Investigation of different contact geometries for partial rear metal contact of high-efficiency silicon solar cells

In this paper, we have investigated the dependence of the parameters of partial rear metal contact (PRC) solar cells on two commonly used geometrical configurations, viz. grid contact and square contact. It is demonstrated that while the geometry of rear metallic contact having the same fractional coverage changes the base spreading resistance significantly, rear surface passivation and back reflectance depend only on the fractional coverage of the real metal contact and are independent of the geometry of the contact. The performed analysis indicates that the base spreading resistance is much higher for square contact cells compared to that of grid contact cells having the same fractional coverage. While open-circuit voltage and short-circuit current are found to be essentially independent of the contact geometry, the fill factor is significantly affected by the geometry, indicating that the design of high-efficiency cells with partial rear grid contact is less critical in comparison to that of square contact cells for optimized performance. Results indicate that for a 180 mu m cell, an efficiency enhancement of 14% is possible for < 10% fractional rear metallization over the baseline efficiency of about 19% for solar cells having full-area rear metallization. For 50 mu m thin cells, the corresponding improvement in efficiency is 17%, leading to 22% efficiency solar cells.