Nanoscopy of Single Charge Carrier Jumps in a Conjugated Polymer Nanoparticle

We present super-resolution (similar to 2nm spatial resolution per frame, 1 ms time resolution) tracking of single charge carriers in nanoparticles of the conjugated polymer PFBT. The motion of the charge carrier is determined from fluctuations in the centroid position of the particle fluorescence spot arising from fluorescence quenching by the polaron. A single polaron is observed to hop between a few sites, consistent with dispersive charge transport in a disordered energy landscape. In some shorter segments of the trajectory, there is repeated hopping between two sites, whereas for longer segments and full trajectories, random walk-like behavior consistent with multiple sites is observed. The hopping times range from a few milliseconds to seconds, following a power law distribution, while the hopping distances range from 2 to 5 nm, roughly following an exponential distribution. From the polaron hopping time distribution, we estimate a barrier height of 430-570 meV, with a nearest neighbor distribution ranging from 2 to S nm, consistent with the presence of deep traps often associated with structural or chemical defects.