Modulating Band Alignment and Passivating Defects with In-Situ Bi-Substituted Cu₂ZnSnS₄ for Superior...

Area of Science:

• Materials Science
• Photocatalysis
• Semiconductor Engineering

Background:

• Tailoring semiconductor properties via cation substitution is crucial for enhancing photoabsorber materials.
• Copper zinc tin sulfide (CZTS) is a promising photoabsorber material for catalytic applications.
• Defects and charge carrier dynamics in CZTS limit its photoelectrocatalytic efficiency.

Purpose of the Study:

• To investigate the effect of bismuth (Bi) substitution for zinc (Zn) in CZTS thin films on their photoelectrocatalytic properties.
• To fabricate and characterize Cu2Zn1-xBixSnS4 (x-CZBTS) thin films for photocathode applications.
• To understand the role of Bi doping in improving charge carrier statistics, kinetics, and overall efficiency.

Main Methods:

• Fabrication of Cu2Zn1-xBixSnS4 (x-CZBTS) thin films with varying Bi content (x = 0.02-0.08).
• Characterization of film properties including crystal structure, band gap, and defect analysis.
• Photoelectrochemical (PEC) measurements of CdS/Pt-coated x-CZBTS photocathodes for hydrogen evolution.
• Density Functional Theory (DFT) calculations to elucidate the electronic structure and reaction mechanisms.

Main Results:

• Bi incorporation reduced bulk defects, secondary phases, and CuZn antisites, facilitating crystallization at lower temperatures.
• Bi-doping modulated the band gap, increased absorption coefficient, red-shifted absorption, and improved charge collection.
• The 4-CZBTS-cp photocathode exhibited a photocurrent density of -7.2 mA cm-2, ηSTH of 1.62%, 95 µmol cm-2 h-1 H2 evolution, and 90% Faradaic efficiency.
• The 4-CZBTS-cp electrode maintained 82% photocurrent retention after 10 hours of operation in a pH 7 buffer.

Conclusions:

• Partial substitution of Zn with Bi in CZTS is an effective strategy to enhance photocathode performance.
• Bi doping improves the electronic structure, charge carrier lifetime, and separation/transport efficiency.
• The optimized Bi-doped CZTS material shows significant potential for efficient and stable solar hydrogen production.