Molecular precursor species and their effects on the energy band-gap of hydrazine solution processed CuIn(S,Se)2 films

We investigate the molecular species present in hydrazine CuIn(Se,S)₂ precursor solutions and their effects on the band-gap of final CuIn(Se,S)₂ films. [Cu6S4]2- ions and [In2(Se,S]4]2- ions are present. Sulfur from [In₂(Se,S)₄]^2- is more effectively incorporated into the final material. This finding makes it possible to precisely control the band gap of CuIn(Se,S)₂ films by adjusting the S/Se ratio of the [In₂(Se,S)₄]^2- ions in the final precursor solution. These results will enable the precise adjustment and optimization of the energy band-gap in solution-processed CuIn(Se,S)₂ absorber layers for the future fabrication of improved photovoltaic devices.