Sb2S3 thin films by ultrasonic spray pyrolysis of antimony ethyl xanthate
Jako S. Eensalu, Kaia Tõnsuaadu, Ilona Oja Açik, Malle Krunks
Abstract
Synthesis of antimony chalcogenides, especially Sb2S3, by facile and area scalable in-air chemical methods, such as spray pyrolysis, from cost-effective chemicals is certain to accelerate development of the related thin film solar cell technology. In this study, antimony ethyl xanthate, a scarcely studied halogenide-free precursor, is proven to be suitable for the deposition of conformal phase pure crystalline Sb2S3 thin films via ultrasonic spray pyrolysis in air by a two-step process. First, a solution of antimony ethyl xanthate with thiourea in a molar ratio of 1/3, or with thioacetamide in a molar ratio of 1/10 was sprayed onto a glass/ITO/TiO2 substrate by ultrasonic spray pyrolysis at 215°C to yield amorphous phase pure Sb2S3 thin films. Second, performing post-growth heat treatment in vacuum at 225°C, was the key to produce phase pure conformal thin films of crystalline Sb2S3 (Eg 1.8 eV) with S/Sb atomic ratio of 1.46 by using thiourea, and 1.41 by using thioacetamide, respectively. Spraying solutions of antimony ethyl xanthate at ≥135°C resulted in the formation of the Sb2O3 phase. Adding thiourea or thioacetamide to the spray solution prevented the oxidation of the growing Sb2S3 layer during deposition at 135°C, 165°C, and 215°C. The suppressed oxidation of Sb2S3 layers is attributed to the liquid state of thiourea and thioacetamide in these conditions.