Feasibility of Exceeding 20% Efficiency for Kesterite/c-Silicon Tandem Solar Cells Using an Alternative Buffer Layer:...

Area of Science:

• Materials Science
• Renewable Energy
• Semiconductor Physics

Background:

• Tandem solar cells offer higher efficiency than single-junction cells by exceeding the Shockley-Queisser limit.
• Kesterite (CZTS) and silicon (c-Si) are promising materials for tandem solar cell applications.
• Cadmium sulfide (CdS) is a common buffer layer, but research into nontoxic alternatives like titanium dioxide (TiO2) is ongoing.

Purpose of the Study:

• To investigate the potential of a nontoxic TiO2 buffer layer to enhance kesterite/c-Si tandem solar cell performance.
• To analyze the optoelectronic characteristics of kesterite top subcells with TiO2 instead of CdS.
• To achieve current matching between the kesterite top cell and c-Si bottom cell for optimal tandem device efficiency.

Main Methods:

• Optical and electrical modeling using SCAPS-1D and the transfer matrix method (TMM).
• Simulation of kesterite absorbers with varying bandgaps (1.4 eV to 1.7 eV) and thicknesses.
• Experimental data was used to establish a simulation baseline for kesterite (CZTS) devices.

Main Results:

• Replacing CdS with TiO2 significantly improved the kesterite top subcell's electrical and optical performance.
• TiO2 reduced parasitic light absorption and heterojunction interface recombination.
• The optimized tandem device with a 1.7 eV bandgap kesterite top cell and TiO2 buffer achieved approximately 20% efficiency.

Conclusions:

• The integration of a TiO2 buffer layer is a promising strategy for enhancing kesterite/silicon tandem solar cell efficiency.
• Further advancements in kesterite materials and device fabrication are necessary for their widespread adoption in tandem applications.
• Nontoxic buffer layers like TiO2 are crucial for developing sustainable and high-performance photovoltaic technologies.