Organic
photovoltaics represent a promising thin-film solar cell technology
with appealing mechanical, aesthetical, and cost features. In recent
years, a strong growth in power conversion efficiency (to over 10%)
has been realized for organic solar cells through extensive material
and device research. To be competitive in the renewable energy market,
further improvements are mandatory though, both with respect to efficiency
and lifetime. High intrinsic stability of the photoactive layer is
obviously a crucial requirement for long lifetimes, but the generally
applied bulk heterojunction blends and their components are prone
to light-induced and thermal degradation processes. In the present
contribution, the high-T
g polymer strategy
is combined with specific side chain functionalization to address
the thermal stability of polymer solar cells. These two design concepts
are applied to a prototype low bandgap copolymer, PCPDTBT. Accelerated
aging tests (at 85 °C) indicate an improved thermal durability
of the PCPDTBT:PC71BM blends and the resulting devices
by the insertion of ester or alcohol moieties on the polymer side
chains. The different stages in the efficiency decay profiles are
addressed by dedicated experiments to elucidate the (simultaneously
occurring) degradation mechanisms.
An overview is provided on the surface functionalization of boron-doped diamond thin films and their application as photoelectrodes and photocatalysts.
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