I always freeze diced pepper, in the way mentioned above- Freezing them on a sheet. Even in winter if I do have to buy a pepper, I will dice any that I don't use immediately and freeze it that way, then put it in a zip lock bag. So handy to grab them when making an omelet or something.
Be careful to put the bag right back into the freezer after using though. My husband uses them to make omelets, then complains to me after awhile that they are all stuck together. Well, yeah, when you leave them out to thaw the put them back, you end up with one frozen lump.
You can also roast a batch of peppers and then scrape off the flesh, freezing it in mounds on a sheet then putting them in a bag. Alternately you can freeze it in ice cube trays, then when they are frozen, move to a freezer bag or container.