Spray deposition of AgBiS2 and Cu3BiS3 thin films for photovoltaic applications

Abstract

Spray pyrolysis of bismuth(III) tris(4-methylbenzodithioate) toluene solutions containing either silver(I) acetate and 1-octanethiol, or copper(I) acetate and 1,2-ethanedithiol is introduced as a low-temperature solution-based method to produce sub-100 nm thick coatings of α cubic rock salt AgBiS₂ or orthorhombic Cu₃BiS₃, respectively. The structure, morphology and optoelectronic properties of the materials thus obtained have been comprehensively characterised using conventional techniques. Extensive optimisation of the deposition conditions has been undertaken to achieve the formation of uniform, 60–70 nm thick films of densely packed AgBiS₂ and Cu₃BiS₃ crystallites with a typical size of 10–20 nm. Planar photovoltaic devices based on spray-deposited AgBiS₂ as a light harvester, ZnO as an electron transporting layer, and spiro-OMeTAD as a hole transporting material produce short-circuit current densities as high as 18.1 ± 0.6 mA cm⁻² under 1 sun AM 1.5 G irradiation. The devices are stable without encapsulation under ambient conditions for at least 1 month.