Supramolecular assembly and nanoscale morphologies for organic photovoltaic devices

Organic photovoltaics is a field of rapidly growing activity in
both research and industry. Flexibility, light-weight, and low-cost
render this technique an appealing alternative to silicon based
devices for solar energy power conversion. Recently, several
donor-acceptor systems have been investigated as active materials
for organic photovoltaic devices and it has been shown that the
morphology of these heterojunction systems has a severe impact on
the device performance. This work focuses on the correlation of
nanoscale morphologies of organic donor-acceptor systems with
resulting spectroscopic and electronic properties of organic
photovoltaic devices. Discotic molecules are used in the active
layer of the devices exhibiting a number of properties highly
desired for the application in organic photovoltaic devices: The
planar core shape of this class of materials allows an assembly to
1-D molecular wires showing anisotropic and exceptionally high
charge carrier mobility.It is the aim to establish supramolecular
assemblies of the discotic molecules and to realize nanoscale
interface morphologies between donor and acceptor compounds in
order to optimize the photovoltaic performance of the resulting
devices. The impact of residue modifications attached to the disc
shaped molecules on morphology, current generation and
recombination is analyzed and design rules for these solution
processable small molecule blend mixtures are derived. Vacuum
sublimation is discussed as an alternative processing route
facilitating the fabrication of devices with mixed but also
bi-layered active material stacking. Using a dye sensitization
method the exciton harvesting and photovoltaic performance can be
significantly increased in these thin film devices. A highly
ordered nanoscale morphology at the donor-acceptor interface,
demonstrated using a template assisted imprinting approach, offers
high potential towards photovoltaic devices with interdigitated
interfaces and superior power conversion efficiency.