Assessment of absorber composition and nanocrystalline phases in CuInS ₂ based photovoltaic technologies by ex-situ/in-situ resonant Raman scattering measurements

This work describes the use of quasi-resonant Raman scattering measurements for the assessment of chemical composition and nanocrystalline phases in CuInS₂ based photovoltaic technologies. Raman spectra measured in S-rich CuIn(S,Se)₂ layers at a fixed wavelength of 785 nm show a strong increase in the intensity of the peaks that are related to the quasi-resonant excitation of the corresponding vibrational modes. The spectra measured at these conditions are characterised by the presence of seven bands that have been identified with four first order peaks in the 200400 cm ^-1 spectral region and three second order peaks in the 550750 cm ^-1 spectral region. These spectra are strongly sensitive to changes in the composition of S-rich CuIn(Se,S)₂ alloys. On the other hand, the strong increase in the intensity of the peaks allows the development of in-situ measurements for real time process monitoring. As an example of this application, Raman spectra have been measured at real time conditions during the growth of colloidal CuInS₂ nanocrystals that are being developed for the fabrication of low cost solar cells. The data obtained corroborate the potential of quasi-resonant Raman scattering measurements for the development of ex-situ and in-situ quality control and process monitoring tools in thin film chalcopyrite photovoltaic technologies.