Penny is a fictional character on the CBS television series The Big Bang Theory, portrayed by a beautiful and charming actress Kaley Cuoco.
The episode where all main characters dress up as the Justice League for the New Year's Eve party was season 4 episode 11 "The Justice League Recombination.

Sheldon Cooper - The Flash

Leonard Hofstadter - Green Lantern

Howard Wolowitz - Batman

Raj Koothrappali - Aquaman

Zack Johnson - Superman