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Exciton‐Charge Annihilation in Organic Semiconductor Films
Author(s) -
Hodgkiss Justin M.,
AlbertSeifried Sebastian,
Rao Akshay,
Barker Alex J.,
Campbell Andrew R.,
Marsh R. Alex,
Friend Richard H.
Publication year - 2012
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201102433
Subject(s) - exciton , annihilation , materials science , semiconductor , spectroscopy , acceptor , organic semiconductor , excitation , ultrafast laser spectroscopy , positron annihilation spectroscopy , molecular physics , charge carrier , atomic physics , photoluminescence , chemical physics , optoelectronics , condensed matter physics , physics , electron , quantum mechanics , positron , positron annihilation
Time‐resolved optical spectroscopy is used to investigate exciton‐charge annihilation reactions in blended films of organic semiconductors. In donor–acceptor blends where charges are photogenerated via excitons, pulsed optical excitation can deliver a sufficient density of temporally overlapping excitons and charges for them to interact. Transient absorption spectroscopy measurements demonstrate clear signatures of exciton‐charge annihilation reactions at excitation densities of ≈10 18 cm −3 . The strength of exciton‐charge annihilation is consistent with a resonant energy transfer mechanism between fluorescent excitons and resonantly absorbing charges, which is shown to generally be strong in organic semiconductors. The extent of exciton‐charge annihilation is very sensitive not only to fluence but also to blend morphology, becoming notably strong in donor–acceptor blends with nanomorphologies optimized for photovoltaic operation. The results highlight both the value of transient optical spectroscopy to interrogate exciton‐charge annihilation reactions and the need to recognize and account for annihilation reactions in other transient optical investigations of organic semiconductors.