Manipulation of Hydrogen Charge States for Passivation of P-Type Wafers in Photovoltaics

Passivation of defects in silicon solar cells using hydrogen has long been an area of significant interest to the photovoltaic community. In this paper, we explore the importance of the charge states of hydrogen for passivation of defects in p-type silicon and how these charge states might be manipulated using illumination. We show that by using illumination during hydrogenation processes at temperatures between 475 and 625 K, the lifetime of wafers containing high concentrations of hydrogen can be strongly increased. The magnitude of the increase depends on temperature, with the most significant increase occurring at 545 K with samples under illumination showing an average effective lifetime of 167 μs, while samples without illumination had an average lifetime of 67 μs. This increase in the lifetime with illumination is explained in terms of how the electron quasi-Fermi energy and, hence, the relative concentrations of the hydrogen charge states respond to illumination at these temperatures. We show a correlation between the predicted charge states of interstitial hydrogen and the effective lifetimes of the wafers.