Origin of Interface Limitation in Zn(O,S)/CuInS₂-Based Solar Cells.

Area of Science:

• Materials Science
• Renewable Energy
• Semiconductor Physics

Background:

• Copper Indium Disulfide (CuInS2) solar cells suffer from poor performance due to interface recombination.
• Cu-rich CuInS2 exhibits high optical quality but is prone to charge carrier recombination at interfaces.
• Unfavorable band alignment at the buffer/CuInS2 interface was hypothesized as a cause for recombination.

Purpose of the Study:

• Investigate the cause of interface recombination in chemical bath-deposited Zn(O,S)/co-evaporated CuInS2-based devices.
• Determine the dominant recombination mechanism affecting solar cell performance.
• Clarify the role of band alignment and near-interface defects.

Main Methods:

• Direct and inverse photoelectron spectroscopy to analyze electronic structure.
• Electrical characterization, including temperature-dependent current-voltage (I-V) analyses.
• Assessment of band bending and conduction band offset at the Zn(O,S)/CuInS2 interface.

Main Results:

• Temperature-dependent I-V analyses confirmed dominant recombination at the Zn(O,S)/CuInS2 interface with activation energy below the bulk band gap.
• Photoelectron spectroscopy revealed a small, "spike"-like conduction band offset (0.1 eV), ruling out unfavorable alignment.
• Observed band bending suggested Fermi-level pinning is not the primary issue.

Conclusions:

• Near-interface defects, analogous to those in Cu-rich CuInSe2, are the likely cause of performance-limiting interface recombination.
• The electronic band alignment at the Zn(O,S)/CuInS2 interface does not significantly impede charge carriers.
• Understanding and mitigating near-interface defects is crucial for improving CuInS2 solar cell efficiency.