Surface passivation of n -type doped black silicon by atomic-layer-deposited SiO₂/Al₂O₃ stacks

Black silicon (b-Si) nanotextures can significantly enhance the light absorption of crystalline silicon solar cells. Nevertheless, for a successful application of b-Si textures in industrially relevant solar cell architectures, it is imperative that charge-carrier recombination at particularly highly n-type doped black Si surfaces is further suppressed. In this work, this issue is addressed through systematically studying lowly and highly doped b-Si surfaces, which are passivated by atomic-layer-deposited Al₂O₃ films or SiO₂/Al₂O₃ stacks. In lowly doped b-Si textures, a very low surface recombination prefactor of 16 fA/cm² was found after surface passivation by Al₂O₃. The excellent passivation was achieved after a dedicated wet-chemical treatment prior to surface passivation, which removed structural defects which resided below the b-Si surface. On highly n-type doped b-Si, the SiO₂/Al₂O₃ stacks result in a considerable improvement in surface passivation compared to the Al₂O₃ single layers. The atomic-layer-deposited SiO₂/Al₂O₃ stacks therefore provide a low-temperature, industrially viable passivation method, enabling the application of highly n- type doped b-Si nanotextures in industrial silicon solar cells.