Berlin 2012 – scientific programme

Parts | Days | Selection | Search | Updates | Downloads | Help

CPP: Fachverband Chemische Physik und Polymerphysik

CPP 24: Poster: Organic Semiconductors

CPP 24.28: Poster

Wednesday, March 28, 2012, 11:00–13:00, Poster A

Triplet Exciton Formation and Electron Back Transfer in High-Efficiency Conjugated Polymer-Fullerene Blends studied by Optically Detected Magnetic Resonance — •Hannes Kraus¹, Stefan Väth¹, Andreas Sperlich¹, Carsten Deibel¹, and Vladimir Dyakonov^1,2 — ¹Experimental Physics VI, Julius Maximilian University of Würzburg, D-97074 Würzburg, Germany — ²ZAE Bayern, D-97074 Würzburg, Germany

The properties of forward and backward electron transfer between (D)onor and (A)cceptor moieties of polymer-fullerene BHJ solar cells, are vital to the photovoltaic performance. The forward electron transfer is the essential part of efficient charge generation, while its backward counterpart can lead to formation of excitonic states with lower energy (e.g. triplet excitons, TE), culminating in complete loss of the excitation for power generation. We investigated the TE formation attributes of P3HT:PC₆₀BM and P3HT:Lu₃N@PCBEH, finding no triplets in the former, while the latter shows a distinct TE yield. This is conclusive with the relative positions of the energy levels of triplet excitons located on the polymer and the fullerene LUMO. To generalize this assumption, we investigated the D-A blends with different donor polymers and acceptor fullerenes using the optically detected magnetic resonance (ODMR), a method sensitive to the spin state and orientation of quasi-particles. The highly performing PTB7:PC₇₀BM was found to also exhibit both CT and triplet states, whereas P3HT:PC₇₀BM shows only CT state generation. We discuss these findings regarding the morphology and energy level driven electron back transfer.