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

Abstract

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%.