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

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 Al2O3 followed by a top layer of either 50.5 nm TiO2 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 Al2O3/TiO2 coating has a low emitter saturation current density J0,e of 38 fA/cm2, while Al2O3/ZnS has 52 fA/cm2. 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.