The underlying data is in the PowerPivot model. You can access this by clicking on the PowerPivot Window button.
If you just want to look at the data, that should be sufficient.
If you want to export the data, you can use a regular PivotTable to connect to the datasource and do the export.
(I do not known if there is a feature in PowerPivot that is exactly the same as in a regular Pivot, but I don't have PowerPivot on this machine, so I can't check it now).