Oxygen-Induced Ordering in Bulk Polycrystalline Cu₂ZnSnS₄ by Sn Removal

Area of Science:

• Materials Science
• Solid-State Chemistry
• Semiconductor Physics

Background:

• Copper zinc tin sulfide (CZTS) is a promising kesterite semiconductor for photovoltaic applications.
• Cation ordering significantly influences the optoelectronic properties of CZTS.
• Controlling cation ordering during CZTS synthesis is a key challenge.

Purpose of the Study:

• To investigate the effect of oxygen incorporation during the growth of CZTS bulk solids on cation ordering.
• To elucidate the mechanisms by which oxygen influences the CZTS crystal structure and phase formation.
• To identify optimal conditions for enhancing cation ordering in CZTS.

Main Methods:

• Solid-state nuclear magnetic resonance spectroscopy
• X-ray diffraction
• Raman spectroscopy
• Controlled synthesis of CZTS in the presence and absence of oxygen

Main Results:

• Oxygen incorporation in precursors led to improved cation ordering in CZTS bulk solids.
• Oxygen showed negligible solubility in the CZTS phase, forming SnO2 and resulting in Sn-deficient CZTS.
• Beneficial ordering was observed with >2 at.% oxygen, linked to Sn removal, not SnO2 or O presence.
• Excess Sn and O did not yield improved ordering; SnO2 formation and subsequent removal are key.

Conclusions:

• The improved cation ordering in CZTS is primarily due to tin deficiency induced by oxygen incorporation.
• Oxygen or air annealing can be used to tailor Sn content, potentially improving CZTS properties.
• A post-annealing etching step to remove SnO2 is proposed for further property enhancement.