From time to time the homopolar motor pulls me back with some new idea or concept which I haven't thought of before. This time it's a photoelectric homopolar motor!
When metals are irritated by a light that exceeds their work function they emit electrons. In case of a homopolar motor these electrons that fly off will produce a torque on the motor/disc combo and rotate the whole thing. The advantage here is that the current is decoupled from the rotation as light (photons) is the "source" of the "current" so there is no back EMF reducing the current.