@phdthesis{ZitzlerKunkel2014,
  author    = {Zitzler-Kunkel, Andr{\´e}},
  title     = {Funktionale Merocyaninfarbstoffe: Synthese, molekulare und Selbstorganisationseigenschaften sowie ihre Anwendung in der organischen Photovoltaik},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-101536},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2014},
  abstract  = {Analog zu den auf hochgeordneten Farbstoffarchitekturen in den biologischen Photosyntheseapparaten basierenden Energiekonversionssystemen sollte die exakte Einstellung zwischenmolekularer Wechselwirkungen auch in k{\"u}nstlichen Halbleitern eine entscheidende Rolle f{\"u}r die Weiterentwicklung organischer Elektronikmaterialien spielen. F{\"u}r eine derartige, pr{\"a}zise Steuerung der nanoskaligen Anordnung in organischen Materialien erscheinen Merocyaninfarbstoffe wegen ihrer hochgerichteten, dipolaren Aggregation {\"a}ußerst aussichtsreich. In diesem Zusammenhang war das Ziel der vorliegenden Arbeit die Ausnutzung funktionaler, stark selbstorganisierender Merocyanine, um eine gezielte Beeinflussung der Morphologie in der aktiven Schicht von BHJ-Solarzellen zu erreichen. Hierzu sollte zun{\"a}chst eine umfangreiche Serie komplexer Merocyanine synthetisiert und vollst{\"a}ndig charakterisiert werden. Im Folgenden wurde angestrebt, die optischen und elektrochemischen Eigenschaften der molekular gel{\"o}sten Farbstoffe zu bestimmen und f{\"u}r ausgew{\"a}hlte, geeignete Strukturen das Selbstorganisationsverhalten im Detail zu studieren. Zuletzt sollte durch eine sorgf{\"a}ltige Optimierung der Prozessierungsbedingungen ein Transfer der in L{\"o}sung gefundenen, supramolekularen Strukturen in den Blend l{\"o}sungsprozessierter BHJ-Solarzellen erreicht werden. Die organischen Elektronikbauteile wurden dabei im Arbeitskreis von Prof. Dr. Klaus Meerholz (Universit{\"a}t K{\"o}ln) gefertigt und charakterisiert. Zusammenfassend zeichnet die vorliegende Arbeit ein umfassendes Bild von der Synthese funktionaler Merocyanine, dem Studium ihrer molekularen und Selbstorganisationseigenschaften sowie ihrer Anwendung als p-Halbleitermaterialien in organischen Solarzellen. Der komplexe Molek{\"u}laufbau der dargestellten Farbstoffe f{\"u}hrte dabei zur Ausbildung verschiedener Farbstofforganisate, deren Struktur sowohl in L{\"o}sung als auch teilweise im Festk{\"o}rper aufgekl{\"a}rt werden konnte. Die erfolgreiche Implementierung von H-aggregierten Spezies der Verbindung 67b in die aktive Schicht organischer BHJ-Solarzellen resultierte in der Bildung effizienter Perkolationspfade f{\"u}r Exzitonen und freie Ladungstr{\"a}ger, wodurch diese Bauteile merklich h{\"o}here Stromdichten generieren konnten und gegen{\"u}ber Zellen ohne H-Spezies {\"u}ber 20 \% gesteigerte Effizienz aufwiesen. Diese Befunde verifizieren die postulierte Hypothese, dass eine gezielte Einstellung der zwischenmolekularen Wechselwirkungen bei organischen Halbleitern zu einer Optimierung der Funktionalit{\"a}t organischer Elektronikmaterialien beitragen kann.},
  subject      = {Merocyanine},
  language  = {de}
}
@phdthesis{Ojala2012,
  author    = {Ojala, Antti},
  title     = {Merocyanine Dyes as Donor Materials in Vacuum-Deposited Organic Solar Cells: Insights into Structure-Property-Performance Relationships},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-70073},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2012},
  abstract  = {In this study, a double-donor concept is used to improve the performance of thermally evaporated merocyanine(s)/C60 bulk heterojunction (BHJ) solar cells. It is shown that the co-evaporation of two merocyanine dyes with absorption bands at ~ 500 nm (SW dye) and ~ 650 nm (LW dye), respectively, together with C60 fullerene results in an improvement of open-circuit voltage (VOC), short-circuit current (JSC) as well as total power conversion efficiency (PCE) compared to the best single-donor cell. The enhancement of JSC is attributed to a higher photon harvesting efficiency of the mixed-donor devices due to a better spectral coverage.},
  subject      = {Merocyanine},
  language  = {en}
}
@phdthesis{Kern2013,
  author    = {Kern, Julia},
  title     = {Field Dependence of Charge Carrier Generation in Organic Bulk Heterojunction Solar Cells},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-91963},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2013},
