Anodic oxidations: excellent process durability and surface passivation for high efficiency silicon solar cells

We investigate the versatility of anodically grown silicon dioxide (SiO₂) films in the context of process durability and exceptional surface passivation for high efficiency (>23%) silicon solar cell architectures. We show that a room temperature anodic oxidation can achieve a thickness of ~70 nm within ~30 min, comparable to the growth rate of a thermal oxide at 1000 °C. We demonstrate that anodic SiO₂ films can mask against wet chemical silicon etching and high temperature phosphorus diffusions, thereby permitting a low thermal budget method to form patterned structures. We investigate the saturation current density J₀ of anodic SiO₂/silicon nitride stacks on phosphorus diffused and undiffused silicon and show that a J₀ of <10 fA cm⁻² can be achieved in both cases. Finally, to showcase the anodic SiO₂ films on a device level, we employed the anodic SiO₂/silicon nitride stack to passivate the rear surface of an interdigitated back contact solar cell, achieving an efficiency of 23.8%.