Understanding and Controlling Organic-Inorganic Interfaces in Mesostructured Titania/Conjugated Polymer Materials for Photovoltaic Applications

The use of surfactant-directed mesostructured inorganic materials allows for the preparation of oxide frameworks as continuous transparent films with high inorganic-organic interfacial contact and the inclusion of diverse functional guest species. For example, mesostructured (10 nm) titania films containing light-absorbing conjugated polymer guest species exhibit photovoltaic properties and may be synthesized by exploiting the compatible solution processabilities of the different molecular components that co-assemble into functional hybrid materials. Subsequent integration of these materials into photovoltaic devices leads to performances that depend on many factors, including the extent of interfacial contact between the conjugated polymer species and titania network. Such contact depends upon the molecular interactions among the titania framework, conjugated polymer species, and different structure-directing surfactants during synthesis and processing of the materials. Detailed molecular-level understanding of the interactions, mobilities, and proximities among the different functional components in the hybrid materials can be obtained through solid-state two-dimensional NMR and other techniques and correlated with macroscopic photo-current properties. In particular, judicious selections of the structure-directing surfactant and solvent species are demonstrated to promote increased contact between the conjugated polymer species and mesostructured titania network leading to improved photovoltaic device performance. Resulting insights allow mesostructured titania-conjugated polymer hybrid materials and device properties to be controllably modified and optimized.