Charge
Dissociation at Interfaces between Discotic
Liquid Crystals: The Surprising Role of Column Mismatch
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Abstract
The semiconducting
and self-assembling properties of columnar discotic
liquid crystals have stimulated intense research toward their application
in organic solar cells, although with a rather disappointing outcome
to date in terms of efficiencies. These failures call for a rational
strategy to choose those molecular design features (e.g., lattice
parameter, length and nature of peripheral chains) that could optimize
solar cell performance. With this purpose, in this work we address
for the first time the construction of a realistic planar heterojunction
between a columnar donor and acceptor as well as a quantitative measurement
of charge separation and recombination rates using state of the art
computational techniques. In particular, choosing as a case study
the interface between a perylene donor and a benzoperylene diimide
acceptor, we attempt to answer the largely overlooked question of
whether having well-matching donor and acceptor columns at the interface
is really beneficial for optimal charge separation. Surprisingly,
it turns out that achieving a system with contiguous columns is detrimental
to the solar cell efficiency and that engineering the mismatch is
the key to optimal performance