Roughness-Controlled Cu₂ZnSn(S,Se)₄ Thin-Film Solar Cells with Reduced Charge Recombination.

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Copper zinc tin sulfo-selenide (CZTSSe) is a cost-effective thin-film solar cell material.
• CZTSSe solar cells exhibit low efficiency due to significant charge recombination, particularly surface recombination.
• Controlling surface roughness is crucial for enhancing device performance by minimizing interfacial area.

Purpose of the Study:

• To develop a simple and effective strategy for reducing surface roughness in electrochemically deposited CZTSSe thin films.
• To investigate the impact of surface morphology on the photovoltaic properties of CZTSSe thin-film solar cells.

Main Methods:

• Implemented an initial nucleation stage with higher deposition currents followed by steady-state galvanostatic deposition for CZTSSe thin films.
• Utilized advanced characterization techniques including diode analysis, lifetime measurements, and temperature-dependent open-circuit voltage analysis.
• Quantified surface roughness reduction using root-mean-square (RMS) measurements (ΔRrms: -43.8% for CZT, -28.9% for CZTSSe).

Main Results:

• Achieved significantly smoother and more uniform surfaces for both copper-zinc-tin (CZT) precursor and CZTSSe thin films.
• Demonstrated reduced charge recombination in devices fabricated with smoother CZTSSe surfaces.
• Observed higher open-circuit voltage and fill factor in devices with reduced surface roughness, leading to a 8.64% active area conversion efficiency.

Conclusions:

• The proposed electrochemical deposition strategy effectively reduces surface roughness in CZTSSe thin films.
• Smoother surfaces lead to decreased charge recombination and improved photovoltaic performance in CZTSSe solar cells.
• This method offers a promising pathway for developing high-efficiency, low-cost CZTSSe thin-film solar cells.