Effect of S/In concentration ratio on the physical properties of AgInS2-sprayed thin films

 AgInS₂ thin films have been prepared on glass substrates by the spray pyrolysis process using an aqueous solution, containing silver acetate (AgCH₃CO₂), thiourea (SC(NH₂)₂) and indium chloride (InCl₃) as precursors. The depositions were carried out at the substrate temperature of 420 °C. The value of the concentration ratio in the spray solution of indium and silver elements x=Ag⁺]/In³⁺] was equal to 1.3, whereas y=S²⁻]/In³⁺] varied between 4 and 7. The structural study (XRD, EPMA and AFM ) shows that all films obtained using y=4 with a nearly stoichiometric composition consist essentially of AgInS₂ chalcopyrite compound and they exhibit in the as-deposited state, the best crystallinity with a (1 1 2) preferential orientation. On the other hand, films obtained using y higher than y=4 exhibit p-type character. Moreover, the optical analysis via the transmittance, reflectance reveals that the band-gap energy E_g increases slightly as a function of y composition (E_g varies from 1.87 to 2.07 eV).