Mechanism of Metallization-Induced Losses in the Rear-Side of Fully Screen-Printed p-type PERC Solar Cells

This article investigates metallization-induced recombination losses associated with the presence of silicon (Si) in the 1) rear passivation layers and 2) aluminum (Al) paste in fully screen-printed p-type passivated emitter and rear cell (PERC) solar cells. For 1), the rear sides of PERCs passivated with aluminum oxide films stacked with silicon nitride (SiN
_y
) films with various refractive indexes (n), as defined by the composition of the SiN
_y
films, were fabricated. Si-rich SiN
_y
films strongly degraded the implied open-circuit voltages of symmetrically passivated samples, that include cells. Elemental mapping analysis confirmed further metallization-induced losses at the cell level because of the formation of an Al-Si alloy within the passivation stacks, with the density of the alloy dependent on the refractive index. For 2), the rear sides of PERCs were metallized with Si-free Al paste or Al pastes that contain Si. High-Si paste had both good and bad effects: it produced thicker aluminum back surface fields but left partially-formed Al-Si alloy within the passivation films.