Annealing of FeS2 nano-crystal thin film

With a band gap of 0.95 eV and high absorption coefficient (~10⁵ cm^-1), FeS₂ is ideal for use as a p-type heterojunction partner in a solar cell. Although pyrite is abundant in nature, getting the right phase for thin films is difficult due to the various phases of iron sulfides. We propose an ink based process for attaining the pyrite phase. Our experimental process involves use of low cost non-toxic chemicals for synthesis. The process involves reacting iron (II) chloride and sulphur complexes made with solvents like oleylamine, octadecylamine and diphenyl ether. The reaction provides perfect nano crystals dispersed in a carbon based solution which is later subjected to centrifugation to separate the crystals. After multiple cleaning cycles, the crystals were dispersed in chloroform for uniform suspension. SEM image of the film formed by drop casting revealed that the nanocrystals were perfect cubes. EDX analysis showed the iron to sulfur atomic percentage ratio 1:1. The nano-crystal films were annealed at temperatures from 400°C to 600°C. The organic residues were removed after annealing but the film annealed at 600°C converted into FeS and consisted of amorphous region. A detail analysis of the films using SEM/EDX/XRD/FTIR/Raman is presented in this article.