Abstract : In organic semiconductors, bi-exciton states are key intermediates in carrier-multiplication and exciton annihilation. Of particular recent interest is the spin-2 (quintet) bi-exciton. Comprised of two triplet excitons, the bi-exciton can be formed by singlet fission (the formation of two triplet excitons from one singlet state) or by triplet-triplet annihilation (the reverse process). Of interest for photovoltaics and photocatalysis, the wavefunction of these optically dark bi-excitons is difficult to probe and predict. However, the local geometry of the pair-state is imprinted in the fine structure of its spin Hamiltonian. To access the fine structure of the quintet-state we develop and deploy broadband optically detected magnetic resonance (0-9 GHz). Here we correlate the experimentally extracted spin structure with the molecular crystal structure to identify the specific molecular pairings on which the bi-exciton state resides.
K. M. M Yunusova 1 S. L. L Bayliss 1 T. Chanelière 2, 3 V. Derkach 4 J. E. E Anthony 5 Alexei Chepelianskii 1 L. R. R Weiss 6
1 LPS – Laboratoire de Physique des Solides
2 NPSC – Nanophysique et Semiconducteurs
NEEL – Institut Néel
3 LAC – Laboratoire Aimé Cotton
4 Usikov’s Institute for Radiophysics and Electronics
5 University of Kentucky
6 Cavendish Laboratory
