Hydrogen diffusion from PECVD silicon nitride into multicrystalline silicon wafers: Elastic recoil detection analysis (ERDA) measurements and impact on light and elevated temperature induced degradation (LeTID)

Hydrogen is a crucial element for crystalline silicon solar cells due to its ability to passivate bulk defects in silicon. The introduction and distribution of hydrogen has gained a lot of interest due to its proposed involvement in the phenomenon termed “light and elevated temperature induced degradation” (LeTID) in multicrystalline silicon (mc-Si) solar cells. LeTID, which can cause an efficiency loss of about 6-14% (relative) for mc-Si PERC (passivated emitter and rear cell) devices upon exposure to elevated temperature and illumination, is a serious cause of concern for the silicon photovoltaic industry. Interaction of hydrogen with mc-Si is complex as mc-Si contains grain boundaries, dislocations, large concentrations of impurities and traps which may affect the diffusivity of hydrogen in silicon. Understanding the diffusion of hydrogen in mc-Si, and how it affects LeTID, is therefore of great interest. In this contribution, the concentration of hydrogen diffused into p-type mc-Si lifetime samples from hydrogen-rich passivation layers (SiN_x:H and AlO_x:H) fired at different peak firing temperatures is measured by elastic recoil detection analysis (ERDA) along with Rutherford backscattering (RBS). Also, experiments are done to study the impact of annealing in the presence of hydrogen on the extent of LeTID. A correlation is established between the hydrogen concentration diffused into silicon bulk and the extent of LeTID in lifetime samples fired at different peak firing profiles.