Ratchets are nonequilibrium devices that produce directional motion of particles from nondirectional forces without using a bias, and are responsible for many types of biological transport, which occur with high yield despite strongly damped and noisy environments. Ratchets operate by breaking time-reversal and spatial symmetries in the direction of transport through application of a time-dependent potential with repeating, asymmetric features. This work demonstrates the ratcheting of electrons within a highly scattering organic bulk-heterojunction layer, and within a device architecture that enables the application of arbitrarily shaped oscillating electric potentials. Light is used to modulate the carrier density, which modifies the current with a nonmonotonic response predicted by theory. This system is driven with a single unbiased sine wave source, enabling the future use of natural oscillation sources such as electromagnetic radiation.
Keywords: charge transport; nonequilibrium; organic semiconductor; ratchet.