Uniform Sb 2 S 3 optical coatings by chemical spray method

Abstract

Antimony sulfide (Sb 2 S 3 ), an environmentally benign material, has been prepared by various deposition methods for use as a solar absorber due to its direct band gap of ≈ 1.7 eV and high absorption coefficient in the visible light spectrum (1.8 × 10 5 cm -1 at 450 nm). Rapid, scalable, economically viable and controllable in-air growth of continuous, uniform, polycrystalline Sb 2 S 3 absorber layers has not yet been accomplished. This could be achieved with chemical spray pyrolysis, a robust chemical method for deposition of thin films. We applied a two-stage process to produce continuous Sb 2 S 3 optical coatings with uniform thickness. First, amorphous Sb 2 S 3 layers, likely forming by 3D Volmer-Weber island growth through a molten phase reaction between SbCl3 and SC(NH 2 ) 2 , were deposited in air on a glass/ITO/TiO2 substrate by ultrasonic spraying of methanolic Sb/S 1:3 molar ratio solution at 200-210 °C. Second, we produced polycrystalline uniform films of Sb 2 S 3 (E g 1.8 eV) with a post-deposition thermal treatment of amorphous Sb 2 S 3 layers in vacuum at 170 °C, < 4 × 10 -6 Torr for 5 minutes. The effects of the deposition temperature, the precursor molar ratio and the thermal treatment temperature on the Sb 2 S 3 layers were investigated using Raman spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and UV-vis-NIR spectroscopy. We demonstrated that Sb 2 S 3 optical coatings with controllable structure, morphology and optical properties can be deposited by ultrasonic spray pyrolysis in air by tuning of the deposition temperature, the Sb/S precursor molar ratio in the spray solution, and the postdeposition treatment temperature.