Analysis of sulphurisation processes of electrodeposited S-rich CuIn(S,Se)₂ layers for photovoltaic applications

This work reports a microstructural analysis of S-rich CuIn(S,Se)₂ layers produced by electrodeposition of CuInSe₂ precursors followed by annealing at 500 °C under sulphurising conditions, as function of the annealing time (t_ann). The characterisation of the layers by Raman scattering (RS) and Scanning Electron Microscopy (SEM) techniques has allowed to observe a strong dependence of the layer microstructure and the secondary phases synthesised during the sulphurising step on the annealing parameters. The experimental data show the existence of two distinct regimes: For t_ann < 20 min, increasing t_ann leads to a significant improvement of the crystalline quality of the absorbers. For longer annealing times, the changes observed in the frequency of the main CuIn(S,Se)₂ A₁ mode in the Raman spectra have been attributed to a higher incorporation of S in the chalcopyrite lattice. The characterisation of devices fabricated with these absorbers has allowed to analyse the impact of the microstructural features on the parameters of the solar cells, observing the existence of a strong correlation between the solar cell parameters and the spectral features of the main Raman mode.