Functional Nanocomposites Formed by Two-step Back-filling Methods

摘要

This thesis investigates the synthesis and properties of nanocomposite materials comprised of inorganic nanocrystals (NCs) combined with a complementary organic compound utilizing sequential two-step synthesis methods. We demonstrate an enhancement in the mechanical and optical properties of electrophoreticially deposited (EPD) cadmium selendide (CdSe) nanocrystal (NC) films through post-deposition addition of organic ligand molecules and polymeric precursor molecules (monomers). Specifically we show that when these organic compounds are added (i.e. back-filled) into the as-deposited, wet EPD NC film, that fracture in the dried film is suppressed and photoluminscent (PL) efficiency of the inorganic NC phase is greatly increased. We go on to study the synthesis and properties of a novel nanocomposite comprised of inorganic NCs back-filled into a mat of semiconducting poly(3-hexylthiophene) [P3HT] nanowires. P3HT nanowire films are synthesized using a novel method developed as part of this thesis; where P3HT is blended with a sacrificial polymer (polystyrene, PS), leading to spontaneous demixing of the two polymers upon casting, and upon selective removal of the PS phase exposes a dense mat of P3HT nanowires. When back filled with CdSe NCs the composite material exhibits photovoltaic (PV) performance and provides a flexible platform for low-cost, hybrid organic/inorganic NC PV device fabrication. We conclude by showing how the above methods, in conjunction with novel ligand chemistry and lithographic techniques, can be utilized to create a photo-active nanocomposite consisting of lithographically defined, micron-scale, electrodes that are selectively decorated with electron-accepting NCs using EPD, and subsequently back-filled with a complementary electron-donating NC phase. The device architecture and resulting nanocomposite material is capable of lateral exciton separation on a potentially low-cost substrate.