The effect of tartaric acid in the deposition of Sb2S3 films by chemical spray pyrolysis

Abstract

Sb2S3 films grown by chemical bath deposition have been used as an absorber in extremely thin inorganic absorber solar cells. In the present work, Sb2S3 thin films were deposited by chemical spray pyrolysis. The aqueous spray solution consisted of SbCl3 (Sb=2mmol/L), thiourea (S) and tartaric acid (TA) in molar ratios of Sb:S:TA=1:3:10 or 1:3:1, and the solution was nebulized onto preheated soda-lime glass substrates. The deposition temperature ranged from 205°C to 230°C and 205°C to 355°C for Sb:S:TA=1:3:10 and 1:3:1, respectively. The effect of the tartaric acid concentration in spray solution, deposition temperature and the annealing temperature on the film properties was studied with X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis (TG/DTA) of tartaric acid was carried out.The films deposited from solutions with Sb:S:TA ratio of 1:3:10 at 205°C are ca. 1µm thick, contain orthorhombic stibnite (Sb2S3) phase and high amount of carbon and oxygen residues. The reduced TA concentration (1:3:1) in the spray solution leads to orthorhombic Sb2S3 films with decreased content of carbon and oxygen in the films compared to solutions with Sb:S:TA=1:3:10. An increase in the deposition temperature from 205°C to 355°C decreases the mean crystallite size from 25nm to 15nm and a decrease in sulfur and an increase in oxygen content was detected. SEM images indicate that the morphology and the thickness of the films grown with Sb:S:TA ratio of 1:3:1 are not homogeneous and an increase in deposition temperature results in thinner films. FTIR spectra of Sb2S3 film substance confirm that the TA has not completely decomposed at the used deposition temperatures. According to the thermal analysis study, TA decomposition takes place in three steps where 95% of mass is lost by 254°C and the TA is completely decomposed only at 495°C. Additionally, we report the first results on growing Sb2S3 films with band gap of 1.7eV by chemical spray pyrolysis using alcohol solutions.