Ultrafast Spectroscopy and Control of Excitations Across Internal Interfaces

Summary

This project focusses on singlet-exciton fission in heterosystems of molecular solids and its competition with charge or energy transfer. Such systems display large exciton binding energies and potentially huge exchange splittings such that the transition energy of one bright, singlet-type exciton exceeds twice the energy of the dark, triplet-type excitons.

Singlet-exciton fission will be controlled by choosing appropriate heterosystems, e.g., where fission is suppressed in either of the constituents yet allowed across the internal interface. The relaxation into triplet-type excitations competes with other interface-specific phenomena such as charge-transfer (CT) states. These can be either pure, both singlet-singlet-type and triplet-triplet-type or mixed singlet-triplet-type. Using time, spectral, and polarisation resolution thus provides several independent means to distinguish interface-related from bulk signatures and identify the nature of the relevant states.

Model interfaces between two molecular solids are studied as well as molecular crystals on 2D materials. The latter are particularly interesting as the appropriate choice of materials allows for vast spectral overlap of the respective lowest-energy singlet exciton transitions. Finally, “triplet-harvesting” into Si, extraction of carriers after singlet fission explores application in photovoltaics.

Project-related publications

1. N. Rinn, L. Guggolz, J. Lange, S. Chatterjee, T. Block, R. Pöttgen, S. Dehnen
   Ternary Mixed-Valence Organotin Copper Selenide Clusters
   Chem. Eur. J. 24, 5840 (2018).
2. P. Klement, C. Steinke, S. Chatterjee, T.O. Wehling, M. Eickhoff
   Effects of the Fermi level energy on the adsorption of O₂ to monolayer MoS₂
   2D Materials 5, 045025 (2018).
3. P. Klement, N. Dehnhardt, C.-D. Dong, F. Dobener, S. Bayliff, J. Winkler, D.M. Hofmann, P.J. Klar, S. Schumacher, S. Chatterjee, J. Heine
   Atomically thin sheets of lead-free onedimensional hybrid perovskites feature tunable white-light emission from self-trapped excitons
   arXiv:2012.02488 (2020).