Gold-Induced Chemical Perturbations in CdTe-Based Photovoltaic Cells.

Area of Science:

• Materials Science
• Photovoltaics
• Surface Chemistry

Background:

• Back-contacting is a critical factor influencing CdTe solar cell efficiency.
• Gold (Au) is frequently used as a back contact material in research settings.
• Oxide layers on CdTe can impact device performance and stability.

Purpose of the Study:

• Investigate the role of native oxide on As-doped, CdCl2-treated CdTe during gold metallization.
• Characterize the chemical reactions at the CdTe/Au interface.
• Quantify the impact of these reactions on device performance metrics.

Main Methods:

• X-ray Photoemission Spectroscopy (XPS) to determine native oxide composition and thickness.
• Angle-resolved XPS and cadmium-modified Auger parameter for detailed analysis.
• Interfacial hole barrier measurements.
• Photoluminescence (PL) spectroscopy and time-resolved PL to assess device parameters.

Main Results:

• A native oxide layer of CdTeO3 (1.6 nm) was identified on the CdTe surface.
• Oxygen and oxidized tellurium are eliminated from the native oxide during gold deposition.
• The native oxide initially alleviates downward band bending but is consumed.
• Significant reductions in internal open circuit voltage (iVoc), carrier lifetime, and PL quantum yield were observed.

Conclusions:

• The native oxide plays a complex role, initially mitigating band bending but ultimately degrading performance.
• Reactions at the back interface during metallization negatively impact CdTe PV device parameters.
• Understanding and controlling the native oxide and interface reactions are crucial for improving CdTe solar cell efficiency.