Berlin 2012 – scientific programme

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DS: Fachverband Dünne Schichten

DS 44: Poster IV: Thin film photovoltaics; Organic electronics and photovoltaics (jointly with CPP, HL, O); Organic thin films; Trends in atomic layer deposition (Focused session)

DS 44.25: Poster

Friday, March 30, 2012, 09:30–12:00, Poster E

Transient spectroscopic studies of high performance PTB7-PCBM films for organic photovoltaics: the effect of processing additive and fullerene absorption — •Clare Dyer-Smith, Hannah Mangold, and Frédéric Laquai — Max-Planck Institut für Polymerforschung, Mainz, Germany

Photovoltaic blends of the thienothiophene-benzodithiophene polymer PTB7 with PC70BM have shown power conversion efficiencies exceeding 7%. Using transient absorption spectroscopy, we study the photoexcitation dynamics in PTB7:PC70BM and PTB7:PC60BM blend films across more than six orders of magnitude in time and across the entire spectral range from the visible to the near-infrared. We observe a fast spectral relaxation in the blend film, as well as a spectral relaxation in the pristine polymer emission detected using picosecond time-resolved fluorescence spectroscopy. We assign the latter to energetic disorder in the polymer, while the assignment of the former is the subject of ongoing investigation. Secondly, we characterize the dynamics of excited states in the heretofore unreported time range from 1 to 100 ns, crucial for the understanding of charge separation and recombination in organic solar cells. Our studies indicate that the use of the processing additive di-iodooctane produces longer lived charges in blend films, despite the presence of a more finely interpenetrating blend morphology and therefore a larger interfacial area. We also study the effect of varying the fullerene acceptor in the blend film to investigate the contribution of light absorption in the fullerene component to charge generation in the solar cell.