Hydrogen has been long known for its ability to passivate defects in silicon devices. However, multiple recent studies on understanding the mechanism behind light- and elevated temperature-induced degradation (LeTID) have proposed that hydrogen plays an important role in this degradation mechanism. Despite its important role in photovoltaic applications, the quantitative assessment of hydrogen is difficult and seldom reported. In this work, we applied hydrogen effusion mass spectroscopy to quantify the hydrogen released from hydrogenated silicon nitride (SiN _x :H) and atomic layer deposited (ALD) aluminum oxide (AlO _x ) dielectric films at elevated temperatures. We demonstrate that the amount of hydrogen effused from these layers strongly correlates with the extent of LeTID observed in the multicrystalline silicon wafers passivated with these monolayers and their stacks. It is shown that the hydrogen effusion scales linearly with the SiN _x :H thickness, similar as the extent of LeTID. The effusion measurements on the AlO _x /SiN _x :H stack revealed that the presence of the AlO _x film modifies the total amount of hydrogen that is effused, whereas it was found to slow the hydrogen in-diffusion. This result is consistent with the LeTID extent determined after contact firing where ALD AlO _x layers were found to act as a hydrogen diffusion barrier, strongly reducing LeTID when placed in between c-Si and SiN _x :H and increasing LeTID when placed on top of SiN _x :H.

Sahar Jafari

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