Quantification of Hydrogen in Nanostructured Hydrogenated Passivating Contacts for Silicon Photovoltaics Combining SIMS-APT-TEM: A Multiscale Correlative Approach

Multiscale characterization of the hydrogenation process of silicon solar cell contacts based on c-Si/SiO_x/nc-SiC_x(p) has been performed by combining dynamic secondary ion mass-spectrometry (D-SIMS), atom probe tomography (APT), and transmission electron microscopy (TEM). These contacts are formed by high-temperature firing, which triggers the crystallization of SiCx, followed by a hydrogenation process to passivate remaining interfacial defects. Due to the difficulty of characterizing hydrogen at the nm-scale, the exact hydrogenation mechanisms have remained elusive. Using a correlative TEM-SIMS-APT analysis, we are able to locate hydrogen trap sites and quantify the hydrogen content. Deuterium (D), a heavier isotope of hydrogen, is used to distinguish hydrogen introduced during hydrogenation from its background signal. D-SIMS is used, due to its high sensitivity, to get an accurate deuterium-to-hydrogen ratio, which is then used to correct deuterium profiles extracted from APT reconstructions. This new methodology to quantify the concentration of trapped hydrogen in nm-scale structures sheds new insights on hydrogen distribution in technologically important photovoltaic materials.