Transparent conductive oxide / encapsulant interface characterization following Damp Heat exposure

The role of surface analysis, specifically XPS (X-ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass Spectrometry) has been explored to broaden our understanding of TCO / encapsulant interactions focusing on TCO resistivity evolution. Peel laminates of PVB, Ionomer and EVA encapsulants with LPCVD boron doped ZnO were exposed to Damp Heat and removed at different points in the aging cycle for analysis. Distinct response patterns were observed for the different encapsulant families and selected ionomers were found to be most effective at protecting and maintaining the conductivity of the TCO. Trends in interfacial ion enrichment as a function of damp heat exposure were determined by a combination of XPS and SIMS to provide the necessary quantitation, sensitivity and surface specificity. In this study, the transition from a cohesive peel within the encapsulant toward an adhesive peel between the TCO and encapsulant layers provided an important point of comparison. Depth profiling to determine the distribution of mobile species throughout the thickness of the TCO added yet another dimension to our understanding of TCO / encapsulant interactions.