Dithienosilole-Based Small-Molecule Organic Solar Cells with an Efficiency over 8%: Investigation of the Relationship between the Molecular Structure and Photovoltaic Performance

Two new acceptor−donor−acceptor (A-D-A)
small molecules with 2,6-(4,4-bis(2-ethylhexyl)-4Hcyclopenta[2,1-b;3,4-b′]-dithiophene (DTC) and (4,4′-bis(2-
ethylhexyl) dithieno[3,2-b:2′,3′-d]silole)−2,6-diyl (DTS) as
the central building block unit and 3-ethyl-rhodanine as the
end-capping groups have been designed and synthesized. The
influence of the bridging atoms on the optical, electrochemical
properties, packing properties, morphology, and device
performance of these two molecules was systematically
investigated. Although with only the difference of one atom
on the central core units, the two molecules showed great
different properties such as film absorption, molecular packing,
and charge transport properties. The optimized device based on molecule DR3TDTS exhibited a power conversion efficiency
(PCE) of >8%.