The ouput voltage of piezoelectric with displacement

Hello All,

I am new with comsol software, now I am trying to solve the basic problem with piezoelectric device. I try to set 'electric potential ' with voltage value as 0, and set 'boundary load' to get the displacement of each layer.

How could I get the output voltage with the pre-define displacement?


I hope the attachment would help you to understand what kind of problem I faced.