Controlling Light- and Elevated-Temperature-Induced Degradation With Thin Film Barrier Layers

In this article, we investigate the extent of lifetime degradation attributed to lightand elevated-temperature-induced degradation (LeTID)inp-type multicrystalline silicon wafers passivated with different configurations of hydrogenated silicon nitride (SiN
_x
:H) and aluminum oxide (AlO
_x
:H). We also demonstrate a significant difference between AlO
_x
:H layers grown by atomic layer deposition (ALD) and plasma-enhanced chemical vapor deposition (PECVD) with respect to the extent of LeTID. When ALD AlO
_x
:H is placed underneath a PECVD SiN
_x
:H layer, as used in a passivated emitter and rear solar cell, a lower extent of LeTID is observed compared with the case when a single PECVD SiN
_x
:H layer is used. On the other hand, the LeTID extent is significantly increased when an ALD AlO
_x
:H is grown on top of the PECVD SiN
_x
:H film. Remarkably, when a PECVD AlO
_x
:H is used underneath the PECVD SiN
_x
:H film, an increase in the LeTID extent is observed. Building on our current understanding of LeTID, we explain these results with the role of ALD AlO
_x
:H in impeding the hydrogen diffusion from the dielectric stack into the c-Si bulk, while PECVD AlO
_x
:H seems to act as an additional hydrogen source. These observations support the hypothesis that hydrogen is playing a key role in LeTID and provide solar cell manufacturers with a new method to reduce LeTID in their solar cells.