Reducing Time and Costs of FT-IR Studies of the Effect of SiNx, Dopants, and Emitter on Hydrogen Species in Si Wafers and Solar Cell Structures

Abstract

Accurately measuring the hydrogen content in silicon (Si) solar cells is essential due to its connection to surface degradation and light and elevated temperature induced degradation (LeTID). Fourier Transform-Infrared (FT-IR) spectroscopy provides a quantitative technique for determining the content of various hydrogen species in Si wafers that have undergone various process steps. In this study, we examine both the effect of a silicon nitride (SiNx:H) layer during FT-IR spectroscopic measurements on hydrogen species, as well as the impact of an emitter present during firing on the amount of hydrogen introduced into Si wafers. We find that the presence of SiNx:H during measurements has negligible effects on the measured hydrogen species, potentially simplifying the preparation steps for FT-IR. For the emitter investigation we analyze boron (B)- and gallium (Ga)-doped p-type wafers to detect H-B, H-Ga, Oi-H2, and H2. We observe that hydrogen species initially present in B- and Ga-doped Si wafers differ significantly. Only H-Ga is detected in Ga-doped wafers, while H-B, Oi-H2, and H2 signals are measured in B-doped wafers. Moreover, we cannot confirm an increased release of H through the emitter into the bulk during the firing process. Finally, we conduct measurements at different temperatures and confirm that cryogenic temperatures are more effective for detecting H-B and H2 with concentrations in the 1014 cm-3 range. Nevertheless, useful spectra can still be obtained at liquid nitrogen (N2) temperatures.