Molecular Modeling of Interfaces between Hole Transport and Active Layers in Flexible Organic Electronic Devices

Molecular modeling methods are used
to understand the interfacial
properties between the hole-transport and active layers in organic
photovoltaic (OPV) devices. The hole-transport layer (HTL) consists
of a blend of poly­(styrene-sulfonate) and poly­(3,4-ethylenedioxythiophene)
(PEDOT:PSS), whereas the active layer (AL) consists of a blend of
poly­(3-hexylthiophene) and phenyl-C61-butyric acid methyl ester (P3HT:PCBM).
Simulation results on the HTL confirm the interpenetrating lamellar
structure with alternating PSS and PEDOT domains as observed in experiments.
In addition, interfacial results show high PCBM interactions with
the HTL, which result in PCBM migration to the HTL surface. The observed
PCBM concentration profile is discussed from the perspective of attractive
interactions, and it is shown that these interactions are governed
by the side chain of PCBM. Calculations also suggest that OPV device
performance could be improved by, for example, increasing the number
of benzene rings and backbone −CH2– groups
in the PCBM side chain, which would be expected to reduce PCBM concentration
at the HTL surface. The results yield important insights into molecular
interactions associated with the HTL and AL interfaces that contribute
to final device morphology and thus provide guidelines toward materials
design approaches for optimized device performance.