The San Sebastian outfit, who have not lost to Barca twice in a season since the 2006-07 campaign, have not won the competition for 27 years.
Barca claimed a 4-1 victory when the sides met at Camp Nou in September, but Prieto is feeling confident ahead of this week's first-leg clash.
"We know the club and how they play," he told Marca. "Competing against them is always very difficult, but we have a lot of enthusiasm and desire to make history.
"This season has been very special. Besides playing the Champions League, we have managed to sneak into the semis of the Copa, which has not been achieved in San Sebastian for a long time. It's necessary to be aware of this and use it.
"We are doing well, although we have been thrashed at the Calderon (4-0 defeat to Atletico Madrid on Sunday). I think the final result does not reflect what was experienced on the pitch."
Prieto has scored two goals in 20 league appearances for Sociedad this season.
