N-type naphthalene diimide copolymers: Synthesis, characterization, and device studies

Organic semiconductors have shown good potential for use in organic electronics applications due to their relatively simple optoelectronic tunability and their low-cost low-temperature processibility. Growth in the field of organic semiconductor research has made good progress, although most research has been dedicated toward developing and optimizing organic p-type semiconductors, while little research has been spent discovering novel organic n-type semiconducting materials. Imide-functionalized conjugated small molecules and polymers have shown great potential for use as the n-type component in device applications due to their low-lying LUMO levels. Imide-functionalized semiconductors are also desirable due to their relatively simple preparation, band-gap and HOMO level tunability, and the ability to change their solubility and crystallinity through imide chain substitution. The most common applications for these materials include: field-effect transistors, photovoltaic devices, light-emitting devices.;A series of highly-soluble naphthalene diimide (NDI) polymers are presented in Chapter 2---each polymer differing in the thiophene content comprising the material. Electron mobilities as high as 0.076 cm2 V -1 s-1 for the novel material PNDI-3Th are reported. Polymer crystallinity and general macromolecular order is shown to effectively improve by increasing the number of thiophene units within the polymer backbone. The structure-property relationship of NDI-thiophene copolymers is also presented and discussed as it pertains to organic field effect transistor (OFET) performance.;Chapter 3 discusses the in-situ n-doping and crosslinking of the NDI polymers presented in the previous chapter to yield efficient electron-transporting materials for inverted configuration polymer solar cells. Crosslinking is performed using bis(perfluorophenyl) azide (bis-PFPA) in generating solvent-resistant films to minimize solvent-induced erosion during solution-based device processing. Chemical n-doping of the semiconducting polymers is performed with (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI), which improved the power conversion efficiency of solar cells from 0.69% to 3.42%---opening the door for further research in the field of polymeric interface materials.;Finally, n-type ladder-polymer precursors based on naphthalene diimide are presented in Chapter 4. These linear precursor polymers possess cleavable functional groups capable of forming imine-bridged ladder polymer structures. Average electron mobilities as high as 0.0026 cm2 V -1 s-1, which show an electron-mobility improvement of 4 orders of magnitude following ladderization, and on/off current ratios on the order of 104 are reported for the novel material PNDI-2BocL.