The incorporation of hole conducting polymer poly(3-hexyl thiophene) (P3HT) into the 8-9 nm cylindrical nanopores of titania is investigated using films with a unique orthogonally oriented hexagonal close packed mesostructure. The films are synthesized using evaporation induced self-assembly (EISA) with Pluronic triblock copolymer F127 as the structure directing agent. The orthogonally oriented cylindrical nanopore structure was chosen over a cubic structure because confinement in uniform cylindrical channels is hypothesized to enhance hole conductivity of P3HT by inducing local polymer chain ordering. Orthogonal orientation of the cylindrical nanopores is achieved by modifying the substrate (FTO-coated glass slides) with crosslinked F127. After thermal treatment to remove organic templates from the films, P3HT is infiltrated into the nanopores by spin coating a 1 wt% P3HT solution in chlorobenzene onto the titania films followed by thermal annealing under vacuum at 200 °C. The results show that infiltration is essentially complete after 30 minutes of annealing, with little or no further infiltration thereafter. A final infiltration depth of ~14 nm is measured for P3HT into the nanopores of titania using neutron reflectometry measurements. Photoluminescence measurements demonstrate that charge transfer at the P3HT-TiO2 interface improves as the P3HT is infiltrated into the pores, suggesting that an active organic-inorganic heterojuction is formed in the materials.
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All experiments were performed as part of a U.S. Department of Energy EPSCoR Implementation award supported by grant no. DE-FG02-07-ER46375. The use of the Advanced Photon Source at Argonne National Laboratory for GISAXS measurements was supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Final data analysis and refinement were completed as part of a NSF EPSCoR research infrastructure award (grant no. IIA-1355438).
Nagpure, Suraj R.; Browning, James F.; and Rankin, Stephen E., "Incorporating Poly(3-hexyl thiophene) into Orthogonally Aligned Cylindrical Nanopores of Titania for Optoelectronics" (2017). Chemical and Materials Engineering Faculty Publications. 63.