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

Abstract

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 10nm Al2O3 followed by a top layer of either 50.5nm TiO2 or 52.5nm 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 159Ω/sq on n-type Si, the Al2O3/TiO2 coating has a low emitter saturation current density J0,e of 38fA/cm2, while Al2O3/ZnS has 52fA/cm2. On low-doped p-type Si wafers, passivation using either coating resulted in minority carrier lifetimes above 1ms, corresponding to surface recombination velocities below 10cm/s.