Bismuth chalcogenide iodides Bi13S18I2 and BiSI: solvothermal synthesis, photoelectric behavior, and photovoltaic performance

Abstract

Bismuth chalcogenide iodides Bi₁₃S₁₈I₂ and BiSI were synthesized and characterized as light absorbers for solar cells. The formations of Bi₁₃S₁₈I₂ and BiSI can be controlled via a facile solvothermal process. BiSI is formed under low S/Bi mole ratio conditions but it easily converts to Bi₁₃S₁₈I₂ under high S/Bi mole ratio conditions. Bi₁₃S₁₈I₂ is an n-type semiconductor with a narrow bandgap of 0.75 eV and exhibits a strong light absorbance in the wide wavelength range from UV to NIR, making it a promising light absorber material for solar cells. A uniform B₁₃S₁₈I₂ nanorod film was fabricated on a porous TiO₂ electrode via a modified solvothermal process for a photovoltaic study. A Bi₁₃S₁₈I₂-based solar cell has demonstrated a power conversion efficiency of 0.85% for the first time, revealing the potential of Bi₁₃S₁₈I₂ as a new type of light absorber material for solar cells which can be fabricated via a low-cost solution process.