Morphology Control in
TiO<sub>2</sub> Nanorod/Polythiophene Composites for Bulk Heterojunction
Solar Cells Using Hydrogen Bonding
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Abstract
Hydrogen bond interactions between a dye adsorbed at
the interface of TiO<sub>2</sub> nanorods and functionalized P3HT
was used to control nanorod dispersion, increase interfacial area,
and improve efficiency in solution-processable hybrid bulk heterojunction
solar cells. A series of poly(3-hexylthiophene-<i>b</i>-ethylene
glycol) (P3HT-<i>b</i>-PEG) copolymers were prepared by
a combination of Grignard metathesis polymerization and click chemistry.
The short PEG segments in P3HT-<i>b</i>-PEG serve as a hydrogen
bond acceptor. TiO<sub>2</sub> nanorods functionalized with N3-dye
bearing multiple COOH groups function as both the electron acceptor
and hydrogen bond donor. The strong preferential H-bonding interaction
between TiO<sub>2</sub> nanorods and the PEG chain limits the aggregation
of the TiO<sub>2</sub> nanorods and affords homogeneously dispersion
of the nanorods within the polymer matrix to form an interpenetrating
network. This structure provides large interfacial area between electron
donor and acceptor and highly efficient transport pathways within
the composite. Hybrid devices constructed from copolymers with 10
wt % PEG and N3-dye TiO<sub>2</sub> nanorods exhibit power conversion
efficiency ∼50% higher than that of conventional P3HT homopolymer
and N3-dye TiO<sub>2</sub> nanorods