Spray deposition of AgBiS2 and Cu3BiS3 thin films for photovoltaic applications

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.