For space applications, you can use the aforementioned solar sail, or charge an ion engine (though this still requires you to relinquish some matter).

For air applications, the old-fashioned propeller is your ticket to thrust. Something like a dirigible or a hot-air balloon, which is able to keep itself in the air without continuous thrust of a minimum force, would be less difficult to make work.

Interestingly enough, weight is more important than efficiency when dealing with aircraft PV. A company I spoke with that was working on "stratellites" (basically high-altitude blimps that stayed in one place indefinitely) used thin film PV instead of high efficiency cells because of their flexibility and high power-per-weight rating.