University of Connecticut |
Polymer Program SeminarVariable Bandgap Conjugated Polymers as Electrochromics and Photovoltaics Friday, September 29, 2006 11:00 am , IMS Room 20 By controlling the energy levels of the HOMO and LUMO states in conjugated polymers, along with the magnitude of the electronic band gap, optoelectronic properties can be optimized for specific applications. To this end, we have developed a family of soluble conjugated polymers with band gaps ranging from 3.2 eV – 1.5 eV and evaluated the utility of these polymers for device applications. Our use of 3,4-alkylenedioxythiophene (XDOT) donors, along with cyanovinylene and pyridopyrazine acceptors has led to the development of a representative class of soluble narrow gap polymers. Variable gap electrochromic polymers, where the HOMO and LUMO levels are set for facile redox chemistry yield multi-color EC materials that can be processed from aqueous and organic solutions. Novel EC devices will be demonstrated that efficiently modulate reflectivity of metal surfaces over broad spectral ranges, while all-polymer EC devices are flexible and exhibit multi-color states. PCBM-based solar cells where the HOMO is set for air stability, the LUMO for excited state donation to the PCBM acceptor, and the band gap for broad absorption of the solar spectrum will be discussed. Of special interest are the narrow gap conjugated polymers that can absorb solar energy most strongly at the peak of solar photon flux near 1.8 eV. We will discuss fundamental optical and electrochemical data in order to establish the band structure of the newly synthesized polymers, along with presenting results from photovoltaic (PV) as platforms for materials property optimization. Conjugated polymer blends using polymers of varied band gap have been used in PV devices in order to obtain spectral broadening of the absorption characteristics.
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