Optoelectronic properties and device simulation of ZnS polymorphs as buffer layers for CZTSSe solar cells

Area of Science:

• Materials Science
• Renewable Energy
• Solid-State Physics

Background:

• Kesterite (CZTSSe) is a sustainable thin-film absorber for solar cells, but its efficiency lags behind leading technologies.
• Optimizing the buffer layer (BL) is a key strategy to enhance CZTSSe solar cell performance.
• Investigating different zinc sulfide (ZnS) polymorphs as buffer layers is crucial for improving device efficiency.

Purpose of the Study:

• To systematically evaluate cubic, hexagonal, and trigonal ZnS polymorphs as buffer layers for CZTSSe solar cells.
• To determine the impact of ZnS crystal phase on photovoltaic performance using theoretical calculations and simulations.
• To identify critical design parameters for enhancing CZTSSe solar cell efficiency.

Main Methods:

• Density functional theory (DFT) calculations (GGA-PBE, CASTEP) were used to analyze the electronic properties of ZnS polymorphs.
• SCAPS-1D simulations were employed to model the performance of CZTSSe solar cells with different ZnS buffer layers.
• Systematic variation of buffer layer and device parameters was performed to identify key performance-governing factors.

Main Results:

• Hexagonal ZnS exhibited superior carrier transport properties (electron mobility: 343.2 cm² V^-1 s^-1, hole mobility: 92.6 cm² V^-1 s^-1) compared to cubic and trigonal phases.
• SCAPS-1D simulations showed that hexagonal ZnS as a buffer layer yielded the highest power conversion efficiency (PCE) of 14.18%.
• Analysis revealed that buffer layer thickness, defect densities, and back-contact work function are critical for device performance.

Conclusions:

• Hexagonal ZnS is identified as the most effective buffer layer for CZTSSe solar cells due to its superior carrier transport and interfacial stability.
• This study provides a theoretical framework for optimizing buffer layers to enhance the efficiency of kesterite solar cells.
• The findings pave the way for developing more efficient and sustainable photovoltaic devices based on CZTSSe.