Mortal Kombat 9 (2011) was never officially released for the PlayStation Portable (PSP), and therefore, a legitimate "MK9 PPSSPP ISO" does not exist.
Since a native MK9 PSP ISO does not exist, here are the best ways to play Mortal Kombat on the go:
If you truly want "better," play on a PC:
Mortal Kombat (2011) received an official, feature-complete port for the PlayStation Vita. Unlike the PSP mods, the Vita version includes: The Full Story Mode: Exactly as seen on PS3/Xbox 360.
Frameskipping: Set to "1" if you experience slow-motion gameplay.