It could be sun scald or blossom-end rot.  It looks more like damage from the sun since pepper fruit is very sensitive to the sun so just some type of shading cloth will help.  If you are sure it is not sun scald then it is blossom-end rot primarily caused by lack of calcium because of irregular moisture availability.  In other words the soil or potting media goes from periods that are too wet to too dry.  This imbalance causes calcium not to taken up correctly.  More frequent and uniform watering will help and a little calcium supplement will help.