Diffuse functions for Ahlrichs/Karlsruhe basis sets in Gaussian?
If they are not in Gaussian yet, there won't be keyword to include these diffuse functions, but you can add them manually to your jobs. 

You can find the basis set specification for def2-TZVPD for the atoms you are interested from the Basis Set Exchange. From there, you can either just insert the diffuse functions after your molecule specifications using the keyword Extrabasis or just insert the whole basis manually using the gen keyword where you would normally put the name of the basis set.