Elucidating the Influence of Sodium Fluoride on the Structural and Photoelectrochemical Properties of Antimony Sulfide Thin Films

Photoelectrocatalysis has become a sustainable and eco-friendly method for water splitting, enabling the production of hydrogen and oxygen using solar energy. Among various photoabsorber materials, antimony sulfide (Sb₂S₃) is regarded as a promising candidate for photoelectrochemical (PEC) water splitting due to its suitable band gap (∼1.7 eV), high optical absorption coefficient, and the earth-abundant nature of its elements. However, its practical application is limited by deep-level defects that can cause charge carrier recombination and reduce PEC efficiency. This work investigates how sodium fluoride (NaF) doping influences the structural, optical, and electrochemical properties of Sb₂S₃ thin films. NaF doping modifies the surface morphology and decreases surface roughness. These structural changes are associated with an increase in photocurrent density from 0.48 to 0.52 mA cm^-2 and a significant rise in carrier concentration from 9.24 × 10¹⁵ to 3.47 × 10¹⁸ cm^-3 under standard illumination. These results demonstrate that NaF plays a key role in controlling charge transport and improving catalytic activity. Overall, the findings highlight how dopant-induced modifications affect the PEC performance of Sb₂S₃-based photoelectrodes.