Electronic Passivation of Crystalline Silicon Surfaces Using Spatial‐Atomic‐Layer‐Deposited HfO2 Films and HfO2/SiNx Stacks

Spatial atomic layer deposition (SALD) is applied to the electronic passivation of moderately doped (≈10 16 cm −3 ) p‐type crystalline silicon surfaces by thin layers of hafnium oxide (HfO 2 ). For 10 nm thick HfO 2 layers annealed at 400 °C, an effective surface recombination velocity S eff of 4 cm s −1 is achieved, which is below what has been reported before on moderately doped p‐type silicon. The one‐sun implied open‐circuit voltage amounts to iV oc = 727 mV. After firing at 700 °C peak temperature in a conveyor‐belt furnace, as applied in the production of solar cells, still a good level of surface passivation with an S eff of 21 cm s −1 is attained. Reducing the HfO 2 thickness to 1 nm, the passivation virtually vanishes after firing (i.e., S eff > 1000 cm s −1 ). However, by adding a capping layer of plasma‐enhanced‐chemical‐vapor‐deposited hydrogen‐rich silicon nitride (SiN x ) onto the 1 nm HfO 2 , a substantially improved firing stability is attained, as demonstrated by S eff values as low as 30 cm s −1 after firing, which is attributed to the hydrogenation of interface states. The presented study demonstrates that SALD‐deposited HfO 2 layers and HfO 2 /SiN x stacks have the potential to evolve into an attractive surface passivation scheme for future solar cells.