Excellent passivation and low reflectivity with atomic layer deposited bilayer coatings for n-type silicon solar cells

摘要

Bilayer coatings deposited by atomic layer deposition are shown to simultaneously achieve excellent passivation and low reflectivity, suitable for application on the front side of high-performance n-type Si solar cells. We designed and fabricated bilayer coatings of 10 nm Al_2O_3 followed by a top layer of either 50.5 nm TiO_2 or 52.5 nm ZnS. The bilayers have absolute reflectivity nearly 2% lower than state-of-the-art silicon nitride anti-reflection coatings. They passivate both highly doped p-type emitter surfaces and also low-doped p-type Si. For a B-doped emitter with sheet resistance of 159 Ω/sq on n-type Si, the Al_2O_3/TiO_2 coating has a low emitter saturation current density J_(0,e) of 38 fA/cm~2, while Al_2O_3/ZnS has 52 fA/cm~2. On low-doped p-type Si wafers, passivation using either coating resulted in minority carrier lifetimes above 1 ms, corresponding to surface recombination velocities below 10 cm/s.