Metal-induced Recombination Losses associated with Si present within Passivation Layers and Aluminum Paste for PERCs

Abstract

We present metal-induced recombination losses associated with the silicon (Si) present both within rear passivation layers and in aluminum (Al) paste for passivated emitter and rear cells (PERCs) with full-area Al screen-printed contacts. In the former case, rear sides of PERCs passivated with aluminum oxide films stacked with silicon nitride (SiNy) films with various refractive indexes (n) defined by the composition of the SiNy films, were fabricated. As a result, the Si-rich SiNy films strongly degraded the open-circuit voltage of the cells. The elemental mapping analysis results clearly confirmed metal-induced further losses in cell level due to the concentration of an Al–Si alloy formed in the passivation stacks, where the density of the alloy is dependent on the refractive index. In the latter case, the rear sides of the PERCs were metallized with two different Al PERC pastes: 0% Si, or 25% Si. The resulting strong presence of Si in the Al paste gave both positive results owing to a thicker aluminum-back surface field and negative results owing to the partially formed Al–Si alloy within the passivation films.