It is interesting that you ask this as it was a topic of concern today in a university article.  You are probably right that it is sunscald.  Even commercial growers have been covering their plants with a sunscreen fabric this year because of the same problem.  Think back on the extreme temperatures and scalding sun we have had.  Our peppers and tomatoes are not bred for that.  It seems to be cooling now so maybe future peppers will not be affected.  Sorry, I know it is frustrating.