Lawrence Berkeley National Laboratory

Sulfur-based passivation for silicon surfaces using H2S gas is an alternative passivation method to reduce the thermal budget for Si photovoltaics. To understand the impact of the high-quality passivation and an observed passivation efficiency decrease after air exposure, we have studied the chemical surface structure by X-ray photoelectron spectroscopy (XPS), X-ray Auger electron spectroscopy (XAES), and S and Si L2,3 X-ray emission spectroscopy (XES). On the S-passivated silicon surfaces, we find the formation of S–Si bonds, in addition to some Si–O bonds. Upon air exposure, sulfur partially desorbs from the Si surface and an increased presence of Si–O and S–O bonds is observed. We identify that well-defined S–Si bonds are crucial to maintain high-quality surface passivation for Si photovoltaics, which allows further optimization of the fabrication process for S-based passivation on silicon.