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 Eg increases slightly as a function of y composition (Eg varies from 1.87 to 2.07 eV).