High Speed Regeneration of BO-Defects : Improving Long-Term Solar Cell Performance within Seconds

Abstract

Boron-oxygen related defects typically limit the efficiency of solar cells made from silicon containing high concentrations of boron as well as oxygen. The detrimental effect of these defects can be eliminated by applying a Regeneration procedure that needs carrier injection at slightly elevated temperatures. The kinetics of this process is influenced by different processing steps like thermal treatment and was found to rely on a high enough hydrogen concentration in the silicon bulk. It is shown here that neither emitter formation nor the use of Al2O3/SiNx:H or SiO2/SiNx:H passivation stacks affect Regeneration in a fundamental way. By contrast, the thickness of a SiNx:H layer acting as hydrogen source during a high temperature firing step has direct influence on Regeneration confirming that better hydrogenation results in faster Regeneration reactions. Condensing different process steps that all accelerate Regeneration allows the application of a high-speed Regeneration process consisting of a combination of relatively high temperature and high carrier injection, resulting in complete Regeneration of BO defects in less than 10 s. This makes Regeneration feasible as an in-line process in solar cell production and thus solves the problem of the boron-oxygen defects. Even further acceleration is achieved by laser induced Regeneration where the substrate is heated and illuminated simultaneously.