I guess your model seems to be okay to me. Here, I attached my project file and exported Matlab file based on the plasmonic solar cell example in KB page. So, you can refer to my attached files.
[Model]solar_plasmonic_normal_with_CW_generation.fsp (306.2 KB)
CW_generation.mat (432.4 KB)
In the CW_generation analysis group, you can expand your model only in x-direction for 3D case.
This is my simulated result for a generation rate “G” in the CW_generation analysis group.
Here is another result for a generation rate “G_export” that considers 3 periods in the CW_generation analysis group. As you can see in the following image, there is apparent 3 periodis in x-direction of the plasmonic solar cell.
You can compare the size difference between “G" and “G_export” as belows.
25 25 59
73 25 59
You can confirm that the size in x-direction of the G_export matrix is almost three times larger than that of G.
If you look at the exported Matlab file (CW_generation.mat), then you can also confirm the matrix size of G as 73X25X59.