I think it's always been assumed that breathable air can pass through the walls of a
wall of force or
forcecage, because otherwise you'd have to pull up the suffocation rules and
do math to determine how much air is already in there. Since
cubes of force are basically those spells in item form, I'd say... it's up to you. The reddit link above says that there would be about 8 hours of air in such a cube, even if no new air enters. And since each charge lasts for 1 minute...
So, as evilly dramatic and cool it might be to suffocate someone in a pitch-black
cube of force, it's likely not actually possible. Sorry.