Correlating Interfacial Interactions and Macroscopic Photovoltaic Properties of Self-Assembled Hybrid Materials

Correlating interfacial interactions and macroscopic photovoltaic properties of self-assembled hybrid materials

Justin P. Jahnke¹, Shany Neyshtadt², Tamar Segal-Peretz², Maria Diaz-Garcia³, Gitti L. Frey², Brad F. Chmelka^1*

¹ Department of Chemical Engineering, University of California, Santa Barbara

²  Department of Materials Engineering, Technion - Israel Institute of Technology

³ Department of Applied Physics, University of Alicante, Spain

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 titania films (with ca. 10 nm channel dimensions) containing light-absorbing conjugated guest species exhibit photovoltaic properties that are influenced strongly by solution processing conditions. Solution compositions must be chosen for compatibility with the dissimilar molecular components, which co-assemble into functional hybrid materials as the solvent is removed. Subsequent integration of these materials into photovoltaic devices leads to performances that depend on many factors, including the degree of exciton dissociation at the conjugated guest-titania interface and charge transport to the electrodes.  The degree of exciton dissociation is strongly influenced by the extent of interfacial contact between the conjugated guest species and titania network, while charge transport may be enhanced by the introduction of orientational order. 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 synthesis and processing conditions are demonstrated to promote enhanced interfacial contact and charge carrier transport, leading to improved photovoltaic device performance.  Resulting insights allow mesostructured titania-conjugated polymer hybrid materials and device properties to be controllably modified and optimized.