Theoretical studies of silicon hetero-junction solar cells with rib structure

Abstract

The open-circuit voltage of a solar cell is known to increase with deceasing wafer thickness if the cell is adequately passivated. However, it is not easy to handle very thin wafers because they are brittle and are subject to warpage. To provide thinned wafers that have adequate mechanical strength, we proposed a thin Si wafer-based solar cell that uses a rib structure in a previous work. We formed a lattice-shaped rib structure on the rear side of a thin Si wafer to improve the wafer's strength and fabricated the conventional Si hetero-junction structure by depositing hydrogenated amorphous Si on the wafer. For optimum design of the rib structure cell, we analytically studied the effect of rib dimensions on wafer strength and photovoltaic characteristics. A simplified structural analysis was performed to investigate the mechanical strength of the rib structure for various rib dimensions. Photovoltaic characteristics of rib structure silicon hetero-junction cells were also studied by a two-dimensional device simulator to understand the effect of rib dimensions. From these analyses, we theoretically demonstrated that the rib structure cell is a very good candidate to realize thin wafer Si solar cell, and can achieve both mechanical strength and electrical performance of thin Si solar cells.