They do make combination panels..
Solimpeks PV-T Hybrid Collectors | SOLIMPEKS Solar Energy Corp.
They just aren't practical.. I think the warranty on this type of panel is likely
only 5 to 10 years. The standard PV panels are for 2 or 3 times as long.
This kind of "hybrid" panel isn't ready for prime time.
Kinda like the Solar Powered car.. Not practical.