Suppressing Element Inhomogeneity Enables 14.9% Efficiency CZTSSe Solar Cells

Area of Science:

• Materials Science
• Renewable Energy
• Semiconductor Physics

Background:

• Kesterite (Cu2ZnSn(SxSe1-x)4 or CZTSSe) solar cells exhibit significant open-circuit voltage (VOC) loss.
• This loss is often attributed to secondary phases and defects, commonly linked to tin loss during selenization.

Purpose of the Study:

• To investigate the primary cause of secondary phases and defects in CZTSSe solar cells.
• To identify strategies for improving crystal quality and photovoltaic performance.

Main Methods:

• Analysis of elemental distribution and diffusion within CZTSSe thin films.
• Implementation of a blocking layer to suppress directional diffusion.
• Characterization of crystal quality and defect density.
• Fabrication and efficiency testing of photovoltaic devices.

Main Results:

• Elemental inhomogeneity, driven by copper diffusion towards the Mo(S,Se)2 layer, was identified as the critical factor, not tin loss.
• Copper diffusion reduced the Cu/(Zn+Sn) ratio, increasing Sn-/Zn-related defects.
• Suppression of copper diffusion via a blocking layer improved crystal quality and reduced defects.
• Achieved a photovoltaic conversion efficiency (PCE) of 14.9% with a VOC of 576 mV, and a certified 14.6% efficiency.

Conclusions:

• Copper-directional diffusion is the main cause of defects and performance loss in CZTSSe solar cells.
• Implementing a blocking layer effectively mitigates this diffusion, enhancing device performance.
• Findings offer crucial insights for advancing CZTSSe solar cell technology.