Light-responsive organic flashing electron ratchet

Ofer Kedem, Bryan Lau, Mark A. Ratner, Emily A. Weiss
  • Proceedings of the National Academy of Sciences, July 2017, Proceedings of the National Academy of Sciences
  • DOI: 10.1073/pnas.1705973114

What is it about?

The device is similar to field effect transistors, in a co-planar, bottom-gate geometry. An array of “finger electrodes” (FEs) with an asymmetric thickness profile applied an electric field to an organic semiconductor transport layer above, inducing a current between source and drain electrodes made of the same metal. As a ratchet, the device produces a short-circuit current – current flows between the source and drain electrodes with no applied source-drain bias, or work-function difference between them. The current is produced due to the local asymmetries in the applied field, but without an overall asymmetry (bias). The current is very sensitive to the oscillation frequency, as ratcheting is a dynamic steady-state. We have previously found in a theoretical study that the shape of the potential critically impacts the direction and magnitude of the ratchet current (see "Potential shape" below), and so developed an experimental design that enables the application of a wide range of potential shapes, and allows us to examine general behaviors. The photoactive transport layer (P3HT:PCBM) enables the modulation of charge carrier density using light, and revealed that sometimes, increasing the carrier density can actually reduce the ratchet current, matching previous theoretical predictions. For the first time in a flashing ratchet device, the ratchet is powered by an unbiased temporal drive, a sine wave, rather than an on/off or sin^2 drive. This will enable the future use of energy sources such as electromagnetic radiation to power a ratchet.

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The following have contributed to this page: Dr Ofer Kedem