Cascade of multi-exciton states generated by singlet fission

TL;DR

This paper investigates multi-exciton states generated by singlet fission using broadband optically detected magnetic resonance, revealing different coupled triplet pair configurations and their potential for quantum information processing.

Contribution

It introduces a detailed analysis of multi-exciton states under varying excitation intensities, identifying weakly and strongly exchange-coupled triplet pairs with implications for quantum applications.

Findings

Identification of weakly exchange-coupled triplet pairs on adjacent molecules.

Observation of a strongly exchange-coupled three-triplet state.

Excellent agreement between experimental data and spin Hamiltonian models.

Abstract

Identifying multi-exciton states generated from singlet fission is key to understanding the carrier multiplication process, which presents a strategy for improving the efficiency of photovoltaics and bio-imaging. Broadband optically detected magnetic resonance is a sensitive technique to detect multi-exciton states. Here we report a dominant species emerging under intense light excitation corresponding to a weakly exchange coupled triplet pair located on adjacent molecules oriented by nearly 90 degrees, contrasting to the pi-stacked triplet pair under low excitation intensity. The weakly coupled species model precisely reproduces the intricate spin transitions in the Hilbert space of the triplet pair. Combining the magneto photoluminescence and high-magnetic field ODMR, we also identify a strongly exchange-coupled state of three triplet excitons formed by photoexcited V2, which manifests through the magnetic field induced level crossings between its quintet and triplet manifolds. The excellent agreement between the experimental Zeeman fan and the two-triplet spin Hamiltonian highlights the potential of multi-exciton states for quantum information processing.