Exciton fission and charge generation via triplet excitons in pentacene/C60 bilayers.
Organic photovoltaic devices are currently studied due to their potential suitability for flexible and large-area applications, though efficiencies are presently low. Here we study pentacene/C(60) bilayers using transient optical absorption spectroscopy; such structures exhibit anomalously high quantum efficiencies. We show that charge generation primarily occurs 2-10 ns after photoexcitation. This supports a model where charge is generated following the slow diffusion of triplet excitons to the heterojunction. These triplets are shown to be present from early times (<200 fs) and result from the fission of a spin-singlet exciton to form two spin-triplet excitons. These results elucidate exciton and charge generation dynamics in the pentacene/C(60) system and demonstrate that the tuning of the energetic levels of organic molecules to take advantages of singlet fission could lead to greatly enhanced photocurrent in future OPVs.
Rao
Akshay
A
Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
Wilson
Mark W B
MW
Hodgkiss
Justin M
JM
Albert-Seifried
Sebastian
S
Bässler
Heinz
H
Friend
Richard H
RH
D037741:Fullerenes / Q000737:chemistry*; D009279:Naphthacenes / Q000737:chemistry*; D011789:Quantum Theory
D037741:Fullerenes; D009279:Naphthacenes; C523499:pentacene; C069837:fullerene C60