The ornamental design for a photovoltaicsubmodule, as shown and described.
FIG. 1 is a top plan view of a photovoltaic submodule;
FIG. 2 is a front elevational view thereof; and,
FIG. 3 is a left side elevational view thereof, the right side elevational view is the same.
The right side elevational view is the same as the left side. The bottom of the photovoltaic submodule is not shown, and forms no part of the claimed design.