Al2O3 surface passivation of silicon solar cells by low cost ald technology

Surface passivation is of vital importance for next generation solar cells. Outstanding properties of atomic layer deposition (ALD) can be employed to passivate Si surface with very good uniformity over large areas, excellent step coverage on non-planar surfaces and precise thickness control of nano-thick layers. The challenge is to apply ALD in a cost effective way acceptable for PV industry. In this work we report on the development of atmospheric pressure spatial ALD for (inline) deposition of Al2O3 layers with a throughput of 2000-3600 wafers/hour and low TMA precursor consumption. Layers with a thickness of 6-10 nm are optimal for rear side passivation, resulting in effective chemical and field-effect passivation without delamination (blistering) at the contact annealing step. This passivation is implemented in mass production and gives an efficiency improvement of 0.4-0.8% for PERC type solar cells.