Raman scattering and structural analysis of electrodeposited CuInSe ₂ and S-rich quaternary Culn(S,Se) ₂ semiconductors for solar cells

This work reports the Raman scattering characterisation of CuInSe ₂ precursors grown by single step electrodeposition and the corresponding layers recrystallised under sulphurising conditions for solar cell devices. The analysis of the spectra measured on the as-grown precursors has allowed identifying the main secondary phases in these layers with elemental Se, Cu-Se phases and chalcopyrite Cu-poor ordered vacancy domains. To deepen in the identification of the Cu-Se phases, these measurements have been correlated with the analysis of binary Cu-Se layers. The experimental data indicate that formation of both Se and Cu-Se phases is likely controlled by the Se content in the layers. For values of stoichiometry below 1.15, excess Cu in the layers is accommodated in a phase with very low Raman efficiency (as Cu ₂Se). Increasing the content of Se leads to an increase in the spectral contribution from both Se and Cu _2-x,Se, being the formation of these phases likely favoured under high excess Se conditions. The characterisation of the corresponding recrystallised layers has allowed analysing the impact of the presence of the secondary phases in the as-grown absorbers on the performance of the final solar cells.