Sub-ns triplet state formation by non-geminate recombination in PSBTBT:PC70BM and PCPDTBT:PC60BM organic solar cells

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DOI

  • Fabian Etzold, Max Planck Inst Polymer Res, Max Planck Society
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  • Ian A. Howard, Max Planck Inst Polymer Res, Max Planck Society
  • ,
  • Nina Forler, Max Planck Inst Polymer Res, Max Planck Society
  • ,
  • Anton Melnyk, Max Planck Inst Polymer Res, Max Planck Society
  • ,
  • Denis Andrienko, Max Planck Inst Polymer Res, Max Planck Society
  • ,
  • Michael Ryan Hansen
  • ,
  • Frederic Laquai, King Abdullah Univ Sci & Technol, King Abdullah University of Science & Technology, SPERC, Phys Sci & Engn Div PSE, MSE

The solid-state morphology and photo-generated charge carrier dynamics in low-bandgap polymer: fullerene bulk heterojunction photovoltaic blends using the donor-acceptor type copolymers PCPDTBT or its silicon-substituted analogue PSBTBT as donors are compared by two-dimensional (2D) solid-state nuclear magnetic resonance (NMR) and femto-to microsecond broadband Vis-NIR transient absorption (TA) pump-probe spectroscopy. The 2D solid-state NMR experiments demonstrate that the film morphology of PCPDTBT:PC60BM blends processed with additives such as octanedithiol (ODT) are similar to those of PSBTBT:PC60BM blends in terms of crystallinity, phase segregation, and interfacial contacts. The TA experiments and analysis of the TA data by multivariate curve resolution (MCR) reveal that after exciton dissociation and free charge formation, fast sub-nanosecond non-geminate recombination occurs which 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 structures of PSBTBT:PC70BM blends reduces non-geminate recombination, leading to superior device performance compared to optimized PCPDTBT:PC60BM blends.

Original languageEnglish
JournalEnergy & Environmental Science
Volume8
Issue5
Pages (from-to)1511-1522
Number of pages12
ISSN1754-5692
DOIs
Publication statusPublished - 2015

    Research areas

  • MULTIVARIATE CURVE RESOLUTION, LOW-BANDGAP POLYMER, SOLVENT ADDITIVES, PHOTOVOLTAIC PERFORMANCE, BULK HETEROJUNCTIONS, CHARGE GENERATION, EXCITED-STATE, EFFICIENCY, NMR, FULLERENE

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