| Popis: |
In organic solar cells, high open circuit voltages may be obtained by choosing materials with a high offset between the donor highest occupied molecular orbital (HOMO) and acceptor lowest unoccupied molecular orbital (LUMO). However, increasing this energy offset can also lead to photophysical processes that compete with charge separation. In this paper the formation of triplet states is addressed in blends of polyfl uorene polymers with a series of PCBM multi-adducts. Specifi cally, it is demonstrated that the formation of such triplets occurs when the offset energy between donor ionization potential and acceptor electron affi nity is ∼ 1.6 eV or greater. Spectroscopic measurements support a mechanism of resonance energy transfer for triplet formation, infl uenced by the energy levels of the materials, but also demonstrate that the competition between processes at the donor‐acceptor interface is strongly infl uenced by morphology. |
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