Minimizing light-induced degradation of the Al₂O₃ rear passivation layer for highly efficient PERC solar cells

Commercializing a highly efficient passivated-emitter-and-rear-cell solar cell requires high passivation quality and stability of the cell's Al₂O₃ layer. This paper reports on light-induced degradation (LID) of the Al₂O₃ layer and the effects of post-annealing temperatures after light soaking on the passivation quality. To understand the LID phenomenon of the Al₂O₃ passivation layer, we used a Ga-doped Si wafer that prevented boron-oxygen LID effects. The fabrication process was carried out on large-area (156 × 156 mm²), commercially available, (100)-oriented Ga-doped Czochralski(Cz) Si wafers in the pilot line. Before and after light soaking, the effective lifetime was measured using Sinton's quasi-steady-state photoconductance as a function of annealing temperature. Chemical binding structures near the interface of the Al₂O₃ film and Si wafer were investigated using X-ray photoelectron spectroscopy (XPS). The passivation quality and light-induced degradation showed the best performance at an annealing temperature of 600^◦C. Analysis of XPS data revealed that the chemical binding structures at the interface of the Al₂O₃ layer and Si wafer were stabilized by optimizing the annealing condition of the Al₂O₃ layer. By optimizing an industrially feasible Al₂O₃ passivation process, an efficiency of 20.1% was achieved on large-area, commercial-grade Cz c-Si wafers.