Detalle de: Raman scattering and microstructural analysis of polycrystalline CuInS2 films for solar cell devices

The detailed microstructural characterization of CuInS2 (CIS) polycrystalline films is performed by combined in depth MicroRaman scattering/Auger Electron Spectroscopy measurements as a function of the chemical composition and temperature of processing. This has allowed to identify the main secondary phases in the layers as CuIn5S8 for Cu-poor samples and CuS for Cu-rich ones. The presence of such phases is strongly related to the temperature of processing, being secondary phase formation inhibited when the growing temperature decreases from 520°C to 370°C. This is also accompanied by a significant degradation of the structural CIS features, as reflected by the increase in both shift and broadening of the A1 CIS mode in the spectra, and by the decrease of the grain size estimated by cross-section TEM. Besides, Raman spectra measured from samples grown at lower temperatures are characterized by the presence of an additional mode at about 305 cm-1. The presence of this mode in the spectra from Cu-rich samples gives experimental support to its previously proposed structural origin. Finally, MoS2 secondary phase has also been identified at the CIS/Mo interface region, being its occurrence also inhibited at low growing temperatures.