on developing an accurate numerical technique that can calculate the correct deformation of the bow, especially for an ultra-thin silicon solar cell with <100μm thickness. To validate the simulation results, we compared them with experimental results from a reverse engineering technique based on an accurate 3D image scanner. The effect from the thickness of the silicon and aluminum layer on the bow was investigated by the non-dimensional deformation ratio. The results revealed that the bowing degree increases with a decreasing thickness of the silicon layer and an increasing thickness of the aluminum layer. Compared to the conventional two-layer models including silicon and aluminum layers, correct modeling of the thickness of the recrystallized layer has been identifed as key factor for accurate simulation. The numerical process proposed in this study can be used as a predicting tool for testing various processing conditions in terms of bowing phenomena. Furthermore, it can be served to generate a suitable design guideline for the mass production of thin crystalline silicon solar cells.