Berlin 2015 – wissenschaftliches Programm
TT 47.7: Vortrag
Dienstag, 17. März 2015, 15:45–16:00, C 130
Triplet Exciton Formation in High-Efficiency Donor-Acceptor Photovoltaic Blends — •Stefan Väth1, Hannes Kraus1, Andreas Baumann2, Kristofer Tvingstedt1, Andreas Sperlich1, Vladimir Dyakonov1,2, John Love3, and Thuc-Quyen Nguyen3 — 1Experimental Physics VI, Julius Maximilian University of Würzburg, 97074 Würzburg — 2ZAE Bayern, 97074 Würzburg — 3University of Santa Barbara, Santa Barbara, CA 93106, USA
In donor-acceptor based bulk-heterojunction solar cells, the splitting of singlet excitons at the donor and acceptor interface is of crucial importance for charge generation. The reversed process, in which two initially free charge carriers meet at the interface to form an exciton with singlet or triplet multiplicity is rather beneficial for light emission in OLEDs but considered as one of the loss factors in OPV.
In our experiments, the occurrence of triplet excitons and CT states was probed by using spin sensitive detection of the photo- and electroluminescence. A substantial generation of molecular triplet excitons was found in high efficiency donor-acceptor OPV systems based on the low bandgap copolymer PTB7 and in the soluble small molecule p-DTS(FBTTh2)2, both blended with PC70BM as acceptor. We ascribe these findings to an electron back transfer from the CT state to the triplet state on the donor material. In summary, the fundamental understanding of the transformation processes involving the CT states, triplet excitons, as well as free electrons and holes and their dependence on nanoscale morphology and energetics of blends is essential for the optimization of OPV devices.