4.8 Article

Understanding the Role of Order in Y-Series Non-Fullerene Solar Cells to Realize High Open-Circuit Voltages

Journal

ADVANCED ENERGY MATERIALS
Volume 12, Issue 12, Pages -

Publisher

WILEY-V C H VERLAG GMBH
DOI: 10.1002/aenm.202103422

Keywords

energetic disorder; non-fullerene acceptors; open-circuit voltage; organic solar cells

Funding

  1. Alexander von Humboldt Foundation
  2. Deutsche Forschungsgemeinschaft, DFG, German Research Foundation through the project Fabulous [450968074]
  3. HIOS [182087777 - SFB 951]
  4. SolarEraNet [NFA4R2ROPV]
  5. Elite Study Program Macromolecular Science within the Elite Network of Bavaria (ENB)
  6. DOE Office of Science by Brookhaven National Laboratory [DE-SC0012704]
  7. King Abdullah University of Science and Technology (KAUST) Office of Sponsored Research (OSR) [OSR-CARF/CCF-3079]
  8. National Natural Science Foundation of China [52125306]
  9. Welsh Government's Ser Cymru II Rising Star and Capacity Builder Accelerator Programs through the European Regional Development Fund, Welsh European Funding Office
  10. Swansea University Strategic Initiative in Sustainable Advanced Materials
  11. Projekt DEAL
  12. [3923306670]

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This study investigates the role of energetic disorder in the blends of PM6 and Y-series NFAs. The results show that energetic disorder affects both the value and temperature dependence of the open-circuit voltage. The PM6:Y6 blend benefits from its narrower state distribution.
Non-fullerene acceptors (NFAs) as used in state-of-the-art organic solar cells feature highly crystalline layers that go along with low energetic disorder. Here, the crucial role of energetic disorder in blends of the donor polymer PM6 with two Y-series NFAs, Y6, and N4 is studied. By performing temperature-dependent charge transport and recombination studies, a consistent picture of the shape of the density of state distributions for free charges in the two blends is developed, allowing an analytical description of the dependence of the open-circuit voltage V-OC on temperature and illumination intensity. Disorder is found to influence the value of the V-OC at room temperature, but also its progression with temperature. Here, the PM6:Y6 blend benefits substantially from its narrower state distributions. The analysis also shows that the energy of the equilibrated free charge population is well below the energy of the NFA singlet excitons for both blends and possibly below the energy of the populated charge transfer manifold, indicating a down-hill driving force for free charge formation. It is concluded that energetic disorder of charge-separated states has to be considered in the analysis of the photovoltaic properties, even for the more ordered PM6:Y6 blend.

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