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Area of Science:

  • Materials Science
  • Organic Electronics
  • Photovoltaics

Background:

  • Nonfullerene acceptors (NFAs) are crucial for organic photovoltaics (OPVs).
  • Understanding exciton dynamics in NFAs is key to improving device performance.
  • Molecular packing significantly influences exciton behavior and charge generation.

Purpose of the Study:

  • To investigate the impact of molecular packing on exciton delocalization and recombination kinetics in Y6 derivatives.
  • To correlate exciton properties with the performance of organic photovoltaic devices.
  • To identify structural factors that enhance internal quantum efficiency (IQE) in OPVs.

Main Methods:

  • Transient absorption spectroscopy to study exciton formation and dynamics.
  • Selective photoexcitation in donor/acceptor blends to probe charge generation mechanisms.
  • Quantification of recombination kinetics using the monomolecular recombination constant (a).
  • Grazing incidence wide-angle X-ray scattering (GIWAXS) to analyze molecular packing.

Main Results:

  • Evidence of both local and delocalized excitons in neat Y6 derivative films.
  • D18 donor acts as a bystander during charge generation after acceptor photoexcitation.
  • Lower recombination constants (a) correlate with higher hole transfer yield and IQE.
  • Face-on molecular packing promotes exciton delocalization and higher IQE (up to 97.2% in T1).

Conclusions:

  • Molecular packing, specifically face-on orientation, is a critical factor for exciton delocalization in NFAs.
  • Controlling exciton recombination kinetics through molecular engineering can significantly enhance OPV performance.
  • This study provides a structural lever to advance organic photovoltaics towards higher efficiencies.