Multilevel metallization for large area point-contact solar cells

An analysis of the series resistances of different metallization schemes for large-area backside-contact (BC) solar cells is presented. The need for developing a multilevel metallization technology for such cells is demonstrated. The authors propose a new design for the metallization of BC cells that present a series resistance independent of the cell size. The particular features required for such a multilevel interconnection are studied, and a process using anodic oxidation of aluminum is presented. BC silicon solar cells of 0.64 cm² have been processed in this technology, resulting in 26.2% efficiencies at 10 W/cm² (100 suns AM1.5, 25.5 degrees C). Subsequent runs with a simplified process and a new cell design have given 27.3% efficiency cells. The cells have been soldered on alumina mounts. Results of thermal cycling are given.