Typically when we think of multilayer piezoelectric stacks, we think of the "burger." That is, piezo layers poled in the thickness stacked on top of on another in an alternating polarization configuration. This provides huge advantages in terms of achieving high displacement with low voltage applied. 

     But the opposite is also true...

     Given an applied force (or applied displacement) the generated voltage will also be small for the burger topology.

     So are multilayers doomed when it comes to using them for sensors? Not at all! Let me introduce you to the bookcase topology. In the bookcase topology case, the actuation ability would be similar to a single bulk piezo crystal of the same size. However, if you take the bookcase topology and wire the electrodes correctly... VOLTAGE WILL ADD between each layer, plus the long length of each element will further increase the voltage!

So what is best for energy harvesting? It depends on if you need more voltage (usually the case) or more current.