Regensburg 2019 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 31: Organic Electronics and Photovoltaics II - Non-Fullerene Organic Solar Cells

CPP 31.3: Talk

Wednesday, April 3, 2019, 10:00–10:15, H18

Triplet Excitons in Non-Fullerene Acceptor-Polymer Blends and Organic Solar Cells? — •Maria Kotova, Johannes Junker, Andreas Baumann, Kristofer Tvingstedt, Andreas Sperlich, and Vladimir Dyakonov — Experimental Physics VI, Julius Maximilian University of Würzburg, 97074 Würzburg

In the past, most organic solar cells (OSCs) employed fullerenes as electron acceptors. Recently, the synthesis of novel non-fullerene acceptors (NFA) resulted in significantly higher power conversion efficiencies (PCE) of over 13%. It has been shown, that in fullerene-based OSCs the formation of triplet excitons (TE) opens an additional recombination pathway. In this work, the formation of TEs in NFA-based OSCs is investigated. We studied optical, electrical and spin properties of the polymer donor PBDB-T and the NFA acceptor ITIC in pristine films, in blend films and OSCs based on the blend. OSCs show a PCE of 9.8% and external quantum yield of up to 73%. Low temperature spin-sensitive photoluminescence measurements reveal the formation of highly localized TEs in pristine films of the donor (D) and acceptor (A), as well as in the blend films. This can occur either via intersystem crossing (ISC) or electron back transfer (EBT). ISC is likely for low mobility singlet excitons that cannot reach D-A interfaces and cannot dissociate into CT states. The EBT forms TE from the CT states. However, no TE signal was observed in solar cells under working conditions, thus no significant ISC or EBT occurs and the triplet formation loss channel is not very efficient. The lack of TEs matches well with the high PCE of NFA-based OSCs and their stability.