1 research outputs found
Charge Transfer Dynamics in Donor–Acceptor Complexes between a Conjugated Polymer and Fluorene Acceptors
We report on ground and excited state
charge transfer in charge-transfer
complexes in films formed between a semiconducting polymer, MEH-PPV
(polyÂ[2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylenevinylene]),
and a series of fluorene electron acceptors. The latter were designed
to vary systematically the electron affinity (EA) over ∼1.5
eV by attachment of various electron withdrawing groups to the fluorene
core. The EAs of the acceptors are determined by cyclic voltammetry
and compared with those from density functional theory calculations.
The charge-transfer dynamics are studied using an ultrafast visible-pump–IR-probe
photoinduced absorption technique. We demonstrate that the acceptor
EA is the keyî—¸but not the onlyî—¸parameter that governs
charge recombination rates that scale exponentially with the acceptor
EA. From the time-resolved data we deduced a model that describes
charge dynamics for acceptors with low and high EAs. The two opposite
trendsî—¸higher acceptor EA increases the driving force for charge
separation but also inevitably increases the rate of undesirable charge
recombinationî—¸should be carefully counterbalanced in designing
novel polymer–fullerene bulk heterojunctions