Non-destructive assessment of ZnO:Al window layers in advanced Cu(In,Ga) Se₂ photovoltaic technologies

The increasing importance of the Cu(In,Ga)Se₂ based thin films photovoltaic industry claims for the development of new assessment and monitoring tools to answer the needs existing in the improvement of the control of the processes involved in the production of solar cells modules. In this frame, a strong interest has been given to the developmentmethodologies for the assessment of the CIGS absorber, nevertheless advanced optical tools for the characterization of the other layers in the solar cells are still missing. In this work,we report a non-destructive optical methodology based on resonant Raman concepts that has been developed for the characterization ofAl doped ZnO layers (AZO) that are used as window layer in Cu(In,Ga)Se₂ solar cells. Doping the ZnO layer with Al leads to the presence of a characteristic defect induced band at 510cm^-1 spectral region. The correlation of the relative intensity of this band with the resistivity of the layers provides a fast and reliable tool for their electrical monitoring. Analysis of solar cells fabricated with layers of different conductivities has allowed demonstration at cell level of the proposed methodology for the determination of efficiency losses related to degradation of the resistivity of the AZO layers.(Graph Presented).