Excellent rear side passivation on multi-crystalline silicon solar cells with 20 nm uncapped Al2O3 layer: Industrialization of ALD for solar cell applications

Current bottlenecks for industrialization of Al₂O₃ deposited by Atomic Layer Deposition (ALD) for crystalline silicon solar cell applications are low growth rate and stability of thin and uncapped layers during co-firing. First results on the performance of a high throughput ALD proto-type, the Levitrack, are presented. Excellent passivation properties have been obtained after firing, for 12 nm thick films deposited on p-Cz (2.3 Ω.cm) with S_eff <; 15cm/s (Δn=3×10¹⁵ cm^-3). These layers are compatible with solar cells that operate at a maximum open-circuit voltage of 720mV. Furthermore, we report on the passivation of 20nm uncapped aluminum oxide layers on the rear of p-type mc-Si bifacial cells. LBIC measurements unveiled excellent passivation properties on areas covered by 20nm of Al₂O₃ characterized by an IQE of 91% at 980nm. Remarkably, these lifetime and cell results were obtained without lengthy post-treatments like forming gas anneal.