Impact of charge carrier injection on single-chain photophysics of conjugated polymers

TL;DR

This study uses single-molecule spectroscopy to explore how charge injection affects the photophysical behavior of conjugated polymers, revealing changes in emission properties and photon statistics relevant for device performance.

Contribution

It provides new insights into the microscopic effects of charge injection on the photophysics of conjugated polymers, combining experimental observations with a qualitative model.

Findings

Charge injection causes a blue-shift in PL emission.

Charge injection shortens PL lifetime due to quenching.

Photon antibunching fidelity deteriorates upon charging.

Abstract

Charges in conjugated polymer materials have a strong impact on the photophysics and their interaction with the primary excited state species has to be taken into account in understanding device properties. Here, we employ single-molecule spectroscopy to unravel the influence of charges on several photoluminescence (PL) observables. The charges are injected either stochastically by a photochemical process, or deterministically in a hole-injection sandwich device configuration. We find that upon charge injection, besides a blue-shift of the PL emission and a shortening of the PL lifetime due to quenching and blocking of the lowest-energy chromophores, the non-classical photon arrival time distribution of the multichromophoric chain is modified towards a more classical distribution. Surprisingly, the fidelity of photon antibunching deteriorates upon charging, whereas one would actually expect the number of chromophores to be reduced. A qualitative model is presented to explain the observed PL changes. The results are of interest to developing a microscopic understanding of the intrinsic charge-exciton quenching interaction in devices.