If you're dealing with an interior, wood-studded wall, you can use one of these behind the TV -
DVFR2W Recessed 2 Gang Wall Box . I've used them behind my TV and equipment rack and they work well.
If you have an existing 120V outlet on the wall below where you want the TV, you can install the new box in the same stud cavity and tie in the new 120V outlet to the outlet below. Just be sure and use proper wiring (Romex, 14 or 12 AWG) between the two.