Singlet-triplet annihilation limits exciton yield in poly(3-hexylthiophene)

TL;DR

This study reveals that singlet-triplet exciton annihilation significantly limits the exciton yield in poly(3-hexylthiophene), affecting its fluorescence efficiency and energy harvesting potential, especially at high excitation densities.

Contribution

It uncovers a universal self-quenching mechanism based on singlet-triplet annihilation in P3HT, providing a detailed photophysical understanding of excited-state losses.

Findings

Singlet-triplet annihilation causes fluorescence loss in P3HT.

Triplet excitons limit organic photovoltaic efficiency.

Single P3HT chains exhibit photon-antibunching behavior.

Abstract

Control of chain length and morphology in combination with single-molecule spectroscopy techniques provide a comprehensive photophysical picture of excited-state losses in the prototypical conjugated polymer poly(3-hexylthiophene) (P3HT). A universal self-quenching mechanism is revealed, based on singlet-triplet exciton annihilation, which accounts for the dramatic loss in fluorescence quantum yield of a single P3HT chain between its solution (unfolded) and bulk-like (folded) state. Triplet excitons fundamentally limit the fluorescence of organic photovoltaic materials, which impacts on the conversion of singlet excitons to separated charge carriers, decreasing the efficiency of energy harvesting at high excitation densities. Interexcitonic interactions are so effective that a single P3HT chain of >100 kDa weight behaves like a two-level system, exhibiting perfect photon-antibunching.