Berlin 2015 – wissenschaftliches Programm
TT 47.6: Vortrag
Dienstag, 17. März 2015, 15:30–15:45, C 130
Sub-ns Triplet State Formation in PSBTBT:PC70BM and PCPDTBT:PC60BM Photovoltaic Blends — Fabian Etzold1, Ian Howard1,2, Frédéric Laquai1, and •Julien Gorenflot1 — 1Max Planck Research Group for Organic Optoelectronics, Max Planck Institute for Polymer Research, D-55128 Mainz, Germany — 2Institute of Microstructure Technology (IMT), Karlsruhe Institute of Technology (KIT), D-76344 Eggenstein-Leopoldshafen, Germany
The excited state dynamics in low-bandgap polymer:fullerene blends using the donor-acceptor copolymers PCPDTBT and its silicon-substituted analogue PSBTBT are investigated by femto- to microsecond broadband Vis-NIR transient absorption (TA) pump-probe spectroscopy. The TA experiments and analysis of the TA data by multivariate curve resolution (MCR-ALS) reveal that after exciton dissociation and free charge formation is completed, fast sub-nanosecond non-geminate recombination occurs and leads to a substantial population of the polymer's triplet state. The extent to which triplet states are formed depends on the initial concentration of free charges, which itself is controlled by the microstructure of the blend, especially in case of PCPDTBT:PC60BM. Interestingly, PSBTBT:PC70BM blends show a higher charge generation efficiency, but less triplet state formation at similar free charge carrier concentrations. This indicates that the solid-state morphology and interfacial structure of PSBTBT:PC70BM blends reduce non-geminate recombination and thus triplet state formation, leading to increased device performance compared to optimized PCPDTBT:PC60BM blends.