Morphology Control in TiO2 Nanorod/Polythiophene Composites for Bulk Heterojunction Solar Cells Using Hydrogen Bonding

Hydrogen bond interactions between a dye adsorbed at the interface of TiO2 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-b-ethylene glycol) (P3HT-b-PEG) copolymers were prepared by a combination of Grignard metathesis polymerization and click chemistry. The short PEG segments in P3HT-b-PEG serve as a hydrogen bond acceptor. TiO2 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 TiO2 nanorods and the PEG chain limits the aggregation of the TiO2 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 TiO2 nanorods exhibit power conversion efficiency ∼50% higher than that of conventional P3HT homopolymer and N3-dye TiO2 nanorods.