Structural Modification of Organic Materials for Energy Harvesting Applications

Abstract

Energy harvesting devices based on organic materials have attracted great attentions because the structural versatility enables the incorporation of functionality by molecular design compared to conventional inorganic solid state electronics. They also allow devices with lower costs, lightweight, large-area coverage, and mechanical flexibility. Intensive research efforts on rational molecular design and synthesis have led to remarkable progress in achieving high performance organic materials through chemical approach. One of the promising classes of organic dyes is bislactam units including diketopyrrolopyrrole (DPP), benzodithiophene (BDT), isoindigo (IIG), thienoisoindigo (TIIG), and so forth. Among them, TIIG moiety was recently developed by McCulloch et al. in 2012 through a structural modification of IIG. It exhibits a high degree of co-planarity via sulfur-oxygen interactions and improved delocalization of molecular states via a quinoidal structure along the backbone, leading to high absorption coefficients, broad light absorption and high charge carrier mobilities. Poly(vinylidene fluoride) (PVDF) is attractive for its special electrochemical and physical properties like a good surface alignment, electrochemical inertness, strong bonding strength, well-controlled porosity, superior thermal properties, and compatibility with flexible substrates. Because of its remarkable properties, it can be tailorable to many fields such as a membrane, a binder for electrode materials, piezoelectric/pyroelectric/triboelectric materials, and dielectric materials for OFETs. Grafting of functional groups to PVDF backbone can offer an effective approach for incorporating specific properties into a material while retaining desirable properties of the parent PVDF polymer. Considering above issues, my research focus was on synthesis and characterization of TIIG or PVDF-based organic materials for application in various energy harvesting devices. Firstly, three TIIG-based small molecules bearing benzene, naphthalene, and benzofuran were synthesized, characterized, and applied for organic photovoltaics (OPVs) and organic field-effect transistors (OFETs). Secondly, PVDF graft copolymers were prepared to use as a binder for Si anode in lithium ion batteries. The grafting of tert-butyl acrylate onto PVDF by ATRP was used to synthesize PVDF-g-PtBA copolymers.