2018 Semmelhack Symposium: Campos & Dichtel
Mon, May. 7, 2018, 3:30pm
Edward C. Taylor Auditorium, Frick B02
Host: Martin Semmelhack
Luis M. Campos, Columbia University
Materials Design for 3rd-Generation Solar Cells
The ability to generate multiple excitons from a single photon has the potential to significantly enhance the photocurrent in single-junction solar cells. This talk will provide an overview on our approach to the design, synthesis, and evaluation of materials for next-generation photovoltaics. The presentation will most likely begin with a joke, a mildly funny one to test the waters. If it all goes well, other hilarious remarks will be peppered throughout the talk. If the reference to “stable genius” is not too old by then, it could appear in one of the slides. By the end of the talk, one can only dream that a standing ovation will erupt. A rose landing on the stage will certainly be welcomed, or the slow clap… yeah, that would be cool too.
William Dichtel, Northwestern University
Synthesis and Applications of 2D Covalent Organic Frameworks
Polymerizing monomers into periodic two-dimensional (2D) networks provides structurally precise, layered macromolecular sheets linked by robust, covalent bonds. These materials exhibit desirable mechanical, optoelectrotronic, and molecular transport properties derived from their designed structure and permanent porosity. 2D covalent organic frameworks (COFs) offer broad monomer scope but are generally isolated as insoluble powders comprised of aggregated nanometer-scale crystallites. Here we overcome this limitation by controlling 2D COF formation using a two-step procedure. In the first step, 2D COF nanoparticle seeds are prepared with approximate diameters of 30 nm. Next, monomers are slowly added to suppress new nucleation while promoting epitaxial growth on the existing seeds to sizes of several microns. The resulting 2D COFs are of exceptional and unprecedented quality, isolated as single crystalline materials with micron-scale domain sizes. Transient absorption spectroscopy of the dispersed, single-crystalline COF nanoparticles enables two to three orders of magnitude improvement of the optical transient absorption signal-to-noise ratio by minimizing scattering photons that plague these measurements on 2D COF powders. These measurements also show evidence for exciton diffusion as a function of crystallite size at longer length scales than available within the small, aggregated crystallites obtained solvothermally. These findings represent the first controlled synthesis of 2D COFs and will enable a broad exploration of synthetic 2D polymer structures and properties.