Minimizing Light-Induced Degradation of the Al2O3 Rear Passivation Layer for Highly Efficient PERC Solar Cells

Abstract

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.