Exciton and charge-transfer dynamics in polymer semiconductors

TL;DR

This paper develops a quantum dynamical model to understand exciton and charge-transfer processes in polymer semiconductors, highlighting vibrational relaxation and state crossings relevant for improving photovoltaic and LED devices.

Contribution

It provides a detailed quantum dynamical framework for excited state relaxation in polymer heterojunctions, emphasizing vibrational effects and charge-transfer state regeneration.

Findings

Vibrational relaxation significantly influences state-to-state transitions.

Charge-transfer and excitonic states can cross, affecting relaxation pathways.

Regeneration of optically active excitons is possible via steady-state charge-transfer states.

Abstract

Organic semiconducting polymers are currently of broad interest as potential low-cost materials for photovoltaic and light-emitting display applications. I will give an overview of our work in developing a consistent quantum dynamical picture of the excited state dynamics underlying the photo-physics. We will also focus upon the quantum relaxation and reogranization dynamics that occur upon photoexcitation of a couple of type II donor-acceptor polymer heterojunction systems. Our results stress the significance of vibrational relaxation in the state-to- state relaxation and the impact of curve crossing between charge- transfer and excitonic states. Furthermore, while a tightly bound charge-transfer state (exciplex) remain the lowest excited state, we show that the regeneration of the optically active lowest excitonic state in TFB:F8BT is possible via the existence of a steady-state involving the bulk charge-transfer state. Finally, we will discuss ramifications of these results to recent experimental studied and the fabrication of efficient polymer LED and photovoltaics.