Flashing ratchet effect for driving carriers to accelerate directional migration in organic photovoltaic devices

Abstract

The organic electron flashing ratchet experiment describes the phenomenon in which an electric current can be detected, even in the absence of a net potential bias. To understand the experimental mechanism at the quantum level, we utilize the quantum nonadiabatic method to simulate the electron dynamics in an organic polymer chain with the flashing ratchet potential. It is found that electrons exhibit directional migration with a velocity, which depends on both the asymmetry and the flashing frequency of the ratchet potential. In addition, the flashing ratchet, which describes the non-uniform and time-varying electric field, increases the velocity by 58.6% compared to the uniform electric field. The flashing ratchet effect exists intrinsically in actual organic photovoltaics (OPVs), due to the naturally uneven and time-varying inherent electric field caused by various inevitable factors in bulk heterojunctions (BHJ). Moreover, the ratchet potential can be artificially constructed by designing the morphology of the BHJ, which opens a promising avenue for driving electrons to accelerate directional migration, and improving the photoelectric conversion efficiency of OPVs.