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@PHDTHESIS{Costantini:453801,
      author       = {Costantini, Roberto},
      othercontributors = {Morgante, Alberto},
      title        = {{E}xciton {D}ynamics in {M}olecular {H}eterojunctions},
      school       = {Universita degli Studi di Trieste},
      type         = {Dissertation},
      reportid     = {PUBDB-2021-00192},
      pages        = {87},
      year         = {2020},
      note         = {Dissertation, Universita degli Studi di Trieste, 2020},
      abstract     = {In recent years, the need for a more sustainable economic
                      development contributed to the increasing interest in
                      renewable energy sources. With encouraging trends on power
                      conversion efficiencies and manufacturing costs,
                      photovoltaics is expected to be the workhorse for the
                      production of green energy in the future. Silicon is
                      currently the dominant photovoltaic technology but, in the
                      past decade, novel solutions based on organic semiconductors
                      became attractive for their potential of overcoming the
                      Shockley-Queisser limit and offering unmatched efficiencies
                      by exploiting singlet fission. The latter is an exciton
                      multiplication process in which, for a certain class of
                      materials, a singlet exciton splits into two triplet
                      excitons, thus potentially doubling the charge carriers.
                      Significant work is still necessary to fully benefit of
                      singlet fission in photovoltaics; in particular, a higher
                      degree of control over exciton transport and dissociation
                      mechanisms at hetero-organic interfaces is required for
                      efficiently harvesting triplet excitons. To the aim of
                      better understanding such processes, at the ANCHOR-SUNDYN
                      endstation of the ALOISA beamline at Elettra we developed an
                      experimental setup for time-resolved X-ray spectroscopies,
                      in which the exciton dynamics in organic films can be
                      characterized by X-ray photoemission and absorption
                      spectroscopies with a 100 ps resolution. Here, we can
                      combine time-resolved measurements with standard X-ray and
                      UV spectroscopies for a more detailed analysis of the
                      samples.We apply this approach to donor/acceptor interfaces,
                      the prototypical architectures of organic photovoltaic
                      devices; we investigate triplet excited states in pentacene
                      by means of time-resolved X-ray absorption, which displays a
                      pump-induced feature with a 0.3±0.2 ns lifetime below the
                      LUMO resonance, that we associated to molecules in the
                      triplet state. On the picosecond time scale, measurements
                      performed at the FLASH free-electron laser reveal a
                      photoelectron response that we deem related to the triplet
                      exciton dissociation at the interface with the underlying
                      C60 film. A similar effect is also observed in pump-probe
                      photoemission spectra of tetracene / copper phthalocyanine
                      interfaces. On this second system, we tuned the pump
                      wavelength to selectively excite the two materials and
                      examined the different behavior of the photogenerated
                      excitons; the presence of a transient field in the
                      microsecond time scale suggests that triplet excitons are
                      involved in the charge transfer that occurs from tetracene
                      to copper phthalocyanine, in agreement with previous
                      studies. The results presented here demonstrate that
                      time-resolved X-ray spectroscopies can provide valuable
                      information for the characterization of exciton dynamics in
                      hetero-organic interfaces.},
      cin          = {DOOR ; HAS-User},
      cid          = {I:(DE-H253)HAS-User-20120731},
      pnm          = {6G2 - FLASH (POF3-622)},
      pid          = {G:(DE-HGF)POF3-6G2},
      experiment   = {EXP:(DE-H253)F-PG2-20150101},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.3204/PUBDB-2021-00192},
      url          = {https://bib-pubdb1.desy.de/record/453801},
}