Is the soil moist? If so, it could be overwatering. Usually, when leaves droop, and curl under like that is when there is too much moisture. If the soil is always as damp as it appears in that picture, I would hold off on watering. It could turn into a much more serious problem with edema if you don't catch it early.
Also, your seedlings appear to be quite leggy. What kind of bulbs do you use, and how far above the plants are they? That could become a problem, as well, if you don't lower the lights or use a more pepper-friendly bulb, whatever the case may be.
Hope your plants turn around!