  abstract  = {In the field of organic photovoltaics, one of the most intensely researched topics to date is the charge carrier photogeneration in organic bulk heterojunction solar cells whose thorough understanding is crucial for achieving higher power conversion efficiencies. In particular, the mechanism of singlet exciton dissociation at the polymer-fullerene interface is still controversially debated. This work addresses the dissociation pathway via relaxed charge transfer states (CTS) by investigating its field dependence for reference material systems consisting of MDMO-PPV and one of the fullerene derivatives PC61BM, bisPCBM and PC71BM. Field dependent photoluminescence (PL(F)) and transient absorption (TA(F)) measurements give insight into the recombination of charge transfer excitons (CTE) and the generation of polarons, respectively. Optically detected magnetic resonance and atomic force microscopy are used to characterize the morphology of the samples. The comparison of the experimental field dependent exciton recombination recorded by PL(F) and the theoretical exciton dissociation probability given by the Onsager-Braun model yields the exciton binding energy as one of the key parameters determining the dissociation efficiency. The binding energies of both the singlet exciton in neat MDMO-PPV and the CTE in MDMO-PPV:PC61BM 1:1 are extracted, the latter turning out to be significantly reduced with respect to the one of the singlet exciton. Based on these results, the field dependence of CTE dissociation is evaluated for MDMO-PPV:PC61BM blends with varying fullerene loads by PL(F) and TA(F). For higher PC61BM contents, the CTE binding energies decrease notably. This behavior is ascribed to a larger effective dielectric constant for well-intermixed blends and to an interplay between dielectric constant and CTE delocalization length for phase separated morphologies, emphasizing the importance of high dielectric constants for the charge carrier photogeneration process. Finally, the CTE binding energies are determined for MDMO-PPV blends with different fullerene derivatives, focusing on the influence of the acceptor LUMO energy. Here, the experimental results suggest the latter having no or at least no significant impact on the binding energy of the CTE. Variations of this binding energy are rather related to different trap levels in the acceptors which seem to be involved in CTS formation.},
  subject      = {Organische Solarzelle},
  language  = {en}
}
@article{GrueneLondiGillettetal.2023,
  author    = {Gr{\"u}ne, Jeannine and Londi, Giacomo and Gillett, Alexander J. and St{\"a}hly, Basil and Lulei, Sebastian and Kotova, Maria and Olivier, Yoann and Dyakonov, Vladimir and Sperlich, Andreas},
  title     = {Triplet Excitons and Associated Efficiency-Limiting Pathways in Organic Solar Cell Blends Based on (Non-) Halogenated PBDB-T and Y-Series},
  series = {Advanced Functional Materials},
  volume    = {33},
  journal   = {Advanced Functional Materials},
  number    = {12},
  doi       = {10.1002/adfm.202212640},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312164},
  year      = {2023},
  abstract  = {The great progress in organic photovoltaics (OPV) over the past few years has been largely achieved by the development of non-fullerene acceptors (NFAs), with power conversion efficiencies now approaching 20\%. To further improve device performance, loss mechanisms must be identified and minimized. Triplet states are known to adversely affect device performance, since they can form energetically trapped excitons on low-lying states that are responsible for non-radiative losses or even device degradation. Halogenation of OPV materials has long been employed to tailor energy levels and to enhance open circuit voltage. Yet, the influence on recombination to triplet excitons has been largely unexplored. Using the complementary spin-sensitive methods of photoluminescence detected magnetic resonance and transient electron paramagnetic resonance corroborated by transient absorption and quantum-chemical calculations, exciton pathways in OPV blends are unravelled employing the polymer donors PBDB-T, PM6, and PM7 together with NFAs Y6 and Y7. All blends reveal triplet excitons on the NFA populated via non-geminate hole back transfer and, in blends with halogenated donors, also by spin-orbit coupling driven intersystem crossing. Identifying these triplet formation pathways in all tested solar cell absorber films highlights the untapped potential for improved charge generation to further increase plateauing OPV efficiencies.},
  language  = {en}
}