Energy transfer and exciplex formation and their impact on exciton and charge carrier dynamics in organic films

We report Förster resonant energy transfer (FRET) with a Förster radius R₀ of 4.8 nm and exciplex formation in composites containing two functionalized anthradithiophene (ADT) derivatives, ADT-TES-F (donor, D) and ADT-TIPS-CN (acceptor, A) depending on the D-A distance. In composites containing bulk D/A heterojunctions, exciplex photoluminescence (PL) emission peaked at ∼668 nm dominated the PL spectra. The exciplex contributed to charge carrier photogeneration on nanosecond time scales in composites, in contrast to sub-500 ps carrier photogeneration observed in ADT-TES-F pristine films. Finally, significantly slower charge carrier recombination was obtained in composites, as compared to that of pristine ADT-TES-F films, due to electron trapping at the ADT-TIPS-CN enabling the hole to propagate in the ADT-TES-F host.