Aluminum fire-through with different types of the rear passivation layers in crystalline silicon solar cells

Aluminum penetration during dielectric layer annealing on silicon was studied for solar cell application. The thickness and uniformity of the aluminum-doped region was examined in variously annealed dielectric layers. Three types of silicon wafers were used with (1) bare Si, (2) SiO₂ layer (80 nm)/Si, and (3) SiN_X layer (80 nm)/Si. Local metal contacts were made through laser-drilled holes, and annealing was tested at four different temperatures. Reactions between aluminum and silicon were observed by cross-sectional scanning electron microscopy. Reactions occurred at 660 °C on bare Si and at ca. 690 °C on the SiO₂ layer. However, the SiO₂ did not withstand annealing at higher temperatures. The SiN _X layer showed no Al-BSF region in samples annealed at up to 760 °C, making it a suitable material for rear passivation layers in local contact Si solar cells. A Si solar cell fabricated by laser drilling and screen printing showed an efficiency of 12.41% without optimization.