Nanoscale photovoltage mapping in CZTSe/CuxSe heterostructure by using kelvin probe force microscopy

Abstract

In the present work, kelvin probe force microscopy (KPFM) technique has been used to study the CZTSe/Cu _x Se bilayer interface prepared by multi-step deposition and selenization process of metal precursors. Transmission electron microscopy (TEM) confirmed the bilayer configuration of the CZTSe/Cu _x Se sample. Two configuration modes (surface mode and junction mode) in KPFM have been employed in order to measure the junction voltage under illumination conditions. The results show that CZTSe/Cu _x Se has small junction voltage of ∼21 mV and the presence of Cu _x Se secondary phase in the CZTSe grain boundaries changes the workfunction of the local grain boundaries region. The negligible photovoltage difference between grain and grain boundaries in photovoltage image indicates that Cu _x Se phase deteriorates the higher photovoltage at grain boundaries normally observed in CZTSe based device. These results can be important for understanding the role of secondary phases in CZTSe based junction devices.

Keywords

• Kesterite
• secondary phases
• KPFM
• surface potential
• interface
• photovoltage