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Impact of the donor polymer on recombination via triplet excitons in a fullerene-free organic solar cell

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Abstract

The greater chemical tunability of non-fullerene acceptors enables fine-tuning of the donor–acceptor energy level offsets, a promising strategy towards increasing the open-circuit voltage in organic solar cells. Unfortunately, this approach could open an additional recombination channel for the charge-transfer (CT) state via a lower-lying donor or acceptor triplet level. In this work we investigate such electron and hole back-transfer mechanisms in fullerene-free solar cells incorporating the novel molecular acceptor 2,4-diCN-Ph-DTTzTz. The transition to the low-driving force regime is studied by comparing blends with well-established donor polymers P3HT and MDMO-PPV, which allows for variation of the energetic offsets at the donor–acceptor interface. Combining various optical spectroscopic techniques, the CT process and subsequent triplet formation are systematically investigated. Although both back-transfer mechanisms are found to be energetically feasible in both blends, markedly different triplet-mediated recombination processes are observed for the two systems. The kinetic suppression of electron back-transfer in the blend with P3HT suggests that energy losses due to triplet formation on the polymer can be avoided, regardless of favorable energetic alignment.

Graphical abstract: Impact of the donor polymer on recombination via triplet excitons in a fullerene-free organic solar cell

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Publication details

The article was received on 05 Jul 2019, accepted on 03 Oct 2019 and first published on 08 Oct 2019


Article type: Paper
DOI: 10.1039/C9CP03793D
Phys. Chem. Chem. Phys., 2019, Advance Article

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    Impact of the donor polymer on recombination via triplet excitons in a fullerene-free organic solar cell

    M. Van Landeghem, R. Lenaerts, J. Kesters, W. Maes and E. Goovaerts, Phys. Chem. Chem. Phys., 2019, Advance Article , DOI: 10.1039/C9CP03793D

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