Nanomorphology and Charge Generation in Bulk Heterojunctions Based on Low-Bandgap Dithiophene Polymers with Different Bridging Atoms
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Deutsch
Original Kurzfassung:
Carbon bridged (C-PCPDTBT) and silicon-bridged (Si-PCPDTBT) dithiophene
donor acceptor copolymers belong to a promising class of low bandgap
materials. Their higher field-effect mobility, as high as 10(-2)cm(2)
V(-1)s(-1) in pristine films, and their more balanced charge transport
in blends with fullerenes make silicon-bridged materials better
candidates for use in photovoltaic devices. Striking morphological
changes are observed in polymer:fullerene bulk heterojunctions upon the
substitution of the bridging atom. XRD investigation indicates
increased pi-pi stacking in Si-PCPDTBT compared to the carbon-bridged
analogue. The fluorescence of this polymer and that of its counterpart
C-PC PDTBT indicates that the higher photogeneration achieved in
Si-PCPDTBT:fullerene films (with either [C60]PCBM or [C70]PCBM) can
be correlated to the inactivation of a charge-transfer complex and to a
favorable length of the donor acceptor phase separation. TEM studies of
Si-PCPDTBT:fullerene blended films suggest the formation of an
interpenetrating network whose phase distribution is comparable to the
one achieved in C-PCPDTBT:fullerene using 1,8-octanedithiol as an
additive. In order to achieve a balanced hole and electron transport,
Si-PCPDTBT requires a lower fullerene content (between 50 to 60 wt\%)
than C-PCPDTBT (more than 70 wt\%). The Si-PCPDTBT:[C70]PCBM OBHJ
solar cells deliver power conversion efficiencies of over 5\%.
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