Exciton Bimolecular Annihilation Dynamics in Push–Pull Semiconductor Polymers
Yulong Zheng, Rahul Venkatesh, Esteban Rojas‐Gatjens, Elsa Reichmanis, Carlos Silva
Abstract
High Resolution Image Download MS PowerPoint Slide Exciton–exciton annihilation is a ubiquitous nonlinear dynamic phenomenon in materials hosting Frenkel excitons. In this work, we investigate the nonlinear exciton dynamics of an electron push–pull conjugated polymer by fluence-dependent transient absorption and excitation-correlation photoluminescence spectroscopy, where we can quantitatively show the latter to be a more selective probe of the nonlinear dynamics. Simulations based on a time-independent exciton annihilation model show a decreasing trend for the extracted annihilation rates with excitation fluence. Further investigation of the fluence-dependent transients suggests that the exciton–exciton annihilation bimolecular rates are not constant in time, displaying a t –1/2 time dependence, which we rationalize as reflective of one-dimensional exciton diffusion, with a diffusion length estimated to be 9 ± 2 nm. In addition, exciton annihilation gives rise to a long-lived species that recombines on a nanosecond time scale. Our conclusions shed broad light onto nonlinear exciton dynamics in push–pull conjugated polymers.