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Charge Generation and Recombination in Fullerene-Attached Poly(3-hexylthiophene)-Based Diblock Copolymer Films
journal contribution
posted on 2014-05-22, 00:00 authored by Shunsuke Yamamoto, Hiroaki Yasuda, Hideo Ohkita, Hiroaki Benten, Shinzaburo Ito, Shoji Miyanishi, Keisuke Tajima, Kazuhito HashimotoThe charge generation and recombination
dynamics in fullerene-attached
poly(3-hexythiophene) (P3HT)-based diblock copolymer were studied
in comparison with those in blend films of P3HT and a fullerene derivative
(PCBM) in order to understand the potential advantage of diblock copolymer-based
polymer solar cells. Upon photoexcitation, P3HT singlet excitons are
promptly converted to P3HT polarons with a time constant of ∼30
ps in both P3HT-PCBM diblock copolymer and P3HT/PCBM blend films.
This similar charge generation dynamics is indicative of analogous
phase-separated morphology both in these films on a scale of nanometers.
After the charge generation, a part of polarons in disorder phases
geminately recombine to the ground state in diblock copolymer films,
while no geminate recombination is observed in blend films. This geminate
recombination loss is probably due to defects of phase-separated structures
in diblock copolymer films. On the other hand, charge carrier lifetime
is as long as 15 μs in diblock copolymer films. Such a long
carrier lifetime may result in a relatively high fill factor in P3HT-PCBM
copolymer films. Finally, we discuss the overall device performance
in terms of phase-separated structures.