Modeling of Edge Losses in Al-BSF Silicon Solar Cells

Specific photovoltaic (PV) applications can require the use of limited-area solar cells. In that case, the edge of the device can have a considerable influence on the conversion efficiency. In this study, limited-area solar cells were fabricated by laser scribing and subsequent mechanical cleavage of large aluminum back surface field solar cells. First, laser parameters were optimized in order to limit the loss in conversion efficiency. It was shown that laser scribing must be performed on the rear side of the device in order to avoid the formation of shunts. The variation in the laser conditions could not improve the cell efficiency, as the discontinuity of the crystal lattice has a prominent impact compared with defects induced by laser scribing and cleaving. The fabrication of various cell geometries confirmed that the reduction of edge recombination was possible by simply limiting the cell periphery over its area. Specific characterization of the fabricated devices was carried out in order to understand the influence of the cell area on the performance. Using the two-diode model, two methods were used to extract the saturation current densities induced by metallization-related recombination (J
_0m
) and edge recombination (J
_0e-dr
). From this model, it is thus possible to predict the open-circuit voltage of any cell format. This study is particularly relevant for specific PV applications requiring the use of small-area solar cells and can be applied to other silicon cell technologies.